Heat shock proteins in human endometrium throughout the menstrual cycle

Human endometrium is a steroid-sensitive tissue and there is evidence that supports the viewpoint that heat shock proteins (HSP) are implicated in the regulation of steroid function. Therefore, in this study we examined the expression of various members of the heat shock family of proteins in the steroid-responsive human endometrium. Western blot analysis revealed that the expression of HSP90 showed minimal changes throughout the menstrual cycle. When normalized to the amount of HSP90, the expression of HSP27, HSP60 and the constitutive form of heat shock protein 70 (HSC70) increased progressively during the late proliferative and early secretory phases, and diminished in the mid- to late secretory and menstrual phases. In contrast, the inducible form of heat shock protein 70 (HSP70) did not undergo these changes. The cellular and subcellular localizations of these proteins were examined in human endometria by immunohistochemical staining. With the exception of HSP70, which was found primarily in the epithelial cells, the immunoreactivity for other heat shock proteins was found in both the stroma and the epithelium. Immunoreactivity for HSP27 was found in the lymphoid aggregates within endometrial stroma, and both HSP27 and HSP90 were found in endothelial cells. The immunoreactive heat shock proteins were found in the nuclei and/or cytoplasm of cells. However, no consistent nuclear versus cytoplasmic staining emerged, and such localization was irrespective of the site, the cell type or the phase of the menstrual cycle. Our findings show that endometrium has a full complement of heat shock proteins. The menstrual cycle-dependent changes in the amounts of heat shock protein suggest regulation by steroid hormones.