Abstract
Glucagon-like peptide1 (GLP-1), a cAMP mobilizing agonist, is an insulinotropic peptide. However, the underlying mechanisms of the stimulatory effect of GLP-1 on insulin secretion remain fully elucidated. One of the mechanisms by which GLP-1 potentiates glucose-induced insulin secretion is to modulate Ca2+signaling. Recently, we have demonstrated that depolarization-evoked Ca2+ influx alone can activate conventional protein kinase C (PKC) and novel PKC in INS-1 cells.The present study was conducted to examine whether GLP-1 can activate PKCα and PKCε, which are predominantly expressed in INS-1 cells at a substimulatory concentration of glucose. We first showed that GLP-1 translocated endogenous PKCα and PKCε from the cytosol to the plasma membrane. Then we assessed the phosphorylation state of the PKC substrate, MARCKS, as a maker of PKC activation. GLP-1 translocated GFP-tagged MARCKS from the plasma membrane to the cytosol and the GLP-1-evoked translocation of MARCKS-GFP was blocked by a PKC inhibitor. The above observations were verified in three different ways by demonstrating: 1) Br-cAMP induced translocation of GFP-tagged C1 domain of PKCγ, 2) Br-cAMP induced translocation of GFP-tagged pleckstrin homology domain of phospholipase Cδ1, 3) forskolin-induced translocation of PKCα and PKCε, as makers of PKC activation.Taken together, these results demonstrate that GLP-1 can activate PKCα and PKCε through a Ca2+-dependent phospholipase C activation. [Jpn J Physiol 55 Suppl:S34 (2005)]
