In prostate cancer cells, calcitriol reduces the expression levels of COX-2 and that of PG receptors EP2 and FP, whereas it increases the expression of 15-hydroxyprostaglandin-dehydrogenase (15-PGDH), a NAD+-dependent enzyme responsible for the degradation of PGE259,60. The gene discussed is HPGD; the disease is prostate carcinoma.