A novel R416C mutation in human DMT1 (SLC11A2) displays pleiotropic effects on function and causes microcytic anemia and hepatic iron overload

A patient suffering from microcytic anemia and hepatic iron overload was found to be compound heterozygote for polymorphisms in the iron transporter DMT1 (Nramp2, SLC11A2), including a 3-bp deletion (DMT1(delCTT)) in intron 4 that partially impairs splicing and an amino acid substitution (DMT1(C1246T), R416C) at a conserved residue in transmembrane domain 9 of the protein. The functional properties and possible contribution to disease of the DMTI R416C mutation were studied in independent mutants at that position (R416C, R416A, R416K, R416E) expressed in LLC-PK1 kidney cells. Non-conservative substitutions at R416 (C, A, E) cause multiple functional deficiencies including defective protein processing, loss of transport activity, impaired cell surface targeting, and recycling through endosomes, concomitant with retention of the transporter in the endoplasmic reticulum. Conversely, a conservative isoclectric substitution (R416K) was less vulnerable, resulting in a functional transporter that was properly processed and targeted to the cell surface and to recycling endosomes. We propose that DMT1(C1246T) (R416C) represents a complete loss-of-function, and that a quantitative reduction in DMTI expression is the cause of the microcytic anemia and iron overload in the patient. (c) 2006 Elsevier Inc. All rights reserved.