The targeted disruption of both alleles of RARβ2 in F9 cells results in the loss of retinoic acid-associated growth arrest

F9 teratocarcinoma cell lines, carrying one or two disrupted alleles of the RAR beta(2) gene, were generated by homologous recombination to study the role of RAR beta(2) in mediating the effects of retinoids on cell growth and differentiation. Retinoic acid (RA) does not induce growth arrest of the RAR beta(2)-/- cells, whereas the F9 WT and RAR beta(2)+/- heterozygote lines undergo RA-induced growth arrest. The RAR beta(2)+/- lines also exhibit a faster cell cycle transit time in the absence of RA. The RAR beta(2)-/- stem cells exhibit an altered morphology when compared with the F9 WT parent line, and after RA treatment, the RAR beta(2)-/- cells do not exhibit a fully differentiated cell morphology, As compared with F9 WT cells, the RAR beta-/- 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 RAR beta(2)-/- cells following differentiation was not impaired. The research presented here, and prior research suggest that RAR beta is required for RA-induced growth arrest in a variety of cell types and that RAR beta also functions in mediating late responses to RA. These findings are significant in view of the reduced expression of RAR beta transcripts in a number of different types of human carcinomas.