Bioassays for retinoic acid-like substances using cultured human keratinocytes

Using cultured human keratinocytes, three bioassays for retinoic acid-like substances have been developed. They are based on the ability of these substances (1) to inhibit cross-linked envelope formation, (2) to inhibit the synthesis of the K1 keratin, and (3) to stimulate the synthesis of the K19 keratin. The data, expressed as 50% inhibitory or activating concentrations were used to rank compounds according to their activity.