CELLULAR SIGNAL TRANSDUCTION2) From the membrane to the nucleus

TEIL F

TRANSCRIPTION FACTORS AND THE REGULATION OF TRANSCRIPTION

Rainer deMartin / Erhard HoferInstitute of Vascular Biology and Thrombosis Research

Vienna Competence CenterLazarettgasse 19, 1090 Wien

Erhard Hoferactivation of transcription factors by surface receptors

Summary selected examplesCREB, SRF, NFAT, SMAD

additional specific example: - Regulation of signaling pathways/transcription factorsby proteolytic cleavage:WNT, NOTCH (embryonic development, adult stem cells)

Nuclear import, -export

Chromatin

Transcription initiation complexes

Rainer deMartin:Principals of transcriptional regulationStructural features of transcription factorsBasic mechanisms of transcriptional regulation

SMAD

SMAD/Co-SMAD

SMAD

STATSTATA-Cyclase PLC Ras

STAT

cAMP

Signaling pathways: Receptor to transcription factors

PKA

SRF

IKKK

NFAT / NFB

CREB, SRF, NFAT, SMAD

Gene regulation by PKA:

CREB bound to CREIs phosphorylated by PKA,activates transcription without effect on DNA binding

Example 3

The phosphorylated MAPK ERK is transported into the nucleus and phosphorylates the transcription factor TCF on the promoter

ERK: extracellular signal regulated kinaseTCF: ternary complex factorSRF: serum response factorSRE: serum response element

(DNA binding sequence for TCF and SRF in promoter of various genes)

Genes forCell cycle/Proliferationearly responsegenes, c-fos

or:PLC-RafMEK

Ca++

Calmodulin

Calcineurin

NFAT

PI

Ca++ Signaling pathway - Gene regulation

the PhosphataseCalcineurindephosphorylatesNFAT

NFAT translocatesInto nucleus

NFAT= transcription factor(nuclear factoractivated T cell) Kern

P

Transport ofphosphorylated SMADs into nucleus

Regulation of transcription factors by proteolytic cleavage

WNT signaling pathway

Secreted signaling peptide,important in embryonic developmentMutatios on proteins of wnt signaling pathway frequent in cancer

Example 4a Wnt Wingless (Drosophila)Int-1 (breast cancer oncogen) (detected experimentally by virus Integration)

In signalling pathway:APC (adenomoteous polyposis coli)mutated in adenoma of colonand 80 % of colon cancer

induces myc geneand proliferation

(LDL rceptor related protein)

(Signaling protein)

(Corepressor)

-Catenin signaling pathway: w/o signal: -catenin is continously phosphorylated, ubiquitinylated, degraded in proteasomWnt-signal: Kinase is inhibited, non-phosphorylated -Catenin transported into nucleus, aktivates transcription by competing of a corepressor

(-Catenin Coaktivator)

Phosphorylation,Ubiquitinylation,degradation in proteasom

components of the WNT signaling pathways e.g. important for maintaining the stem cell population in gastro-intestinal tract,Over-activation by APC mutation - cancer

Notchhedgehog

1- Embryonic developmentE.g. nerve cells Drosophila,Delta on nerve cells signals to neighbouring cell: Do not differentiate to nerve cell,Peptide translocates into nucleus and convertsCSL to become an activator

2- Angiogenesis: Tip versus stalk cell, tip cell signals stalk cell not to become another tip cell

example 5b

Nuclear import / -export

Nuclear membrane:Double membrane with nuclear pores

26 nm

Nuclear pore complex

innere Seite

The nuclear localization signal is a basic amino acid sequence

Model of nuclear importMediated by the small G-protein Ran

Model of nuclear import and export

CHROMATIN

Summary

Interphase

Metaphase

Eigenschaften von Insulatorelementen

model

Change of chromatin structure by activator protein

Ac

Ac

HAT

HDAC

condensed CHROMATIN

no TRANScRIPTION

Z.B. HETEROCHROMATIN

loose CHROMATIN

TRANCRIPTION

Z.B. EUCHROMATIN

HAT = HISTONACETYLTRANSFERASE ACTIVATOR OF TRANSCRIPTION

HDAC = HISTONDEACETYLASE REPRESSOR of TRANSCRIPTION

DNADNA

NUCLEOSOM

CHROMATINCHROMATIN

GENEXCS18

A

REPRESSION

ACTIVIERUNG

HDAC

X

Y

HAT

Target GENE

Target GENE

Z

REGULATION OF TRANSCRIPTION BY REGULATION OF TRANSCRIPTION BY CHANGE OF CHROMATIN STRUCTURCHANGE OF CHROMATIN STRUCTUR

condensed Chromatin

open Chromatin

Repressor

Aktivator

GENEXCS19

Gene regulatory proteins form frequently large

complexes

DNA Looping

Mediator

Gene expression