Final answer:
The inhibition of RAS protein's GTPase activity in certain cancers leads to uncontrolled cell proliferation through the MAPK kinase cascade.
Step-by-step explanation:
RAS is a small G-protein that activates the MAPK kinase cascade in response to receptor tyrosine kinases (RTKs). It is activated when GDP is released and GTP is bound. In certain cancers, the GTPase activity of RAS protein is inhibited, preventing the hydrolysis of GTP into GDP.
This inhibition leads to uncontrolled cell proliferation because RAS remains constantly activated, initiating continuous signaling through the MAPK kinase cascade. This unregulated phosphorylation cascade can promote cell growth and division, contributing to the development of cancer.