Rat somatostatin sst(2(a)) and sst(2(b)) receptor isoforms mediate opposite effects on cell proliferation

We have investigated the actions of somatostatin (SRIF) and angiopeptin on cell proliferation of CHO-K1 cells expressing the recently cloned rat sst(2 (b)) receptor (CHOsst(2(b))) and compared these to their effects in cells e xpressing the sst(2(a)) receptor (CHOsst(2(a))). In contrast to the sst(2(a )) receptor, the sst(2(b)) receptor did not mediate inhibition of bFGF (10 ng ml(-1))-stimulated re-growth and cell proliferation. Rather, SRIF (0.1-1 000 nM) and angiopeptin (0.1-1000 nM) stimulated basal regrowth and prolife ration of CHOsst(2(b)) cells in a concentration-dependent manner (estimated pEC(50) values of 7.8 and 7.9, respectively). The opposite effects of SRIF on cell proliferation mediated through the two sst(2) receptor isoforms we re both abolished by 18 h pre-treatment with pertussis toxin. The prolifera tive effect via the sst(2(b)) receptor was also abolished by the tyrosine k inase inhibitor, genistein. In conclusion, the present study shows that the rat sst(2(a)) and sst(2(b)) receptor splice variants mediate opposite effe cts on cell proliferation.