Inhibition of nuclear factor-kappa B activation confers sensitivity to tumor necrosis factor-alpha by impairment of cell cycle progression in human glioma cells
G. Otsuka et al., Inhibition of nuclear factor-kappa B activation confers sensitivity to tumor necrosis factor-alpha by impairment of cell cycle progression in human glioma cells, CANCER RES, 59(17), 1999, pp. 4446-4452
Tumor necrosis factor (TNF)-alpha has been shown to exert cytotoxic or cyto
static effects on tumor cells, but susceptibility to TNF-alpha varies among
different types of cells. TNF-alpha activates a transcription factor, nucl
ear factor-kappa B (NF-kappa B), which induces a wide variety of genes and
causes pleiotrophic responses. In this study, the relationship between susc
eptibility to TNF-alpha and activation of NF-kappa B was investigated in si
x human malignant glioma cell lines. Cell proliferation analysis revealed t
hat only one cell line, SK-MG-1, was sensitive to TNF-alpha and that the ot
her five, including U-251MG, were resistant. Electrophoretic mobility-shift
assay showed that TNF-alpha strongly activated a subtype of NF-kappa B, th
e p50-p65 heterodimer, in all of the resistant cell lines tested. However,
this activation was weak in the sensitive cell line, SK-MG-1. Activation of
NF-kappa B by TNF-alpha in the resistant cell lines resulted in a signific
ant increase of a reporter gene expression driven by NF-kappa B site, sugge
sting a possibility that activation of p50-p65 confers resistance to TNF-al
pha. To test this hypothesis, we established a stable cell line that expres
ses an inducible dominant negative NF-kappa B (p65 DN) protein in one of th
e TNF-alpha-resistant cell lines, U-251MG. In the established clone, induct
ion of p65 DN protein decreased TNF-alpha-dependent increase in the DNA bin
ding of p50-p65 heterodimer and NF-kappa B-dependent reporter gene activity
. Although no growth inhibition of this clone was observed by TNF-alpha tre
atment, induction of p65 DN together with TNF-alpha resulted in a significa
nt decrease in cell number. Cell cycle analysis revealed that this growth i
nhibition was due to the impairment of cell cycle progression. These result
s indicate that an active NF-kappa B complex, such as the p50-p65 heterodim
er, plays a crucial role in the progression of cell cycle in malignant glio
ma cells. Refractoriness to TNF-alpha treatment could be prevented by inhib
iting NF-kappa B activation.