CORRELATION BETWEEN GLUTATHIONE OXIDATION AND TRIMERIZATION OF HEAT-SHOCK FACTOR-1, AN EARLY STEP IN STRESS INDUCTION OF THE HSP RESPONSE

The heat shock protein (Hsp) response is induced by heat shock and a l arge variety of different chemicals. Searching for a common denominato r of these different inducers, we and others developed the notion that all inducers may generate abnormally folded, i.e. non-native, protein s, and that such non-native proteins may trigger the Hsp response. Exp erimentation prompted by this notion resulted, for example, in the dem onstration that chemically denatured proteins, introduced in cells by microinjection, can activate the response. Based on the chemical natur e of inducers and on results reported from several studies, we hypothe sized that inducers of the Hsp response may be generally capable of tr iggering oxidation of non-protein thiols, particularly glutathione. Su ch oxidation is known to lead to formation of glutathione-protein mixe d disulfides and protein-protein disulfides. Presumably, thiol adducti on and cross-linking would affect the structure of proteins involved, resulting in unfolding of a fraction of these proteins, causing heat s hock factor (Hsf) activation. To test the feasibility of this hypothes is, thirteen different inducers were selected, and it was shown that a ll chemical inducers as well as heat shock cause drastic oxidation of glutathione under conditions under which they induce HSE DNA-binding a ctivity. Under the same conditions, ail chemical inducers and heat sho ck also cause trimerization of Hsf1. For several inducers, it was also shown that they enhance thiol oxidation of proteins. Finally, in vitr o experiments support the notion that activation of Hsf1 does not requ ire oxidation of the factor itself or of its coregulators. These resul ts are in complete agreement with the above hypothesis.