| Two pancreatic acinar cell lines were investigated as in vitro models for hormonal regulation of exocrine pancreatic cell proliferation and differentiation. Rat pancreatic AR42J cells were compared with normal rat acini with respect to secretory protein expression, secretion, and hormonal regulation. In AR42J cells, four major secretory proteins were identified: amylase, procarboxypeptidase A, chymotrypsinogen, and rat acinar pancreas secretory protein M{dollar}sb{lcub}rm r{rcub}{dollar} = 68,000 (unknown activity). The secretion of these 4 proteins was stimulated 2-3.5 fold by CCK. Dexamethasone treatment for 48 hours caused a 150-250% increase in the biosynthesis of all four proteins. The proportion of total protein released into the medium by CCK was equivalent for both dexamethasone-treated and non-treated cells (210% of control). Dexamethasone (10nM) inhibited proliferation in AR42J cultures by 95%. Inhibition of DNA synthesis was half-maximal after 12 hours, and maximal after 18 hours of dexamethasone treatment. The K{dollar}sb{lcub}rm ED{rcub}{dollar} for inhibition of DNA synthesis was 0.5 nM; maximal inhibition was achieved with 10nM dexamethasone. Inhibition of DNA synthesis was specific for adrenal glucocorticoids. The time-course, dose-response, and steroid specificity for increased amylase synthesis and increased CCK binding paralleled inhibition of DNA synthesis. It was determined that inhibition of proliferation alone would not cause differentiation since hydroxyurea or serum starvation inhibited growth to the same extent as dexamethasone, but did not induce differentiation. To determine whether cell proliferation was compatible with cellular differentiation, EGF and insulin were combined with sub-maximal dexamethasone. In AR42J cultures released from growth inhibition by EGF or insulin, 1nM dexamethasone increased cellular amylase content 5.9-6.5 fold, equivalent to the amylase increase in growth inhibited cultures. Mouse 266-6 cells responded to 10nM dexamethasone with a 3-12 fold increase in amylase content. In contrast to AR42J cells, proliferation of mouse 266-6 cells was not inhibited by dexamethasone. It was concluded that, in AR42J and in 266-6 cells, glucocorticoid effects on differentiation and cell proliferation were independent and separable. |
