FIG. 1.

Targeted deletion of Smad3 results in elimination of TGF-β growth inhibitory effects and elevated levels of c-Myc. (A) The rate of DNA synthesis of primary keratinocytes derived from wild-type (+/+) and Smad3^ex1/ex1 homozygous null (−/−) murine keratinocytes treated with vehicle or 100 pM TGF-β was measured by [³H]thymidine incorporation as described in Materials and Methods. The difference of the measured amount of incorporated [³H]thymidine of cells treated with vehicle minus that of TGF-β-treated cells was divided by the vehicle control counts per minute and plotted as the percent growth inhibition. The presented data are representative of values obtained from three individual lines of each genotype. (B) Murine colon epithelium was isolated from wild-type (+/+) and Smad3^ex1/ex1 homozygous null (−/−) 3- to 5-month-old littermates, and Western analysis for c-Myc and actin, as a loading control, of 30 μg of protein from the epithelium lysate are depicted. Brackets indicate two individual sets of wild-type and Smad3^ex1/ex1 homozygous null littermates (litter A and litter B).