Germ cell-specific heat shock protein 105 binds to p53 in a temperature-sensitive manner in rat testis

Heat shock protein (HSP)105 is a testis-specific and HSP90-related protein. The aim of this study was to explore the functions of HSP105 in the rat te stis. Signals of HSP105 were detected immunohistochemically in the germ cel ls and translocated from the cytoplasm to the nucleus at 2 days after exper imental induction of cryptorchidism. In cultured testicular germ cells, a s ignificant increase in the expression of HSP105 in response to heat stress (37 degrees C) was detected in the insoluble protein fractions. Several bin ding proteins were isolated from rat testis using a HSP105 antibody immunoa ffinity column, and p53, the tumor suppressor gene product, was copurified with these. Furthermore, immunoprecipitation using antibodies to p53 led to coprecipitation of HSP105 together with p53 after culturing germ cells at 32.5 degrees C, but not at 37 or 42 degrees C. In conclusion, HSP105 is spe cifically localized in the germ cells and may translocate into the nucleus after heat shock. HSP105 is suggested to form a complex with p53 at the scr otal temperature, and dissociate from it at suprascrotal temperatures. At s crotal temperature, HSP105 may thus contribute to the stabilization of p53 proteins in the cytoplasm of the germ cells, preventing the potential induc tion of apoptosis by p53.