Transglutaminase expression in rat parotid gland after isoproterenol stimulation

Identification of human salivary transglutaminases

Transglutaminases (TGs) expression and enzymatic activities in human saliva were investigated. Specific antibodies showed the co-existence of TG1, TG2, TG3 and TG4. TG2 and TG3 were found in native and multiple proteolytic forms. Our data indicate that TG1 and TG2 isoenzymes are highly active with the major activity attributed to TG1. These findings pave the way for future studies on the physiological role of TG in the oral cavity and the potential impact of their deregulation in TG-associated oral diseases.

Quantitative immunocytochemical study of secretory protein expression in parotid glands of rats chronically treated with isoproterenol

Chronic treatment of mice and rats with isoproterenol (IPR) causes marked hypertrophy and hyperplasia of the salivary glands, and alters the expression of several secretory proteins. We used quantitative postembedding immunogold labeling to study the cellular responses in the rat parotid gland during daily (up to 10 days) injections of IPR and during recovery (up to 14 days) after cessation of IPR treatment. Labeling densities of acinar cell secretory granules with antibodies to amylase and protein SMG-B1 (cross-reactive with the rat homologue of Parotid Secretory Protein, PSP) fell to 10% of control levels after 8-10 IPR injections, then increased during recovery, paralleling previous biochemical determinations of changes in protein and mRNA levels. With antibodies to proline-rich proteins (PRP), labeling densities initially fell, then subsequently showed considerable variability, but never exceeded control levels. These results contrast with biochemical determinations showing a marked induction of PRP synthesis, and may have both immunological and structural explanations. Occasional intercalated duct cells located close to the acini underwent differentiation toward an acinar-like phenotype as a result of IPR treatment. After 1-2 IPR injections, the secretory granules of these cells labeled with antibodies to amylase and PRP. Subsequently, the granules appeared electron-lucent and were increased in size and number. These observations support earlier work, suggesting that intercalated duct cells may differentiate into other gland cell types.

Adrenergic regulation of RNA synthesis in the rat parotid gland

Adrenergic regulation of RNA synthesis by in vivo stimulated parotid glands and dispersed parotid lobules was studied by a combination of in vivo and in vitro methods. Following a single intraperitoneal injection of isoproterenol, [3H]uridine incorporation into RNA was increased by 50% after the first hour. Amylase mRNA content was also elevated within 1 hr and was 2-3-fold higher than control values at 4 hr. An increase in the rate of total protein synthesis was detectable after 2 hr, and maximal rates were achieved 6 hr after isoproterenol administration. In dispersed parotid lobules, both isoproterenol and epinephrine stimulated [3H]uridine incorporation and at optimal concentrations increased incorporation by almost 200%. Phenylephrine (10 microM) caused a slight increase of about 20% whereas methoxamine (10 microM) had no effect. Stimulation by epinephrine was reversed by propranolol, but not by either phentolamine or prazosin. The increase in RNA synthesis induced by isoproterenol or epinephrine was dose dependent and half-maximal stimulation required 5.0 x 10(-8) M isoproterenol and 7.9 x 10(-7) M epinephrine. Dibutyryl cyclic AMP also stimulated [3H]uridine incorporation, whereas 8-bromo cyclic GMP, A23187 and phorbol myristate acetate had no effect. The importance of protein phosphorylation in mediating the observed stimulation was evaluated using protein kinase and phosphatase inhibitors. N-[2-(Methylamino)ethyl]-5-isoquinolinesulphonamide, an inhibitor of cyclic nucleotide-dependent protein kinases, substantially diminished the isoproterenol-induced stimulation. Okadaic acid treatment of lobules increased [3H]uridine incorporation. Furthermore, okadaic acid synergistically potentiated the stimulatory effect of a suboptimal concentration of isoproterenol. The results demonstrate that activation of the beta-adrenergic receptor induces the synthesis of certain RNA species in the parotid gland and that protein phosphorylation by a cyclic AMP-dependent protein kinase is a key event in the signal transduction pathway.