EXPRESSION LEVELS OF HEAT-SHOCK FACTORS ARE NOT FUNCTIONALLY COUPLED TO THE RATE OF EXPRESSION OF HEAT-SHOCK GENES

The expression patterns of two mammalian heat shock factors (HSFs) wer e analysed in cell systems known to reflect an altered heat shock resp onse. For being able to discriminate between the two closely related f actors HSF 1 and HSF 2, specific cDNA sequences were cloned and used t o generate antisense RNAs as hybridization probes. In general, in vari ous cell lines expression of the two heat shock factors was clearly di fferent. These expression patterns of the HSF genes were not influence d by retinoic acid-induced differentiation of human NT2 and mouse F9 t eratocarcinoma cells. Generally, HSF 2 expression was extremely low, w hereas the significantly higher expression of HSF 1 revealed cell spec ific differences. The highest expression rates of both HSFs were obser ved in 293 cells. To examine whether these high levels are involved in the constitutive expression of heat shock genes in these cells, we an alysed the binding pattern of 293 cell proteins to the heat shock elem ents (HSEs). As with other cells, HSE-binding activity in 293 cells wa s only observed after heat shock treatment. This points to an HSE-inde pendent way for high level expression of heat shock genes in these cel ls.