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Fig. 3. Modulation of 53BP1 and MDC1 levels by STAT-1. (A) Cell lysates from 2fTGH, U3A and U3A-ST1 cells were immunoblotted for MDC1 and 53BP1. 53BP1 and MDC1 expression is reduced in STAT-1-deficient U3A cells. (B) RT-PCR showing reduced 53BP1 and MDC1 mRNA levels in U3A cells. MDC1 and 53BP1 mRNA levels were assessed from 2fTGH, U3A or U3A-ST1 cells. (C) 2fTGH, U3A or U3A-ST1 cells were exposed to {gamma}-IR (2 Gy), fixed after 2 hours and stained with anti-53BP1 or anti-MDC1 antibody. The dimensions of the field of view are 40 mM x40 mM. (D,E) The MDC1 promoter is modulated by STAT-1. The MDC1-reporter construct was transfected into STAT-1+/+ and STAT-1–/– MEF cells, and U3A and U3A-ST1 cells together with either full length STAT-1 (ST1), STAT-1ß (ST1B) or a control vector. Upper panels in D and E show immunoblots of transfected cells for STAT-1{alpha} (ST1{alpha}) or STAT-1ß (ST1ß).