Association of HSP90 with the heme-regulated eukaryotic initiation factor 2α kinase—A collaboration for regulating protein synthesis

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Among the various heat shock proteins (HSPs), members of the HSP70 and HSP90 families have drawn particular attention due to their heat shock-unrelated functions. HSP90, an ubiquitous and abundant member of the HSP90 family has been shown to be associated with a large array of protein factors. These proteins reside in the nucleus as well as in the cytoplasm and are involved in various physiological processes, such as, regulation of chromatin structure, cell cycle, cytoskelelal architecture, protein trafficking and protein synthesis. In this article, we focus our interest on the role of HSP90 in protein synthesis. Recent data obtained from a few laboratories strongly suggest that HSP90 interacts with the heme-regulated eukaryotic initiation factor 2α (elF-2α) kinase, also called the heme-regulated inhibitor, and causes its activation which leads to inhibition of protein synthesis. On the basis of data reported from various laboratories, including our own, we propose a possible model on the mechanism of HSP90-mediated activation of heme-regulated inhibitor and regulation of protein synthesis.