Opposite effects on early HIV transcription in U1 cells stimulated with PMA or GM-CSF. (A). Chromatin preparations from control (unstimulated), PMA, and GM-CSF stimulated U1 cells were immunoprecipitated with a polyclonal Ab against total RNA-polymerase II. The two LTR regions and the B13 region were analyzed by real-time PCR as described in Figure 6. (B) Real-time PCR analysis of HIV RNA levels at early time points after either PMA or GM-CSF stimulation of U1 cells. PMA, but not GM-CSF, stimulation increases HIV RNA accumulation versus the basal levels observed in control, unstimulated cells. (C). Opposite effects of constitutively phosphorylated STAT5 versus STAT5Δ on HIV-1 LTR transactivation. 293T cells were cotransfected with 100 ng of an LTR-GFP reporter construct and 900 ng of either an empty vector or constitutive phosphorylated (*) STAT5FL or STAT5Δ-expressing vectors or with STAT5FL*/STAT5Δ* vectors at the indicated molar ratios. The results are expressed as fold induction of the percentage of GFP⁺ cells normalized to the levels observed after transfection with an empty vector (mean ± standard error of mean of four independent experiments for empty vector versus STAT5FL* versus STAT5Δ* and of three independent experiments for the competition experiments, respectively). *P <.05; **P<.005; ns: not significant (t test for paired samples).