The receptor tyrosine phosphatase-like protein ICA512 binds the PDZ domains of β2-syntrophin and nNOS in pancreatic β-cells

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Summary

Islet cell autoantigen (ICA) 512 of type I diabetes is a receptor tyrosine phosphatase-like protein associated with the secretory granules of neurons and endocrine cells including insulin-secreting β-cells of the pancreas. Here we show that in a yeast two-hybrid assay its cytoplasmic domain binds β2-syntrophin, a modular adapter which in muscle cells interacts with members of the dystrophin family including utrophin, as well as the signaling molecule neuronal nitric oxide synthase (nNOS). The cDNA isolated by two-hybrid screening corresponded to a novel β2-syntrophin isoform with a predicted molecular mass of 28 kDa. This isoform included the PDZ domain, but not the C-terminal region, which in full-length β2-syntrophin is responsible for binding dystrophin-related proteins. In vitro binding of the β2-syntrophin PDZ domain to ICA512 required both ICA512′s C-terminal region and an internal polypeptide preceding its tyrosine phosphatase-like domain. Immunomicroscopy and co-immunoprecipitations from insulinoma INS-1 cells confirmed the occurrence of ICA512-β2-syntrophin complexes in vivo. ICA512 also interacted in vitro with the PDZ domain of nNOS and ICA512-nNOS complexes were co-immunoprecipitated from INS-1 cells. Finally, we show that INS-1 cells, like muscle cells, contain β2-syntrophin-utrophin oligomers. Thus, we propose that ICA512, through β2-syntrophin and nNOS, links secretory granules with the actin cytoskeleton and signaling pathways involving nitric oxide.

Key words

Protein tyrosine phosphatase
secretory granule
cytoskeleton
pancreatic β-cells
protein complex

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