Regulation of Insulin Secretion by Overexpression of Ca²⁺/Calmodulin-Dependent Protein Kinase II in Insulinoma MIN6 Cells

Abstract

Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) may play a key role in Ca2+-induced insulin secretion. We have previously reported that treatment of insulinoma MIN6 cells with secretagogues activated CaM kinase II and increased the phosphorylation of synapsin I, followed by insulin secretion. Here, we identified isoforms of CaM kinase II in MIN6 cells and rat islets. Immunoblot analysis suggested that the major isoforms of CaM kinase II were beta'e and delta2 at the protein level in MIN6 cells. Only the beta'e isoform was detected in rat islets by both RT-PCR and immunoblot analysis. We transiently overexpressed beta'e and delta2 isoforms in MIN6 cells and confirmed that treatment of cells with tolbutamide and glucose activated the isoforms. Immunoblot analysis with an antibody against synapsin I phosphorylated by CaM kinase II demonstrated that treatment with tolbutamide and glucose rapidly increased phosphorylation of synapsin I and that phosphorylation was potentiated by overexpression of the isoforms. The secretagogue-induced insulin secretion was potentiated by overexpression of the isoforms. Our results further support our conclusion that activation of CaM kinase II and the concomitant phosphorylation of synapsin I contribute to insulin secretion from pancreatic beta-cells.

Activation of Pyk2 by CaM kinase II in cultured hypothalamic neurons and gonadotroph cells

“…The anti‐CaM kinase IIδ1–δ4 antibody detected a 55‐kDa protein strongly in αT3‐1 cells, but no clear band was observed in LβT2 cells (Figure b). In the previous study, we reported that the apparent molecular masses of the β’e and δ2 isoforms were 55 kDa (Tabuchi et al, ; Yamanaka et al, ). These results strongly suggested that β’e and δ2 were major isoforms in αT3‐1 cells, and that a small amount of β’e isoform was expressed in LβT2 cells at the protein level.…”

Analysis on the promoter region of exon IV brain‐derived neurotrophic factor in NG108‐15 cells

“…CaM KII, which is highly expressed in neuronal tissues, is involved in many calcium‐mediated functions such as release and biosynthesis of neurotransmitters and hormones (Matsumoto et al . 1999; Tabuchi et al . 2000), regulation of receptor functions (McGlade‐McCulloh et al .…”