Induction of premature senescence by oncogenic ras correlates with p38 activation. (A) PD of BJ cells transduced at PD 20 with Ha-RasV12 or a vector control. Values are means ± standard deviations for duplicates. (B) Morphology of BJ cell populations transduced with Ha-RasV12 or a vector control, after staining for SA-β-gal (pH 6.0) at day 7 postselection. (C) Western blot analysis of BJ cells transduced with Ha-RasV12 (Ras) or a vector control (BP), showing the levels of Ha-Ras, phospho-ERK (P-ERK1/2), ERK2, phospho-p38 (P-p38), p38, phospho-JNK (P-JNK), JNK, p16INK4A, and p53. (D) p38 protein kinase activity in BJ cells transduced with Ha-RasV12 (Ras) or a vector control (BP), determined at day 4 postselection in a kinase assay by using [γ-32P]ATP and GST-ATF2 as substrates, following immunoprecipitation of p38 with an anti-p38 antibody (αp38) or an antiactin antibody (αActin). Shown are the relative amounts of phosphorylated ATF2 substrate after normalization to background. The signals were visualized and quantitated with a phosphorimager.