MEK/ERK-dependent B7-H1 expression in MM cells. (A) Western blot analysis of ERK1/2 and STAT1 phosphorylation in RPMI 8226 MM cells after incubation at indicated times with 500 IU/mL IFN-γ or 1 ng/mL PMA, both with or without 1-hour preincubation with 20 μM UO126. (B) Same as (A) but in a representative MM CD138-selected sample. (C) Flow cytometric analysis of B7-H1 expression in RPMI 8226 cells exposed for 24 hours to 1 ng/mL PMA with or without 1-hour preincubation with 20 μM UO126. (D) Flow cytometric analysis of B7-H1 expression in RPMI 8226 cells or 5 MM CD138-selected cell samples incubated for 24 hours with 500 IU/mL IFN-γ (set at 100%) and transfected with MEK1 or control nonspecific siRNA (NS siRNA).