Characterization and cellular distribution of human spermatozoal heat shock proteins

Heat shock proteins (hsp) are ubiquitous components of all living systems. They are up-regulated in response to adverse changes in the cellular environment and at least one highly conserved group (hsp 70) is associated with the development of tolerance to various physico-chemical stress inducers. Spermatozoa have highly condensed chromatin and unlike somatic cells, are consequently unable to mount a stress response. However, using a combination of gel electrophoresis and immunoblotting with hsp-specific monoclonal antibodies, we report that proteins of M(r) 95 kDa and 70-75 kDa corresponding to hsp 90, and multiple forms of hsp 70 are present in human spermatozoa. Immunohistochemistry localized hsp 90 to the neck and tail of unfixed, acrosome-intact spermatozoa. In contrast, an equatorial ring surrounding the nucleus was observed in unfixed spermatozoa, acrosome-reacted with the calcium ionophore A23187. The ring was stained in cells fixed and permeabilized with ethanol, regardless of acrosomal status. Hsp 70 was an abundant surface antigen and as this protein was also abundant in seminal plasma, we believe that it may have been directly adsorbed onto the cell surface. More specific midpiece, equatorial and nuclear staining was also observed. Possible functions for spermatozoal heat shock proteins are discussed.