Modulation of the biologic activities of IgE binding factor. VI. The activation of phospholipase by glycosylation enhancing factor.

Abstract

Glycosylation enhancing factor (GEF) from rat T cells is a kallikrein-like enzyme and enhances the assembly of N-linked oligosaccharides to IgE binding factors during their biosynthesis, whereas another T cell factor, i.e., glycosylation inhibiting factor (GIF), is a fragment of phosphorylated lipomodulin (i.e., phospholipase inhibitor), which when dephosphorylated inhibits phospholipase and the glycosylation process. The two T cell factors compete with each other when they are added to normal mesenteric lymph node cells during the formation of IgE binding factors. The addition of GEF to T cell hybridoma 23A4 cell switches the cells from the formation of unglycosylated IgE binding factor to the formation of N-glycosylated IgE binding factor. However, GEF neither inactivated GIF nor inhibited the formation of GIF by the T cell hybridoma. Stimulation of the T cell hybridoma with either affinity-purified GEF or bradykinin resulted in the release of GIF from the cells. GIF released by GEF stimulation had a m.w. of approximately 15,000 and bound to monoclonal antibody against lipomodulin. GEF and bradykinin also induced normal mesenteric lymph node cells to release GIF. Incorporation of 14C-arachidonic acid into 23A4 cells, followed by stimulation of the cells with GEF, resulted in the release of 14C-arachidonate. The results suggest that lipomodulin, a phospholipase inhibitory protein, is present in lymphocytes, and indicate that GEF and bradykinin induce the activation of phospholipase by stimulating cells to release lipomodulin.