Oncogenic Ras induces p19(ARF) and growth arrest in mouse embryo fibroblasts lacking p21(Cip1) and p27(Kip1) without activating cyclin D-dependent kinases

Oncogenic Res induces two products of the INK4a/ARF tumor suppressor locus (p16(INK4a) and p19(ARF)) in primary human and rodent fibroblasts, ultimate ly leading to a permanent state of cell cycle arrest resembling replicative senescence. Whereas p16(INK4a) antagonizes the activities of cyclin D-depe ndent kinases, p19(ARF) activates the p53 transcription factor. Immortalize d rodent fibroblast cell lines that lack INK4a/ARP function, ARF alone, or p53 are resistant to the growth inhibitory effects of oncogenic Res and ins tead continue to proliferate and undergo morphological transformation. Prim ary mouse embryo fibroblasts lacking Cip1 and Kip1 genes encoding inhibitor s of cyclin-dependent kinase-2 were used to further explore the effects of oncogenic Res on arrest of the cell division cycle. Although early passage primery fibroblast strains that lack both p21(Cip1) and p27(Kip1) fail to a ssemble cyclin Ii-dependent kinases, oncogenic has retained its ability to induce p19(ARF), but not p16(INK4a), protecting Cip/Kip-null cells from pro liferating and undergoing transformation. Under these conditions, Res did n ot induce G(1) phase arrest but instead triggered DNA synthesis, abnormal n uclear divisions, failure of cytokinesis, and emergence of polyploid cells. Therefore, in the absence of p16(INK4a), p21(Cip1), and p27(Kip1), oncogen ic Res affects the functions of genes required for completion of the cell c ycle.