Most proteins can be classified as either tumor suppressors or oncogenes. As their names suggest, whereas tumor suppressors halt tumor progression, oncogenes drives tumorigenesis.
Oncogenes:
RTKs (HER2, EGFR, VEGFR):
Her2 and EGFR belong to the epidermal growth factor receptor family or receptor tyrosine kinases (RTK). VEGFR is similar but it responds to a different growth factor, the vascular endothelial growth factor. They are located at the periphery of the cell, on the cell membrane and relay signals from outside the cell into the cell. Their activation can lead to numerous different downstream effects including enhanced proliferation, survival, migration, or angiogenesis depending on both the type of RTK and the proteins they activate. For this reason, most RTKs are considered oncogenes.
AKT-P13K Signaling Axis
PI3K is a kinase that becomes activated in response to signals from RTKs. Once activated, it can activate AKT, another kinase. AKT is considered a pro-survival, anti-apoptosis protein. It enhances progression through the cell cycle as well as the generation of biomolecules necessary to generate additional proteins.
RAS-MAPK Signaling Axis
RAS is a protein that balances between an "on" and "off" state. This balance is tightly controlled. Signals from RTKs push RAS into the "on" state, leading to activation of downstream kinases. At each state, the kinase activates downstream kinases, amplifying the signal. Ultimately, these signals converge on ERK1/2, two transcription factors that travel to the nucleus to increase transcription of pro-survival genes.
Tumor Suppressors:
p53
p53 is a transcription factor. It controls the expression of numerous different genes, including several pro-apoptotic genes as well as inhibitors of the cell cycle. For this reason, p53 is considered a guardian of the cell. Its activation leads to decisions to either halt the cell cycle and/or for the cell to commit suicide. It was one of the first tumor suppressors to be identified.
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