Inositol Hexakisphosphate Promotes Dynamin I-Mediated Endocytosis

Membrane homeostasis is maintained by exocytosis and endocytosis. The molecular mechanisms regulating the interplay between these two processes are not clear. Inositol hexakisphosphate (InsP6) is under metabolic control and serves as a signal in the pancreatic β cell stimulus-secretion coupling by increasing Ca2+-channel activity and insulin exocytosis. We now show that InsP6also promotes dynamin I-mediated endocytosis in the pancreatic β cell. This effect of InsP6depends on calcineurin-induced dephosphorylation and is accounted for by both activation of protein kinase C and inhibition of the phosphoinositide phosphatase synaptojanin and thereby formation of phosphatidylinositol 4,5-bisphosphate. In regulating both exocytosis and endocytosis, InsP6thus may have an essential integral role in membrane trafficking.