PKCepsilon mediates glucose-regulated insulin production in pancreatic beta-cells

Endocrine cells produce large amounts of one or more peptides. The post-translational control of selective production of a single protein is often unknown. We used 3 unrelated approaches to diminish PKCε in rat islets to evaluate its role in preferential glucose-mediated insulin production. Transfection with siRNA (siR-PKCε) or expression of inactive PKCε (PKCε-KD) resulted in a significant reduction in insulin response to glucose (16.7 mmol/l). Glucose stimulation resulted in concentration of PKCε in the perinuclear region, an area known to be rich in ER-Golgi systems, associated with insulin-containing structures. ß'COP1 (RACK2) is the anchoring protein for PKCε. Glucose-stimulated proinsulin production was diminished by 50% in islets expressing PKCε-KD, and 60% in islets expressing RACK2 binding protein (εV1-2); total protein biosynthesis was not affected. In islets expressing εV1-2, a chase period following glucose stimulus resulted in a reduced proinsulin conversion to mature insulin. We propose that PKCε plays a specific role in mediating the glucose-signal into insulin production: binding to ß'COP1 localizes the activated enzyme to the RER where it modulates the shuttling of proinsulin to the TGN. Subsequently the enzyme may be involved in anterograde trafficking of the prohormone or in its processing within the TGN.