Critical Reviews in Oral Biology & Medicine, Vol 4, 537-543, Copyright © 1993 by International & American Associations for Dental Research
Rat parotid gland acinar cell proliferation: signal transduction at the plasma membrane
K. R. Purushotham, Y. Nakagawa, M. G. Humphreys-Beher, N. Maeda and C. A. Schneyer
Department of Oral Biology, University of Florida, Gainesville 32610.
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.
