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

Abstract

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 testis. Signals of HSP105 were detected immunohistochemically in the germ cells and translocated from the cytoplasm to the nucleus at 2 days after experimental induction of cryptorchidism. In cultured testicular germ cells, a significant increase in the expression of HSP105 in response to heat stress (37 8C) was detected in the insoluble protein fractions. Several binding proteins were isolated from rat testis using a HSP105 antibody immunoaffinity 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 8C, but not at 37 or 42 8C. In conclusion, HSP105 is specifically 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 scrotal temperature, and dissociate from it at suprascrotal temperatures. At scrotal temperature, HSP105 may thus contribute to the stabilization of p53 proteins in the cytoplasm of the germ cells, preventing the potential induction of apoptosis by p53.Keywords: binding proteins; heat shock protein; heat stress; p53; testis.Cells exposed to elevated temperature and other environmental stress conditions respond rapidly by synthesizing a group of polypeptides known as heat-shock proteins (HSPs) [1,2]. Among the HSPs, a cytoplasmic 90 kDa protein (HSP90) is expressed constitutively in unstressed mammalian cells and functions as a molecular chaperone, facilitating the synthesis and correct folding of other intracellular proteins [3]. HSP90 has been shown to associate with several intracellular proteins including inductive transcription factors such as steroid receptors and the dioxin receptor [4±6]. Recently, Itoh and Tashima [7] found a novel 105-kDa protein (HSP105) in the rat testis, which cross-reacts with polyclonal antibody specific to HSP90. The similarity between HSP90 and HSP105 was higher than 60% on peptide mapping with trypsin digestion but, in contrast to the wide distribution of HSP90, HSP105 is localized only in testis and brain, although the concentration found in brain was very low [7]. As seen by western blot analysis, HSP105 appeared at approximately the age of 5 weeks (postbirth), during the development of the rat testis and coinciding with the appearance of spermatozoa. It was abundant in isolated spermatozoa but not present in a somatic cell line derived from a Leydig cell tumor [8]. These results indicate that HSP105 is a germ cell-specific protein, although its functions are largely unknown.Testicular germ cells are vulnerable to heat stress and undergo apoptosis in vivo [9±12] or in vitro [13] in response to suprascrotal temperatures. The tumor suppressor gene product, p53, is a potent inducer of apoptosis [14±16], and is present in unusually high concentrations in testicular germ cell...

HSPH1 inhibition downregulates Bcl-6 and c-Myc and hampers the growth of human aggressive B-cell non-Hodgkin lymphoma

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