Fig. 2.

p19^ARF, p53, and p21^waf1 but not p16^INK4A are required to suppress Ras-dependent tumorigenesis and senescence. (A) MMECs nullizygous for the indicated gene, or wild-type controls, were transduced with oncogenic Ras and transplanted to the cleared fat pads of naive hosts. Graph shows tumor incidence (>2 mm) 5 weeks after transplantation. n > 9 for each group. (B) p16ink4a^−/− MMECs were transduced with oncogenic Ras and 4 weeks after mammary fat pad transplantation and stained for SA-βGal activity. S, stroma; T, transplanted cells. (Scale bar: 100 μm.) (C) p19arf^−/− MMECs were transduced with oncogenic Ras in vitro, and extracts were analyzed by Western blot for Ras^V12, p16^INK4A, p21^waf1, and tubulin.