LIGATION OF THE ALPHA-M-2 SIGNALING RECEPTOR ELEVATES THE LEVELS OF P21RAS-GTP IN MACROPHAGES

Ligation of the alpha(2)-macroglobulin signalling receptor (alpha(2)MS R) with alpha(2)-macroglobulin (alpha(2)M)-methylamine or a cloned and expressed receptor binding fragment (RBF) stimulates DNA synthesis. T o examine the possible role of the Ras pathway in the mitogenic effect s observed on ligating alpha(2)MSR, we studied the formation of p21Ras -GTP in murine peritoneal macrophages upon treatment with alpha(2)M-me thylamine and RBF, respectively. Both alpha(2)M-methylamine (50 pM) an d RBF (50 pM) stimulated a 2-3-fold increase in the formation of the p 21Ras-GTP complex compared with unstimulated cells. p21Ras-GT(32)P com plex formation was both time and RBF concentration dependent and was c omparable to p21Ras-GT(32)P complex formation induced by EGF (200 ng/m L) and platelet derived growth factor (50 mg/mL). Up-regulation of cel ls with phorbol dibutyrate prior to stimulation with RBF had no effect on p21Ras-GT(32)P formation. However, treatment of macrophages with t he tyrosine kinase inhibitor genestein drastically reduced RBF-induced formation of the p21Ras-GT(32)P complex. Wortmannin, an inhibitor of phosphatidylinositol-3'-kinase (PI3K), had no effect on p21Ras-GT(32)P complex formation. It is concluded that the mitogenic effects of liga ting alpha(2)MSR are mediated through a Ras-dependent pathway. (C) 199 8 Elsevier Science Inc.