Heat shock proteins in human endometrium throughout the menstrual cycle

Human endometrium is a steroid-sensitive tissue and there isevidence 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 variousmembers of the heat shock family of proteins in the steroid-responsivehuman endometrium. Western blot analysis revealed that the expressionof 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 earlysecretory phases, and diminished in the mid- to late secretoryand menstrual phases. In contrast, the inducible form of heatshock protein 70 (HSP70) did not undergo these changes. Thecellular and subcellular localizations of these proteins wereexamined in human endometria by immunohistochemical staining.With the exception of HSP70, which was found primarily in theepithelial cells, the immunoreactivity for other heat shockproteins was found in both the stroraa and the epithelium. Immunoreactivityfor HSP27 was found in the lymphoid aggregates within endometrialstroma, and both HSP27 and HSP90 were found in endothelial cells.The immunoreactive heat shock proteins were found in the nucleiand/or cytoplasm of cells. However, no consistent nuclear versuscytoplasmic staining emerged, and such localization was irrespectiveof the site, the cell type or the phase of the menstrual cycle.Our findings show that endometrium has a full complement ofheat shock proteins. The menstrual cycle-dependent changes inthe amounts of heat shock protein suggest regulation by steroidhormones.