Induction of tissue-specific proline-rich protein multigene families in rat and mouse parotid glands by isoproterenol. Unusual strain differences of proline-rich protein mRNAs

Proline-rich proteins and glycoproteins: expression of salivary gland multigene families

Our recent research interests have focused on a group of unusual proteins and glycoproteins high in proline content, or the so-called proline-rich proteins (PRPs). The PRPs are tissue-specific expressions of salivary gland multigene families. Normally PRPs are not detected or are present in very low amounts in rat, mouse and hamster salivary glands, but these unusual proteins are dramatically induced by treatment with the catecholamine isoproterenol. The structures and organizations of several PRP mRNAs and PRP genes have been determined. The amino acid sequences of all PRPs show 4 distinct regions, namely, a signal peptide, a transition region, a repeat region and a carboxyl-terminal region. Glycoproteins induced by isoproterenol treatment may be N-glycosylated or O-glycosylated. The N-glycosylated glycoprotein GP-158 from rat submandibular glands has a 12 amino acid glycopeptide which repeats possibly 49 times. Proline-rich proteins of the parotid glands of rats and mice are also greatly induced by dietary tannins. The apparent unique occurrence of PRPs in saliva suggests that one biological role is to neutralize the detrimental effects of dietary tannins and other polyphenols. The upstream regions of the mouse and hamster PRP genes contain cyclic AMP-regulated sequences as demonstrated by deletions and transient transfections. The PRP multigene family members of mouse are all located on chromosome 8.

Regulation of proto-oncogenes in rat parotid acinar cells in vitro after stimulation of beta-adrenergic receptors

Stimulation of beta-adrenoreceptors in rat parotid acinar cells in vitro by the beta-adrenergic agonist isoproterenol induces steady-state levels of c-fos mRNA and c-fos protein in these cells. A dramatic increase in the steady-state levels of c-fos mRNA was observed at 60 min, followed by a decrease at 2 h with a second peak at 4 h. c-fos induction in rat parotid acinar cells in vitro seems to be mediated by cAMP. Increased levels of p53 and c-myc mRNA were detected only at 60 min. c-abl and c-sis were also induced by isoproterenol but in a pattern different from that seen with c-fos. c-abl was the only oncogene in rat parotid gland which showed increased expression after chronic isoproterenol treatment of rats. In rat parotid acinar cells we observed no correlation between DNA synthesis and c-fos induction.