Tumor suppressor function of a dominant negative retinoic acid receptor mutant.

Mutations in receptors for the vitamin A metabolite retinoic acid (RAR) that repress retinoic acid (RA)-responsive gene expression have been identified and characterized. We previously reported an absence of target gene response to RA in all but one of a series of transformed human epithelial cell lines. To elucidate the mechanisms of this unresponsiveness, we created stable transfectants that expressed an RARalpha mutant (RARalpha403) previously shown to have dominant negative activity due to a C-terminal truncation. All clones exhibited repressed RA-responsive gene expression. These cells grew slowly and demonstrated greater growth inhibition by RA. Pretreatment of both control and experimental groups with RA enhanced epidermal growth factor-induced proliferation despite RA-dependent downregulation of epidermal growth factor receptor expression. In addition, clones expressing the mutant RARalpha were 60% less invasive in an in vitro assay. This reduced invasiveness correlated with decreased gelatinase activity in these cells. We showed for the first time that a dominant negative mutation in RARalpha can function as a tumor suppressor in transformed epithelial cells.