Retinoic acid receptor beta is the retinoid receptor most frequently associated with the growth suppressive effects of retinoic acid in various epithelial turner-derived cell lines. In particular, it has been shown that transfection of RAR beta 2 in epidermoid lung tumor cells could reduce their in vitro growth rate in the presence of retinoic acid and in vivo tumorigenicity. However, the question remained as to the isoform specificity of this effect. To investigate this, we transfected RAR alpha 1, RAR beta 1 and RAR beta 2 into the epidermoid lung cancer cell line Calu-1 and assessed the in vitro growth capacities of the transfected cells. The expression of the fetal RAR beta 1 or overexpression of the ubiquitous RAR alpha 1 isoforms could not mimick the growth suppressive effect of RAR beta 2. In addition we analyzed the expression of another RAR isoform, alpha 2, in many tumor-derived lines and conclude from its expression pattern that RAR alpha 2 is unlikely to be involved in retinoic acid growth suppression of lung cancer. Overall our data suggest that the suppressive effect of RAR beta 2 is isoform specific. (C) 7000 Elsevier Science Ireland Ltd. All rights reserved.