A-D, MCF-7 (A & B) or MDA-MB-231 (C & D) cells were transfected with control (cRNAi) or AHR (AHRi) siRNA for 72 or 48 hrs, respectively. A & C, Total cellular protein was then isolated and subjected to Western blot analysis. Blots were then probed with the indicated antibodies. Relative levels of AHR or LAT1 protein was expressed as a ratio of AHR/GAPDH or LAT1/GAPDH, respectively. *, P < 0.05; **, P >0.01. B & D, RT-qPCR analyses of LAT1 mRNA levels in MCF-7 (B) or MDA-MB-231 (D) cells transfected with cRNAi or AHRi. GAPDH mRNA levels were used to normalize samples. *, P < 0.05. A-D, Data shown are the means ± S.E. of three independent experiments.