CYP27B1 and hepatocellular carcinoma: The second hydroxylation occurs in the kidney where 25(OH)D3 is metabolized to calcitriol by 25-hydroxyvitamin D 1α-hydroxylase encoded by Cyp27B1. Although the kidney was initially thought to be the sole organ expressing CYP27B1, it is now appreciated that its expression in tissues other than the kidney is widespread including in the hepatocarcinoma cell (HCC) line Huh7.5 [4].