Effect of Retinoids on Hyperproliferation-Associated Keratins K6 and K16 in Cultured Human Keratinocytes: A Quantitative Analysis

The keratin patterns of human epidermal keratinocytes cultured on a 3T3-feeder layer in the presence of 10−8 M non-aromatic (all-trans retinoic acid and 13-cis retinoic acid) and polyaromatic (arotinoid, arotinoid-sulfone, and free arotinoic-acid) retinoids were analyzed by high resolution one- and two-dimensional gel electrophoresis and immunoblotting. Laser densitometric evaluation of one-dimensional gels allowed to quantitate the changes within the keratin patterns and revealed an increase in the expression of keratins K13, K15, and K19 as induced by both non-aromatic and polyaromatic retinoids, except for the parent compound arotinoid. This would then indicate that such keratinocytes are pursuing a more embryonic type of differentiation.In evaluating the data for the hyperproliferation-associated keratins K6 and K16 we noticed an unexpected result: except for all-trans retinoic acid, these two keratins showed opposite responses. As compared to control cultures, the amount of K6 did generally increase, while K16 was reduced, with arotinoid acid being the most effective retinoid. The apparently uncoupled expression of K6 and K16 appeared also to be concentration dependent when 13-cis retinoic acid at concentrations of 10−9, 10−8, and 10−7 M was analyzed.Considering the overall antiproliferative potency of retinoids, we therefore conclude that K16 alone, rather than the pair K6/K16, should be regarded as a proliferation-related keratin and as such may be used as a sensitive marker to evaluate keratinocyte proliferation