A polypeptide is identified as being functionally included in a signal transduction pathway having a biological effect. Contemplated polypeptides are different from a retinoic acid receptor, a retinoid X receptor, or a cellular retinoic acid binding protein, however bind a retinoid or retinoid metabolite, and binding of the retinoid or retinoid metabolite lead to a modulation of the biological effect. In particularly contemplated methods, a retinoid or retinoid metabolite is administered to a cell or mammal in a concentration effective to modulate the biological effect.