The role of the methionines and histidines in the transmembrane domain of mammalian copper transporter 1 in the cellular accumulation of cisplatin.

Mammalian copper transporter 1 (CTR1) is a high-affinity copper influx transporter that also mediates the uptake of platinum-containing chemotherapeutic agents including cisplatin (cDDP). Methionines 150, 154, and histidine 139 have been proposed to form a series of stacked rings in the pore formed by the CTR1 homotrimer, each of which is required for maximal copper transport. To examine the mechanism by which hCTR1 also transports cDDP, variant forms of hCTR1 in which methionines 150 and 154 were converted to isoleucines or in which histidine 139 was converted to alanine were re-expressed in cells in which both alleles of CTR1 had been knocked out. Each of these conversions disabled copper transport and increased cellular resistance to the cytotoxic effect of copper. In contrast, conversion of the methionines increased the uptake and cytotoxicity of cDDP well above that attained with wild-type hCTR1. Conversion of His139 to alanine did not impair cDDP uptake and actually enhanced cytotoxicity. Thus, although Met150 and Met154 facilitate the movement of copper through the pore, they serve to obstruct the passage of cDDP. None of the modifications altered the ability of cDDP to trigger the degradation of hCTR1, indicating that cDDP must interact with hCTR1 at other sites as well. Although both copper and cDDP may rely on a series of transchelation reactions to pass through the hCTR1 trimeric complex, the details of the molecular interactions must be different, which provides a potential basis for selective pharmacological modulation of copper versus cDDP cytotoxicity.