The targeted disruption of both alleles of RARbeta(2) in F9 cells results in the loss of retinoic acid-associated growth arrest.

Abstract F9 teratocarcinoma cell lines, carrying one or two disrupted alleles of the RARβ2 gene, were generated by homologous recombination to study the role of RARβ2 in mediating the effects of retinoids on cell growth and differentiation. Retinoic acid (RA) does not induce growth arrest of the RARβ2−/− cells, whereas the F9 WT and RARβ2+/− heterozygote lines undergo RA-induced growth arrest. The RARβ2+/− lines also exhibit a faster cell cycle transit time in the absence of RA. The RARβ2−/− stem cells exhibit an altered morphology when compared with the F9 WT parent line, and after RA treatment, the RARβ2−/− cells do not exhibit a fully differentiated cell morphology. As compared with F9 WT cells, the RARβ−/− cells exhibited a markedly lower induction of several early RA-responsive genes and no induction of laminin B1, a late response gene. The induction of RA metabolism in the F9 RARβ2−/− cells following differentiation was not impaired. The research presented here, and prior research suggest that RARβ is required for RA-induced growth arrest in a variety of cell types and that RARβ also functions in mediating late responses to RA. These findings are significant in view of the reduced expression of RARβ transcripts in a number of different types of human carcinomas.