C-ABL PROTO-ONCOPROTEIN IS EXPRESSED AND TYROSINE-PHOSPHORYLATED IN HUMAN SPERM CELL

The presence and possible role of c-Abl proto-oncoprotein was investig ated in human sperm cell. The c-Abl monoclonal antibody (mAb), against the protein tyrosine kinase domain of v-Abl protein, reacted specific ally with the acrosomal region of methanol-fixed capacitated and non-c apacitated human sperm cell in the indirect immunofluorescence techniq ue. The c-Abl mAb predominantly recognized two protein bands of 145 kD and 95 kD in detergent-solubilized (Triton X-100 and NP-40) sperm and testes preparations in the Western blot procedure. The 95 kD protein band reacted stronger than the 145 kD band and was the only band detec ted in the lithium diiodosalicylate (LIS)-solubilized sperm preparatio n, and even in the Triton X-100/NP-40 extracts of sperm of some men. I n the in vitro kinase assay using the Triton X-100-solubilized capacit ated sperm preparation, the 95 kD protein was autophosphorylated at th e tyrosine residues, which was inhibited in the presence of c-Abi mAb. The tyrosine phosphorylation of sperm proteins, especially of the 95 kD protein, has been shown to have a vital role in human sperm functio n, namely, the sperm capacitation/acrosomal exocytosis and binding to zona pellucida of oocyte. These findings suggest that the c-Abl or c-A bl-like proteins are present in mature sperm cells that are tyrosine a utophosphorylated and may have a role in human sperm cell function. (C ) 1998 Wiley-Liss, Inc.