FIG 4.

miR-155 regulation of DNA damage is cell and context specific. Mature B cells, thymocytes, and bone marrow cells were harvested from miR-155 null or WT mice. Exposure of these cell to ionizing irradiation (IR) (5 Gy, with collection after 3 h) and etoposide (30 μM for 20 h) induced robust γH2AX accumulation at the DSB foci in all three cell populations (compare control [vehicle exposed, nonirradiated] versus etoposide- or IR-treated cells). However, irrespective of the cell type or genotoxic stimuli, there was no significant difference in the number γH2AX foci between WT and miR-155^−/− cells. Data shown are mean ± SD for foci per nucleus. For each assay, approximately 50 nuclei were counted per mouse. p53 activity data are shown in Fig. S3 in the supplemental material.