The receptor tyrosine phosphatase-like protein ICA512 binds the PDZ domains of beta 2-syntrophin and nNOS in pancreatic beta-cells

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 beta-cells of the pancreas, Here we show that in a yeast two-hybrid assay its cytoplasmic domain binds beta 2-syntrophin, a modular adapter which in muscle cells interacts with members of the dystrophin family including utrophin, as well as the signali ng molecule neuronal nitric oxide synthase (nNOS), The cDNA isolated by two -hybrid screening corresponded to a novel beta 2-syntrophin isoform with a predicted molecular mass of 28 kDa, This isoform included the PDZ domain, b ut not the C-terminal region, which in full-length beta 2-syntrophin is res ponsible for binding dystrophin-related proteins. In vitro binding of the b eta 2-syntrophin PDZ domain to 1CA512 required both 1CA512's C-terminal reg ion and an internal polypeptide preceding its tyrosine phosphatase-like dom ain. Immunomicroscopy and co-immunoprecipitations from insulinoma INS-I cel ls confirmed the occurrence of ICA512-beta 2-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 th at INS-1 cells, like muscle cells, contain beta 2-syntrophin-utrophin oligo mers, Thus, we propose that ICA512, through beta 2-syntrophin and nNOS, lin ks secretory granules with the actin cytoskeleton and signaling pathways in volving nitric oxide.