Stress (heat shock) proteins and rheumatic disease. New advance or just another band wagon?

Protein synthesis in all cells is readily interrupted by environmental stresses such as hyperthermia. However, stressed cells also have mechanisms which, even under conditions where normal protein synthesis is completely inhibited, allow them to synthesise a group of highly conserved proteins--the so-called heat shock proteins (HSP). Some of these proteins are now known to facilitate the recovery of normal RNA processing and protein synthesis after exposure to hyperthermia and to protect the cell against further damage. They also play an important role in the synthesis and transport of normal proteins in unstressed cells, and perhaps also the export from cells of abnormal proteins of host or viral origin. Synthesis of HSP is also triggered by exposure to stresses other than hyperthermia, for example heavy metals (e.g. gold complexes), thiol-reactive chemicals, near UV radiation, viruses, oxyradicals and certain cytokines. Furthermore, there are also a number of proteins which are induced by these physicochemical stresses but not by heat; for this reason "stress protein" will be used as a general term to describe both HSP and related, physicochemically-induced, proteins. The cysteine-rich metallothioneins, which behave in some respects as stress proteins, will not be included in this review. Because many of the factors which stimulate stress protein induction occur during inflammatory and immune responses, there has been increasing interest in the possible role of stress proteins in inflammatory disease such as arthritis. The purpose of this article is to review the basic biochemical mechanisms involved in the induction of stress proteins and offer some speculations on their potential role in rheumatic disease.