Figure 2.

PrlR and JAK2 are required for activation of STAT3 and STAT5A/5B in STAT1^−/− mammary tumor cells. (a) PrlR knockdown resulted in a reduction in pJAK2 levels in SSM2 and SSM3. Cells were also treated with a JAK2-specific shRNA (JAK2-225) as positive controls. (b) Knocking down PrlR led to a reduction in pSTAT3 in SSM2 and SSM3, as measured by flow cytometry. (c and d) Reduction in JAK2 expression significantly reduced the levels of pSTAT3 (c) and pSTAT5A/5B (d) in SSM2 and SSM3, as measured by flow cytometry. (e) Flow cytometry analysis of pSTAT3 and pSTAT5 in SSM2 and SSM3 cells treated with increasing doses of BMS-911543. IC₅₀=94 nM for SSM2 and 182–234 nM for SSM3. **P<0.01, ***P<0.0001. Error bars, S.E.M.