S. Kastenbauer et Hwl. Ziegler-heitbrock, NF-kappa B1 (p50) is upregulated in lipopolysaccharide tolerance and can block tumor necrosis factor gene expression, INFEC IMMUN, 67(4), 1999, pp. 1553-1559
Monocytes respond to lipopolysaccharide (LPS) stimulation with a rapid expr
ession of the tumor necrosis factor (TNF) gene. Upon repeated LPS stimulati
on there is, however, little production of TNF mRNA and protein; i.e., the
cells are tolerant to LPS, Analysis of NF-kappa B proteins in gel shift ass
ays demonstrated that the DNA binding activity that is induced by LPS stimu
lation in tolerant cells consists mainly of p50-p50 homodimers, Since p50 c
an bind to DNA but lacks a transactivation domain, this may explain the blo
ckade of TNF gene expression. We now show that in the monocytic cell line M
ono Mac 6, this inability to respond can be largely ascribed to NF-kappa B,
since a reporter construct directed by a trimeric NF-kappa B motif is stro
ngly transactivated by LPS stimulation of naive cells whereas LPS-tolerant
cells exhibit only low activity. Also, Western blot analyses of proteins ex
tracted from purified nuclei showed mobilization of threefold-higher levels
of p50 protein in tolerant compared to naive cells, while mobilization of
p65 was unaltered. Overexpression of p50 in HEK 293 cells resulted in a str
ong reduction of p65-driven TNF promoter activity at the levels of both luc
iferase mRNA and protein. These data support the concept that an upregulati
on of p50 is instrumental in LPS tolerance in human monocytes.