The second intron of the K-ras gene contains regulatory elements associated with mouse lung tumor susceptibility

We have previously demonstrated the preferential activation of the K-ras gene from the susceptible A/J parent in lung tumors from F₁ mouse hybrids. In the present study, the mechanism of this observation is further investigated. Higher levels of expression of A/J K-ras allele were detected in lung adenomas (30 of 30) from the C3A mouse. In addition, three K-ras alleles, designated as susceptible (K(s)), intermediate (K(i)), or resistant (K(r)), were identified by sequence analysis of the second intron of the K- ras gene from 32 strains of mice. These K-ras alleles are associated with differences in mouse lung tumor susceptibility. All K(r) alleles have a tandem 37-bp direct repeat (nt 282-355) in the second intron of the K-ras gene. K(s) and K(i) alleles have only one copy of the 37-bp sequence (nt 282- 318). K(s) strains have three base variations at nt 288, 296, and 494, and K(i) strains have two base variations at nt 288 and 494 in the second intron of the K-ras gene. Differential protein-binding patterns were observed in gel-mobility-shift experiments between the duplicated 37-bp sequence of the K(r) allele and the single 37-bp sequence of the K(s) and K(i) alleles. DNase I footprinting assay revealed protein binding sites in the second intron of the K-ras gene that correspond to the tandem repeat sequences. Our data suggest that higher expression of the A/J allele relative to C3H allele may be responsible for the allele-specific activation of the K-ras gene in lung tumors from F₁ hybrid mice.