| Akt3 (RAC‑γ serine/threonine kinase) is a member of the Akt/PKB family of AGC kinases that functions as a key effector of PI3K signaling and shows preferential expression and activity in brain, kidney, and heart, where it contributes to regulation of growth, metabolism, survival, and inflammatory responses in a tissue‑selective manner. The kinase shares the conserved domain architecture of Akt isoforms with an N‑terminal pleckstrin homology domain that binds phosphoinositides, a central kinase domain that contains the activation loop threonine site corresponding to Thr305 in Akt3, and a C‑terminal hydrophobic motif that includes Ser472, with phosphorylation at both regulatory sites acting in concert to generate full catalytic activity in response to PI3K‑generated PIP3 and PDK1/mTORC2 input. Akt3 is recruited to membranes after stimulation of receptor tyrosine kinases, cytokine receptors, GPCRs, or antigen receptors that activate class I PI3K, and membrane localization permits PDK1 phosphorylation of the activation loop and mTORC2 phosphorylation of the hydrophobic motif, while phosphatases such as PTEN, PP2A, and PHLPP restrain this activation cycle and set the signaling threshold for downstream responses. Akt3 shares many substrates with Akt1 and Akt2, including regulators of apoptosis, cell‑cycle progression, metabolism, and mTORC1, and phosphorylates proteins that control TSC1/TSC2 complex activity, mTORC1 output, GSK3‑dependent control of cyclin D1 and glycogen synthesis, and FoxO transcription factors, thereby linking growth factor and nutrient availability to biosynthesis, proliferation, and survival. Akt3 also displays isoform‑biased functions: high expression and signaling activity in neural tissues supports brain growth and neuronal survival, and disruption or reduction of Akt3 activity is associated with decreased brain size and neurodevelopmental phenotypes, while elevated Akt3 signaling contributes to tumor cell survival and proliferation in estrogen receptor‑negative breast cancer, PTEN‑deficient prostate cancer, and other malignancies where it frequently represents the predominant active Akt isoform. In immune and inflammatory contexts Akt3 modulates responses such as inflammatory demyelinating disease and adipose tissue expansion, where Akt3 activity influences balance between proliferation, differentiation, and inflammatory signaling, supporting disease‑specific roles that are partly distinct from Akt1 and Akt2 and that make Akt3 a candidate isoform‑selective target in oncology, neurology, and metabolic disease. |
