Neuronal nitric oxide synthase is a SHP-1 substrate involved in sst2 somatostatin receptor growth inhibitory signaling

Somatostatin receptor sst2 is an inhibitory G protein-coupled receptor, whi ch inhibits normal and tumor cell growth by a mechanism involving the tyros ine phosphatase SHP-1. We reported previously that SHP-1 associates transie ntly with and is activated by sst2 and is a critical component for sst2 gro wth inhibitory signaling. Here, we demonstrate that in Chinese hamster ovar y cells expressing sst2, SHP-1 is associated at the basal level with the ne uronal nitric oxide synthase (nNOS). Following sst2 activation by the somat ostatin analog RC-160, SHP-1 rapidly recruits nNOS tyrosine dephosphorylate s and activates it. The resulting NO activates guanylate cyclase and inhibi ts cell proliferation. Coexpression of a catalytically inactive SHP-1 mutan t with sst2 blocks RC-160-induced nNOS dephosphorylation and activation, as well as guanylate cyclase activation. In mouse pancreatic acini, RC-160 tr eatment reduces nNOS tyrosine phosphorylation accompanied by an increase of its activity. By opposition, in acini from viable motheaten (me(v)/me(v)) mice, which express a markedly inactive SHP-1, RC-160 has no effect on nNOS activity. Finally, expression of a dominant-negative form of nNOS prevents both RC-160-induced p27 up-regulation and cell proliferation inhibition. W e therefore identified nNOS as a novel SHP-1 substrate critical for sst2-in duced cell-growth arrest.