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Molecular Cell

Article

Granzyme B-Dependent Proteolysis Acts as a Switchto Enhance the Proinflammatory Activity of IL-1a

Inna S. Afonina,1 Graham A. Tynan,2 Susan E. Logue,1 Sean P. Cullen,1 Michael Bots,3 Alexander U. Luthi,1

Emer P. Reeves,4 Noel G. McElvaney,4 Jan P. Medema,3 Ed C. Lavelle,2 and Seamus J. Martin1,*1Molecular Cell Biology Laboratory, Department of Genetics, The Smurfit Institute, Trinity College, Dublin 2, Ireland2Adjuvant Research Group, School of Biochemistry and Immunology, Trinity College, Dublin 2, Ireland3LEXOR (Lab of Experimental Oncology and Radiobiology), Center for Experimental Molecular Medicine,

Academic Medical Center (AMC), Amsterdam, The Netherlands4Respiratory Research Division, Department of Medicine, Education and Research Centre, Royal College of Surgeons in Ireland,

Beaumont Hospital, Dublin 9, Ireland

*Correspondence: [email protected]

DOI 10.1016/j.molcel.2011.07.037

SUMMARY

Granzyme B is a cytotoxic lymphocyte-derived pro-

tease that plays a central role in promoting apoptosis

of virus-infected target cells, through direct proteol-

ysis and activation of constituents of the cell death

machinery. However, previous studies have also

implicated granzymes A and B in the production of

proinflammatory cytokines, via a mechanism that

remains undefined. Here we show that IL-1a is a sub-

strate for granzyme B and that proteolysis potently

enhanced the biological activity of this cytokine

in vitro as well as in vivo. Consistent with this, com-

pared with full-length IL-1a, granzyme B-processed

IL-1a exhibited more potent activity as an immu-

noadjuvant in vivo. Furthermore, proteolysis of

IL-1a within the same region, by proteases such as

calpain and elastase, was also found to enhance its

biological potency. Thus, IL-1a processing by

multiple immune-related proteases, including gran-

zyme B, acts as a switch to enhance the proinflam-

matory properties of this cytokine.

INTRODUCTION

Granzyme (Gzm) B is a protease typically found in the cytotoxicgranules of Natural Killer (NK) and cytotoxic T cells (CTLs) and,

upon delivery into the cytoplasm of virus-infected target cells,

promotes apoptosis to limit virus replication and dissemination

(reviewed in Afonina et al., 2010). Gzm B promotes apoptosis

through proteolysis of the BH3-only protein Bid, as well as via

proteolytic processing and activation of caspase-3 (Afonina

et al., 2010). However, accumulating evidence suggests that

granzymes A and B may also influence the production of proin-

flammatory cytokines, although the molecular targets of these

proteases in inflammatory contexts remain to be defined (Sower

et al., 1996a,b; Metkaret al., 2008; Froelich et al., 2009). Interest-

ingly, a number of noncytotoxic cell types, such as mast cells

and basophils, have also been found to secrete Gzm B upon

activation (Tschopp et al., 2006; Strik et al., 2007). Furthermore,Gzm B is found at elevated levels in serum from rheumatoid

arthritis (RA) patients and in other inflammatory conditions asso-

ciated with elevated levels of IL-1 (Lauw et al., 2000; Tak et al.,

1999; Kim et al., 2007). For these reasons, we explored whether

Gzm B may contribute to the processing and activation of IL-1.

IL-1 is a cytokine with diverse biological activities and is

produced in the early stages of infection or sterile injury, where

it plays an importantrole in instigating immune responses(Dinar-

ello, 1996; Kono et al., 2010). Although IL-1 is produced in two

different forms (IL-1a and IL-1b), encoded by distinct genes,

these cytokines bind to the same receptor and share similar bio-

logical activities (Dinarello, 1996). Despite their relatedness in

structure and biological activity, IL-1a and IL-1b are posttransla-

tionally processed in a very different manner. IL-1a is expressed

as a $31 kDa polypeptide, and in this form is capable of binding

to the IL-1 receptor and is biologically active (Mosley et al.,

1987a,b). IL-1b is also expressed as a $31 kDa polypeptide,

but in marked contrast to IL-1a, full-length IL-1b is incapable of

binding to the IL-1 receptor and, consequently, exhibits little bio-

logical activity (Mosley et al., 1987a,b; Hazudaet al., 1991). IL-1b

acquires biological activity upon limited internal processing by

the aspartic acid-specific protease caspase-1 (Thornberry

et al., 1992). Caspase-1-dependent processing of IL-1b at

Asp116 unlocks the biological activity of this cytokine. Gzm A

has also been found to cleave IL-1b in vitro, however the func-

tional consequences of this event remain unclear (Irmler et al.,

1995).IL-1a is typically released from cells as a result of injury or

death, and circulating IL-1a levels are persistently elevated in

inflammatory conditions such as RA. Although full-length IL-1a

displays biological activity, this cytokine is susceptible to

proteolysis by certain intracellular proteases. For example, the

calcium-activated protease, calpain-1, promotes restricted

proteolysis of IL-1a to produce a $17 kDa protein, although

this reportedly has little effect on the biological activity of this

cytokine (Kobayashi et al., 1990; Carruth et al., 1991). Therefore,

it remains unclear what role calpain-mediated processing of

IL-1a serves. As a full-length protein, IL-1a is typically cell-asso-

ciated, and a portion of this cell-associated form may be present

Molecular Cell 44, 265278, October 21, 2011 2011 Elsevier Inc. 265
mailto:[email protected]://dx.doi.org/10.1016/j.molcel.2011.07.037http://dx.doi.org/10.1016/j.molcel.2011.07.037mailto:[email protected]

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Figure 1. IL-1a Is a Substrate for Granzyme B

(A) 35S-labeled IL-1a, IL-1b, and Bid were incubated at 37C for 2 hr, either alone or in the presence of recombinant caspase-1, -4, -5 (20 nM), caspase-3, -7, or

granzyme B (200 nM), followed by analysis by SDS-PAGE/fluorography.

(B)35

S-labeled IL-1a, IL-1b, and Bid were incubated for 2 hr at 37C with the indicated concentrations of granzyme B and analyzed as in (A).

(C) Recombinant purified full-length IL-1a was incubated at 37C for 2 hr with the indicated concentrations of granzyme B and analyzed by SDS-PAGE with

Coomassie staining. IL-1a cleavage fragments were excised from the gel and analyzed by MALDI-TOF mass spectrometry. Mass spectra of cleavage fragments

are indicated, with coverage of the two cleavage fragments underlined in blue and red, respectively.

(D) Schematic representation of IL-1a indicating nuclear localization signal and granzyme B and calpain-1 cleavage sites. A sequence alignment of the putative

granzyme B cleavage site in IL-1a from a number of mammals is shown to the right. The P1 Asp residue is indicated.

(E) 35S-labeled IL-1aWT and IL-1aD103A mutant were incubated at 37C for 2 hr with the indicated concentrations of granzyme B, followed by analysis by

SDS-PAGE/fluorography.

Molecular Cell

Proteolysis of IL-1a Potentiates Bioactivity

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at the plasma membrane (Kurt-Jones et al., 1985). Proteolytic

processing of IL-1a may remove a nuclear localization signal or

permit shedding of membrane-associated IL-1a and increase

thelikelihood of secretion (Watanabe and Kobayashi, 1994; Mat-

sushima et al., 1986). Thus, proteolysis of IL-1a may convert thiscytokine from a cell-associated form to a soluble molecule that

could exert more systemic effects. An additional possibility is

that proteolysis of IL-1a may modulate the biological potency

of this cytokine, although this issue has not been explored in

any detail.

Here we report that human IL-1a, but not IL-1b, is a substrate

for the CTL/NK cell protease, Gzm B, and that processing of this

cytokine by the latter protease enhanced its biological activity

several-fold. A similar increase in IL-1a activity was also seen

upon processing of IL-1a by other proteases, such as calpain-1,

elastase, and mast cell chymase. Thus, Gzm B and other prote-

ases that are produced during inflammatory responses may

promote inflammation, at least in part, through conversion of

pro-IL-1a to its mature form.

RESULTS

IL-1a Is a Substrate for Granzyme B

Because recent studies have suggested that CTL/NK granzymes

may have extracellular proinflammatory roles, we set out to

explore whether Gzm B was capable of processing any of the

major proinflammatory cytokines. To address this issue, we

screened a panel of in vitro transcribed and translated members

of the interleukin family (IL-1 to IL-17) for susceptibility to prote-

olysis by Gzm B, as well as a range of other aspartic acid-

specific proteases as controls (data not shown). All proteases

were confirmed to be active by virtue of their ability to cleave

synthetic tetrapeptide substrates (data not shown) or control

proteins such as Bid (Figure 1A). The outcome of this screen

identified full-length IL-1a as a substrate for Gzm B but not for

any of the other proteases tested. As Figure 1A shows, whereas

caspases-1, -3, -4, -5, -and -7 failed to cleave IL-1a, Gzm B

produced a major cleavage product at $17 kDa. In contrast,

Gzm B did not cleave IL-1b, whereas caspase-1 did so, as ex-

pected (Figure 1A). To confirm the specificity of IL-1a proteolysis

by Gzm B, we titrated this protease over a range of concentra-

tions from 12.5 to 100 nM. IL-1b failed to be cleaved by Gzm B

at any of these concentrations, whereas proteolysis of IL-1a,

as well as theknown Gzm B substrate, Bid, wasreadily observed

(Figure1B).Importantly, because human andmurineGzmB have

been shown to have divergent substrate preferences (Cullenet al., 2007), we also tested whether murine IL-1awasa substrate

for Gzm B and found thatboth human and mouse Gzm B cleaved

murine IL-1a within the nanomolar range (Figures S1A and S1B).

IL-1a Is Cleaved by Granzyme B at Asp103

To map the Gzm B cleavage site within IL-1a, we expressed and

purified the full-length cytokine from E. coli and incubated re-

combinant IL-1a with Gzm B to promote proteolysis. Cleavage

products were then analyzed by mass spectrometry, which sug-

gested that proteolysis occurred between amino acids 80 and

112 (Figure 1C). Because Gzm B has an almost absolute prefer-

ence for proteolysis after Asp residues and typically cleaves

within IXXD/S motifs, this suggested that IL-1a was cleaved afterAsp103, within the motif IAND103, which is conserved among

mammals (Figure 1D). To confirm this as the site of proteolysis,

we generated a point mutation Asp > Ala103 in IL-1a and tested

the susceptibility of this mutant to proteolysis by Gzm B. As

Figure 1E shows, this mutant fully resisted proteolysis, as did a

deletion mutant of IL-1a lacking the N-terminal 103 amino acids

(Figure 1F), confirming that Gzm B cleaves IL-1a at Asp103.

Granzyme B-Mediated Proteolysis of IL-1a Potentiates

Biological Activity

Previous studies have shown that calpain-1 can process IL-1a at

Phe118 (Kobayashi et al., 1990), however the significance of this

cleavage event for IL-1a bioactivity has not been determined.

Indeed, it is widely assumed that proteolytic processing of

IL-1a within its N-terminal region has little effect on the biological

activity of this cytokine. For these reasons, we wondered

whether Gzm B-mediated processing of IL-1a could impact

upon its biological activity. To explore this issue, we measured

the ability of IL-1a to stimulate production of IL-6 and IL-8 from

HeLa cells and primary HUVECs, as both cell types are known

to respond to this cytokine (Bertelsen and Sanfridson, 2007;

Rhim et al., 2008).

To mimic the Gzm B cleavage product of IL-1a, we generated

a truncated form of this cytokine, missing the N-terminal 103

amino acids (IL-1a104271). Using this form of IL-1a we confirmed

that both HeLa cells and primary HUVECs were highly respon-

sive to this cytokine (Figure 2A), with both cell types producing

IL-6 and IL-8 in response to IL-1a104271. HUVECs also pro-

duced GM-CSF under the same conditions (Figure 2A). These

observations confirmed that truncation of IL-1a after Asp103

produced a biologically active cytokine. However, this type of

artificial truncation does not necessarily faithfully reproduce

the natural cleaved form of full-length IL-1a, as proteolysis of a

protein does not necessarily disassociate the resulting cleavage

products.

To compare the effects of Gzm B-mediated proteolysis of

IL-1a with the full-length cytokine, we incubated bacterially ex-

pressed IL-1a precursor in the presence or absence of Gzm B,

followed by assessment of biological activity as above. Surpris-

ingly, proteolytic processing of IL-1a by Gzm B increased the

activity of this cytokine several-fold (Figure 2B). Similar observa-tions were also made in time course experiments, once again

indicating that Gzm B-mediated proteolysis dramatically

increased the bioactivity of IL-1a (Figure 2C).

Importantly, we ruled out the possibility that co-purifying

microbial contaminants in the Gzm B preparations contributed

to the effects seen. First, we expressed and purified a catalyti-

cally inactive Gzm B mutant (Gzm BSA) in the same yeast system

that was used to generate wild-type Gzm B (Figures S2AS2C).

(F) Recombinant IL-1a1-271

and IL-1a104-271

were incubated for 2 hr at 37C with the indicated concentrations of granzyme B, then analyzed by SDS-PAGE and

Coomassie staining. All data shown are representative of at least three independent experiments.

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Figure 2. Granzyme B-Dependent Proteolysis of IL-1a Enhances Cytokine Bioactivity

(A) HeLa(top panels) or HUVEC cells (lower panels) were incubated with 1 nM of recombinant IL-1a104-271

or annexin V as a control protein. Culture supernatants

were collected at the indicated time-points, with IL-6, IL-8, and GM-CSF concentrations then determined by ELISA.

(B) HeLa or HUVEC cells were incubated with the indicated concentrations of full-length or granzyme B-cleaved IL-1a for 8 hr, and concentrations of IL-6, IL-8,

and GM-CSF in the supernatants were determined by ELISA.

(C) HeLa cells were left untreated or incubated with 2 nM of full-length or granzyme B-cleaved IL-1a. Culture supernatants were collected at the indicated time-

points, with IL-6 and IL-8 concentrations subsequently determined by ELISA. All results are representative of at least three independent experiments. Error bars

represent the mean the SEM of triplicate experiments.

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This mutant failed to cleave IL-1a and also failed to enhance the

activity of IL-1a on HeLa or HUVECs (Figures S2C and S2D).

Second, neither wild-type nor mutant forms of Gzm B inducedcytokines when added directly to HeLa cells in the absence of

IL-1a (Figure S2E).Third, whereas HeLa cells arevery responsive

to IL-1a, these cells fail to produce IL-6 or IL-8 in response to

a wide panel of microbial components (i.e., pathogen-associ-

ated molecular patterns), such as lipopolysaccharide, which

would represent possible contaminants (Figure S2F).

Granzyme B Does Not Directly Influence Inflammatory

Cytokine Production by HeLa or HUVECs

To further rule out the possibility that residual Gzm B activity

within the cleaved IL-1a preparations was responsible for the

increased proinflammatory effects seen, we neutralized this

Figure 3. Granzyme B Activity Does Not

Directly Promote Inflammatory Cytokine

Production

(A) Recombinant IL-1a was incubated with gran-

zyme B (200 nM) for 3 hr at 37C. Residual gran-

zyme B activity was then measured after furtherincubation for 30 min either alone or in the pres-

ence of the granzyme B inhibitor PI-9 (1 mM).

Granzyme B activity was measured by monitoring

hydrolysis of the synthetic granzyme B substrate

IETD-AFC by fluorometry.

(B)35S-labeled Bid was incubated, either alone or

withthe indicated concentrations of active or PI-9-

treated granzyme B for 2 hr at 37C. Reactions

were analyzed by SDS-PAGE followed by fluo-

rography.

(C) HeLa cells were incubated for 8 hr with the

indicated concentrations of full-length or gran-

zymeB-cleaved IL-1a, where residual granzyme B

activity after proteolysis of IL-1a was inhibited by

addition of saturating amounts of PI-9. IL-6 and

IL-8 levels in culture supernatants were deter-

mined by ELISA.

(D) HeLa cells were incubated for 8 hr with the

indicated concentrations of IL-1aFL

or IL-1a104-271

.

IL-6 and IL-8 levels were determined by ELISA.

(E) HeLa cells were incubated for 8 hr with the

indicated concentrations of IL-1aFL

, granzyme

B-treated IL-1aFL

, IL-1a104-271

, or granzyme

B-treated IL-1a104-271

, as indicated. IL-6 and IL-8

levels were determined by ELISA. Results are

representative of at least three independent ex-

periments. Error barsrepresentthe mean SEMof

determinations from three independent experi-

ments.

granzyme with the serpin protease inhib-

itor PI-9, confirming that no residual

protease activity remained after the incu-

bation period with IL-1a (Figures 3A and

3B). Addition of PI-9 after Gzm B-medi-

ated proteolysis of IL-1a had no effect

on the increased potency of the Gzm

B-treated IL-1a preparations (Figure 3C),

demonstrating that Gzm B was not

directly acting upon the cells used to assay IL-1a activity.

Similar observations were also made with HUVECs (data not

shown).We also directly comparedthe potency of full-length IL-1awith

the artificially-truncated IL-1a104-271 protein (which mimics the

Gzm B-cleaved form of this cytokine) and once again observed

considerable differences in activity between these forms of

IL-1a (Figure 3D). Furthermore, incubation of truncated

IL-1a104-271 with Gzm B did not have any effect on the activity

of this cytokine, as expected (Figure 3E). Similarly, incubation

of the Gzm B-noncleavable form of IL-1a (IL-1aD103A) with this

granzyme also failed to enhance the activity of this protein

(data not shown). Collectively, these data provide strong

evidence that proteolysis of IL-1a by Gzm B enhances the

biological activity of this protein up to 10-fold.

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Figure 4. Proteolysis of IL-1a by Calpain and Other Proteases Also Enhances Cytokine Bioactivity

(A)35

S-labeled IL-1aWT

andIL-1aD103A

wereincubatedfor 2 hrat 37C withthe indicatedconcentrations of granzymeB or calpain-1. Reactions wereanalyzed by

SDS-PAGE/fluorography.

(B) HeLa or HUVEC cells were incubated with the indicated concentrations of full-length IL-1a, or granzyme B- or calpain-1-cleaved IL-1a for 8 hr. IL-6 and IL-8

levels were determined by ELISA.

(C)35

S-labeled in vitro transcribed/translated IL-1a andIL-1b were incubatedfor 2 hr at37C with theindicated concentrationsof elastase, or with granzymeB or

calpain-1 (both at 200 nM) as controls. Reactions were then analyzed as in (A).

(D) HeLacells wereincubated for 8 hr withthe indicated concentrations of full-length IL-1a, orIL-1a cleaved witheither granzymeB or elastase, as indicated. IL-6

and IL-8 levels were then determined by ELISA.

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Figure 5. IL-1a Is Cleaved, either Extracellularly or Intracellularly, by Endogenous Granzyme B

(A) YT cells were either left untreated or were permeabilized via 2 cycles of freeze-thaw (Fr-Th), or addition of 10 mg/ml of streptolysin O (SLO) for 90 min.

Recombinant IL-1a was added to the supernatants, which were further incubated for 2 hr at 37C and analyzed for IL-1a processing by immunoblotting.

(B) YT cells wereincubated for 18 hr withHeLa target cells at the indicated effector:target ratios in the presenceof recombinant IL-1a. Culture supernatants were

analyzed by immunoblot for IL-1a processing. Serum-derived transferrin served as a loading control.

(C) HeLacells wereincubated withrecombinantextracellularIL-1a for the indicated times in the presenceor absence of YT cells, as indicated. Supernatantswere

then analyzed for IL-1a processing by immunoblot.

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IL-1a Cleaving Activity in Inflammatory Patients

To explore whether IL-1a also underwent processing during

inflammation, we obtained bronchoalveolar lavage fluids

(BALF) from patients with persistent inflammatory lung condi-

tions (cystic fibrosis, chronic obstructive pulmonary disease,bronchiectasis) as well as healthy donors. Previous studies

have shown that such fluids contain high levels of inflammatory

proteases, particularly elastase, due to invasion of the lungs by

neutrophils and other cells of the innate immune system (McEl-

vaney et al., 1991; Reeves et al., 2010). As Figure 5H illustrates,

IL-1a underwent rapid proteolysis to fragments very similar to

the Gzm B/elastase/calpain-cleaved forms of this cytokine in

BALF from several cystic fibrosis and bronchiectasis patients,

whereas little processing was seen in controls. Thus, proteases

capable of processing IL-1a to its mature form are secreted into

the extracellular space under inflammatory conditions in vivo.

Granzyme B-Cleaved IL-1a Exhibits Enhanced Activity

In Vivo

We next explored whether the Gzm B-cleaved form of IL-1a also

exhibited greater bioactivity in vivo. To address this question, we

compared the adjuvant activity of full-length versus Gzm

B-cleaved IL-1a in an antigen-driven model, using ovalbumin

(OVA). BALB/c mice were immunized with OVA, either alone,

or in combination with full-length or Gzm B-cleaved IL-1a,

followed by boosting with the same combinations two weeks

later. One week after boosting, OVA-specific antibodies were

measured in the serum as well as OVA-specific T cell responses

in the peritoneal lavage and spleens of these mice. As Figures 6A

and S3 show, both forms of IL-1a significantly boosted antibody

responses to OVA, with the cleaved form of this cytokine exhib-

iting considerably greater potency in this regard. Furthermore,

OVA-specific IL-4, IL-5, and IL-10 production from peritoneal

lavage cell preparations was also significantly greater in mice

that received the Gzm B-cleaved form of IL-1a (Figure 6B). Poly-

clonal stimulation with anti-CD3 also produced more robust

cytokine responses from mice that had received cleaved IL-1a

(Figure 6C). A similar trend toward more robust OVA-specific

responses was also observed in splenocytes from the same

mice, but this was less statistically significant than in peritoneal

exudates (Figure 6D). Collectively, these data lend further

support to our in vitro observations that Gzm B-dependent

proteolysis of IL-1a acts to enhance the proinflammatory effects

of this cytokine.

To again rule out the possibility that a contaminant within the

Gzm B preparations could contribute to the enhanced IL-1aactivity seen in vivo, we used the catalytically inactive mutant

form of this protease (Gzm BSA) (Figures S2AS2C) to explore

whether this mutant could enhance IL-1a activity in vivo. As Fig-

ure 7A shows, preincubation with Gzm BSA failed to potentiate

IL-1a activity under conditions where incubation with wild-type

Gzm B clearly did so.We also asked whether the IL-1a mutant (D103A) incapable

of undergoing processing by Gzm B (Figure 1E) possessed

reduced activity in vivo, when compared to wild-type IL-1a.

As Figure 7B illustrates, IL-1a-dependent enhancement of OVA-

specific antibody responses were consistently less pronounced

with IL-1aD103A than with wild-type IL-1a, suggesting that endog-

enous Gzm B contributes to the potency of IL-1a in vivo.

Finally, we also explored IL-1a-dependent enhancement

of OVA-specific antibody responses in wild-type versus

gzmB/mice. Although it is importantto note that several prote-

ases can process IL-1a to a more active form, as we have shown

here, we were nonetheless interested to explore whether the

absence of Gzm B had a significant impact on IL-1a activity

in vivo. As Figures 7C and 7D show, we found that IL-1a-depen-dent enhancement of OVA-specific antibodies was greater in

wild-typeanimals than that seen ingzmB/ mice. Note however

that baseline antibody responses to OVA alone were higher in

gzmB/ animals for reasons that are unclear. Nonetheless,

the enhancement effect of IL-1a on OVA-specific responses

was significantly higher in wild-type animals than in knockouts,

again suggesting that endogenous Gzm B contributes to IL-1a

processing in vivo.

Collectively, these data reveal a hitherto unappreciated

consequence of IL-1a processing to the mature $17 kDa cyto-

kine. The N-terminal IL-1a propeptide appears to function as a

sensor for multiple proinflammatory proteases, proteolysis of

which switches the activity of this cytokine from a basal to a

hyperactive state.

DISCUSSION

Here we report that IL-1a is a substrate for the CTL/NK protease

Gzm B and that proteolysis of this cytokine by the latter protease

very significantly increased its biological potency. These data

suggest that Gzm B may enhance inflammatory responses in

certain situations through proteolytic processing of IL-1a. We

have further shown that proteolysis of IL-1a by calpain-1, elas-

tase, and mast cell chymase, at sites close to but distinct from

the Gzm B processing site, also potentiated the activity of this

cytokine. This suggests that proteolysis of IL-1a within its N

terminus, irrespective of the protease involved, acts as a switchto increase the biological potency of this cytokine. Thus,contrary

(D) YT cells were incubated for 6 hr with HeLa target cells at an E:T ratio of 10:1 in the presence of recombinant IL-1a and PI-9, as indicated. Supernatants were

then analyzed for IL-1a processing by immunoblot. Serum-derived transferrin served as a loading control.

(E) YT cells were incubated for 6 hr with HeLa target cells at an E:T ratio of 10:1 in the presence of either recombinant IL-1aWT or IL-1aD103Amutant, as indicated.

Supernatants were then analyzed for IL-1a processing by immunoblot. Serum-derived transferrin served as a loading control.

(F andG) HeLa cellsweretransfected with IL-1a expression plasmid.24 hr latercells were exposed to YT cells(F) or NK-92 cells(G) cellsat an E:Tratio of 20:1 or

5:1, respectively. NK cells were removed 35 hr later and HeLa cells were further incubated for the total of 24 hr, after which cell lysates were generated and

immunoblotted for the indicated proteins. Cell death was assessed by annexin V/propidium iodide binding, measured by flow cytometry. All data shown are

representative of at least three independent experiments.

(H) Recombinant purified full-length IL-1a was incubated at 37C for 20 min with 10 ml of BALF samples from control patients or patients with cystic fibrosis,

bronchiectasis, or chronic obstructive pulmonary disease (COPD). IL-1a processing was analyzed by immunoblot. As controls, full-length IL-1a and IL-1a104-271

were expressed in HEK293T cells and were included to facilitate size comparison of cleavage products.

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to current thinking, limited proteolysis of IL-1a increases biolog-

ical activity and serves as a further level of regulation on this

cytokine.

Proteolysis of IL-1a may induce a conformational change in

this protein that increases its affinity for the IL-1 receptor

complex, thereby increasing biological potency. Alternatively,

Figure 6. Granzyme B-Cleaved IL-1a Exhibits Enhanced Activity In Vivo

BALB/c mice(five miceper group) wereimmunized either withovalbumin (OVA) alone(200mg), OVA in combination withfull-lengthIL-1a (5 mg permouse), orOVA

in combination with granzyme B-cleaved IL-1a (5 mg per mouse). All mice were boosted with the same combinations on day 14. Peripheral blood, spleens, and

peritoneal lavages were collected on day 21.

(A) OVA-specific total IgG, IgG1, IgG2a, and IgG2b in plasma samples were determined by ELISA.

(BD) Cells from peritoneal lavages (B and C) and spleens (D) were restimulated for 3 days with indicated concentrations of OVA, anti-CD3, or anti-CD3/PMA, as

indicated. IL-4,IL-5, IL-10, and IFN-g productionwas determined by ELISA. All measurementswere taken in triplicate. Error barsrepresent the mean SEMfrom

each group of five mice. Significance levels, *** = p < .01, ** = p < .05, * = p < .1, by Students t test.

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Figure 7. Granzyme B Contributes to IL-1a Processing In Vivo

(A and B) BALB/c mice (fiveanimals per group) were immunized either with ovalbumin (OVA) alone (200mg) or OVA in combination with the full-length IL-1a, Gzm

BWT

-treated IL-1a, Gzm BSA

-treated IL-1a, or noncleavable mutant IL-1aD103A

(5 mg per mouse). On day 21, peripheral bloods were collected and OVA-specific

total IgG, IgG1, IgG2a, and IgG2b antibodies in plasma samples were determined by ELISA.

(C)WT orGranzymeB/C57BL/6 mice(five per group) wereimmunized either withOVA alone (200mg)or with OVA in combinationwithfull-lengthIL-1a (5 mg per

mouse). On day 21, peripheral bloods were collected and OVA-specific total IgG, IgG1, IgG2a, and IgG2b in plasma samples were determined by ELISA.

(D) Fold increasein antibody production in WT versus GranzymeB/ micetreated with OVA plus IL-1a, compared with OVA alone. The analysis shown is based

on the data presented in (C). Error bars represent the mean SEM from each group of five mice.

Significance levels, *** = p < .01, ** = p < .05, * = p < .1, by Students t test.

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the IL-1a N terminus may partly occlude the receptor binding

domain, removal of which now permits a more stable interaction

with the IL-1R complex. This possibility is consistent with a

previous study that utilized sensitivity to proteinase K-mediated

proteolysis to explore whether IL-1a underwent a conformationalchange as a consequence of removal of its N terminus (Hazuda

et al., 1991). Although the latter study did not explore the func-

tional effects of IL-1a proteolysis in any detail, it did suggest

that proteolysis of this cytokine initiated a profound conforma-

tional change in the molecule from a proteinase K-sensitive to

a proteinase K-insensitive state (Hazuda et al., 1991). This

change is most likely reflected in an altered conformation that

has increased IL-1 receptor affinity.

There are a number of scenarios where Gzm B may encounter

IL-1a. First, in a classical CTL/NK killing reaction, where the

target cell expresses IL-1a, this cytokine may become pro-

cessed within the target cell and exacerbate proinflammatory

responses if released from dying cells prior to clearance of the

latter by phagocytes. In this context, it is relevant to note thatBid was substantially more sensitive to Gzm B-mediated prote-

olysis than IL-1a. Thus, although the concentration of Gzm B

achieved in a CTL/NK killing reaction is unknown, at low nano-

molar concentrations of Gzm B robust proteolysis of Bid and

apoptosis might occur without significant proteolysis of IL-1a,

with proteolysis of the latter becoming more significant upon

exposure to higher granzyme concentrations.

Second, there arenow a numberof studies suggesting that NK

cells and CTLs, as well as other cell types, may actively secrete

granzymes into the extracellular space (Spaeny-Dekking et al.,

1998; Prakash et al., 2009). In this scenario, where injury or infec-

tion has resulted in necrosis and release of IL-1a, Gz m B

released from CTL/NK cellsor indeed one of the growing

number of noncytotoxic cell types that have been found to

express this granzymecould process this cytokine and

enhance its potency. In this context it is noteworthy to mention

that several studies have detected circulating Gzm B at elevated

levels in rheumatoid arthritis patients and in patients with melioi-

dosis (Spaeny-Dekking et al., 1998; Tak et al., 1999; Lauw et al.,

2000). Furthermore, Gzm B expression and secretion has been

repeatedly detected in noncytotoxic, proinflammatory immune

cells such as macrophages, plasmacytoid dendritic cells, acti-

vated mast cells, basophils, B lymphocytes, macrophages, ker-

atinocytes, platelets, human articular chondrocytes, and breast

carcinoma cells (reviewed in Afonina et al., 2010), further sug-

gesting that this granzyme may have alternative, noncytotoxic

functions. Proteases such as elastase and mast cell chymaseare abundantly released via degranulation of neutrophils and

mast cells during inflammatory reactions, providing a ready

means by which these proteases may encounter IL-1a released

through cell damage. Indeed, several recent studies have shown

that IL-1a is a major initiator of inflammatory responses to

necrotic cells (Chen et al., 2007; Kono and Rock, 2008; Kono

et al., 2010).

A recent study found that whereas IL-1a was readily released

from cells undergoing necrosis, this cytokine was retained within

the nucleus of cells undergoing apoptosis (Cohen et al., 2010).

Retention of IL-1a within the nucleus appears to be facilitated

by a nuclear localization signal within its N terminus, the region

that is separated from the molecule through Gzm B-dependent

proteolysis. Thus, in addition to increasing biological potency

through enhancing IL-1a binding to its receptor, proteolysis of

IL-1a by proteases such as Gzm B may also facilitate its release

by overriding the nuclear retention mechanisms that appear tooperate during some forms of cell death.

In summary, in addition to acting as a direct instigator of cell

death upon delivery into target cells, Gzm B may also serve in

a hitherto unsuspected capacity as an amplifier of inflammatory

responses through restricted proteolysis of IL-1a. We have also

shown that proteolysis of IL-1a by several other proteases, each

of which cleave this cytokine at distinct sites within its N

terminus, enhanced the biological potency of this cytokine.

IL-1a processing to the mature $17 kDa protein acts as a switch

to enhance the proinflammatory properties of this cytokine, from

a basal level of activity to a hyperactive one. Thus, in common

with IL-1b, the biological activity of IL-1a is also regulated

through restricted proteolysis.

EXPERIMENTAL PROCEDURES

Reagents

Recombinant caspase-1, -3, -4, -5, and -7 were expressed and purified from

bacteria as described previously (Luthi et al., 2009). Recombinant polyhisti-

dine-tagged human PI-9 was expressed and purified from bacteria according

to standard procedures. Recombinant wild-type Gzm B (both human and

murine) and the catalytically inactive mutant Gzm BSA were expressed and

purified from Pichia pastoris yeast as described previously (Cullen et al.,

2007). cDNA clones encoding full-length human and murine IL-1a were

obtained from OriGene and subcloned into pET45b. Recombinant IL-1a and

derivatives were expressed in E. coli and purified as described in Supple-

mental Experimental Procedures. Human calpain-1 and human mast cell

chymase were purchased from Calbiochem, human elastase was purchased

from SERVA. Polyclonal anti-IL-1a antibody was from AbD Serotec, goat

anti-rabbit HRPO secondary antibody was from Jackson ImmunoResearch.

Ac-IETD-AFC was purchased from Bachem (UK). Lipopolysaccharides

(LPS), mannan, lipoteichoic acid (LTA), and muramyl dipeptide (MDP) were

purchased from Sigma (Ireland) Ltd. Pam3CSK4, flagellin, and CpG were

purchased fromInvivogen (France).Unlessotherwisestated,all other reagents

were purchased from Sigma (Ireland) Ltd.

Cell Culture

HeLa cells were cultured in RPMI media supplemented with 5% fetal calf

serum, and YT cells were cultured in RPMI supplemented with 10% serum

and HUVEC (PromoCell, Germany)in endothelial cellgrowthmedia withadded

growth supplement (PromoCell, Germany). Cells were cultured at 37C in

humidified atmosphere with 5% CO2.

Cell-Killing Assays

HeLa cells were transiently transfected with IL-1a expression plasmid using

GeneJuice transfection reagent (Merck, Ireland). For NK-mediated killing,

HeLa cells were incubated with YT or NK-92 cells at 20:1 and 5:1 effector-

to-target ratios, respectively. NK cells were removed from the target cell

monolayer after 35 hr, and HeLa cells were further incubated for a total of

24 hr. Celllysateswere generated at 23 107 cells/mland analyzed by western

blotting.

Animals

BALB/c mice were purchased from Harlan (UK). Animal experiments were in

accordance with the regulations of the Trinity College Dublin ethics committee

and the Irish Department of Health. Granzyme B null mice, on the C57BL/6

background, were bred at Academic Medical Center (AMC), Amsterdam,

The Netherlands.

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Determination of Cytokine and Antibody Concentrations

Cytokines were determined by ELISA as described previously (Luthi et al.,

2009). Paired antibodies for mouse IL-4, IL-5, IL-10, and IFN-g were

purchased fromBD Pharmingen(UK); human IL-6,IL-8, and GM-CSF DuoSets

were purchased from R&D Systems (UK). Serum immunoglobulin titers were

determined as described previously (Lavelle et al., 2001).

IL-1a Bioactivity Assay

HeLa cells were plated at a density of 4 3 104 cells per well, and primary

HUVECs were platedat 23 104

cellsper well on24-wellplates. 24hr latercells

were incubated with the indicated concentrations of recombinant IL-1a, or

recombinant annexin V (as a control protein), and culture supernatants were

collected at the specified time-points for quantitative cytokine analysis by

ELISA.

Bronchoalveolar Lavage Fluid Analysis

Bronchoalveolar lavage fluid samples from control individuals or patients

with cystic fibrosis (CF), chronic obstructive pulmonary disease (COPD), or

bronchiectasis were collected as described previously (Reeves et al., 2010).

Informed patient consent was obtained and ethical approval was granted by

the Beaumont Hospital Institutional Review Board.

SUPPLEMENTAL INFORMATION

Supplemental Information includes three figures and Supplemental

Experimental Procedures and can be found with this article online at

doi:10.1016/j.molcel.2011.07.037.

ACKNOWLEDGMENTS

Work in the Martin laboratory is supported by SRC and PI grants from Science

Foundation Ireland (07/SRC/B1144 and 08/IN.1/B2031) and The Wellcome

Trust UK (082749). The Lavelle laboratory is supportedby Science Foundation

Ireland grant 07/SRC/B1144. I.S.A. was a Health Research Board of Ireland

scholar. S.J.M. is a Science Foundation Ireland Principal Investigator. The

authors have no conflicting financial interests to declare.

Received: September 1, 2010

Revised: June 17, 2011

Accepted: July 15, 2011

Published: October 20, 2011

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