FIGURE 3.

STAT3 inhibits T-cell proliferation through up-regulation of FoxO transcription factors. Analysis of WT or STAT3KO naïve CD4⁺ T cells by RT-PCR or qPCR (A) and by Western blot (B). C, WT or STAT3KO CD4⁺ T cells were stimulated with anti-CD3/CD28 for 24 h under Th0 condition and naïve or activated CD4⁺ T cells were analyzed by qPCR (C). WT CD4⁺ T cells were polarized for 4 days under Th0, Th17, or Treg conditions and expression of FoxO1 and FoxO3a was analyzed by qPCR (D). E and F, WT or STAT3KO CD4⁺ T cells were stimulated with anti-CD3/CD28 for 6 h. Nuclear extracts were isolated and analyzed for FoxO3a transcriptional activity by EMSA and supershift analysis was performed with Abs specific to N (FoxO3a#1) or C (FoxO3a#2) terminus of the Foxo3a protein (E). F, FoxO1 transcriptional activity was analyzed by an ELISA-based DNA protein binding assay. G and H, we detected p27kip1 expression by naïve WT or STAT3KO T cells by Western blotting (G) or qPCR (H). Results are representative of at least three independent experiments.