Figure 1. BCL10 is a chromatin-associated protein and accumulates at DSB site in an ATM- dependent manner. (A) BCL10 was present in the chromatin-enriched fraction. 293T cells were treated with bleomycin or mock-treated, and then subjected to chromatin fractionation. S2, cytosol; S3, nuclear soluble; P3, chromatin-enriched fraction. (B) BCL10 formed discrete nuclear foci in response to etoposide treatment. HeLa cells were subjected to DMSO/Etoposide treatment for 1 hour and immunostained with mouse anti-γ-H2AX monoclonal antibody and rabbit anti-BCL10 polyclonal antibodies. (C) DNA damage-induced focus formation of BCL10 was compromised by the ATM-specific inhibitor KU55933. HeLa cells were treated with DMSO or PIKK inhibitors 1.5 h before etoposide was added and processed for immunostaining as described in (B). (D) Depletion of ATM compromised DNA damage-induced focus formation of BCL10. HeLa cells were transfected with control siRNA (si-CTR) or ATM-specific siRNA (si-ATM), treated 2 d after transfection with DMSO or etopside for 1.5 h, and fixed for immunostaining with antibodies as indicated. The efficiency of ATM knockdown was determined by immunoblotting with antibodies against ATM and β-actin.