Heat shock proteins (Hsps) are a family of proteins whose function is to protect the cells from environmental or pathophysiologic stimuli. Apart from thermal stimuli Hsps are activated by other causes such as irradiation, heavy metals, toxins and oxidants. Viral and bacterial infections, ischemia and glucose starvation also stimulate Hsps' response. Several of the Hsps participate in the cell cycle and are also involved in different stages of development and differentiation under the regulation by hormones and growth factors. Hsps function as molecular chaperones regulating the correct folding and intracellular translocation of polypeptides and play a critical role in the maintenance of hormone receptors in the inactive state. Hsps are classified according to their molecular weight in six groups: Hsp27, Hsp40, Hsp60, Hsp70, Hsp90 and Hsp100. Some of these proteins are constitutively expressed, whereas others are induced by stresses depending on the type of cell and stress stimulus. Hsps' synthesis is regulated by heat shock transcription factors (HSFs) which act through a higly conserved upstream response element of the promoter region of Hsp genes characterized by multiple inverted repeats of AGAAn sequence. Hsp27 and Hsp70 have been associated with the presence of estrogen and progesterone receptors in breast carcinomas and they have been found to have negative prognostic significance in node-negative breast cancer patients. In human cancer and cell lines it has been reported that Hsp27 and Hsp70 play an important role to the resistance in some of the chemotherapeutic drugs. Hsps are also involved in the immune response in cancer and in the cellular protective mechanisms in ischemic and imflammatoty conditions. The functions, the mechanisms of transcriptional regulation and the clinical significance of Hsps are summarized in this review.

Key words: Heat shock proteins, Hsp, HSF, thermotolerance, tumor progostic factors, ischemic injury, drug resistance.

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