Rat submandibular gland expression of the glutamine/glutamic acid-rich proteins

Previously, this laboratory isolated and characterized the rat submandibular gland (RSMG) glutamine/glutamic acid-rich proteins (GRP). We have examined the regulated expression of this abundant salivary proteins. GRP are secreted in response to {dollar}beta{dollar}-adrenergic stimulation. Chronic treatment of rats with the {dollar}beta{dollar}-adrenergic drug, isoproterenol (IPR) alters the expression of GRP isoforms in RSMG saliva. One mechanism which could account for these changes could be stimulus-coupled changes in the steady-state abundance of GRP-encoding transcripts.; To test this hypothesis, we isolated variant GRP-encoding cDNAs (termed GRP-Ca and GRP-Cb) from {dollar}lambda{dollar} gt11 libraries representing mRNAs of RSMG from saline and isoproterenol treated animals. These transcripts differ only within a 90-95 bp region located 3{dollar}spprime{dollar} to five, centrally located, 69 bp tandem repeats. Using unique sequences, we next measured IPR-induced changes in the steady-state abundance of the variant GRP transcripts which encode the salivary isoforms. GRP-Ca levels decrease, while GRP-Cb levels increase. These alterations in transcript abundance are consistent with changes observed in salivary GRP.; To determine the molecular basis of these GRP transcripts and to begin an investigation of both the strict tissue-specific and IPR-regulated expression of GRP transcripts, we isolated and characterized a GRP gene. Analysis of this GRP gene indicates that GRP-Ca and GRP-Cb transcripts are encoded by separate, single copy genes. Thus, one mechanism that could account for the differential expression of GRP transcripts is the discoordinate regulation of expression from distinct GRP encoding genes.; Comparison of GRP-Ca and several other salivary genes including the rat SMR 2 and the mouse, hamster and human proline-rich protein genes, demonstrated the extreme conservation of the sequence and location of TATA-like and CAAT-like proximal promoter elements. There is also a 28 bp element (located {dollar}sim-{dollar}120 to {dollar}sim-{dollar}180) that demonstrates 85% sequence conservation among GRP/PRP genes but is not found in other reported genes. This putative element may be related to tissue and cellular-specific expression of these highly abundant and regulated transcripts by salivary acinar cells.