Real-time quantitative PCR analyses of the expression of key genes of the HPA axis were carried out for CRF (A), UCN1 (B), UCN2 (C), UCN3 (D), CRFR1 (E), POMC (F), MC1R (G), MC2R (H), MC3R (I) and NR3C1 (J) in primary human epidermal keratinocytes stimulated with 0.1 µM 1,25(OH)2D3, 20(OH)D3 or 21(OH)pD for 24 h. Data are presented as means ± SD. *P < 0.05, **P < 0.01, ***P < 0.001 compared to control.