Fig. 5.

The ability of MYC to interact with WDR5 is required for tumor growth and maintenance. (A) Schematic of tumor formation assay. Unswitched WT, ∆264, or WBM cells were grown in culture and pulsed 3 times with OHT to induce the switch. Cells were then injected into a flank of nude mice, and tumor growth was monitored. (B) Average tumor volumes in mice injected with the indicated switched Ramos cells over days 5 to 17 of the experiment. Tumor volumes for ∆264 and WBM cells were significantly different (*) from WT (P < 4.84E-3; 2-tailed t test). (C) Kaplan–Meier survival curves of mice injected with switched WT, ∆264, or WBM cells (n = 9 per group); P < 0.0001 (log-rank test). (D) PCR assay for presence of unswitched cells in tumor samples taken at time of sacrifice. Each dot represents a single mouse. The horizontal cross represents the mean for each group. Note that we were unable to extract usable DNA from one of the tumors in the ∆264 group. (E) Schematic of tumor maintenance assay. Unswitched WT, ∆264, or WBM cells were injected into a flank of nude mice, and tumor growth was monitored. At day 15, mice received 3 consecutive daily injections of tamoxifen to induce the switch, and tumor development was monitored. (F) Average tumor volumes in mice injected with the indicated unswitched Ramos cells before and after switching were induced, beginning at day 15 (red arrow “Tam”). After switch, tumor volumes for ∆264 and WBM cells were significantly different (*) from WT (P < 7.0E-9; 2-tailed t test). (G) Kaplan–Meier survival curves of mice (in F) (n = 9 per group); P < 0.0001 (log-rank test). (H) For the indicated cell types, tumors were harvested (n = 4 per group) 48 and 96 h following tamoxifen administration. Apoptosis was evaluated in the isolated lymphoma cells by staining for Annexin V positivity (Annexin V+) and analysis by flow cytometry. The extent of Annexin V positivity in ∆264 and WBM tumor cells was significantly different (*) from WT tumors (P < 1.65E-5; 2-tailed t test).