Decreased CPT1 enzyme activity due to knock-down of CPT1A, LKB1, and AMPKα-1 is partially attenuated by PRL in breast cancer cells. A) Treatment with 100 ng/ml of PRL for 24 hr had no effect on CPT1 enzyme activity in 184B5 cells transiently transfected with CPT1A siRNA. In both B) MCF-7 and C) MDA-MB-231 breast cancer cells, stimulation of CPT1A siRNA-transfected cells with PRL increased enzyme activity by 10 and 17%, respectively. A PRL-mediated recovery of 8 and 9% was also observed in B) MCF-7 and C) MDA-MB-231 cells, respectively, in which LKB1 was knocked down. In AMPKα1 siRNA-transfected B) MCF-7 and C) MDA-MB-231 cells, PRL increased enzyme activity by 12 and 9%, respectively. The dotted line corresponds to baseline, representing treatment with vehicle only. Vehicle = V, CPT1A siRNA = C, LKB1 siRNA = L, and AMPKα siRNA = A. Results represent the mean ± SEM of three independent experiments.