Downstream signalling events regulated by phosphatidylinositol 3-kinase activity

The phosphatidylinositol (PI) 3-kinase family of enzymes is now known to be regulated by several different upstream pathways in response to virtually all growth factors and cytokines. In the past few years, the phosphoinositides phosphorylated at the 3-OH position of the inositol ring have been shown to be lipid second messengers that may directly or indirectly regulate the activity of several different serine/threonine kinases. Consistent with the many different cellular events in which PI 3-kinase plays an important role, a diverse group of serine/threonine kinases are regulated downstream of PI 3-kinases, including protein kinase C (PKC) isoforms, p70 S6 kinase, and PKB/Akt. This review summarises studies done primarily in the past few years that have begun to unravel these targets of PI 3-kinase activity.