When insulin enters the bloodstream and binds to its receptor, members of the insulin receptor substrate (IRS) family are activated. IRS, in turn, activates tyrosine kinase adaptor molecules on the cell membrane that recruit class I PI3K to the receptor complex. After receptor engagement, PI3K phosphorylates phosphatidylinositol 4,5 bisphosphonate (PIP2) to generate phosphatidylinositol 3,4,5 triphosphate (PIP3) as a second messenger to recruit and activate downstream targets including AKT. AKT, also referred to as Protein Kinase B, is the key downstream effector of PI3K.69