Characterization of an SH2 containing protein tyrosine phosphatase in rat parotid gland acinar cells

The Role of Phosphotyrosine Signaling Pathway in Parotid Gland Proliferation and Function

“…Isoproterenol and EGF treatment increased dephosphorylation of MBP, while the level of p65 Syp remained unchanged between unstimulated and stimulated parotid glands (Purushotham et al, , 1995b. Syp protein itself is a substrate for both tyrosine and threonine phosphorylation in activated cells (Purushotham et al, , 1995b. Thus, unlike the activation of phosphotyrosine signaling kinases, which undergo both increased synthesis and activation in response to growth stimuli, Syp concentration in the cell remains constant, and its activity is increased by direct phosphorylation (unpublished results).…”

“…The level of secretory granule membrane-associated protein tyrosine phosphatase, namely, Syp, was found to be twice that of a cytoplasmic fraction (Purushotham et al, 1995b). Further, the secretory granule-associated protein tyrosine phosphatase possesses the ability to dephosphorylate tyrosine-phosphorylated myelin basic protein to a significantly higher degree than the protein tyrosine phosphatases associated with cytoplasm, total membrane, plasma membrane, and total lysate fractions (Purushotham et al, 1995b). The parotid gland protein tyrosine phosphatases appear to be consistent with pancreatic protein tyrosine phosphatases, in that the specific activities of the granule membraneassociated protein tyrosine phosphatase are higher than in other subcellular fractions (Jena etal, 1991).…”

“…Total cell lysates from stimulated parotid glands have been immunoprecipitated with antibody to Syp and used in dephosphorylation reactions with [ 32 P)-labeled myelin basic protein (MBP) as the substrate. Isoproterenol and EGF treatment increased dephosphorylation of MBP, while the level of p65 Syp remained unchanged between unstimulated and stimulated parotid glands (Purushotham et al, , 1995b. Syp protein itself is a substrate for both tyrosine and threonine phosphorylation in activated cells (Purushotham et al, , 1995b.…”

“…The parotid gland protein tyrosine phosphatases appear to be consistent with pancreatic protein tyrosine phosphatases, in that the specific activities of the granule membraneassociated protein tyrosine phosphatase are higher than in other subcellular fractions (Jena etal, 1991). The Ca 2+ -dependent release of amylase stimulated by recombinant protein tyrosine phosphatase, the inhibition of phosphatase activity and release of amylase in the presence of sodium orthovanadate (a PTPase inhibitor), and the association of protein tyrosine phosphatase with the secretory granules-all suggest the potential involvement of tyrosine phosphorylations in regulated secretion {jenaetal, 1991; Purushotham et al, 1995b).…”