Graeme Finlay 4 Flashcards
What are the three RAS proteins?
H-Ras, N-Ras and K-Ras these are directed to and anchored in the cell membrane
How do Ras proteins function in normal cells?
The Ras proteins bind to GDP and Growth factor signals act through guanine nucleotide exchange factors to have GTP replace GDP causing a conformational change in the Ras protein is stimulated by GTPase activator proteins causes GTPase activity by Ras returning it to the off conformation
How do oncogenic mutations impact normal Ras function?
They reduce the GTPase activity of Ras which causes a longer lived on conformation
What GTPase activator protein is also a tumour suppressor gene?
The NF-1 geene which encodes neurofibromin which loss of it deregulates Ras activity causing neurofibromatosis type I.
Loss also makes cells more sensitive to GM-CSF, myeloid leukaemias are caused by either Ras mutation or neurofiromin loss
How does Ras and EGFR co-operation allow for a benign to malignant tumour transition?
Neurofibromas are usually benign but can transform to malignant peripheral nerve sheath tumours if the EGFR gene is amplified allowing co-operation of EGFR and Ras
What are two important signalling molecules that bind to the activated conformation of Ras?
Raf kinase and Phosphatidylinositol-3-kinase.
How does Ras interact with Raf kinase?
Activated Ras binds the inhibitory domain of raf kinase leading to its displacement which may contribute to activation of the raf protein
How does Ras interact with phosphatidylinositol-3-kinase?
PI3K undergoes an allosteric conformational change becoming orientated to access its lipid substrate inserted in the membrane
What Raf mutations can lead to cancers?
BRaf mutations have been found to occur in nevi, melanomas and carcinomas.
What is the relationship between Ras and B-Raf mutations?
These mutations occur in the same types of cancer but are very rarely noted in the same cancer as either mutation is sufficient to activate the signalling pathway
Where do Raf mutations occurs?
In the kinase domain such as the T1799A resulting in V600E and introduces a negative charges. This increases the basal kinase activity by 12.5-fold
What are the Ras pathway targets?
All raf proteins phosphorylate the protein kinases MEK 1 and 2 leading to activation of extracellular signal-regulated kinases (ERK). These phosphorylate the Ets transcription factors causing the production of proteins that drive cellular proliferation such as Cyclin D and the transcriptional activator c-Fos.
How does the production of Fos lead to cancers?
The production of Fos stimulates activator protein-1 which is a complex of transcription factors from the Fos and Jun families which are activated by tumour promoters to induce a malignant phenotype.
What is the rous sacoma virus (src)?
It is the archetypal acutely transforming retrovirus. V-src was the first oncogene known to have a normal cellular progenitor. It may regulate signalling by both its kinase activity and protein-protein interactions mediated by SH3 and SH2 domains.
How is SRC activity regulated?
Src is held in an inactive conformation by an inhibitory C-phosphorylation by Y527causing the domain to bind to SH2, interactions between SH3 domain and sequences preceeding the kinase domain
This activity is deregulated in cancer by increased tyrosine phosphatase activity, decreased Y527 kinase activity potentially through loss inducing mutations, displacement of intramolecular interactions through binding proteins
