Substitution of Trp 1242 of TM 17 alters substrate specificity of human multidrug resistance protein 3 CURTIS

Oleschuk, Curtis J., Roger G. Deeley, and Susan P. C. Cole. Substitution of Trp1242 of TM17 alters substrate specificity of human multidrug resistance protein 3. Am J Physiol Gastrointest Liver Physiol 284: G280–G289, 2003. First published October 9, 2002; 10.1152/ajpgi.00331.2002.—Multidrug resistance protein 3 (MRP3) is an ATP-dependent transporter of 17 -estradiol 17 (D-glucuronide) (E217 G), leukotriene C4 (LTC4), methotrexate, and the bile salts taurocholate and glycocholate. In the present study, the role of a highly conserved Trp residue at position 1242 on MRP3 transport function was examined by expressing wild-type MRP3 and Ala-, Cys-, Phe-, Tyr-, and Pro-substituted mutants in human embryonic kidney 293T cells. Four MRP3Trp1242 mutants showed significantly increased E217 G uptake, whereas transport by the Pro mutant was undetectable. Similarly, the Pro mutant did not transport LTC4. By comparison, LTC4 transport by the Ala, Cys, Phe, and Tyr mutants was reduced by 35%. The Ala, Cys, Phe, and Tyr mutants all showed greatly reduced methotrexate and leucovorin transport, except the Tyr mutant, which transported leucovorin at levels comparable with wild-type MRP3. In contrast, the MRP3-Trp1242 substitutions did not significantly affect taurocholate transport or taurocholate and glycocholate inhibition of E217 G uptake. Thus Trp1242 substitutions markedly alter the substrate specificity of MRP3 but leave bile salt binding and transport intact.