Regulation of mitochondrial cytochromeb mRNA by copper in cultured human hepatoma cells and rat liver

Copper overload and deficiency are known to cause morphological and functional mitochondrial abnormalities. The reverse transcriptase-polymerase chain reaction (RT-PCR)-based method of differential display of mRNA was used to identify genes with altered expression in cultured human hepatoma cells (Hep G2) exposed to increasing concentrations of copper (0–100 ΜM, 24 h). Copper regulation of a cloned PCR product, identified as the gene for the mitochondrially encoded cytochromeb, was confirmed by Northern analysis andin situ hybridization. Copper toxicity increased cytochromeb mRNA abundance up to 3.6-fold, and copper chelation reduced it by 50%. Hepatic cytochromeb mRNA was also increased in rats fed a high-copper diet. Thapsigargin treatment resulted in a significant increase in cytochromeb mRNA, suggesting that an increase in intracellular calcium may be involved in the mechanism of copper action. Furthermore, although cyclohexamide (CHX) alone did not increase cytochromeb mRNA, the addition of CHX and copper resulted in a sixfold increase. These data suggest a role for cytochromeb in the response to increases or decreases in hepatic copper.