RARβ2 specificity in mediating RA inhibition of growth of lung cancer- derived cells

Retinoic acid receptor β is the retinoid receptor most frequently associated with the growth suppressive effects of retinoic acid in various epithelial tumor-derived cell lines. In particular, it has been shown that transfection of RARβ2 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 RARα1, RARβ1 and RARβ2 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 RARβ1 or overexpression of the ubiquitous RARα1 isoforms could not mimick the growth suppressive effect of RARβ2. In addition we analyzed the expression of another RAR isoform, α2, in many tumor-derived lines and conclude from its expression pattern that RARα2 is unlikely to be involved in retinoic acid growth suppression of lung cancer. Overall our data suggest that the suppressive effect of RARβ2 is isoform specific. (C) 2000 Elsevier Science Ireland Ltd.