Akt/PKB signaling pathway

The Akt signaling pathway or PI3K-Akt signaling pathway is a signal transduction pathway that promotes survival and growth in response to extracellular signals. Key proteins involved are PI3K (phosphatidylinositol 3-kinase) and Akt (protein kinase B).

Initial stimulation by one of the growth factors causes activation of a cell surface receptor and phosphorylation of PI3K. Activated PI3K then phosphorylates lipids on the plasma membrane, forming second messenger phosphatidylinositol (3,4,5)-trisphosphate (PIP₃). Akt, a serine/threonine kinase, is recruited to the membrane by interaction with these phosphoinositide docking sites, so that it can be fully activated.^[1] Activated Akt mediates downstream responses, including cell survival, growth, proliferation, cell migration and angiogenesis, by phosphorylating a range of intracellular proteins. The pathway is present in all cells of higher eukaryotes and is highly conserved.^[2]

The pathway is highly regulated by multiple mechanisms, often involving cross-talk with other signaling pathways. Problems with PI3K-Akt pathway regulation can lead to an increase in signaling activity. This has been linked to a range of diseases such as cancer and type 2 diabetes. A major antagonist of PI3K activity is PTEN (phosphatase and tensin homolog), a tumour suppressor which is often mutated or lost in cancer cells. Akt phosphorylates as many as 100 different substrates, leading to a wide range of effects on cells.^[3]