['Pancreatic thread proteins (PTPs) are acinar cell products and members of the regenerating gene (reg) family. reg expression increases during islet regeneration, is depressed during aging-related islet dysfunction, and may be important in beta-cell growth and maintenance. The aim of this study was to examine the genetic expression of reg in pancreatic-derived cells in vitro and the mitogenic effect of PTP/reg protein on these cells.', 'reg gene expression was measured by Northern analysis in three rat pancreatic cell lines: ARIP (ductal), AR42J (acinar), and RIN (beta-cell). PTP/reg protein was isolated from bovine and human pancreas. Cells were cultured with PTP/reg for 72 hours, and thymidine incorporation was measured.', 'reg messenger RNA was detected in AR42J but not in ARIP or RIN. PTP/reg protein was mitogenic to RIN and ARIP in a dose-related fashion but not to AR42J. It was not mitogenic to cultured mature rat islets.'] Is pancreatic thread protein mitogenic to pancreatic-derived cells in culture?