Transcription factor binding and transactivation capacity of the ISRE of β₂m.

(A) EMSA showing binding of complexes to the ISRE of β₂m. Using specific Abs, the complex binding to the ISRE was shown to contain in IRF2, and little IRF1, in Jurkat T and Raji B cells. In the B cells MSH and SB there was, in addition, a strong presence of IRF4 and a weak presence of IRF8. IRF4 and IRF8 were also found in THP-1 cells, whereas in THP-1 cells induced with IFN-γ, there was an additional strong presence of IRF1. Arrowheads indicate the complex containing IRF factors; *, supershifted complex(es). (B) Transient transfection of the β₂m reporter construct with IRF1, IRF2, IRF3(5D), IRF4, IRF8, and PU.1 expression vectors (1 μg) in Tera-2 cells, as indicated. IRF1 or IRF3(5D) could barely transactivate the ISRE-mutated reporter construct in Tera-2 cells (3-fold by IRF1 and 2-fold by IRF3(5D); data not shown). The luciferase activity values were normalized with the Renilla luciferase activity values and are expressed as mean ± SD of 4 samples. The induction ratios are indicated above the histogram. RLU indicates relative light units.