c-Abl proto-oncoprotein is expressed and tyrosine phosphorylated in human sperm cell.

The presence and possible role of c-Abl proto-oncoprotein was investigated in human sperm cell. The c-Abl monoclonal antibody (mAb), against the protein tyrosine kinase domain of v-Abl protein, reacted specifically with the acrosomal region of methanol-fixed capacitated and non-capacitated human sperm cell in the indirect immunofluorescence technique. 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 detected in the lithium diiodosalicylate (LIS)-solubilized sperm preparation, and even in the Triton X-100/NP-40 extracts of sperm of some men. In the in vitro kinase assay using the Triton X-100-solubilized capacitated sperm preparation, the 95 kD protein was autophosphorylated at the tyrosine residues, which was inhibited in the presence of c-Abl mAb. The tyrosine phosphorylation of sperm proteins, especially of the 95 kD protein, has been shown to have a vital role in human sperm function, namely, the sperm capacitation/acrosomal exocytosis and binding to zona pellucida of oocyte. These findings suggest that the c-Abl or c-Abl-like proteins are present in mature sperm cells that are tyrosine autophosphorylated and may have a role in human sperm cell function.