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  • Title: Myosin light-chain phosphorylation controls insulin secretion at a proximal step in the secretory cascade.
    Author: Iida Y, Senda T, Matsukawa Y, Onoda K, Miyazaki JI, Sakaguchi H, Nimura Y, Hidaka H, Niki I.
    Journal: Am J Physiol; 1997 Oct; 273(4):E782-9. PubMed ID: 9357809.
    Abstract:
    The aim of this study was to investigate how insulin secretion is controlled by phosphorylation of the myosin light chain (MLC). Ca2+-evoked insulin release from pancreatic islets permeabilized with streptolysin O was inhibited by different monoclonal antibodies against myosin light-chain kinase (MLCK) to an extent parallel to their inhibition of purified MLCK. Anti-MLCK antibody also inhibited insulin release caused by the stable GTP analog guanosine 5'-O-(3-thiodiphosphate), even at a substimulatory concentration (0.1 microM) of Ca2+. Free Ca2+ increased MLC peptide phosphorylation by beta-cell extracts in vitro. In contrast to the phosphorylation by purified MLCK or by calmodulin (CaM) kinase II, the activity partially remained with the beta-cell under nonstimulatory Ca2+ (0.1 microM) conditions. The MLCK inhibitor ML-9 inhibited the activity in the beta-cell with both substimulatory and stimulatory Ca2+, whereas KN-62, an inhibitor of CaM kinase II, only exerted an influence in the latter case. ML-9 decreased intracellular granule movement in MIN6 cells under basal and acetylcholine-stimulated conditions. We propose that MLC phosphorylation may modulate translocation of secretory granules, resulting in enhanced insulin secretion.
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