Effect of DMT1 knockdown on iron, cadmium, and lead uptake in Caco-2 cells

DMT1 (divalent metal transporter 1) is a hydrogen-coupled divalent metal transporter with a substrate preference for iron, although the protein when expressed in frog oocytes transports a broad range of metals, including the toxic metals cadmium and lead. Wild-type Caco-2 cells displayed saturable transport of lead and iron that was stimulated by acid. Cadmium and manganese inhibited transport of iron, but zinc and lead did not. The involvement of DMT1 in the transport of toxic metals was examined by establishing clonal DMT1 knockdown and control Caco-2 cell lines. Knockdown cell lines displayed much lower levels of DMT1 mRNA and a smaller V(max) for iron uptake compared with control cell lines. One clone was further characterized and found to display an approximately 50% reduction in uptake of iron across a pH range from 5.5 to 7.4. Uptake for cadmium also decreased 50% across the same pH range, but uptake for lead did not. These results show that DMT1 is important in iron and cadmium transport in Caco-2 cells but that lead enters these cells through an independent hydrogen-driven mechanism.