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Transcript
CELLULAR SIGNAL TRANSDUCTION
2) From the membrane to the nucleus
TEIL F
TRANSCRIPTION FACTORS AND THE
REGULATION OF TRANSCRIPTION
Rainer deMartin / Erhard Hofer
Institute of Vascular Biology and Thrombosis Research
Vienna Competence Center
Lazarettgasse 19, 1090 Wien
Erhard Hofer
activation of transcription factors by surface receptors
Summary selected examples
CREB, SRF, NFAT, SMAD
additional specific example:
- Regulation of signaling pathways/transcription factors
by proteolytic cleavage:
WNT, NOTCH (embryonic development, adult stem cells)
Nuclear import, -export
Chromatin
Transcription initiation complexes
Rainer deMartin:
Principals of transcriptional regulation
Structural features of transcription factors
Basic mechanisms of transcriptional regulation
Signaling pathways: Receptor to transcription factors
A-Cyclase
PLC
Ras
SMAD
STAT
IKKK
SMAD/Co-SMAD
cAMP
PKA
NFAT
/ NFkB
SRF
STAT
SMAD
CREB, SRF, NFAT, SMAD
Gene regulation by PKA:
CREB bound to CRE
Is 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
or:
PLC-g
Raf
MEK
ERK: extracellular signal regulated kinase
TCF: ternary complex factor
SRF: serum response factor
SRE: serum response element
(DNA binding sequence for TCF and SRF
in promoter of various genes)
Genes for
Cell cycle/
Proliferation
early response
genes, c-fos
Ca++ Signaling pathway - Gene regulation
the Phosphatase
Calcineurin
dephosphorylates
NFAT
NFAT translocates
Into nucleus
P
I
Ca++
NFAT
Calmodulin
Calcineurin
P
NFAT= transcription factor
(nuclear factor
activated T cell)
Kern
Transport of
phosphorylated
SMADs into nucleus
Regulation of transcription factors
by proteolytic cleavage
WNT signaling pathway
Secreted signaling peptide,
important in embryonic development
Mutatios 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 colon
and 80 % of colon cancer
induces myc gene
and proliferation
b-Catenin signaling pathway:
w/o signal: b-catenin is continously phosphorylated, ubiquitinylated, degraded in proteasom
Wnt-signal: Kinase is inhibited, non-phosphorylated b-Catenin transported into nucleus,
aktivates transcription by competing of a corepressor
(LDL rceptor related protein)
(Signaling protein)
Phosphorylation,
Ubiquitinylation,
degradation in proteasom
(Corepressor)
(b-Catenin
Coaktivator)
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
Notch example 5b
hedgehog
1- Embryonic development
E.g. nerve cells Drosophila,
Delta on nerve cells signals to neighbouring cell:
Do not differentiate to nerve cell,
Peptide translocates into nucleus and converts
CSL to become an activator
2- Angiogenesis: Tip versus stalk cell, tip cell signals stalk cell not to become another tip cell
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 import
Mediated 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
CHROMATIN
NUCLEOSOM
HAT
Ac
DNA
HDAC
Ac
condensed CHROMATIN
loose CHROMATIN
no TRANScRIPTION
TRANCRIPTION
Z.B. HETEROCHROMATIN
Z.B. EUCHROMATIN
HAT = HISTONACETYLTRANSFERASE ACTIVATOR OF TRANSCRIPTION
HDAC = HISTONDEACETYLASE REPRESSOR of TRANSCRIPTION
GENEXCS18
REGULATION OF TRANSCRIPTION BY
CHANGE OF CHROMATIN STRUCTUR
REPRESSION
Repressor
HDAC
X
Target GENE
condensed Chromatin
ACTIVIERUNG
Aktivator
Z
Y
A
HAT
open Chromatin
GENEXCS19
Target GENE
Gene regulatory proteins
form frequently large
complexes
Mediator
DNA Looping
Gene expression