Synergistic effects of acitretin and narrow-band UVB on inducing the expression of heparin-binding epidermal-growth-factor-like growth factor in normal human keratinocytes

It has been reported that heparin-binding epidermal-growth-factor-like growth factor (HB-EGF) plays an important role in regulating keratinocyte growth after retinoic acid treatment. In clinic, there are synergistic effects of retinoic acid plus ultraviolet (UVB) on improving efficacy and reducing the side effects in treating psoriasis, while the mechanism is not fully clear. Therefore, this study was taken to examine the alteration of cell proliferation and HB-EGF expression in cultured normal human keratinocytes after acitretin and/or narrow-band UVB (NB-UVB) exposure. After 12 h incubation with acitretin (0.1–1 μmol/L) and/or following NB-UVB (50–100 mJ/cm2) irradiation in normal human keratinocytes, the proliferation potency of the cells was evaluated by MTT colorimetric assay, and HB-EGF protein and mRNA was detected by cytoimmunochemistry and real-time quantitative reverse transcription polymerase chain reaction (RT-PCR), respectively. Our results revealed 1 μmol/L acitretin combined with 100 mJ/cm2 NB-UVB showed strongest inhibition of keratinocyte proliferation and highest induction of HB-EGF mRNA expression (19.7% and 8.6-fold, respectively), the others were 1 μmol/L acitretin (14.4%, 7.1-fold), 0.1 μmol/L acitretin (10.2%, 3.2-fold), 100 mJ/cm2 NB-UVB (8.7%, 2.5-fold) and 50 mJ/cm2 NB-UVB (5.4%, 1.8-fold). Pattern of HB-EGF protein expression was similar to mRNA expression in keratinocytes upon above cultural conditions. Our results suggest acitretin or NB-UVB single treatment can dose-dependently inhibit keratinocyte proliferation and induce HB-EGF expression and there are synergistic effects when they are combined.