Signalling Pathways Flashcards
How is Raf activated?
GTP-Ras recruits Raf. 14-3-3 lost from regulatory domain (uncertain dephosphorylation) - Raf dimer forms. Raf phosphorylated at additional sites by; PAK, Src or itself to activate kinase domain.
What is ATF2 and what happens when it becomes deregulated?
A leucine zipper TF. Binds CRE and can form a heterodimer with c-Jun, inducing the transcription of CRE-dependent genes. (HAT activity in vitro)
In melanoma strong nuclear expression correlates with metastasis.
In pancreatic cancer - somatic Jnk and ATF2 mutations seen.
What is a typical cascade involving p38?
Cytokine –> TRAF6 –> TAK1 –> MKK3 –> p38 –> ATF-2
The JAK / STAT pathway is not a kinase receptor. How does the receptor induce signalling?
The tyrosine phosphorylated receptor (by constitutively bound JAKs) recruit SH2 containing STATs which are phosphorylated by JAKs forming dimers.
STAT signalling can be via RTKs and what else?
v-Src can activate Y phosphorylation of STAT3 and DNA binding and transcriptional activation.
How Raf is downstream of Ras?
Injecting antibodies to Ras protein blocks transformation by v-Src and Fms. Doesn’t block transformation by Raf or SV40. So Raf must be downstream.
Micro injection of antibodies to Ras also blocks stimulation of DNA synthesis by PDGF and EGF.
Where does Src lie in the MAPK pathway?
Depicted upstream of Ras however Ras required for v-Src transformation of human epithelial cells.
Src transformation not blocked when either Ras-MAPK OR PI3K pathways blocked… BUT when both blocked transformation inhibited.
How does Vemurafenib function?
specifically binds V600E mutation in Braf - downregulates ERK phosphorylation (clean as doesn’t target WT Raf)
Which mechanisms can induce resistance to vemurafenib?
- C cells overexpress PDGFR –> alternative survival pathway.
- Promotes WT Raf dimers.
- NRas mutates - reactivates normal BRAF pathway.
- C Cells reactivate via stromal secretion of HGF.
How does Erlotinib show resistance?
Mutation at at T790M.
