MUC1 regulates c-myc expression via miR34a in AML cells. MOLM-14 and THP-1 cells were transduced with a miR34a mimic or control, using lentiviral transduction. (A) Lysates were prepared, and c-myc expression was assessed using Western blot analysis. MOLM-14 AML cells overexpressing miR34a were then silenced for miR34a, by lentiviral transduction of miR34a-ZIP or control. (B) Lysates were prepared, and c-myc expression was assessed using Western blot analysis. THP-1 AML cells silenced for MUC1 expression using specific MUC1 shRNA were silenced for miR34a, using lentiviral transduction of miR34a-ZIP or control. (C) Lysates were prepared and c-myc expression was assessed using Western blot analysis. Healthy PBMCs were cocultured with irradiated, fluorescently labeled AML cells with overexpressed miR34a levels, for 5 days at a ratio of 100:1 (PBMC:AML). After coculture, cells were analyzed with flow cytometry, and fluorescently labeled blast cells were excluded; CD11b⁺/HLA-DR⁻/CD33⁺ MDSCs were quantified as a percentage of immature CD11b⁺/HLA-DR⁻ myeloid cells. (D) A summary of three independent experiments is shown for MOLM-14 and THP-1. Similarly, MDSCs were detected in coculture of PBMCs with miR34a-silenced AML cells MOLM-14 (n = 3) (E) and THP-1 AML cells (n = 3) (F). RNA was isolated from miR34a-overexpressing or miR34a-silenced AML cells and subjected to qPCR with primers against miR34a. (G) The miR34a expression in MUC1-silenced MOLM-14 and THP-1 is quantified in relation to control cells; a summary of three experiments is shown. *P < .05.