REGULATION OF PROLINE-RICH PROTEIN GENE-EXPRESSION BY CYCLIC-AMP IN PRIMARY CULTURES OF HAMSTER PAROTID-GLANDS

Proline-rich proteins (PRPs) constitute a group of unusual salivary proteins encoded by tissue-specific multigene families which can be dramatically induced (20- to 70-fold) in vivo in rats, mice and hamsters by treatment with the β-agonist isoproterenol. Addition of dibutyryl cyclic AMP (dbcAMP) or forskolin to hamster parotid gland primary cultures resulted in a large increase (15- to 30-fold) in PRP mRNA levels. The same time-course and levels of induction of PRP mRNA by dbcAMP and isoproterenol were found in primary cultures, indicating that both effectors act through the same mechanism. Induction by isoproterenol, but not by dbcAMP or forskolin, was blocked by the β-antagonist propranolol. Incorporation of [3H]proline into PRPs was stimulated in primary cultures by all three effectors. The greatest increase in proline incorporation was in the [3H]PRPs recovered in the culture medium of induced cells. These studies demonstrate that cAMP or agents which increase intracellular cAMP levels increase PRP gene expression in primary cultures of parotid glands. Pretreatment of the cells with cycloheximide blocked the induction of PRP mRNAs which indicates that the synthesis of a trans-acting factor may be necessary for transcriptional activation of the PRP genes. α-Amylase mRNA, another tissue-specific gene product, was not significantly affected by cycloheximide treatment.