AHR and carcinoma: When AhR was silenced by short hairpin RNA interference in P19 cells, an embryonic carcinoma cell line, expression of the downstream signal molecules of AhR such as ARNT and CYP1A1 and the key molecule in WNT signaling, β-catenin, were suppressed, following by the increase in expression of the cardiomyogenesis-specific GATA4 and Nkx2.5 genes.