p38δ acts downstream of c-Jun and Ets1 to mediate senescence. (A) BJ cells transduced with a scrambled shRNA (shSC) or shRNA for c-Jun (shJun1555) or Ets1 (shEts257) and a constitutively active mutant of p38δ (p38δF324S) or vector (WH) were seeded into 12-well plates on day 5 after p38δF324S transduction, after selection of transduced cells. Cell numbers (top graph) were counted 6 days after seeding. Cells were stained for SA-β-Gal on day 10 after p38δF324S transduction. The percentage of cells positive for SA-β-Gal was quantified (bottom graph). Values are means ± SDs for duplicates. *, P < 0.05 versus WH by Student's t test. (B) BJ cells transduced with a scrambled shRNA (shSC) or shRNA for c-Jun (shJun1555) or Ets1 (shEts257), wild-type p38δ (p38δWT) or vector (WN), and Ha-rasV12 (Ras) or vector (WH) were seeded into 12-well plates on day 5 after ras transduction, after selection of transduced cells. Cells (top graph) were counted 3 days after seeding. Cells were stained for SA-β-Gal on day 10 after ras transduction. The percentage of cells positive for SA-β-Gal was quantified (bottom graph). Values are means ± SDs for duplicates. *, P < 0.05 versus WN; **, P < 0.01 versus WN (by Student's t test).