Effects of retinoic acid on proliferation and gene expression of cleft and non-cleft palatal keratinocytes

BACKGROUND: Retinoic acid (RA) is a key regulator of embryonic development and linked to several birth defects including cleft lip and palate (CLP). The aim was to investigate the effects of RA on proliferation and gene expression of human palatal keratinocytes (KCs) in vitro. Methods: KCs from children with and without CLP were cultured with 2 and 5 mu M RA. Proliferation was measured by quantification of DNA after 2, 4, 6, and 8 days. In addition, we analysed the effects of RA on messenger RNA expression of genes for proliferation, differentiation, apoptosis, and RA receptors. Results: RA similarly inhibited proliferation of palatal KC from cleft and non-cleft subjects. The proliferation of KCs from cleft subjects was reduced to 59.8 +/- 13.4% (2 mu M) and 41.5 +/- 14.0% (5 mu M, Day 6), while that of cells from age-matched non-cleft subjects was reduced to 66.9 +/- 12.1% (2 mu M) and 33.9 +/- 10.1% (5 mu M). RA treatment reduced the expression of several of the investigated genes; the proliferating cell nuclear antigen (PCNA) was reduced in CLP KCs only. Keratins 10 and 16 were downregulated in keratinocytes from both cleft and non-cleft subjects. P63, a master regulator for epithelial differentiation, was only downregulated in KCs from cleft subjects, as was the RXRa receptor. Two P63 target genes (GJB6 and DLX5) were strongly downregulated by RA in all cell lines. None of the apoptosis genes was affected. Conclusion: Overall, RA similarly inhibits proliferation of palatal KCs from cleft and non-cleft subjects and reduces the expression of specific genes.