Induction of the synthesis of a specific protein in rat submandibular gland by isoproterenol.

Prolonged treatment of rats with the beta-adrenergic agonist, isoproterenol (IPR), produces hypertrophy and hyperplasia of the parotid and submandibular glands. The drug induces the synthesis of several secretory proteins that are absent or occur at very low concentrations in the gland or saliva of the untreated rat. We have measured the relative concentrations of one of these proteins (termed "large mobile" (LM) protein, Menaker et al. (1974) Lab. Invest. 30, 341-349) by using a solid phase enzyme-linked immunoabsorption assay. LM protein was not measurable in gland extracts of 20-day-old fetuses or 2-day-old rats. Its concentration was very low in the glands of 6- and 13-day-old and adult rats. Administration of IPR for 4 to 7 days to adult or 6-day old rats increased the levels of the LM protein by 20 to 25-fold. The LM protein was localized immunocytochemically primarily in the acinar cells in the glands of control and IPR-treated adult rats. In vitro translation studies using a mRNA-dependent reticulocyte lysate system and labeling with [35S]methionine showed: little synthesis of pro-LM from poly(A+) RNA from glands of adult rats and none from 13-day-old animals, and that, in comparison, poly(A+) RNA from glands of adult or 13-day-old IPR-treated rats directed the synthesis of a much greater concentration of pro-LM. The in vitro precursor of the LM protein migrated electrophoretically as a single band in anti-LM immunoprecipitates, and had a molecular weight of 14,000. The LM protein, which appears to be a single, unique polypeptide induced by IPR in the submandibular glands of developing and adult rats, will be useful in studies examining the effects of catecholamine beta-agonists on gene expression in an exocrine cell.