Figure 4. Elimination of Mek1/2 kinases prevents induction of NSCLCs by an endogenous K-Ras^G12V oncogene.

(A) Survival of K-Ras^+/G12V;Mek1^+/+;Mek2^+/+ (n=10) (open circles) and K-Ras^+/G12V;Mek1^lox/lox;Mek2^−/− (n=14) (solid circles) mice treated with Ad-Cre at 8 weeks of age.

(B) Whole mount X-Gal staining of lung sections collected from mice with the indicated genotypes 6 months after Ad-Cre treatment. β-Geo positive cells identified by X-Gal staining (blue color) correspond to cells expressing K-Ras^G12V.

Scale bars 5 mm.

(C) Number of tumors, classified by grade (I-IV), observed in K-Ras^+/G12V;Mek1^+/+;Mek2^+/+ (n=6) (open bars) and K-Ras^+/G12V;Mek1^lox/lox;Mek2^−/− (n=8)(solid bars) mice.

Error bars indicate +/− SD of the mean.

p values were calculated according to Student’s t test.

(D) (Top) Southern blot analysis of genomic DNA isolated from individual tumors of K-Ras^+/G12V;Mek1^lox/lox;Mek2^−/− mice 8 months after Ad-Cre treatment. DNAs were digested with HindIII and probed with a 680 bp DNA fragment obtained from a region downstream from the second loxP site. The migration of the unrecombined Mek1^lox allele (1.7 kbp) and the Mek1⁻ allele (1.5 kbp) is indicated by arrowheads. (Bottom) Western blot analysis of Mek1 and Mek2 expression in lysates obtained from individual tumors collected 8 months after Ad-Cre treatment of K-Ras^+/G12V;Mek1^+/+;Mek2^+/+ and K-Ras^+/G12V;Mek1^lox/lox;Mek2^−/− mice. The presence of Mek1 in tumors of Ad-Cre treated K-Ras^+/G12V;Mek1^lox/lox;Mek2^−/− mice, due to partial cleavage of the Mek1^lox allele, indicates that Mek1 is essential for tumor development. Gapdh was used as loading control.

Migration of the above proteins is indicated by arrowheads

(E) Survival of Mek1^+/+;Mek2^+/+;RERT^ert/ert (n=6) (open circles) and Mek1^lox/lox;Mek2^−/−;RERT^ert/ert (n=6) (solid circles) mice fed ad libitum a tamoxifen-containing diet to activate the knocked in CreERT2 recombinase encoded by the RERT^ert alleles.

See also figure S4.