PITUITARY ADENYLATE-CYCLASE-ACTIVATING POLYPEPTIDE STIMULATES PROTOONCOGENE EXPRESSION AND ACTIVATES THE AP-1 (C-FOS C-JUN) TRANSCRIPTION FACTOR IN AR4-2J PANCREATIC-CARCINOMA CELLS/

Pituitary adenylate-cyclase-activating polypeptide (PACAP) has been sh own to possess mitogenic activity in various tumor cells. The present study was designed to investigate signal transduction mechanisms and e xpression of the proto-oncogenes c-fos and c-jun linked to the mitogen ic effect of PACAP in the pancreatic carcinoma cell line AR4-2J. PACAP -(1-27)-peptide and PACAP-(1-38)-peptide, but not the structurally rel ated vasoactive intestinal polypeptide (VIP), potently stimulated [H-3 ]thymidine incorporation and cell number at doses of 0.1-10 nM. Both m olecular forms of PACAP strongly increased formation of cAMP and inosi tol trisphosphate, elevated cytosolic Ca2+ levels and induced mitogen- activated protein (MAP) kinase activity. Quantitative reverse-transcri ption PCR revealed that PACAP-(1-27)-peptide and PACAP-(1-38)-peptide elevated c-fos mRNA levels 50-100-fold, whereas c-jun mRNA levels incr eased only moderately (2-3-fold). The effect of PACAP on c-fos and c-j un expression in AR4-2J cells was rapid (20 min), transient (1-2 h), d ose-dependent (IC50, 0.5 nM) and was abolished by the specific PACAP r eceptor antagonist PACAP-(6-38)-peptide or inhibitors of protein kinas e C or tyrosine kinases. Compared with PACAP, epidermal growth factor and gastrin equipotently stimulated c-Sos transcription whereas VIP, s ecretin, forskolin or phorbol ester showed only marginal effects. Both PACAP(1-27)-peptide and PACAP-(1-38)-peptide strongly increased the D NA binding activity of the c-fos/c-jun heterodimer transcription facto r AP-1 at 10 nM and also stimulated AP-1 transcriptional activity up t o 20-fold in AR4-2J cells. These findings indicate that the mitogenic effect of PACAP mediated via activation of the GTP-binding protein cou pled PACAP/VIP-1 (PV1) receptor is linked to the MAP kinase cascade, i ncreased expression of the proto-oncogenes c-fos and c-jun and activat ion of the heterodimeric transcription factor AP-1.