BAX and pachyonychia congenita: VDA’s antiproliferative effect on PC cells depended on VDR expression. VDA treatment increased the G1 population and decreased S and G2 populations. Apoptotic rate also increased after VDA treatment. β-Catenin and phosphorylated Akt expression decreased, but p21 expression increased in VDA-treated PC cells. Also, Bcl-2 expression decreased, but Bax expression increased in VDA treated PC cells.