Strain-specific differences in the proline-rich proteins and glycoproteins induced in rat salivary glands by chronic isoprenaline treatment

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Abstract
Parotid and submandibular glands were isolated from five strains of rat after chronic injection of the .beta.-adrenergic receptor agonist isoprenaline (isoproterenol). The glands were observed to have undergone a marked increase in wet weight, owing to hypertrophy and hyperplasia. The 100,000 g soluble fraction of gland cell lystates were extracted with 10% (w/v) trichloroacetic acid, and the soluble material subsequently analysed by SDS (sodium dodecyl sulphate) polyacrylamide-gel electrophoresis. By this procedure, evidence was obtained for the induction, in isoprenaline-treated parotid and submandibular glands, of proline-rich proteins with apparent Mr values ranging form 20,000 to 40,000. Heterogeneity was evident in the proteins produced for a specific gland between the rat strains, although the amino acid compositions were the same. Products from induced mRNAs translated in vitro had similar mobilities in SDS/polyacrylamide gels, despite the apparent difference in mobility of trichloracetic acid-extracted proline-rich proteins from the various strains. Strain-specific differences were noted for the proline-rich glycoproteins from control salivary glands as well as those induced as a consequence of isoprenaline treatment. Although the glycoproteins had similar amino acid compositions, there was considerable heterogeneity in the carbohydrate compositions for these proteins, suggesting that the differences were the result of post-translational modifications during glycosylation. Induction of the increased activity of the Golgi membrane marker enzyme UDP-galactose: 2-acetamido-2-deoxy-D-glucosamine 4.beta.-galactosyltransferase (EC 2.4.1.22) occurred to the same extent in the parotid glands of all strains examined. There was no change in the specific activity of a second enzyme, UDP-galactose: N-acetylgalactosaminyl-protein 3.beta.-galactosyltransferase (no EC designation).