EXPRESSION OF CYCLIC ADP-RIBOSE-SYNTHESIZING CD38 MOLECULE ON HUMAN PLATELET MEMBRANE

CD38 is a cell surface molecule widely used as a marker for immature a nd activated lymphocytes. It has been recently shown that CD38 display s three enzymatic activities: hydrolysis of NAD(+) to ADP-ribose, synt hesis of cyclic ADP-ribose from NAD(+), and hydrolysis of cyclic ADP-r ibose to ADP-ribose. Thus, CD38 plays a key role in the synthesis of c yclic ADP-ribose, a calcium-mobilizing compound. We investigate here t he expression and cellular localization of CD38 in human platelets usi ng a specific monoclonal antibody. Results showed that CD38 is express ed by human platelet membranes. Moreover, we show that platelet CD38 p ossesses NAD glycohydrolase, ADP-ribose cyclase, and cyclic ADP-ribose hydrolase activities. This finding indicates that the calcium-mobiliz ing agent cyclic ADP-ribose can be synthetized by human platelets and raises the question about the possible role of CD38 expression and enz ymatic activities in the signal transduction pathways leading to plate let activation. (C) 1996 by The American Society of Hematology.