Light-induced tyrosine phosphorylation of rod outer segment membrane proteins regulate the translocation, membrane binding and activation of type II α phosphatidylinositol-5-phosphate 4-kinase.

Type II phosphatidylinositol 5-phosphate 4-kinase (PIPKIIα) catalyzes the synthesis of phosphatidylinositol-4,5-bisphosphate (PI-4,5-P(2)), an essential lipid second messenger that may be involved in the regulation of phototransduction, neuroprotection, and morphogenesis in the vertebrate retina. Here we report that in rodent and transgenic frogs, the light-mediated activity and membrane binding of PIPKIIα in rod outer segments (ROS) is dependent on tyrosine phosphorylation of ROS proteins. The greater type II α PIP kinase activity in the light-adapted ROS membrane results from light-driven translocation of PIPKIIα from the rod inner segment to ROS, and subsequent binding to the ROS membrane, thus improving access of the kinase to its lipid substrates. These results indicate a novel mechanism of light regulation of the PIPKIIα activity in photoreceptors, and suggest that the greater PIPKIIα activity in light-adapted animals and the resultant accumulation of PI-4,5-P(2) within the ROS membrane may be important for the function of photoreceptor cells.