Inactivation of Rce1 inhibits the growth of K-RAS^G12D–expressing fibroblasts. (A) Cell proliferation assay of spontaneously immortalized Rce1^fl/flK^LSL and Rce1^fl/+K^LSL embryonic fibroblasts treated with Cre and β-gal-adenoviruses. Data are mean of 2 independent cell lines per genotype. The experiment was repeated with a pair of primary cell lines and yielded similar results. (B) PCR amplification of genomic DNA from the cells in panel A demonstrating the activation of the Kras2^G12D allele and the inactivation of the Rce1^fl allele. Lane 1, β-gal-adenovirus-treated Rce1^fl/+K^LSL cells; lane 2, Cre-adenovirus-treated Rce1^fl/+K^LSL cells; lane 3, β-gal-adenovirus–treated Rce1^fl/flK^LSL cells; lane 4, Cre-adenovirus-treated Rce1^fl/flK^LSL cells.