Loss of Dhx9 induces replicative stress and exacerbates Myc induction of p53. (A) Immunoblot analysis of extracts prepared from MycER/3T3 cells that had been infected with MLS expressing the indicated shRNAs. Cells were harvest 48 hours after exposure to vehicle or 250 nM 4-OHT. (B) Immunoblot analysis of extracts prepared from Myc-ER/3T3 that had been infected with MLS expressing the indicated shRNAs. Cells were then transfected with the indicated siRNA, and 48 hours later, lysates were generated and blotted with the indicated antibodies. (C) Immunoblot analysis of extracts prepared from Arf^−/−Eμ-myc/Bcl-2 cells infected with the indicated shRNAs. (D) Cell cycle distribution of Arf^−/−Eμ-myc/Bcl-2 lymphomas expressing the indicated shRNAs. Error bars represent standard error of the mean; n = 5; *P = .01; **P = .05, ***P < .01 (calculated using an unpaired Student t test). (E) S-phase progression of Arf^−/−Eμ-myc/Bcl-2 expressing the indicated shRNAs on release from a double thymidine block. BrdU⁺ lymphomas were monitored at the indicated times after release. Cells were stained with PI and analyzed by flow cytometry. (F) Genomic (line graph) and nascent DNA (bar graph) was isolated from MycER/3T3 cells expressing the indicated shRNAs. DNA was harvested 48 hours after exposure to vehicle or 250 nM 4-OHT. The presence of nascent DNA corresponding to Tsix, Xist, Ada-1, and Myc origins was quantitated with quantitative reverse transcription-polymerase chain reaction. Error bars represent standard deviation; n = 3. (G) Schematic representation of a model by which Dhx9 knockdown enhances ABT-737 sensitivity.