Secretion of protease nexin-1 by C6 glioma cells is under the control of a heterotrimeric G protein, G(o1)

Abstract

Heterotrimeric G(o) proteins have recently been described as regulators of vesicular traffic. The G(o)α gene encodes, by alternative splicing, two G(o)α polypeptides, G(o1)α and G(o2)α. By immunofluorescence and electron microscopy, we detected G(o1)α on the membrane of small intracellular vesicles in C6 glioma cells. After stable transfection of these cells, overexpression of G(o1)α but not G(o2)α was followed by a rise in the secretion of a serine protease inhibitor, protease nexin-1 (PN-1). This secretion was enhanced as a function of the amount of expressed G(o1)α. Metabolic cell labeling indicated that this increase in PN-1 secretion was not the result of an enhancement in PN-1 biosynthesis or a decrease in its uptake, but revealed a potential role of G(o1)α in the regulation of vesicular PN-1 trafficking. Furthermore, activators of G(o) proteins, mastoparan and a peptide derived from the amino terminus of the growth cone- associated protein GAP43, increased PN-1 secretion in parental and G(o1)α- overexpressing cells. Brefeldin A, an inhibitor of vesicular traffic, inhibited both basal and mastoparan-stimulated PN-1 secretions. These results indicate, that in C6 glioma cells, PN-1 secretion could be regulated by both G(o1)α expression and activation.