RARbeta2 specificity in mediating RA inhibition of growth of lung cancer-derived cells.

Retinoic acid receptor beta 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 RARbeta2 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 RARalpha1, RARbeta1 and RARbeta2 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 RARbeta1 or overexpression of the ubiquitous RARalpha1 isoforms could not mimick the growth suppressive effect of RARbeta2. In addition we analyzed the expression of another RAR isoform, alpha2, in many tumor-derived lines and conclude from its expression pattern that RARalpha2 is unlikely to be involved in retinoic acid growth suppression of lung cancer. Overall our data suggest that the suppressive effect of RARbeta2 is isoform specific.