RNA was extracted from keratinocytes or skin tissue with Trizol (Invitrogen) according to the manufacturer's protocol. cDNA was generated using oligo-dT primers and the Superscript II kit (Invitrogen). The primers used for PCR were Snail forward: 5′- CAGCTGGCCAGGCTCTCGGT-3′; Snail reverse: 5′- GCGAGGGCCTCCGGAGCA-3′; GAPDH forward 5′- CGTAGACAAAATGGTGAAGGTCGG-3′; and GAPDH reverse: 5′- AAGCAGTTGGTGGTGCAGGATG-3′.