Stress proteins mercury

The proximal mechanism for induction of stress protein synthesis leading to the activation of HSF and gene activation is not completely understood, but evidence for several possibilities exists. Activation of HSF by prooxidants does not result in the accumulation of specific stress proteins (Bruce et al. 1993). These results suggest that induction of stress proteins by specific metals, whose toxicity is mediated via oxidative damage to membranes or DNA, may be fundamentally different from that of the heat-induced activation of the stress response (Keyse and Tyrrell 1987 Bruce et al. 1993). Thus, metals such as cadmium, mercury, nickel, arsenite, copper, lead, and iron, which induce oxygen free radicals or promote formation of lipid peroxides (Stacey and Klaassen 1981 Halliwell and Gutteridge 1984 Christie and Costa 1984 Kasprzak 1991 Donati et al. 1991), may... 

Mercury elicits the synthesis of stress proteins in vitro and in vivo. A comparison of mercury-induced stress proteins shows they vary from heat-induced proteins and these differences may partially be determined by the experimental system. Bournias-Vardiabasis et al. (1990) reported that the spectrum of proteins induced in Drosophila embryonic cells were identical after heat or mercury treatment. In contrast, yeast cells Candida albicans) exposed to mercury induced the synthesis of three stress proteins, only one of which corresponded in molecular mass to a major hsp. 

Goering et al. (1992) demonstrated that mercury in vivo produced dose-and time-dependent alterations in expression of renal gene products as evidenced by enhanced synthesis of stress proteins and inhibition of the synthesis of constitutive proteins. Enhanced de novo synthesis of 43-, 70-, 90-, and 110-kDa proteins was detected in kidney but not liver from mercury-injected rats. The synthesis of the three proteins was discoordinate, suggesting that the synthesis of these proteins may be independently regulated. The changes in renal protein synthesis were rapid (2-4h), and occurred prior to overt renal injury as assessed by functional and histopathological evidence. 

The intracellular localization of stress proteins is problematic for the evaluation of the response in humans. Because the cells for the assay of stress proteins are not readily available through noninvasive procedures, the application of this response to human monitoring is limited. Recently, however, enhanced synthesis of stress proteins was demonstrated in primary cultures of human lymphocytes exposed to several metals (Yamada and Koizumi 1993). The specificity of the response was dependent on the metal to which the cultures were exposed. For example, cadmium and zinc induced both hsp70 and MT, while cobalt and triphenyltin induced only hsp70. Conversely, copper, mercury, nickel, and silver all induced synthesis of MT, but not of hsp70. Enhanced synthesis of stress proteins has also been demonstrated in vivo in lymphocytes and spleen cells excised from mice exposed to hyperthermia (Rodenhiser et al. 1985). 

This chapter reviewed current research pertaining to selected environmental agents and autoimmune diseases (Table 25.3). Other infectious agents (e.g., parvovirus, varicella), occupational exposures (e.g., mercury), dietary factors (dietary supplements, nutrients such as antioxidants, and specific proteins in wheat and other grains implicated in celiac disease), and stress have been the focus of additional research that was not included in this review. 

These proteins are important for binding potentially toxic metals such as cadmium, mercury, and lead, which all bind to sulfydryl groups. Consequently, the binding and removal of these metals are protective functions. Metallothioneins are markedly induced by cadmium exposure and the small protein, rich in SH groups, can then sequester the metal. They also may have a protective role in oxidative stress and protect redox-sensitive processes. The protein also has a role in cadmium nephrotoxicity (see chap. 7). 

The metabolism of zinc is influenced by hormones, stress situations, lipopolysaccharides, toxins, oxygen radicals, lipid peroxidations, etc. This may lead to fluctuations in the zinc concentration, mainly due to the induction of metallothioneine (MT), which is a transport and intracellular depot protein. One third of this protein consists of cysteine, which binds zinc, copper, cadmium, cobalt and mercury. This protects the body from toxic heavy metal... 

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