Final answer:
The claim that PI3-K directly phosphorylates RTK to activate it is false as RTKs are activated through autophosphorylation of tyrosine residues in response to ligand binding. PI3-K is part of downstream signaling pathways, such as the MAP kinase pathway, which can be implicated in uncontrolled cell proliferation when mutated.
Step-by-step explanation:
The statement that PI3-K directly phosphorylates RTK to activate it is false. PI3-K is involved in the signaling pathways that are activated after RTKs are phosphorylated. Receptor tyrosine kinases (RTKs) are activated when specific ligands bind to them, which results in autophosphorylation of tyrosine residues on their intracellular domains. This autophosphorylation triggers a downstream cellular response, initiating several signaling cascades, including the MAP kinase pathway.
Mutations or abnormalities in the MAPK pathway can lead to uncontrolled cell proliferation and cancer. One protein in this pathway is the Ras protein, which when activated by GTP binding, initiates a phosphorylation cascade leading to the activation of MAP kinase. Then, MAP kinase phosphorylates various transcription factors that enter the nucleus and affect gene activity, leading to cell proliferation and differentiation.
Furthermore, the MAP kinase ERK contributes to protein synthesis regulation. Once activated, ERK phosphorylates MNK1, which then phosphorylates eIF-4E, an initiation factor associated with mRNA. This phosphorylation results in the unfolding of mRNA and initiation of protein synthesis in the nucleus.