FIGURE 1.

STAT5 inhibition results in decreased proliferation of breast cancer cells. A, effectiveness of chemical inhibition of STAT5 in preventing PRL-induced STAT5 phosphorylation and nuclear translocation. T47D cells were pretreated with the STAT5 inhibitor CAS 285986-31-4 or DMSO as the vehicle control (VC) for 1 h before stimulation with PRL. Nuclear and cytoplasmic lysates were isolated, and activation of STAT5 was analyzed by Western blotting using an antibody against phosphorylated (p-) STAT5. The membranes were then stripped and reprobed with an antibody against total STAT5. Histone H4 and tubulin were used as loading controls for the nuclear and cytoplasmic fractions, respectively. B, STAT5 inhibition reduces cell proliferation and prevents the PRL-induced increase in proliferation. T47D cells were treated with the indicated concentrations of STAT5 inhibitor or vehicle control, with or without PRL, for 3 days. BrdU incorporation was measured by absorbance as an indication of cell proliferation. Results are presented as the mean ± S.E. (error bars) of three independent experiments. Within each individual experiment, each set of treatment conditions was carried out in triplicate. Statistical significance was determined by two-sided t test assuming equal sample variance, comparing without versus with PRL (No PRL versus +PRL) at each concentration of STAT5 inhibitor. *, p ≤ 0.05; **, p ≤ 0.01.