Abstract
Human endometrium, in response to steroid hormones, undergoes characteristic cycles of proliferation, secretory changes, and tissue shedding. Human endometrium expresses a molecular repertoire which includes the heat shock proteins (Hsps) Hsp27, Hsp60, Hsp70, Hsp90, and alpha crystallin B chain. The expression of Hsp27, Hsp60, and the constitutive form of Hsp70 (Hsc70) shows a sharp increase in human endometrium after ovulation. The maximal expression of the molecular chaperone, alpha crystallin B chain, occurs during the secretory phase. In view of known functions of the Hsps, it is likely that these proteins are involved in protection of the endometrial proteins against factors with the potential to lead to protein denaturation. Tumor necrosis factor-alpha (TNF-alpha) is a cytotoxic cytokine that is produced in progressive amounts during the secretory phase. The function of the Hsps may be to protect cells against the cytotoxic damage of TNF-alpha, particularly during the critical period of "implantation window."
Highlights
Human endometrium, in response to steroid hormones, undergoes characteristic cycles of proliferation, secretory changes, and tissue shedding
Nonliganded forms of the steroid hormone receptors exist as complexes associated with various members of the heat shock proteins (Hsps), such as Hsp[90], HspT0, and Hsp[56] (p59), a 40-kDa cyclophilin-related protein, and an uncharacterized 22-kDa protein species. 7,16-18 The alpha crystallin consists of two types of highly homologous 20/22-kDa alphaA and alphaB subunits. 9,z The A and B chains noncovalently self-associate to form a large macromolecular complex of approximately 40 subunits. 9,z originally it was believed that the expression of the alpha crystallin was strictly confined to the lens, this protein has been found in a variety of normal tissues, z More recently, evidence accumulated that allows classifying these proteins as small Hspszz and identifies them as molecular chaperones, z’z4
Our findings showed that the endometrium has a full complement of Hsps.zs The expression of Hsp[90], HspT0, and Hsp[27] has been reported previously in human endometria, z6,z7 Koshiyama et al z7 reported that both HspT0 and Hsp[90] were expressed in human endometrium throughout the menstrual cycle
Summary
Over 30 years ago, Ritossa et al noted that an increase in the incubation temperature of Drosophila melanogaster larvae results in the development of a defined set of new transcription loci on the polytene chromosome. The first gene products involved in this response were identified, and the term "heat shock protein" (Hsp) was applied to this family of proteins,e Subsequently, it was shown that these proteins exist in all species and are well conserved.[3] Even in thermophilic organisms, a sudden temperature upshift leads to the overexpression of Hsps. It has become clear that stress proteins participate in a diverse range of actions in cells. This includes thermotolerance, stress tolerance, cell proliferation, cell metabolism, embryogenesis, and drug resistance.
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