Rat Parotid Gland Acinar Cell Proliferation: Signal Transduction at the Plasma Membrane

Abstract

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 β-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 Cy, 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.