CELL SCIENCE AT A GLANCE

Intramembrane proteolysis at a glance: from signalling to proteindegradationNathalie Kuhnle, Verena Dederer and Marius K. Lemberg*

ABSTRACTOver the last two decades, a group of unusual proteases, so-calledintramembrane proteases, have become increasingly recognized fortheir unique ability to cleave peptide bonds within cellularmembranes. They are found in all kingdoms of life and fulfilversatile functions ranging from protein maturation, to activation ofsignalling molecules, to protein degradation. In this Cell Science at a

Glance article and the accompanying poster, we focus onintramembrane proteases in mammalian cells. By comparingintramembrane proteases in different cellular organelles, we set outto review their functions within the context of the roles of individualcellular compartments. Additionally, we exemplify their mode ofaction in relation to known substrates by distinguishing cleavageevents that promote degradation of substrate from those that releaseactive domains from the membrane bilayer.

KEY WORDS: Regulated intramembrane proteolysis, Rhomboid,Presenilin, γ-secretase, Signal peptide peptidase, SPP-like protease,Site-2 protease, RCE1, ZMPSTE24, Limited proteolysis,Protein homeostasis

Centre for Molecular Biology of Heidelberg University (ZMBH), DKFZ-ZMBHAlliance, Im Neuenheimer Feld 282, 69120 Heidelberg, Germany.

*Author for correspondence (m.lemberg@zmbh.uni-heidelberg.de)

M.K.L., 0000-0002-0996-1268

1

© 2019. Published by The Company of Biologists Ltd | Journal of Cell Science (2019) 132, jcs217745. doi:10.1242/jcs.217745

Journal

ofCe

llScience

IntroductionEukaryotic cells are highly structured and contain numerousorganelles. To guarantee proper functionality of these distinctcellular entities, cells have to tightly control distribution, abundanceand activity of each and every compartment-specific protein.Furthermore, damaged protein species need to be efficientlyrecognized and removed. Although cells have developed severalsafeguarding mechanisms that control protein homeostasis(proteostasis), including the ubiquitin proteasome system(Ciechanover and Kwon, 2015) and lysosomes (Winckler et al.,2018), intramembrane proteases are additional key regulators of theorganelle proteome (Avci and Lemberg, 2015). In a biologicalcontext, proteolysis is an irreversible reaction; hence, anintramembrane cut introduces directional changes to membrane-associated processes. From a structural point of view, allintramembrane proteases are polytopic membrane proteins thatform aqueous active sites within the lipid bilayer and harbourcatalytic residues or a prosthetic zinc ion either adjacent to or insidethe plane of the membrane (Sun et al., 2016). These unusualproteases are divided into four families according to their catalytic

mechanism: metalloproteases, aspartyl proteases, serine (rhomboid)proteases and one unique glutamyl protease (see Box 1). With theexception of peroxisomes, at least one intramembrane protease isfound in every membrane-enclosed cellular compartment (seeposter).

Since cellular organelles fulfil a wide range of functions, differentintramembrane proteases contribute to a large variety of differentpathways. From what is known about intramembrane proteolysis, wedifferentiate here between two biological consequences, namelyprotein activation and degradation. On the one hand, limitedproteolysis that generates a stable protein fragment with a specificfunction is a key step in protein activation. On the other hand,intramembrane proteolysis can also generate metastable fragments thatare subsequently turned over by cellular degradation systems such asthe proteasome. In this Cell Science at a Glance, we will focus onknown functions of intramembrane proteases in mammalian cells. Wewill compare intramembrane proteases present within particularcellular compartments instead of reviewing individual examples oftheir respective mechanistic class. With this, we aim to describe howorganelle-specific protease functions mirror the compartment’srequirements. Initially, intramembrane proteolysis referred tocleavage of transmembrane proteins within the hydrophobic core ofthe lipid bilayer (Brown et al., 2000), we extend our definition toproteases that position their active sites in the broader context of themembrane. Therefore, we include ZMPSTE24 (zinc metalloproteinaseSte24 homologue), which is a zincmetalloproteasewith a large hollowbarrel-shaped membrane-integral chamber that encloses the active sitein the membrane head group region (see Box 2 for further details).Focusing on mammalian cells, we will describe key functions ofintramembrane proteases within all major cellular organelles, startingwith mitochondria, followed by the inner nuclear membrane, and thesecretory and the endocytic pathways.

MitochondriaMitochondria fulfil a plethora of essential functions includingrespiration, biosynthesis of lipids and other metabolites, calciumsignalling, and control of apoptosis. To ensure adequate function, anumber of different mechanisms constantly survey themitochondrial membrane proteome (Haynes and Ron, 2010). Theonly mitochondrial intramembrane protease, the rhomboid proteasePARL (presenilin-associated rhomboid-like – named by an artefactobserved in a yeast two hybrid interaction screen) is localized at theinner mitochondrial membrane (Jeyaraju et al., 2006). PARLprovides an important safeguarding system to target damaged

Box 2. ZMPSTE24 has a membrane-integral substrate-binding chamberThe second CAAX protease, ZMPSTE24 (known as Ste24 in yeast),plays a crucial role in the maturation of farnesylated proteins (Michaelisand Barrowman, 2012). Although these canonical ZMPSTE24/Ste24substrates are peripheral membrane proteins, crystal structures ofZMPSTE24 and Ste24 revealed a membrane-spanning hollow barrel-shaped active site comprising seven antiparallel transmembrane helices(Pryor et al., 2013; Quigley et al., 2013). Whereas three α-helices closethis barrel from the ER luminal site to the cytoplasmic and nucleoplasmicside, a zinc-metalloprotease domain with two openings allows substratesto enter the membrane-integral active-site chamber. Since substratesare supposed to access the catalytic zinc ion from within the membrane,we suggest the inclusion of ZMSPTE24/Ste24 in the class ofintramembrane proteases. Consistent with this, ZMPSTE24/Ste24cleaves proteins that clog the Sec61 translocon channel by anunknown mechanism (Ast et al., 2016; Kayatekin et al., 2018).

Box 1. Architecture of intramembrane proteasesIntramembrane proteases have the unusual property of cleaving theirsubstrates in the plane of cellular membranes. Based on their structureand catalytic mechanism they can be grouped into different families.

Aspartyl intramembrane proteasesMembers of the GxGD aspartyl proteases have been intensively studiedas their inaugural member, presenilin, is linked to familial Alzheimer’sdisease (Langosch and Steiner, 2017;Wolfe, 2019). Presenilin associateswith thenon-catalytic subunits nicastrin, presenilin enhancer 2 (PEN2) andanterior pharynx-defective 1 (APH1) to form a 250 kDa protease complexknown as γ-secretase (Langosch and Steiner, 2017; Wolfe, 2019).Mammals have two presenilin paralogues and several APH1 isoforms(three in human and four in rodents) that form functionally distinctcomplexes (Sannerud and Annaert, 2009). A related group of enzymes,with the signal peptide peptidase (SPP) as the first identified example andfour SPP-like (SPPL) proteases, also carries a presenilin fold but has aninverted active-site topology (Weihofen et al., 2002). The structures of thearchaeal SPP/presenilin homologue MCMJR1 (Li et al., 2013) and thehuman γ-secretase complex (Yang et al., 2019) revealed the architectureof the conserved membrane-embedded active site domain and the firstmechanistic insights of how substrates are recognized.

RhomboidsRhomboids are serine proteases that were first discovered inD. melanogaster where they act as key activators of epidermal growthfactor secretion by cleaving membrane-tethered precursors (Lee et al.,2001). Crystal structures of the E. coli rhomboid protease GlpG showedthat rhomboids consist of a conserved six transmembrane domain corewith an active site cavity that opens to the periplasmic (luminal) side ofthe membrane (Wang et al., 2006).

Site-2 proteaseSite-2 protease (S2P) is a zinc metalloprotease that is conserved in allkingdoms of life, except the budding yeast S. cerevisiae. The structure ofan archaeal S2P showed that catalytic zinc is coordinated in the centre ofa six transmembrane helix bundle with a channel-like openingconnecting the active site to the cytoplasmic side (Feng et al., 2007).

Ras-converting enzyme 1Ras-converting enzyme 1 (RCE1) belongs to a group of so-called CAAXproteases that process prenylated peptides at the cytoplasmic interfaceof the ER. Although, so far, no bona fide membrane-protein substratesfor CAAX proteases have been identified, the RCE1 crystal structurerevealed that the active site catalytic glutamate residues are positioned inthe plane of the membrane (Manolaridis et al., 2013).

2

CELL SCIENCE AT A GLANCE Journal of Cell Science (2019) 132, jcs217745. doi:10.1242/jcs.217745

Journal

ofCe

llScience

mitochondria to the macroautophagy (mitophagy) pathway, which,when defective, is associated with familial Parkinson’s disease(Pickrell and Youle, 2015; Spinazzi and De Strooper, 2016). In thiscontext, PARL cleaves the serine/threonine kinase PTEN-inducedkinase 1 (PINK1) while it is imported into mitochondria (Jin et al.,2010; Meissner et al., 2015). This processing releases theC-terminal cleavage fragment of PINK1 into the cytoplasm,where it is subsequently degraded by the ubiquitin proteasomesystem (see poster). However, when the mitochondrial membranepotential is disrupted by the ionophore CCCP, PINK1 does notreach the inner mitochondrial membrane (Narendra et al., 2010) andis not cleaved by PARL. Instead, PINK1 is targeted to the outermitochondrial membrane and becomes fully activated (Pickrell andYoule, 2015). Among other events, this leads to the recruitmentof the E3 ubiquitin ligase Parkin and removal of damagedmitochondria by mitophagy (for more details see Pickrell andYoule, 2015). Interestingly, upon CCCP treatment, the serine/threonine phosphatase PGAM5, another factor linked tomitochondrial homeostasis, is cleaved by PARL, leading to itsmature dodecameric assembly, which results in the formation oflarge fibres that eventually get released from mitochondria by anunknown mechanism (Ruiz et al., 2019; Sekine et al., 2012).Consistent with this inverse regulation of PARL activity upon CCCP-induced chemical stress, a regulatory complex consisting of thematrix protein SLP2 (also known as STOML2) and the innermembrane AAA-protease YME1L1 controls substrate access (Waiet al., 2016). Moreover, a recent proteomic survey has identifiedseveral additional PARL substrates (Saita et al., 2017). One of those isthe apoptosis factor SMAC (also known as DIABLO), which iscleaved in response to inner membrane depolarization, resulting in itsrelease into the cytosol where it sets the stage for apoptosis. Overall,PARL occupies an important role in modulating the mitochondrialmembrane proteome by performing cleavages that lead to proteinactivation, as well as triggering protein degradation, in concert withthe cytoplasmic proteasome and other mitochondrial proteases.

Endoplasmic reticulum and inner nuclear membraneThe endoplasmic reticulum (ER) is the largest cellular organelle andforms a continuous compartment with the nuclear envelope. For thesecretory pathway, the ER is the main entry point of newlysynthesized proteins and, therefore, serves as the first proteinquality control checkpoint. Since all translocated proteins begin tofold and mature here, the ER faces a huge burden of misfoldedproteins, which, if they are not removed, lead to stress (Christiansonand Ye, 2014; Ellgaard et al., 2016). The ER membraneaccommodates several proteases including the rhomboid serineprotease rhomboid-like protein 4 (RHBDL4, also known by its genename Rhbdd1) (Fleig et al., 2012), the aspartyl protease signalpeptide peptidase (SPP, encoded by HM13) (Weihofen et al., 2002),the glutamyl protease Ras-converting enzyme 1 (RCE1)(Manolaridis et al., 2013) and the metalloprotease ZMPSTE24(Quigley et al., 2013). Although most ER-membrane proteins areexcluded from the inner nuclear membrane, RCE1 and ZMPSTE24localize to peripheral ER, as well as to the inner nuclear membrane(Barrowman et al., 2008; Burrows et al., 2009).The unique proteome of the inner nuclear membrane is ensured by

nuclear pore complexes that restrict diffusion between the peripheralER and the nucleoplasm (Schirmer et al., 2003). The inner nuclearmembrane proteins, including lamins, give the nucleus its uniqueshape and are crucial for chromosome organization, and DNAreplication and repair (Guerreiro and Kind, 2019). Interestingly,RCE1 and ZMPSTE24 are important for the removal of the last three

amino acids from the so-called CAAX proteins (where ‘C’ is aprenylated cysteine that is important formembrane attachment, ‘A’ isan aliphatic amino acid and ‘X’ is any amino acid) (see poster). TheCAAX motif is found in a number of cytoplasmic and/ornucleoplasmic peripheral membrane proteins, including the RasGTPase and lamins, and its processing is a crucial step inmaturation ofthese essential factors (Michaelis and Barrowman, 2012). In addition,ZMPSTE24 is known to catalyse another cut in pre-lamin A at a sitedistinct from the CAAX motif (see poster) (Barrowman et al., 2008).This cleavage removes the prenylated C-terminal domain that anchorsthe protein at the membrane and is essential to generate mature nuclearlamin A (Pendás et al., 2002). Homozygous loss-of-functionmutations in ZMPSTE24 or mutation of the pre-protein cleavage siteboth lead to the accumulation of unprocessed pre-lamin A, which islinked to a severe laminopathy known asHutchinson–Gilford progeriasyndrome (Michaelis and Barrowman, 2012). Yet, the molecularfunction of lamin A maturation and how cleavage affects its interplaywith the nuclear lamina are important open questions.

In the peripheral ER, ZMPSTE24 serves as a crucial proteostasisfactor by removing proteins that get stuck in the Sec61 transloconchannel, one of the main protein transport pathways into the ER, asobserved for oligomers of the human islet amyloid polypeptide(IAPP) (see poster) (Ast et al., 2016; Kayatekin et al., 2018). Thisshows that ZMPSTE24 has a dual role as a protease involved inmaturation and/or activation, and protein degradation. The sameholds true for SPP, which has been initially described to removesignal peptides from the ERmembrane after they have been releasedfrom nascent chains by the signal peptidase complex (SPase) (seeposter) (Weihofen et al., 2002). For most ER-targeting signalpeptides this is predicted to lead to turnover. However, for some,such as the signal peptide of the MHC class I molecule HLA-A(SP-HLA-A; see poster), a regulatory peptide is generated, which,after its transport into the ER lumen and loading on HLA-Ereceptors, is monitored at the cell surface by natural killer cells,thereby reporting integrity of the antigen-presenting machinery(Lemberg et al., 2001). Another variation of this two-edged functionis the role of SPP as a non-canonical factor of the ER-associateddegradation (ERAD) pathway (Christianson and Ye, 2014).Although most ERAD substrates are displaced from the ER to thecytoplasm by a dislocon complex, which consists of an ERAD E3ubiquitin ligase and several auxiliary factors (Wu and Rapoport,2018), SPP-mediated proteolysis directly triggers the release anddegradation of several homeostatic ER-membrane proteins,including the unspliced form of the unfolded protein responseregulator XBP1 (Chen et al., 2014), heme oxygenase 1 (Bonameet al., 2014) and the SNARE protein syntaxin-18 (Avci et al., 2019).For the purpose of this regulated abundance control, SPP is part of a500 kDa ERAD complex that consists of the E3 ligase translocationin renal carcinoma on chromosome 8 (TRC8, also known asRNF139) and the rhomboid pseudoprotease Derlin1 (Boname et al.,2014; Chen et al., 2014; Stagg et al., 2009). Although the molecularmechanism remains to be determined, the emerging picture is that theERAD factors prime SPP-released fragments for turnover by theproteasome. Very recently, a testis-specific SPP homologue SPPL2C(SPP-like 2C) has been shown to promote male germ celldevelopment by cleaving phospholamban and ER-resident SNAREproteins (Niemeyer et al., 2019; Papadopoulou et al., 2019). Last butnot least, the rhomboid serine protease RHBDL4 funnels certainunstable membrane proteins such as the orphan subunit of the pre-Tcell antigen receptor α (pTα, also known as PTCRA) into a non-canonical branch of the ERAD pathway (see poster) (Fleig et al.,2012). In addition, RHBDL4 may also have regulatory functions in

3

CELL SCIENCE AT A GLANCE Journal of Cell Science (2019) 132, jcs217745. doi:10.1242/jcs.217745

Journal

ofCe

llScience

controlling protein secretion (Paschkowsky et al., 2016; Wan et al.,2012; Wunderle et al., 2016). In conclusion, there is a fine linebetween limited proteolysis that tunes the specific properties of asubstrate and proteolytic processing that destabilizes the protein,leading to its subsequent turnover by other degradation systems.

Golgi apparatusWith its central role in protein maturation and trafficking, the Golgicomplex hosts three intramembrane proteases, namely site-2protease (S2P, also known as MBTPS2) (Rawson et al., 1998),the aspartyl protease SPP-like 3 (SPPL3) (Nyborg et al., 2006), andthe rhomboid serine protease rhomboid-like protein 1 (RHBDL1)of unknown function (Lemberg and Freeman, 2007). Themetalloprotease S2P was the first intramembrane proteaseidentified. It acts as a key rheostat in the secretory pathwayby regulating the proteolytic release of membrane-tetheredtranscription factors, such as the sterol regulatory element-bindingproteins (SREBPs) (Rawson et al., 1998), cyclic AMP-dependenttranscription factor (ATF6) (Ye et al., 2000) and cyclic AMP-responsive element-binding protein, hepatocyte-specific (CREBH,also known as CREB3L3) (Zhang et al., 2006). This regulation bylimited proteolysis is achieved through a combination of controlledtrafficking and by the site-1 protease (S1P, also known asMBTPS1)-catalysed shedding of the luminal portion – either aloop connecting two transmembrane domains of SREBP proteins orthe ectodomain of ATF6 and CREBH – that prepares the membrane-tethered transcription factors for cleavage by S2P (see poster) (Sakaiet al., 1998). In contrast, SPPL3 influences the maturation ofother proteins by triggering the proteolytic release of Golgiglycosyltransferases such as N-acetylglucosaminyltransferase V(GnT-V, also known as MGAT5), which is thought to lead to theirdegradation within lysosomes or by extracellular proteases (seeposter) (Voss et al., 2014). Once again, some of the outlined Golgiintramembrane proteases play a role in the activation of regulatorymolecules whereas others contribute to regulated degradationcontrol of membrane-anchored enzymes.

Plasma membrane and endosomesThe plasma membrane and endosomal system together contain sixintramembrane proteases: the two catalytic subunits of γ-secretase,presenilin-1 (PSEN1) and presenilin-2 (PSEN2) (Mentrup et al.,2017; Wolfe, 2019), two additional aspartyl proteases, namely SPP-like 2A and 2B (SPPL2A and SPPL2B), and two rhomboid serineproteases, rhomboid-like proteins 2 and 3 (RHBDL2 and RHBDL3)(Lohi et al., 2004). The emerging picture is that one version of eachprotease type localizes to the plasma membrane, while a secondparalogue is found in endosomal vesicles (see poster) (Friedmannet al., 2006; Lohi et al., 2004; Sannerud and Annaert, 2009). At theinterface to the extracellular space, intramembrane proteases of thelate secretory pathway and the endosomal system join a largenumber of sheddases that remodel the cell surface and triggersecretion of bioactive molecules (Lichtenthaler et al., 2018).Presenilin proteins form the catalytic active site subunit of theγ-secretase complex, which, similarly to PARL and SPP, joinsnon-proteolytic subunits and auxiliary factors (see Box 1) (Shahet al., 2005) in order to select its substrates. Currently, around 100membrane proteins have been identified as substrates (Haapasaloand Kovacs, 2011; Hemming et al., 2008; Lichtenthaler et al.,2018). A unifying feature is that all known γ-secretase substratesface the extracellular or luminal environment with their N-terminus,a topology commonly referred to as type I membraneprotein orientation. However, the physiological consequence of

intramembrane cleavage has been revealed for only a small fractionof these γ-secretase substrates, such as its role in Alzheimer’sdisease as reviewed elsewhere (Langosch and Steiner, 2017; Wolfe,2019). Here, we will solely exemplify its activating and degradingfunction on cell-surface receptors. Upon ligand binding, receptorssuch as neurogenic locus notch homologue protein 1 (Notch1)undergo shedding by a member of the a metalloprotease of thedisintegrin and metalloproteinase (ADAM) family (Lichtenthaleret al., 2018), which prepares the remaining membrane-integralportion for a subsequent cut by the γ-secretase complex (Struhl andAdachi, 2000). The released intracellular domain of Notch1functions as a transcription activator in signalling (De Strooperet al., 1999). However, for the vast majority of other cell-surfaceproteins, cleavage by γ-secretase is believed to be crucial tomaintain plasma membrane proteostasis, thereby preventing theaccumulation of remaining transmembrane anchors (see poster)(Kopan and Ilagan, 2004). However, given the redundancy with theendolysosomal system, which removes the vast majority of plasmamembrane proteins (Winckler et al., 2018), the physiologicalrelevance of γ-secretase-mediated protein degradation remains to bedetermined.

The second group of aspartyl intramembrane proteases in theendosomal system are SPPL2A and SPPL2B, which cleave single-pass membrane proteins with the N-terminus facing the cytoplasm,referred to as type II membrane proteins (Friedmann et al., 2006;Mentrup et al., 2017). Under overexpression conditions, SPPL2Aand SPPL2B have overlapping substrate specificity; however, workin mice suggests distinct physiological functions (Schröder andSaftig, 2016). SPPL2A-catalysed cleavage of CD74, which is theinvariant chain of MHC class II molecules, has been shown tocontrol B-cell development (Beisner et al., 2013; Bergmann et al.,2013; Schneppenheim et al., 2013). During transport of MHC classII molecules to late endosomes, CD74 is proteolytically processedby the soluble cysteine protease cathepsin S (CatS, also known asCTSS), generating a membrane-anchored stub that is further cleavedby SPPL2A (see poster). While the released intracellular domain ofCD74 impacts activation of nuclear factor κB (NF-κB), defects inB-cell maturation in SPPL2A-knockout mice have been primarilyattributed to accumulation of the uncleaved CD74 transmembranestubs that disturb membrane trafficking by an unknown mechanism(Schröder and Saftig, 2016). Likewise, in the absence of SPPL2Aand/or SPPL2B, the lectin-like oxidized LDL receptor 1 (LOX1,also known as OLR1) accumulates in late endosomes, leading to itsprolonged activation and increased atherosclerosis (Mentrup et al.,2019). Whether SPPL2A and SPPL2B also play a direct role inregulated protein degradation remains to be determined.

Rhomboid proteases were initially identified in a Drosophilascreen as regulators of growth factor secretion (Freeman, 2014);however, in mammalian cells, this function is primarily performedby ADAM proteases (Lichtenthaler et al., 2018). As a recentproteomics screen identified a heterogenous set of substrates to becleaved by the plasma membrane rhomboid RHBDL2 (Johnsonet al., 2017), it is attractive to speculate about a more general role inthe proteostasis surveillance. Although the physiological functionfor the majority of identified substrates remains to be determined,RHBDL2-catalysed cleavage of thrombomodulin has been shown tocontrol remodelling of cell–cell contact points during wound healing(Cheng et al., 2011; Lohi et al., 2004), whereas cleavage of theC-type lectin domain family 14 member A (CLEC14A) has beenimplicated in regulation of angiogenesis (Noy et al., 2016). ForRHBDL3, which localizes mainly to endosomes (Lohi et al., 2004),so far no substrates are known. The emerging picture is that in both

4

CELL SCIENCE AT A GLANCE Journal of Cell Science (2019) 132, jcs217745. doi:10.1242/jcs.217745

Journal

ofCe

llScience

the late secretory pathway and the endosomal system, intramembraneproteases act as bivalent proteostasis factors, with wide physiologicalfunctions ranging from regulated intramembrane proteolysis to bulkprotein degradation.

Conclusions and outlookAlong our way through the secretory and endocytic pathways, weencounter homologous intramembrane proteases in differentcellular compartments. While the γ-secretase complex andrhomboids cleave primarily type I membrane proteins, the SPPfamily shows the opposite substrate orientation and cleaves type IImembrane proteins. Some of these intramembrane cleavage eventsrequire a preceding shedding of their substrate for recognition,whereas others can recognize full-length proteins (Lichtenthaleret al., 2018). Moreover, cleavage of polytopic membrane proteinshas been described (Fleig et al., 2012). Together with a large set ofprotein sheddases, intramembrane proteases are able to target allmembrane topologies. With the two CAAX motif-processingproteases RCE1 and ZMPSTE24 joining the intramembraneproteases (see Boxes 1 and 2), the substrate spectrum broadens toperipheral membrane proteins. Furthermore, because bacterialRCE1 homologues such as Bacillus subtilis BrsW triggerdegradation of membrane-anchored anti-sigma factors (Heinrichet al., 2009), we may speculate that mammalian CAAX proteasescan also cleave transmembrane substrates. For most intramembraneproteases, it is sufficient to overexpress the protease together with itssubstrate to observe robust cleavage. However, for RHBDL1 andRHBDL3, no substrates are yet known. Hence, under physiologicalconditions, additional factors may be required. In agreement withthis, certain intramembrane proteases have been described to formmembrane protein complexes that are potentially involved insubstrate selection and regulation (Chen et al., 2014; Lichtenthaleret al., 2018; Sekine et al., 2012; Wolfe, 2019). Other possible meansof controlling intramembrane proteolysis are regulated substratetrafficking, or the prerequisite for tailoring the substrate by sheddingthe substrate’s ectodomain, which prevents interaction with someintramembrane proteases (Lichtenthaler et al., 2018). However,some proteases, such as rhomboids, can cleave membrane proteinswithout prior shedding, pointing to a more diverse substrate-selection mechanism. In some cases, this is linked to recognition ofmetastable transmembrane domains, but site-specific recognition ofconsensus sequences has also been observed (Langosch et al.,2015). This bivalent substrate recognition mechanism, includingsampling transmembrane helix stability as well recognizing putativecleavage-site motifs, mirrors the wide range of different functions.For certain intramembrane proteases such as the SPP and presenilinfamilies, a function in activation and degradation is already known.Owing to the growing understanding of the protease–substraterelationship as outlined in this review, it emerges that in contrast tomost other proteases, a given intramembrane protease can do both –activate and degrade their membrane protein substrates. It will beimportant to reveal whether the cleavage decision-making process isentirely determined by the substrates, or whether differences on theprotease side such as varying adaptor proteins govern this biologicaldistinction. A detailed understanding of the intramembrane proteasemechanism as well as defining their physiological substratespectrum will reveal whether such a dual role in activationcleavage and protein degradation is a common principle.

AcknowledgementsWe thank Donem Avci for critical reading of the manuscript. Due to word limitation,we cannot cite every study and want to apologise to colleagues whose work couldnot be mentioned.

Competing interestsThe authors declare no competing or financial interests.

FundingThis work was supported by funds from the Deutsche Forschungsgemeinschaft(grants SFB1036, TP12).

Cell science at a glanceA high-resolution version of the poster and individual poster panels are available fordownloading at http://jcs.biologists.org/lookup/doi/10.1242/jcs.217745.supplemental.

ReferencesAst, T., Michaelis, S. and Schuldiner, M. (2016). The protease Ste24 clears

clogged translocons. Cell 164, 103-114. doi:10.1016/j.cell.2015.11.053Avci, D. and Lemberg, M. K. (2015). Clipping or extracting: two ways to membrane

protein degradation. Trends Cell Biol. 25, 611-622. doi:10.1016/j.tcb.2015.07.003Avci, D., Malchus, N. S., Heidasch, R., Lorenz, H., Richter, K., Nessling, M. and

Lemberg, M. K. (2019). The intramembrane protease SPP impacts morphologyof the endoplasmic reticulum by triggering degradation of morphogenic proteins.J. Biol. Chem. 294, 2786-2800. doi:10.1074/jbc.RA118.005642

Barrowman, J., Hamblet, C., George, C. M. and Michaelis, S. (2008). Analysis ofprelamin A biogenesis reveals the nucleus to be aCaaX processing compartment.Mol. Biol. Cell 19, 5398-5408. doi:10.1091/mbc.e08-07-0704

Beisner, D. R., Langerak, P., Parker, A. E., Dahlberg, C., Otero, F. J., Sutton,S. E., Poirot, L., Barnes, W., Young, M. A., Niessen, S. et al. (2013). Theintramembrane protease Sppl2a is required for B cell and DC development andsurvival via cleavage of the invariant chain. J. Exp. Med. 210, 23-30. doi:10.1084/jem.20121072

Bergmann, H., Yabas, M., Short, A., Miosge, L., Barthel, N., Teh, C. E., Roots,C. M., Bull, K. R., Jeelall, Y., Horikawa, K. et al. (2013). B cell survival, surfaceBCR and BAFFR expression, CD74 metabolism, and CD8- dendritic cells requirethe intramembrane endopeptidase SPPL2A. J. Exp. Med. 210, 31-40. doi:10.1084/jem.20121076

Boname, J. M., Bloor, S., Wandel, M. P., Nathan, J. A., Antrobus, R., Dingwell,K. S., Thurston, T. L., Smith, D. L., Smith, J. C., Randow, F. et al. (2014).Cleavage by signal peptide peptidase is required for the degradation of selectedtail-anchored proteins. J. Cell Biol. 205, 847-862. doi:10.1083/jcb.201312009

Brown, M. S., Ye, J., Rawson, R. B. and Goldstein, J. L. (2000). Regulatedintramembrane proteolysis: a control mechanism conserved from bacteria tohumans. Cell 100, 391-398. doi:10.1016/S0092-8674(00)80675-3

Burrows, J. F., Kelvin, A. A., McFarlane, C., Burden, R. E., McGrattan, M. J., Dela Vega,M., Govender, U., Quinn, D. J., Dib, K., Gadina, M. et al. (2009). USP17regulates Ras activation and cell proliferation by blocking RCE1 activity. J. Biol.Chem. 284, 9587-9595. doi:10.1074/jbc.M807216200

Chen, C., Malchus, N. S., Hehn, B., Stelzer, W., Avci, D., Langosch, D. andLemberg, M. K. (2014). Signal peptide peptidase functions in ERAD to cleave theunfolded protein response regulator XBP1u. EMBO J. 33, 2492-2506. doi:10.15252/embj.201488208

Cheng, T.-L., Wu, Y.-T., Lin, H.-Y., Hsu, F.-C., Liu, S.-K., Chang, B.-I., Chen,W.-S., Lai, C.-H., Shi, G.-Y. and Wu, H.-L. (2011). Functions of rhomboid familyprotease RHBDL2 and thrombomodulin in wound healing. J. Invest. Dermatol.131, 2486-2494. doi:10.1038/jid.2011.230

Christianson, J. C. and Ye, Y. (2014). Cleaning up in the endoplasmic reticulum:ubiquitin in charge. Nat. Struct. Mol. Biol. 21, 325-335. doi:10.1038/nsmb.2793

Ciechanover, A. and Kwon, Y. T. (2015). Degradation of misfolded proteins inneurodegenerative diseases: therapeutic targets and strategies. Exp. Mol. Med.47, e147. doi:10.1038/emm.2014.117

De Strooper, B., Annaert, W., Cupers, P., Saftig, P., Craessaerts, K., Mumm,J. S., Schroeter, E. H., Schrijvers, V., Wolfe, M. S., Ray, W. J. et al. (1999). Apresenilin-1-dependent gamma-secretase-like protease mediates release ofNotch intracellular domain. Nature 398, 518-522. doi:10.1038/19083

Ellgaard, L., McCaul, N., Chatsisvili, A. and Braakman, I. (2016). Co- and post-translational protein folding in the ER. Traffic 17, 615-638. doi:10.1111/tra.12392

Feng, L., Yan, H., Wu, Z., Yan, N., Wang, Z., Jeffrey, P. D. and Shi, Y. (2007).Structure of a site-2 protease family intramembrane metalloprotease. Science318, 1608-1612. doi:10.1126/science.1150755

Fleig, L., Bergbold, N., Sahasrabudhe, P., Geiger, B., Kaltak, L. and Lemberg,M. K. (2012). Ubiquitin-dependent intramembrane rhomboid protease promotesERAD of membrane proteins. Mol. Cell 47, 558-569. doi:10.1016/j.molcel.2012.06.008

Freeman, M. (2014). The rhomboid-like superfamily: molecular mechanisms andbiological roles. Annu. Rev. Cell Dev. Biol. 30, 235-254. doi:10.1146/annurev-cellbio-100913-012944

Friedmann, E., Hauben, E., Maylandt, K., Schleeger, S., Vreugde, S.,Lichtenthaler, S. F., Kuhn, P. H., Stauffer, D., Rovelli, G. and Martoglio, B.(2006). SPPL2a and SPPL2b promote intramembrane proteolysis of TNFalpha inactivated dendritic cells to trigger IL-12 production. Nat. Cell Biol. 8, 843-848.doi:10.1038/ncb1440

5

CELL SCIENCE AT A GLANCE Journal of Cell Science (2019) 132, jcs217745. doi:10.1242/jcs.217745

Journal

ofCe

llScience

Guerreiro, I. and Kind, J. (2019). Spatial chromatin organization and generegulation at the nuclear lamina. Curr. Opin. Genet. Dev. 55, 19-25. doi:10.1016/j.gde.2019.04.008

Haapasalo, A. and Kovacs, D. M. (2011). The many substrates of presenilin/gamma-secretase. J. Alzheimers Dis. 25, 3-28. doi:10.3233/JAD-2011-101065

Haynes, C. M. and Ron, D. (2010). The mitochondrial UPR-protecting organelleprotein homeostasis. J. Cell Sci. 123, 3849-3855. doi:10.1242/jcs.075119

Heinrich, J., Hein, K. andWiegert, T. (2009). Two proteolytic modules are involvedin regulated intramembrane proteolysis of Bacillus subtilis RsiW. Mol. Microbiol.74, 1412-1426. doi:10.1111/j.1365-2958.2009.06940.x

Hemming, M. L., Elias, J. E., Gygi, S. P. and Selkoe, D. J. (2008). Proteomicprofiling of gamma-secretase substrates and mapping of substrate requirements.PLoS Biol. 6, e257. doi:10.1371/journal.pbio.0060257

Jeyaraju, D. V., Xu, L., Letellier, M.-C., Bandaru, S., Zunino, R., Berg, E. A.,McBride, H. M. and Pellegrini, L. (2006). Phosphorylation and cleavage ofpresenilin-associated rhomboid-like protein (PARL) promotes changes inmitochondrial morphology. Proc. Natl. Acad. Sci. USA 103, 18562-18567.doi:10.1073/pnas.0604983103

Jin, S. M., Lazarou, M., Wang, C., Kane, L. A., Narendra, D. P. and Youle, R. J.(2010). Mitochondrial membrane potential regulates PINK1 import and proteolyticdestabilization by PARL. J. Cell Biol. 191, 933-942. doi:10.1083/jcb.201008084

Johnson, N., Brezinova, J., Stephens, E., Burbridge, E., Freeman, M., Adrain,C. and Strisovsky, K. (2017). Quantitative proteomics screen identifies asubstrate repertoire of rhomboid protease RHBDL2 in human cells and implicatesit in epithelial homeostasis. Sci. Rep. 7, 7283. doi:10.1038/s41598-017-07556-3

Kayatekin, C., Amasino, A., Gaglia, G., Flannick, J., Bonner, J. M., Fanning, S.,Narayan, P., Barrasa, M. I., Pincus, D., Landgraf, D. et al. (2018). Translocondeclogger Ste24 protects against IAPP oligomer-induced proteotoxicity. Cell 173,62-73.e9. doi:10.1016/j.cell.2018.02.026

Kopan, R. and Ilagan, M. X. (2004). Gamma-secretase: proteasome of themembrane? Nat. Rev. Mol. Cell Biol. 5, 499-504. doi:10.1038/nrm1406

Langosch, D. and Steiner, H. (2017). Substrate processing in intramembraneproteolysis by gamma-secretase - the role of protein dynamics. Biol. Chem. 398,441-453. doi:10.1515/hsz-2016-0269

Langosch, D., Scharnagl, C., Steiner, H. and Lemberg, M. K. (2015).Understanding intramembrane proteolysis: from protein dynamics to reactionkinetics. Trends Biochem. Sci. 40, 318-327. doi:10.1016/j.tibs.2015.04.001

Lee, J. R., Urban, S., Garvey, C. F. and Freeman, M. (2001). Regulatedintracellular ligand transport and proteolysis control EGF signal activation inDrosophila. Cell 107, 161-171. doi:10.1016/S0092-8674(01)00526-8

Lemberg, M. K. and Freeman, M. (2007). Functional and evolutionary implicationsof enhanced genomic analysis of rhomboid intramembrane proteases. GenomeRes. 17, 1634-1646. doi:10.1101/gr.6425307

Lemberg, M. K., Bland, F. A., Weihofen, A., Braud, V. M. and Martoglio, B.(2001). Intramembrane proteolysis of signal peptides: an essential step in thegeneration of HLA-E epitopes. J. Immunol. 167, 6441-6446. doi:10.4049/jimmunol.167.11.6441

Li, X., Dang, S., Yan, C., Gong, X., Wang, J. and Shi, Y. (2013). Structure of apresenilin family intramembrane aspartate protease. Nature 493, 56-61. doi:10.1038/nature11801

Lichtenthaler, S. F., Lemberg, M. K. and Fluhrer, R. (2018). Proteolyticectodomain shedding of membrane proteins in mammals-hardware, concepts,and recent developments. EMBO J. 37, e99456. doi:10.15252/embj.201899456

Lohi, O., Urban, S. and Freeman, M. (2004). Diverse substrate recognitionmechanisms for rhomboids; thrombomodulin is cleaved by Mammalianrhomboids. Curr. Biol. 14, 236-241. doi:10.1016/S0960-9822(04)00008-9

Manolaridis, I., Kulkarni, K., Dodd, R. B., Ogasawara, S., Zhang, Z., Bineva, G.,O’Reilly, N., Hanrahan, S. J., Thompson, A. J., Cronin, N. et al. (2013).Mechanism of farnesylated CAAX protein processing by the intramembraneprotease Rce1. Nature 504, 301-305. doi:10.1038/nature12754

Meissner, C., Lorenz, H., Hehn, B. and Lemberg, M. K. (2015). Intramembraneprotease PARL defines a negative regulator of PINK1- and PARK2/Parkin-dependent mitophagy. Autophagy 11, 1484-1498. doi:10.1080/15548627.2015.1063763

Mentrup, T., Fluhrer, R. and Schroder, B. (2017). Latest emerging functions ofSPP/SPPL intramembrane proteases. Eur. J. Cell Biol. 96, 372-382. doi:10.1016/j.ejcb.2017.03.002

Mentrup, T., Theodorou, K., Cabrera-Cabrera, F., Helbig, A. O., Happ, K.,Gijbels, M., Gradtke, A. C., Rabe, B., Fukumori, A., Steiner, H. et al. (2019).Atherogenic LOX-1 signaling is controlled by SPPL2-mediated intramembraneproteolysis. J. Exp. Med. 216, 807-830. doi:10.1084/jem.20171438

Michaelis, S. and Barrowman, J. (2012). Biogenesis of the Saccharomycescerevisiae pheromone a-factor, from yeast mating to human disease. Microbiol.Mol. Biol. Rev. 76, 626-651. doi:10.1128/MMBR.00010-12

Narendra, D. P., Jin, S. M., Tanaka, A., Suen, D.-F., Gautier, C. A., Shen, J.,Cookson, M. R. and Youle, R. J. (2010). PINK1 is selectively stabilized onimpaired mitochondria to activate Parkin. PLoS Biol. 8, e1000298. doi:10.1371/journal.pbio.1000298

Niemeyer, J., Mentrup, T., Heidasch, R., Muller, S. A., Biswas, U., Meyer, R.,Papadopoulou, A. A., Dederer, V., Haug-Kroper, M., Adamski, V. et al. (2019).

The intramembrane protease SPPL2c promotes male germ cell development bycleaving phospholamban. EMBO Rep. 20, e46449. doi:10.15252/embr.201846449

Noy, P. J., Swain, R. K., Khan, K., Lodhia, P. and Bicknell, R. (2016). Sproutingangiogenesis is regulated by shedding of the C-type lectin family 14, member A(CLEC14A) ectodomain, catalyzed by rhomboid-like 2 protein (RHBDL2). FASEBJ. 30, 2311-2323. doi:10.1096/fj.201500122R

Nyborg, A. C., Ladd, T. B., Jansen, K., Kukar, T. and Golde, T. E. (2006).Intramembrane proteolytic cleavage by human signal peptide peptidase like 3 andmalaria signal peptide peptidase. FASEB J. 20, 1671-1679. doi:10.1096/fj.06-5762com

Papadopoulou, A. A., Muller, S. A., Mentrup, T., Shmueli, M. D., Niemeyer, J.,Haug-Kroper, M., von Blume, J., Mayerhofer, A., Feederle, R., Schroder, B.et al. (2019). Signal peptide peptidase-like 2c (SPPL2c) impairs vesiculartransport and cleavage of SNARE proteins. EMBO Rep. 20, e46451. doi:10.15252/embr.201846451

Paschkowsky, S., Hamze, M., Oestereich, F. and Munter, L. M. (2016).Alternative processing of the amyloid precursor protein family by rhomboidprotease RHBDL4. J. Biol. Chem. 291, 21903-21912. doi:10.1074/jbc.M116.753582

Pendas, A. M., Zhou, Z., Cadinanos, J., Freije, J. M. P., Wang, J., Hultenby, K.,Astudillo, A., Wernerson, A., Rodrıguez, F., Tryggvason, K. et al. (2002).Defective prelamin A processing and muscular and adipocyte alterations inZmpste24 metalloproteinase-deficient mice. Nat. Genet. 31, 94-99. doi:10.1038/ng871

Pickrell, A. M. and Youle, R. J. (2015). The roles of PINK1, parkin, andmitochondrial fidelity in Parkinson’s disease. Neuron 85, 257-273. doi:10.1016/j.neuron.2014.12.007

Pryor, E. E., Jr., Horanyi, P. S., Clark, K. M., Fedoriw, N., Connelly, S. M.,Koszelak-Rosenblum, M., Zhu, G., Malkowski, M. G., Wiener, M. C. andDumont, M. E. (2013). Structure of the integral membrane protein CAAX proteaseSte24p. Science 339, 1600-1604. doi:10.1126/science.1232048

Quigley, A., Dong, Y. Y., Pike, A. C. W., Dong, L., Shrestha, L., Berridge, G.,Stansfeld, P. J., Sansom, M. S. P., Edwards, A. M., Bountra, C. et al. (2013).The structural basis of ZMPSTE24-dependent laminopathies. Science 339,1604-1607. doi:10.1126/science.1231513

Rawson, R. B., Cheng, D., Brown, M. S. and Goldstein, J. L. (1998). Isolation ofcholesterol-requiring mutant Chinese hamster ovary cells with defects in cleavageof sterol regulatory element-binding proteins at site 1. J. Biol. Chem. 273,28261-28269. doi:10.1074/jbc.273.43.28261

Ruiz, K., Thaker, T. M., Agnew, C., Miller-Vedam, L., Trenker, R., Herrera, C.,Ingaramo, M., Toso, D., Frost, A. and Jura, N. (2019). Functional role of PGAM5multimeric assemblies and their polymerization into filaments. Nat. Commun. 10,531. doi:10.1038/s41467-019-08393-w

Saita, S., Nolte, H., Fiedler, K. U., Kashkar, H., Venne, A. S., Zahedi, R. P.,Kruger, M. and Langer, T. (2017). PARLmediates Smac proteolytic maturation inmitochondria to promote apoptosis. Nat. Cell Biol. 19, 318-328. doi:10.1038/ncb3488

Sakai, J., Rawson, R. B., Espenshade, P. J., Cheng, D., Seegmiller, A. C.,Goldstein, J. L. and Brown, M. S. (1998). Molecular identification of the sterol-regulated luminal protease that cleaves SREBPs and controls lipid composition ofanimal cells. Mol. Cell 2, 505-514. doi:10.1016/S1097-2765(00)80150-1

Sannerud, R. and Annaert, W. (2009). Trafficking, a key player in regulatedintramembrane proteolysis. Semin. Cell Dev. Biol. 20, 183-190. doi:10.1016/j.semcdb.2008.11.004

Schirmer, E. C., Florens, L., Guan, T., Yates, J. R., III and Gerace, L. (2003).Nuclear membrane proteins with potential disease links found by subtractiveproteomics. Science 301, 1380-1382. doi:10.1126/science.1088176

Schneppenheim, J., Dressel, R., Huttl, S., Lullmann-Rauch, R., Engelke, M.,Dittmann, K., Wienands, J., Eskelinen, E.-L., Hermans-Borgmeyer, I.,Fluhrer, R. et al. (2013). The intramembrane protease SPPL2a promotes B celldevelopment and controls endosomal traffic by cleavage of the invariant chain.J. Exp. Med. 210, 41-58. doi:10.1084/jem.20121069

Schroder, B. and Saftig, P. (2016). Intramembrane proteolysis within lysosomes.Ageing Res. Rev. 32, 51-64. doi:10.1016/j.arr.2016.04.012

Sekine, S., Kanamaru, Y., Koike, M., Nishihara, A., Okada, M., Kinoshita, H.,Kamiyama, M., Maruyama, J., Uchiyama, Y., Ishihara, N. et al. (2012).Rhomboid protease PARL mediates the mitochondrial membrane potential loss-induced cleavage of PGAM5. J. Biol. Chem. 287, 34635-34645. doi:10.1074/jbc.M112.357509

Shah, S., Lee, S.-F., Tabuchi, K., Hao, Y.-H., Yu, C., LaPlant, Q., Ball, H., Dann,C. E., III, Sudhof, T. and Yu, G. (2005). Nicastrin functions as a gamma-secretase-substrate receptor. Cell 122, 435-447. doi:10.1016/j.cell.2005.05.022

Spinazzi, M. and De Strooper, B. (2016). PARL: the mitochondrial rhomboidprotease. Semin. Cell Dev. Biol. 60, 19-28. doi:10.1016/j.semcdb.2016.07.034

Stagg, H. R., Thomas, M., van denBoomen, D., Wiertz, E. J. H. J., Drabkin, H. A.,Gemmill, R. M. and Lehner, P. J. (2009). The TRC8 E3 ligase ubiquitinates MHCclass I molecules before dislocation from the ER. J. Cell Biol. 186, 685-692.doi:10.1083/jcb.200906110

6

CELL SCIENCE AT A GLANCE Journal of Cell Science (2019) 132, jcs217745. doi:10.1242/jcs.217745

Journal

ofCe

llScience

Struhl, G. and Adachi, A. (2000). Requirements for presenilin-dependent cleavageof notch and other transmembrane proteins. Mol. Cell 6, 625-636. doi:10.1016/S1097-2765(00)00061-7

Sun, L., Li, X. and Shi, Y. (2016). Structural biology of intramembrane proteases:mechanistic insights from rhomboid and S2P to gamma-secretase. Curr. Opin.Struct. Biol. 37, 97-107. doi:10.1016/j.sbi.2015.12.008

Voss, M., Kunzel, U., Higel, F., Kuhn, P. H., Colombo, A., Fukumori, A., Haug-Kroper, M., Klier, B., Grammer, G., Seidl, A. et al. (2014). Shedding of glycan-modifying enzymes by signal peptide peptidase-like 3 (SPPL3) regulates cellularN-glycosylation. EMBO J. 33, 2890-2905. doi:10.15252/embj.201488375

Wai, T., Saita, S., Nolte, H., Muller, S., Konig, T., Richter-Dennerlein, R.,Sprenger, H. G., Madrenas, J., Muhlmeister, M., Brandt, U. et al. (2016). Themembrane scaffold SLP2 anchors a proteolytic hub in mitochondria containingPARL and the i-AAA protease YME1L. EMBORep. 17, 1844-1856. doi:10.15252/embr.201642698

Wan, C., Fu, J., Wang, Y., Miao, S., Song, W. and Wang, L. (2012). Exosome-relatedmulti-pass transmembrane protein TSAP6 is a target of rhomboid proteaseRHBDD1-induced proteolysis. PLoS ONE 7, e37452. doi:10.1371/journal.pone.0037452

Wang, Y., Zhang, Y. and Ha, Y. (2006). Crystal structure of a rhomboid familyintramembrane protease. Nature 444, 179-180. doi:10.1038/nature05255

Weihofen, A., Binns, K., Lemberg, M. K., Ashman, K. and Martoglio, B. (2002).Identification of signal peptide peptidase, a presenilin-type aspartic protease.Science 296, 2215-2218. doi:10.1126/science.1070925

Winckler, B., Faundez, V., Maday, S., Cai, Q., Guimas Almeida, C. and Zhang, H.(2018). The endolysosomal system and proteostasis: from development todegeneration. J. Neurosci. 38, 9364-9374. doi:10.1523/JNEUROSCI.1665-18.2018

Wolfe, M. S. (2019). Dysfunctional gamma-secretase in familial Alzheimer’sdisease. Neurochem. Res. 44, 5-11. doi:10.1007/s11064-018-2511-1

Wu, X. and Rapoport, T. A. (2018). Mechanistic insights into ER-associated proteindegradation. Curr. Opin. Cell Biol. 53, 22-28. doi:10.1016/j.ceb.2018.04.004

Wunderle, L., Knopf, J. D., Kuhnle, N., Morle, A., Hehn, B., Adrain, C.,Strisovsky, K., Freeman, M. and Lemberg, M. K. (2016). Rhomboidintramembrane protease RHBDL4 triggers ER-export and non-canonicalsecretion of membrane-anchored TGFalpha. Sci. Rep. 6, 27342. doi:10.1038/srep27342

Yang, G., Zhou, R., Zhou, Q., Guo, X., Yan, C., Ke, M., Lei, J. and Shi, Y. (2019).Structural basis of Notch recognition by human gamma-secretase. Nature 565,192-197. doi:10.1038/s41586-018-0813-8

Ye, J., Rawson,R. B., Komuro, R., Chen, X., Dave, U. P., Prywes, R., Brown,M. S.and Goldstein, J. L. (2000). ER stress induces cleavage of membrane-boundATF6 by the same proteases that process SREBPs. Mol. Cell 6, 1355-1364.doi:10.1016/S1097-2765(00)00133-7

Zhang, K., Shen, X., Wu, J., Sakaki, K., Saunders, T., Rutkowski, D. T., Back,S. H. and Kaufman, R. J. (2006). Endoplasmic reticulum stress activatescleavage of CREBH to induce a systemic inflammatory response. Cell 124,587-599. doi:10.1016/j.cell.2005.11.040

7

CELL SCIENCE AT A GLANCE Journal of Cell Science (2019) 132, jcs217745. doi:10.1242/jcs.217745

Journal

ofCe

llScience