Functional analyses of copper transporter genes in the human liver cell line HepG2

Copper (Cu) is an essential element regulated by four genes (hCTR1, hATOX1, hATP7A, and hATP7B in humans and zctr1, zatox1, zatp7a, and zatp7b in zebrafish) in copper uptake, distribution, and transport in animal cells. Zebrafish (Danio rerio) shows a higher endogenous ratio of zatp7a to zatp7b in the liver, is relatively intolerant to copper ions and has a different zatp7a and zatp7b expression patterns in different organs. As high-affinity copper transporters, both zctr1 and hCTR1 increased copper toxicity, whereas hATOX1 and zatox1 slightly reduced copper toxicity in HepG2 cells after copper administration for 24 h. The transfected zatp7b functioned in HepG2 cells as effectively as hATP7B after both 24-h and 96-h copper exposure, but zatp7a failed to function in HepG2 cells as effectively as hATP7A. Our findings suggest that ATP7A dysfunction would increase cytotoxicity in the liver; the reason for zebrafish's copper intolerance could be the bulk dysfunction and abnormal localization of zATP7A.