Involvement of c-Myc in CD154 expression.

(A) Western blot of c-Myc expression in PBL or Jurkat T cells 18 hours after addition of the indicated amount (ng/mL) of FR901228. PBLs were stimulated (stim) with or without 3 × 28 beads as indicated. (B) PBLs were incubated with the indicated phosphothioate oligo probes, 10 μM, for 6 hours prior to stimulation with or without 3 × 28 beads as indicated. CD154 expression was measured after 18 hours by flow cytometry on gated CD4 T cells. (C) Jurkat cells were transiently transfected, in a 1:3 ratio, with CD154 promotor–GFP construct in combination with empty vector, c-Myc vector, or Madmyc vector as indicated. Cells were then stimulated with (black bars) or without (white bars) anti-CD3 Ab for 24 hours. Figure shows CD154 promotor activity as MFI of gated GFP-expressing cells multiplied by the percentage of GFP-positive cells in order to take into account both the level and percentage of GFP expression.