THE PROTEIN CD63 IS IN PLATELET DENSE GRANULES, IS DEFICIENT IN A PATIENT WITH HERMANSKY-PUDLAK SYNDROME, AND APPEARS IDENTICAL TO GRANULOPHYSIN

The levels and expression of the proteins CD63 and granulophysin in pl atelets from control and from a Hermansky-Pudlak syndrome subject (a c ondition characterized by dense granule and lysosomal deficiencies and the accumulation of ceroid-like material in reticuloendothelial cells ) were examined. Immunofluorescence studies indicated that anti-CD63 a nd anti-granulophysin antibodies recognized similar numbers of granule s; coapplication of antibodies did not identify more granules than the individual antibodies. Significantly fewer granules were recognized i n Hermansky-Pudlak syndrome platelets than in control using either ant ibody. Immunoblotting studies demonstrated that anti-CD63 and anti-gra nulophysin antibodies apparently recognize the same protein, which was deficient in Hermansky-Pudlak platelets. Analysis by fluorescence-act ivated cell sorter (FACS) showed biphasic expression of CD63 and granu lophysin after thrombin stimulation of control but not Hermansky-Pudla k platelets. Anti-CD63 effectively blocked detection of the protein by anti-granulophysin using immunofluorescence, ELISA, immunoblotting, a nd FACS analysis. Amino-terminal sequencing over the first 37 amino ac ids revealed that granulophysin was homologous to CD63, melanoma antig en ME491, and pltgp40. These results suggest that granulophysin and CD 63 are possibly identical proteins. This is the first report of a prot ein present in platelet dense granules, lysosomes, and melanocytes, bu t deficient in a patient with Hermansky-Pudlak syndrome.