p38 MAPK and STAT1 synergistically increase Ttp mRNA expression. p38α^+/+ and p38α^–/– MEFs were left untreated (w/o) or treated for 1 hour with IFN-γ (g), anisomycin (a) or both (a/g) (A), or treated with IFN-β (b), anisomycin (a) or both (a/b) (B). STAT1^+/+ and STAT1–/–fibroblasts were stimulated as described for panels A and B, respectively (C,D). Total RNA was isolated and Ttp mRNA levels were determined using qRT-PCR. To obtain Ttp mRNA induction, values were normalized to those of untreated cells. Error bars indicate SD. *P < .01 (a/g) or (a/b) versus (a) treatment in +/+ cells; †P < .01 +/+ versus –/–MEFs by univariate linear regression models; n = 3 experiments.