Phenol red modulates PRL-responsiveness of the LKB1 promoter in T47D cells. T47D cells were co-transfected with LKB1 and pRL-TK, followed by culture without (open bars) or with (solid bars) 100 ng/mL of PRL for 24 hr in (A) media containing phenol red or (B) phenol red-free media. Cells in (A) and (B) were first transfected with non-specific siRNA (NS) or specific siRNAs targeting JAK2 (J2), STAT3 (S3), or STAT5A (S5A) for 48 hr. Transfected T47D cells in (C) media with phenol red or (D) phenol red-free media were pretreated for 2 hr with WP1066 or the STAT5 inhibitor prior to adding PRL for an additional 24 hr. Lysates were assayed for dual luciferase activity. Data represent the mean of three independent experiments (±SEM) calculated relative to untreated controls, with different letters denoting significant differences between the PRL-treated groups and a star (*) indicating statistically significant increases in PRL-treated LKB1 promoter activity (p<0.05) compared with untreated controls.