PKA antagonist blocks β-catenin phosphorylation at Ser552 and Ser675 and down-stream c-Myc regulation in a human colon cancer cell line. A. Representative immunoblots with indicated antibodies of HCT 116 colon carcinoma cells cultured in the presence of PGE2, indomethacin, Rp-8-Br-cAMPS or combinations as indicated. B. Levels of immunoreactive phospho-β-catenin Ser552 and Ser 675 and c-Myc were quantified by densitometric scanning of immunoblots. Results were normalized to total β-catenin or actin (c-Myc) levels in the same experiment. Amalgamated data from n = 3-4 experiments in individual cell cultures are shown. Median values were compared with Mann-Whitney Rank Sum test when Shapiro-Wilk Normality test failed; otherwise mean values were compared by Student's t-test (n = 3, left panel and n = 4, right panel) *: P < 0.05 when compared to untreated samples; +: P < 0.05 when compared to PGE2-treated samples. C. Schematic model of Wnt-Frz and PGE2-EP2-PKA pathways regulating β-catenin activity in colorectal cancer.