Jj. Li et al., Inhibition of AP-1 and NF-kappa B by manganese-containing superoxide dismutase in human breast cancer cells, FASEB J, 12(15), 1998, pp. 1713-1723
One of the primary antioxidant enzymes, manganese-containing superoxide dis
mutase (MnSOD), has shown the ability to reverse malignant phenotypes in a
variety of human tumor cells that are low or absent in MnSOD expression. We
have observed that overexpression of human MnSOD in human breast cancer MC
F-7 cells inhibits tumor growth both in vitro and in vivo. The signaling pa
thway underlying the MnSOD induced tumor suppression is unknown. We demonst
rate here that transcriptional and DNA binding ability of AP-1 and NF-kappa
B, but not SP-1, were inhibited (by 50%) in the MCF-7 cell line overexpres
sing MnSOD, When transiently expressing, MnSOD inhibited AP-I but increased
NF-kappa B transactivation, which can be abolished by sodium pyruvate, a h
ydrogen peroxide scavenger. To analyze the target genes responsible for MnS
OD-induced tumor suppression, genes related to tumor growth and responsive
to AP-1 or NF-kappa B were analyzed. AP-1 responsive collagenase I, stromel
ysin I, and NF-kappa B responsive IL-1 and IL-6 were down-regulated in the
MnSOD stable transfectants compared to the control cell lines. Since TPA in
duces differentiation in human breast cancer cells and up-regulates MnSOD g
ene in HeLa cells, MnSOD expression and AP-1 and NF-kappa B activity were m
easured under TPA treatment. The results showed that TPA induced endogenous
MnSOD expression and inhibited both AP-1 and NF-kappa B, Together, these r
esults suggest that tumor suppression by overexpressing MnSOD is related to
a modulation of AP-1 and NF-kappa B, which causes a downregulation of gene
s responsible for tumor malignant phenotype.