Differential expression of heparin-binding EGF-like growth factor (HB-EGF) mRNA in normal human keratinocytes induced by a variety of natural and synthetic retinoids.

It was recently revealed that epidermal growth following topical treatment with all-trans retinoic acid (atRA) was at least partly induced by heparin-binding epidermal growth factor-like growth factor (HB-EGF) released from suprabasal keratinocytes. Since proliferation of keratinocytes appears to be one of the critical roles of atRA in depigmentation treatment and promotion of wound healing, HB-EGF is considered suitable for assessing the therapeutic value of topical retinoids. In this study, HB-EGF mRNA expression in normal human keratinocytes after atRA treatment was examined, and the effects of a variety of natural and synthetic retinoids were compared. The results of reverse transcription polymerase chain reaction (RT-PCR) suggested that induction of differentiation increased HB-EGF mRNA expression in cultured keratinocytes. Real-time PCR analyses revealed that HB-EGF mRNA expression was elevated dose-dependently with atRA, peaking at 12 h. This elevation was more prominent in confluent keratinocytes than in subconfluent cells, suggesting that differentiated keratinocytes are more subject to stimulation of HB-EGF expression by atRA than proliferating keratinocytes. HB-EGF mRNA was upregulated in differentiation-induced keratinocytes by all retinoids used in this study at 1 micromol/l, and marked upregulation was seen when treated with three isotypes of retinoic acid (atRA, and 9-cis and 13-cis retinoic acid). RARalpha-selective agonists (Am80, Am580, ER-38925, and TAC-101) and a panagonist of RARs (Re80) caused relatively low elevation of HB-EGF transcripts, as did all-trans retinol (Rol) and all-trans retinal (Ral). Although another panagonist (Ch55) showed the highest elevation of HB-EGF mRNA, it was relatively cytotoxic at the concentration employed. Ral and Rol were found to upregulate HB-EGF when used at 100 micromol/l to 1 mmol/l, to a similar extent of atRA at 1-10 micromol/l. The capacity of retinoids to upregulate HB-EGF may be an important index for investigation and development of an ideal synthetic retinoid, which has maximum benefits and minimum side-effects