Gs. Kuncio et al., TNF-ALPHA MODULATES EXPRESSION OF THE TISSUE TRANSGLUTAMINASE GENE INLIVER-CELLS, American journal of physiology: Gastrointestinal and liver physiology, 37(2), 1998, pp. 240-245
One of several postulated roles for tissue transglutaminase (tTG) is t
he stabilization and assembly of extracellular matrix via peptide cros
s-linking. We previously determined that tTG activity increased in an
animal model of hepatic fibrogenesis and in human liver disease. To fu
rther study the role of tTG in liver disease, we initiated investigati
ons into the effect of a proinflammatory mediator, tumor necrosis fact
or (TNF)-alpha, on tTG activity in cultured liver cells. Treat ment of
human Hep G2 cells with 1 ng/ml TNF-alpha increased [C-14]putrescine
cross-linking to cellular proteins. An increase in tTG mRNA content wa
s observed 1 h after addition of TNF-alpha, and levels of tTG mRNA rem
ained elevated after 24 h. Hep G2 cells, transiently transfected with
a luciferase reporter containing 1.67 kb of the human tTG promoter, sh
owed an increase in reporter activity after addition of TNF-alpha. Gel
shift experiments using nuclear extracts from TNF-alpha-treated cells
and oligonucleotides containing the tTG nuclear factor (NF)-kappa B m
otif revealed increased binding, concordant with mRNA data. Transient
transfections with a truncated reporter construct lacking the tTG NF-k
appa B sequence showed an attenuated response to TNF-alpha treatment.
Similar responses were seen in stably transfected HeLa cells. Primary
hepatocytes isolated from a trangenic mouse Line containing the mouse
tTG promoter driving the beta-galactosidase reporter, show similar tim
e-dependent increases in promoter activity when treated with TNF-alpha
. Furthermore, Hep G2 cells are incapable of upmodulating tTG promoter
reporter activity in the presence of TNF-alpha when those cells overe
xpress a transdominant, negative mutant NF-kappa B subunit. Because TN
F-alpha expression is upregulated in hepatic inflammation, the data su
ggest TNF-alpha-mediated increases in tTG expression may play an impor
tant role in the process of hepatic fibrogenesis.