ELEVATED GLUTATHIONE LEVELS CONFER CELLULAR SENSITIZATION TO CISPLATIN TOXICITY BY UPREGULATION OF COPPER TRANSPORTER HCTR1

摘要

Previous studies have demonstrated that treating cultured cells with cisplatin (CDDP) upregulated the expression of glutathione (GSH) and its de novo rate-limiting enzyme, glutamate-cysteine ligase (GCL), which consists of a catalytic (GCLC) and a modifier (GCLM) subunits. It has also been shown that many CDDP-resistant cell lines exhibit high levels of GCLC/GCLM and GSH. Since GSH system is the major intracellular regulator of redox conditions that serve as an important detoxification cytoprotector, these results have been taken into considerations that elevated levels of GCL/GSH are responsible for the CDDP resistance. In contrast to this context, we demonstrated here that overexpression of GSH by transfection with expression plasmid containing the GCLC cDNA conferred sensitization to CDDP through upregulation of human copper transporter 1 (hCtr1), which is also a transporter for CDDP. Depleting GSH levels in these transfected cells reversed CDDP sensitivity with concomitant reduction of hCtr1 expression. While rates of Cu transport were also upregulated in the transfected cells, these cells exhibited biochemical signature of Cu deficiency, suggesting that GSH functions as an intracellular Cu-chelator and that overexpression of GSH can alter Cu metabolism. More importantly, our results reveal a new role of GSH in the regulation of CDDP sensitivity. Overproduction of GSH depletes bioavailable Cu pool, leading to upregulation of hCtr1 and sensitization of CDDP transport and cell killing. These findings also have important implications that modulation of intracellular Cu pool may be a novel strategy for improving chemotherapeutic efficacy of platinum-based antitumor agents.