Vehicle control (EtOH) or 4-OHT was added to Mdm2fl/flp53−/− fibroblasts expressing CreERT2 and GFP or GFP alone. A, B) PCR Mdm2 gene rearrangement (A, top) and Western blotting (A, bottom) performed. C–F) Proliferation (MTT assay, quadruplicate; B), cell number (C), viability (D), Annexin-V (E), and sub-G1 DNA (F) measured. G) Cells in G2/M and phospho-histone H3 evaluated 24hrs following 4-OHT or EtOH administration. C–G, triplicates. B, *p<0.009; C, *p<0.003, **p<0.0009; D, *p<0.006; E, *p<0.0004; F, *p<0.00009; G, *p=0.0042.