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Wednesday 29 October 2003

second messenger in signal transduction

Many cell-surface receptors induce production of second messengers like PIP3 (phosphatidylinositol 3,4,5-trisphosphate) that convey signals to the cytoplasm from the cell surface.

PIP3 signals activates the kinase PDK1 (3-phosphoinositide-dependent protein kinase-1), which in turn activates the kinase AKT, also known as protein kinase B (PKB).

Proteins phosphorylated by activated AKT promote cell survival.

Phosphorylation of Ikappa-B kinase leads to activation of the transcription factor NF-kB to oppose apoptosis. Bad is a protein in the Bcl-2 gene family that opposes Bcl-2 to induce apoptosis. Phosphorylation of Bad by AKT blocks anti-apoptotic activity to promote cell survival.

Similarly, phosphorylation of the protease caspase 9 or forkhead transcription factors by AKT block the induction of apoptosis by these factors. AKT promotes cell survival and opposes apoptosis by a variety of routes. (Biocarta)

See also

- PI3K
- PIP2
- PI3K/PTEN/AKT signaling pathway


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- Schulz I, Krause E. Inositol 1,4,5-trisphosphate and its co-players in the concert of Ca2+ signalling—new faces in the line up. Curr Mol Med. 2004 May;4(3):313-22. PMID: 15101688

- Irvine RF. 20 years of Ins(1,4,5)P3, and 40 years before. Nat Rev Mol Cell Biol. 2003 Jul;4(7):586-90. PMID: 12838341