Annexins and Heparan Sulfate Proteoglycans in Pancreatic Endocrine β Cells

概要

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We previously demonstrated that annexins are localized in exocrine tissues such as kidney, liver, intestine and pancreatic acinar cells. We also elucidated the glycosaminoglycan (GAG) binding properties of annexins IV, V and VI and showed that each of them has its own specific binding activities to GAGS. In this study, we examined the function of annexin VI and GAGs in pancreatic β cells. Immunohistochemical studies and immunoblot assays showed that annexin VI localized in rat pancreatic islets, HIT-T15 cells derived from rat insulinorna and MIN6 cells derived from mouse insulinoma. Immunoblot assay detected heparan sulfate proteoglycan in those cell lysates but not chondroitin sulfate proteoglycan. Affinity adsorption assay showed annexin VI bound to the heparan sulfate proteoglycans derived from HIT-T15 cells indicating that these proteoglycans the endogenous ligand of annexin VI in β cells. Insulin secretion assay from permeabilized MIN6 cells showed that full-length human annexin VI promotes insulin release, but not other mutants. Inhibition of Ca^<2+>-dependent insulin release by GAGs was inferred that GAGs blocked binding of annexin VI and membrane vesicle. These results suggest that annexin VI was considered to exit in pancreatic endocrine cells, and to interact with both cell-extracellular matrix heparan sulfate proteoglycan and membrane vesicle in β cells.
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