SignalStain^® Akt Pathway IHC Sampler Kit #8107

The protein kinase Akt (also called PKB or Rac) is activated by insulin and growth and survival factors to function in a wortmannin-sensitive pathway involving PI3 kinase (1,2). Akt is activated by phospholipid binding and activation loop phosphorylation at Thr308 by PDK1 (3) and by carboxy terminal phosphorylation at Ser473 by the mTORC2 complex composed of mammalian target of rapamycin (mTOR) in a complex with rictor and Sin1 (4,5). Akt signaling is negatively regulated via the PTEN phosphatase (6).
Akt’s several functions include inhibition of apoptosis (7-9), regulation of glycogen synthesis via GSK-3 (10), and promotion of the cell cycle (11). Akt also regulates protein synthesis by phosphorylating mTOR in a rapamycin-sensitive complex containing raptor (mTORC1) (12). Akt also effects mTOR activity via phosphorylation and inhibition of PRAS40 (40 kDa, proline-rich protein), which binds to raptor in the mTORC1 complex and inhibits mTOR activity (13). Phosphorylation of PRAS40 by Akt at Thr246 relieves PRAS40 inhibition of mTORC1 (14), allowing protein synthesis to occur. Active of mTORC1 signals to p70 S6 kinase, which in turn phosphorylates S6 ribosomal protein. Phosphorylation of S6 ribosomal protein correlates with an increase in translation of a subset of mRNA transcripts that encode ribosomal proteins, translation elongation factors as well as regulators of cell cycle progression (15). Important S6 ribosomal protein phosphorylation sites include Ser235, Ser236, Ser240 and Ser244 within a small carboxy-terminal region (16).