DOWN-REGULATION OF NF-KAPPA-B PROTEIN-LEVELS IN ACTIVATED HUMAN-LYMPHOCYTES BY 1,25-DIHYDROXYVITAMIN-D-3

The effect of 1,25-dihydroxyvitamin D-3 [1,25(OH)(2)D-3], a steroid ho rmone with immunomodulating properties, on nuclear factor kappa B (NF- kappa B) proteins was examined in in vitro activated normal human lymp hocytes by Western blot analysis. Over a 72-hr period of activation, t he expression of the 50-kDa NF-kappa B, p50, and its precursor, p105, was increased progressively. When cells were activated in the presence of 1,25(OH)(2)D-3, the levels of the mature protein as well as its pr ecursor were decreased. The effect of the hormone on the levels of p50 was demonstrable in the cytosolic and nuclear compartments; it requir ed between 4 and 8 hr and was specific, as 25-hydroxyvitamin D-3 and 2 4,25-dihydroxyvitamin D-3 were ineffective, Besides p50, 1,25(OH)(2)D- 3 decreased the levels of another NF-kappa B protein, namely c-rel. In addition, 1,25(OH)(2)D-3 decreased the abundance of a specific DNA-pr otein complex formed upon incubation of nuclear extracts from activate d lymphocytes with a labeled NF-kappa B DNA binding motif. Further, 1, 25(OH)(2)D-3 inhibited the transcriptional activity of NF-kappa B in J urkat cells transiently transfected with a construct containing four t andem repeats of the NF-kappa B binding sequence of the immunoglobulin kappa light chain gene linked to the chloramphenicol acetyltransferas e reporter gene, These observations demonstrate directly that there is de novo synthesis of NF-kappa B during human lymphocyte activation an d suggest that this process is hormonally regulated.