Phosphoinositide-3-Kinase Regulatory Subunit 2 (PIK3R2)

Phosphatidylinositol 3-kinase (PI3K) is a lipid kinase that phosphorylates the inositol ring of phosphatidylinositol and related compounds at the 3-prime position. The products of these reactions serve as second messengers in growth signaling pathways. The kinase itself is made up of a catalytic subunit of molecular mass 110 kD (PIK3CA) and a regulatory subunit of either 85 kD, 55 kD, or 50 kD.

Both p85-alpha and p85-beta bound Xbp1s and increased its nuclear translocation, and it appeared that the p110 PI3K catalytic subunit and Xbp1s competed for binding of these regulatory subunits. p85-alpha and p85-beta formed an inactive dimer that was disrupted by insulin in a time-dependent manner, which promoted their association with Xbp1s.