Levels and membrane localization of the c-K-ras p21 protein in lungs of mice of different genetic strains and effects of 2,3,7,8- tetrachlorodibenzo-p-dioxin (TCDD) and Aroclor 1254

Mutational activation of the K-ras oncogene often occurs in human and mouselung adenocarcinomas. Since K-ras p21 functions in trans-membranesignaling, we have investigated whether the amount of this protein in lungcell membranes is a variable that could influence lung tumorigenesis,either due to genetic differences or in response to tumor promoters. Thesix mouse strains assessed showed little difference in the total lung K-rasp21 after immunoprecipitation and immunoblotting. However, amount of rasp21 in the membrane fraction showed significant differences, with C57BL/6and BALB/c having 3-5-fold more than NIH Swiss, AKR and DBA mice.Interestingly, a congenic AKR strain having the Ahr(b-1) Ah receptor allelefrom C57BL/6 mice (designated AKR.B6Ah) had high lung membrane K-ras p21similar to that of C57BL/6. To test for possible changes related to lungtumor promotion, mice were treated with a promotional dose of TCDD (5nmol/kg). After 48 h C57BL/6 lungs showed an increase in p21 in both totaland membrane fractions. BALB/c, DBA and Swiss mice showed an increase onlyin membranes. There was no change in the AKR and AKR.B6Ah. Aroclor 1254(250 mg/kg) caused an increase in membrane/cytosol ratio in Swiss mice.Thus the membrane:cytosol K-ras p21 ratio may be influenced by the Ahrphenotype, and TCDD and PCBs can induce p21 or increase its membrane levelin certain strains, but these properties are not fully dependent on Ahrreceptor type. In confirmation of the relevance of these findings for thetumor target cell type, the immortalized alveolar type 2 E10 cell linepresented K- ras p21 in membrane, and this was increased 4-fold bytreatment with 10 nM TCDD.