LIPOPOLYSACCHARIDE INDUCES PHOSPHORYLATION OF MAD3 AND ACTIVATION OF C-REL AND RELATED NF-KAPPA-B PROTEINS IN HUMAN MONOCYTIC THP-1 CELLS

Many effects of lipopolysaccharide (LPS) on gene expression, including that of human immunodeficiency virus (HIV), in monocytic cells are me diated by activation of kappaB DNA-binding proteins. However, the spec ific members of the NF-kappaB/Rel transcription factor family involved in the LPS response, and the mechanisms through which LPS-generated s ignals are transduced remain unclear. Here we show that LPS induces nu clear expression of c-Rel/p50 heterodimers as well as p50/p65 (NF-kapp aB) kappaB DNA-binding complexes in human monocytic THP-1 cells. Nucle ar localization of these proteins occurred concomitantly with a rapid decrease in their cytosolic levels and was independent of phorbol este r-sensitive protein kinase C. Within 24 h following LPS stimulation th ere was a striking increase in the levels of c-Rel, p105, and p50 in t he cytosol. The increased levels of these proteins correlated with inc reases in the amounts of their mRNAs during LPS activation of THP-1 ce lls. LPS activation of THP-1 cells resulted in phosphorylation of MAD3 (an IkappaB-like protein), a rapid increase in MAD3 mRNA, and an incr ease in MAD3 protein by 2 h. Thus, LPS activation of human monocytic c ells results in nuclear expression of c-Rel/p50 and p50/p65 (NF-kappaB ) and induces phosphorylation of MAD3.