Antagonistic Effects of Retinoic Acid and Hydrocortisone on Terminal Differentiation of Human Squamous Carcinoma Cells

Differentiation of SqCC/Y1, a human malignant squamous carcinoma, can be modulated by the presence of both corticosteroids and retinoids. To evaluate the regulation of the differentiation of epidermal cells by these agents, we have employed delipidized serum from which glucocorticoids and retinoids were removed. Thirty percent of SqCC/Y1 cells spontaneously expressed the terminally differentiated phenotype after 6 d in culture, as measured by the capacity to form detergent-insoluble cornified envelopes. Exposure of SqCC/Y1 cells to hydrocortisone at concentrations of 30, 100 and 300 nM produced a 25, 100, and 175%, increase, respectively, in the number of differentiated cells over untreated control cultures. Exposure of cells to retinoic acid at levels of from 3 to 300 nM caused a 24 to 85% decrease in the quantity of differentiated cells. Simultaneous treatment of SqCC/Y1 cells with hydrocortisone and retinoic acid resulted in mutual antagonism of cornified envelope formation. Treatment of SqCC/Y1 cells with a 1000-fold molar excess of retinoic acid did not directly alter the uptake of hydrocortisone, and a 100-fold molar excess did not directly inhibit the binding of the corticosteroid to its receptor. Pretreatment of cells for 48, 72, or 96 h with 100 nM retinoic acid decreased the binding of hydrocortisone to its receptor by only 20%, and only resulted in a small decrease in the total amount of hydrocortisone associated with cells 48 h after the addition of retinoic acid. These findings suggest that the antagonism between hydrocortisone and retinoic acid on the terminal differentiation of SqCC/Y1 is not expressed at the level of the corticosteroid receptor.