- High-cell-density phorbol ester and retinoic acid upregulate involucrin and downregulate suprabasal keratin 10 in autocrine cultures of human epidermal keratinocytes. Poumay, Y., Herphelin, F., Smits, P., De Potter, I.Y., Pittelkow, M.R. Mol. Cell Biol. Res. Commun. (1999)