BOMBESIN-MEDIATED AP-1 ACTIVATION IN A HUMAN GASTRIC-CANCER (SIIA)

Background. Bombesin, a gut tetradecapeptide homologous to the mammali an gastrin-releasing peptide (GRP), stimulates the growth of the human gastric cancer line SIIA through specific GRP receptors (GRP-Rs); the cellular mechanisms are not known. The purpose of our study was to (1 ) confirm functional GRP-R in SIIA and (2) determine whether bombesin alters the expression and binding activity of the AP-1 transcription f actors, c-jun and jun-B. Methods. SIIA cells were treated with bombesi n, and intracellular calcium mobilization was measured by means of fur a-2 spectrofluorometry. To access changes in c-jun and jun-B, RNA and protein were extracted for Northern and Western blots, respectively; n uclear protein was extracted for gel mobility shifts to determine AP-1 binding activity. Results. SIIA cells mobilized intracellular calcium in response to bombesin, exhibiting a functional cell-surface GRP-R. Bombesin treatment increased expression for both c-jun and jun-B mRNA by 0.5 hours, with maximal expression at 1 hour, concomitant increase in steady-state levels of c-Jun and Jun-B protein were identified. Mor eover, bombesin increased bonding of the AP-1 proteins as shown by gel shifts. Conclusion. The SIIA human gastric cancer possesses functiona l GRP-R coupled to the calcium second messenger pathway. Further, bomb esin stimulates expression of c-jun and jun-B mRNA and protein and inc reases binding activity of AP-1 proteins. Delineating the cellular pat hways involved in bombesin-mediated gene activation will provide impor tant into the mechanisms responsible for normal and neoplastic gut gro wth.