FIG. 2.

Activation of Tcf-4 by PKA. (A) Activation of Tcf-4 by PGE₁ and Bt₂cAMP. L cells transfected with pEF-BOS-HA/hTcf-4E (0.1 μg) and TOP-fos-Luc (0.5 μg) or FOP-fos-Luc (0.5 μg) were treated with PGE₁, Bt₂cAMP and IBMX, or Wnt-3a for 8 h. The luciferase activity was measured and expressed as the fold increase compared with the level observed in cells without treatment. (B) Effects of PKA on the Tcf-4 activity toward a natural Tcf-responsive promoter. pEF-BOS-HA/hTcf-4E (0.1 μg) or pEF-BOS-HA/hTcf-4E (Δ1-53) (0.1 μg) was transfected into L cells with Axin2-Luc (0.5 μg). The cells were treated with PGE₁, Bt₂cAMP and IBMX, or Wnt-3a in the presence or absence of H-89 for 8 h. The luciferase activity was measured and expressed as the fold increase compared with the level observed in the cells without treatment. (C) Effects of PKA on expression of the Axin2 mRNA. Total RNA from HEK-293 cells stimulated with Bt₂cAMP and IBMX or Wnt-3a for 2 h in the presence or absence of H-89 was subjected to quantitative RT-PCR. The results shown were normalized by the GAPDH mRNA levels, and the corresponding quantification results for the Axin2 mRNA levels were expressed as the fold increase compared with that of cells without treatment. The results shown are means ± standard errors from four independent experiments.