The levels and expression of the
proteins CD63 and
granulophysin in platelets from control and from a
Hermansky-Pudlak syndrome subject (a condition 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 and anti-
granulophysin antibodies recognized similar numbers of granules; coapplication of
antibodies did not identify more granules than the individual
antibodies. Significantly fewer granules were recognized in
Hermansky-Pudlak syndrome platelets than in control using either antibody. Immunoblotting studies demonstrated that anti-CD63 and anti-
granulophysin antibodies apparently recognize the same
protein, which was deficient in Hermansky-Pudlak platelets. Analysis by fluorescence-activated cell sorter (FACS) showed biphasic expression of CD63 and
granulophysin after
thrombin stimulation of control but not Hermansky-Pudlak platelets. Anti-CD63 effectively blocked detection of the
protein by anti-
granulophysin using immunofluorescence, ELISA, immunoblotting, and FACS analysis. Amino-terminal sequencing over the first 37
amino acids revealed that
granulophysin was homologous to CD63,
melanoma antigen ME491, and
pltgp40. These results suggest that
granulophysin and CD63 are possibly identical
proteins. This is the first report of a
protein present in platelet dense granules, lysosomes, and melanocytes, but deficient in a patient with
Hermansky-Pudlak syndrome.