FIG. 3.

Western analysis of p19^ARF. (A) Expression of p19^ARF is commonly down-regulated in MMLV-induced CD2-myc primary tumors from Trp53^+/− and Trp53^+/+ mice but not in those from Trp53^−/− littermates. In contrast, p19^ARF expression is strong in spontaneous primary tumors from Trp53^−/− and Trp53^+/− mice. It should be noted that the spontaneous tumors (p/m28, 30, 47, 48) from Trp53^+/− mice lost the Trp53 wt allele. Gels were routinely run in parallel and stained using Coomassie blue to ensure that there were equal amounts of protein in each lane on the Western blots. The presence or absence of the Trp53 wild-type allele is indicated in each case. (B) Repression of p19^ARF expression in the presence of p53. p19^ARF expression is repressed in early passages (E) of two cell lines which maintain functional p53, but the repression is not irreversible since on later passage (L), p53 is lost and p19^ARF expression is comparable to that of a control cell line (C) that lacks functional p53. Amounts of protein loaded are indicated by β-actin staining.