Fig. 4.

Mrp4/Abcc4 absence reveals nelfinavir is a substrate and inhibitor. (A) Immunoblot analysis of three independent clones for each genotype revealed no upregulation of Abcc1, Abcc5, and Abcg2 in Mrp4 KO MEFS (left). MEFs expressed Mrp4 at levels comparable with normal tissues containing functional Mrp4 (middle). Bcrp/Abcg2 was only minimally functional in Mrp4 KO MEFs (right). (B) NFV blocks Mrp4/Abcc4-mediated export of PMEA. KO and WT MEFs were incubated with Bis(POM)-PMEA under energy-depleted conditions. Subsequently, energy-containing media were restored and export of PMEA was determined (left). The proportion of PMEA in the media and cells was determined and expressed as the percentage of the of total 120 minutes after PMEA export was initiated (right). (C) Mrp4 KO MEFs were more sensitive to the cytotoxic effects of Bis(POM)-PMEA (left) and NFV (middle) but not to etoposide (right). Etop, etoposide; FTC, fumitremorgin C.