signaling pathway involving second messengers phosphatidylinositol 3-kinase signaling pathway PI3K Cascade PI3K signaling pathway PW:0000595 Phosphatidylinositol kinases represent a family of lipid kinases that phosphorylate the 3' position of the inositol ring in target substrates. They are grouped into three classes: class I, further subdivided into subclass A and B, class II and class III. By far the best known and characterized is class I, particularly IA that signals downstream of receptor tyrosine kinases and engages the Akt family of kinases. pathway phosphatidylinositol 3-kinase signaling phosphoinositide 3-kinase signaling pathway