Final answer:
PKB (AKT) becomes activated through a series of steps starting with growth factor signaling leading to AKT phosphorylation by PDK1 and mTORC2 after PI3K creates PIP3 docking sites. This results in the promotion of various cellular processes, including metabolism, growth, and survival.
Step-by-step explanation:
Activation of PKB (AKT)
PKB (also known as AKT) is a crucial kinase in various signaling pathways within the cell that promotes survival and growth. The process of AKT activation involves multiple steps and cellular components. It begins with the binding of a growth factor to its receptor on the cell membrane, which then undergoes autophosphorylation and recruits an adaptor protein. This leads to the activation of PI3 kinase (PI3K), which catalyzes the formation of PIP3. PIP3 acts as a docking site for AKT and its upstream activator, PDK1. AKT is then phosphorylated at two key residues, one by PDK1 and another by the mTORC2 complex, resulting in full activation. The activated AKT can phosphorylate a myriad of substrate proteins, leading to varied cellular responses, including an increase in cellular metabolism, growth, survival, and transcriptional changes.
The activation of AKT is counter-regulated by PTEN, a phosphatase that dephosphorylates PIP3 back to PIP2, effectively preventing AKT activation. This shows how a balance between phosphorylation and dephosphorylation maintains cellular homeostasis.