PRG1 - A NOVEL EARLY-RESPONSE GENE TRANSCRIPTIONALLY INDUCED BY PITUITARY ADENYLATE-CYCLASE ACTIVATING POLYPEPTIDE IN A PANCREATIC-CARCINOMA CELL-LINE

The rat pancreatic carcinoma cell line AR4-2J was screened for growth- associated genes linked to the mitogenic effect of the novel gut brain hormone, pituitary adenylate cyclase activating polypeptide (PACAP). Using the mRNA differential display technique, we identified and seque nced an unknown rat gene, PACAP-responsive gene 1 (PRG1), which is hig hly homologous to gly96, a novel murine gene of unknown function. The PRG1 cDNA sequence of 1.1 kb encodes a 160-amino acid protein. Using t argeted PCR, the gene structure of PRG1, constituting 0.6 kb of the pr omotor region, and the DNA coding region, including a single 107-bp in tron, were established from rat genomic DNA. In AR4-2J cells, PACAP(1- 38) increased PRG1 mRNA levels up to 10-fold in a rapid (30 min), tran sient (3-6 h), and dose-dependent (ED(50), <1 nM) fashion. The growth- stimulating gastrointestinal hormones cholecystokinin and gastrin show ed a similar degree of PRG1 induction, and the PACAP-related peptides vasoactive intestinal peptide and secretin were without effect. The tr anscriptional inhibitor actinomycin D, various protein kinase C inhibi tors, and the calmodulin inhibitor W-7 strongly reduced PRG1 induction by PACAP, whereas the translational inhibitor cycloheximide potently increased PRG1 mRNA levels in unstimulated and PACAP-stimulated cells, Feedback-mediated hyperplasia of the rat exocrine pancreas induced by oral treatment of rats with the protease inhibitor camostate (FOY-305 ) was preceded by a 15-fold transient elevation of PRG1 mRNA levels. T hese data suggest that PRG1 is an early-response gene linked to PACAP- induced growth of AR4-2J cells as well as to hyperplasia of the rat ex ocrine pancreas in vivo.