Final answer:
Mutations in the RAS protein that impair its GTPase activity lead to persistent activation of downstream signaling pathways involved in cell division, causing uncontrolled cell proliferation which is a hallmark of cancer progression.
Step-by-step explanation:
The Ras protein, as a G-protein, is involved in the MAPK kinase cascade crucial for cellular signaling within the process of cell division. Upon the binding of growth factors such as EGF to receptor tyrosine kinases (RTKs), Ras is activated by the exchange of GDP for GTP. However, RAS protein unable to hydrolyze its bound GTP due to mutations can result in an overactive Ras and a continuous signal for cell division without the normal regulatory checks. This uncontrolled cell proliferation is a key characteristic of cancer, and such mutations in RAS are common in various types of cancer, highlighting the connection between RAS activity and cancer.
Normally, Ras facilitates a series of phosphorylation events leading to cellular responses including proliferation. It activates RAF, which then phosphorylates MEK, leading to the phosphorylation of ERK. Once ERK is activated, it can enter the nucleus and affect gene expression related to cell division and differentiation. However, with a mutation causing the RAS oncogene to remain in its GTP-bound state, the downstream signaling cascade through RAF, MEK, and ERK is perpetuated, leading to persistent activation of pathways that drive cell division.