Arctic char (Salvelinus alpinus) metallothionein: cDNA sequence, expression, and tissue-specific inhibition of cadmium-mediated metallothionein induction by 17 beta-estradiol, 4-OH-PCB 30, and PCB 104

In this study, we have examined the basal level expression and tissue-speci fic expression patterns of metallothionein (MT) in Arctic char following me tal and E2 (17 beta-estradiol) treatment. To study the gene regulation in A rctic char, the two MT isoforms were isolated from a lambda-ZAP hepatic cDN A library and characterized. Determination of basal MT mRNA and MT expressi on for 10 different tissues revealed a lack of correlation between MT mRNA and MT levels. The inducibility of MT mRNA and the correlation to resulting MT levels were then determined for liver and kidney. We found a more rapid and stronger induction of MT mRNA in liver than in kidney at day 1 and 3 p ostinjection, whereas the MT protein quantification showed higher MT levels in kidney than in liver at days 3 and 7 postinjection. These discrepancies indicate that differences in metal handling or posttranscriptional regulat ion of MT exists between tissues. Whereas metals induce MT synthesis, E2, i nhibit the hepatic MT expression. To examine the tissue specificity of this inhibition, we determined the effect of 17 beta-estradiol (E2) and two est rogenic PCBs (4'-OH-PCB 30 and PCB 104) on Cd-mediated MT induction in live r and kidney. Although E2 and the estrogenic PCBs inhibited cadmium-mediate d hepatic MT induction. these compounds did not interfere with renal MT ind uction.