PRKG1 and colonic neoplasm: Consistent with a role of cGMP/PKG in regulating Wnt/β-catenin signaling as reported previously [21, 22, 31], MY5445 and papaverine reduced β-catenin levels, TCF transcriptional activity, and the expression of survivin in HCT116 colon tumor cells at concentrations that parallel those required for PKG activation (Figure 5A, 5B).