FIG. 3.

E2F1 proteins induce a senescence-like phenotype. (A) Morphology and SA-β-Gal expression. WI-38 cells were infected with the indicated E2F1-expressing retroviruses, selected, and, 2 to 3 days thereafter, stained for SA-β-Gal, as described in Materials and Methods. The cells were photographed under phase-contrast optics. WT, wild type. (B) Expression of matrix-remodeling genes. RNA, isolated from WI-38 cells infected as described for panel A, was analyzed for interstitial collagenase (MMP-1), stromelysin-1 (Strom-1), PAI-1, and β-actin (control) mRNA by RT-PCR, as described in Materials and Methods. Signals were normalized to β-actin, and the MMP-1, stromelysin-1, and PAI-1 mRNA levels in control cells (B0) were each set at 1. Relative to that by B0, levels of induction by B-WT were 2.7, 2.2, and 1.8, respectively; levels of induction by B-E132 were 0.9, 1.0, and 1.1, respectively; and levels of induction by B-CterDl were 0.9, 1.2, and 1.0, respectively.