PP2C phosphatase activity is coupled to cAMP-mediated pathway in rat parotid acinar cells.

A 26 kDa particulate protein is phosphorylated during stimulation of amylase secretion by a beta-adrenergic agonist in the rat parotid gland. Previous study has shown that PP2C phosphatase is involved in dephosphorylation of this 26 kDa protein [Yokoyama, N. et al. (1994) Biochem. Biophys. Res. Commun. 200, 497-503]. In this study, immunotransblot analysis using anti-PP2C phosphatase antibody showed that PP2C phosphatase was found prominently in the cystolic fractions and less in secretory granule membranes. When cells were stimulated by isoproterenol, cytosolic PP2C phosphatase activity increased to 145% at 5 min and returned to basal level at 30 min. Forskolin increased PP2C phosphatase activity. H89 inhibited increase of PP2C phosphatase activity following beta-adrenergic stimulation. These results suggest that PP2C phosphatase activity is regulated by cAMP-mediated signaling following beta-adrenergic stimulation and participates in dephosphorylation of this 26 kDa protein.