Rat parotid gland acinar cell proliferation: signal transduction at the plasma membrane

Galactosyltransferase (Gal Tase) is involved in a "receptor-ligand-type" interaction at the cell surface that mediates signal transduction following isoproterenol (ISO) treatment leading to acinar cell proliferation. Evidence is presented herein for the identification of the cell-surface glycoprotein signaling component. Using intact cells or isolated plasma membranes, the EGF-receptor (EGF-R) was specifically radiolabeled with [14C]-Galactose following ISO treatment. Injection of a polyclonal antibody monospecific for rat EGF-R also inhibited proliferation in a dose-dependent manner. The immunoaffinity purified receptor demonstrated altered lectin binding and increased in vitro Gal Tase substrate capacity following beta-agonist treatment when compared with EGF-R isolated from control animals. When acinar cells were incubated in the presence of EGF, plasma membranes from control and ISO-treated animals showed autophosphorylation of EGF-R tyrosine moieties, transient increases in membrane associated phospholipase C gamma, and increased cellular levels of cAMP. These properties of the tyrosine phosphate signaling pathway could be duplicated by the exogenous addition of bovine Gal Tase to ISO-treated cells but not control cells. The results suggest that cell surface Gal Tase interacts with a form of the EGF-R, having altered carbohydrate moieties to promote intracellular signaling for acinar cell proliferation.