SIGNAL-TRANSDUCTION VIA GLYCOSYL PHOSPHATIDYLINOSITOL-ANCHORED PROTEINS IN T-CELLS IS INHIBITED BY LOWERING CELLULAR CHOLESTEROL

Glycosylphosphatidylinositol (GPI)-anchored proteins can deliver costi mulatory signals to lymphocytes, but the exact pathway of signal trans duction involved is not yet characterized. GPI anchored proteins are f ixed to the cell surface solely by a phospholipid moiety and are clust ered in distinct membrane domains that are formed by an unique lipid c omposition requiring cholesterol. To elucidate the role of membrane li pids for signal transduction via GPI-anchored proteins, we studied the influence of reduced cellular cholesterol content on calcium signalin g via GPI-anchored CD59 and CD48 in Jurkat T cells. Lowering cholester ol by different inhibitors of cellular cholesterol synthesis suppresse d calcium response via GPI anchored proteins by about 50%, whereas sti mulation via CD3 was only minimally affected (<10%). The decrease in o verall calcium response via GPI-anchored proteins was reflected by inh ibition of calcium release from intracellular stores. Cell surface exp ression of GPI-anchored proteins was not changed quantitatively by low ering cellular cholesterol, and neither was the pattern of immunofluor escence in microscopic examination. In addition, the distribution of G PI-anchored proteins in detergent-insoluble complexes remained unalter ed. These results suggest that cellular cholesterol is an important pr erequisite for signal transduction via GPI-anchored proteins beyond fo rmation of membrane domains.