A pro-apoptotic effect requires the depletion of Hdac1 and Hdac2 in Eµ-Myc lymphoma. We produced tractable Eµ-Myc lymphoma cells with conditional knockout of Hdac1, Hdac2, or Hdac6 (Eµ-Myc.Hdac1^−/−; Eµ-Myc.Hdac2^−/−; Eµ-Myc.Hdac6^−/−) and transduced these with shRNAs against Hdac1, Hdac2, Hdac3, or Hdac6. (A) Eµ-Myc.Hdac1^−/− lymphoma was transduced with constitutive (pLMS) vectors containing shRNA cassettes against Hdac2, Hdac3, or Hdac6, FACS-sorted to approximately 50% GFP⁺, and 50% GFP⁻, and cell representation followed over time using competitive proliferation assays, as described previously. Individual bars represent daily flow cytometry assessment of GFP positive cells (days 0, 1, 3, 5, 7, 9, 11, 13) from 3 independent replicates (mean ± SEM) and normalized to day 0. (B) Effects of constitutively depleting Hdac1, Hdac2, or Hdac3 in Eµ-Myc.Hdac6^−/− cells using competitive assays. Each bar represents different days of testing: days 0, 1, 3, 5, 7, 9, 11, 13. Data are presented as mean ± SEM of 3 biological replicates. (C) Eµ-Myc.Hdac1^−/− cells transduced with shHdac2.439 were FACS-sorted (GFP⁺) immediately following transduction and assessed for the induction of apoptosis by Annexin/propidium iodide staining using flow cytometry. Individual bars represent daily mean percentages of Annexin V–positive cells (days 0, 1, 2, 3) ± SEM (3 biological replicates). (D) Eµ-Myc lymphoma cells (no. 107) were treated with HDAC1/2-selective RGFP233 (5 µM) and assessed for apoptosis (Annexin/propidium iodide) by flow cytometry at indicated time points. Data are presented as mean ± SEM (3 biological replicates).