Their Effects on Expression of Stress Proteins

Metals and Their Effects on Expression of Stress Proteins 

The enhanced expression of metal-induced stress proteins is controlled primarily at the transcriptional level similar to the induction of hsps by heat (Wu et al. 1986). Regulation of hsp genes in eukaryotic systems is mediated by a cw-acting heat shock control element (HSE) that is found in multiple copies upstream of the transcriptional start site (Pelham 1982). Transcriptional activation of the hsp genes is mediated by a ran -acting protein, known as the heat shock factor (HSF), which binds specifically to the HSE (Wu 1984a,b). 

In experiments demonstrating subset induction, the proteins induced by metals represent a subset of the proteins induced by heat (Table 1). Findings from these studies indicate that some of the proteins induced by heat are insensitive to metal induction. Additional accounts of subset induction have been reported in murine lymphocytes (Rodenhiser et al. 1986) and human melanoma cells (Delpino et al. 1992). In contrast, in metal-specific induction, specific proteins have been identified that are only sensitive to metals (Table 1). Other examples of metal-specific induction have been reported in human periodontal ligament cells (Sauk et al. 1988), rat aortic smooth muscle (Kohane et al. 1990), and Chinese hamster ovary cells (Lee et al. 

The table does not present an exhaustive comparison of the three patterns. In III, bold numbers represent molecular masses of metal-specific proteins which were not induced by heat. Abbreviation kDa = kilodaltons. 

The findings summarized in these last two induction categories imply that the regulatory mechanism(s) involved in some heat-induced proteins is independent of the mechanisms responsible for some metal-induced stress proteins. 

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