Role of transglutaminase 2 in liver injury via cross-linking and silencing of transcription factor Sp1.
OBJECTIVE
Despite high morbidity and mortality of alcoholic liver disease worldwide, the molecular mechanisms underlying alcohol-induced liver cell death are not fully understood. Transglutaminase 2 (TG2) is a cross-linking enzyme implicated in apoptosis. TG2 levels and activity are increased in association with various types of liver injury. However, how TG2 induces hepatic apoptosis is not known.


METHODS
Human hepatic cells or primary hepatocytes from rats or TG2+/+ and TG2-/- mice were treated with ethanol. Mice were administered anti-Fas antibody or alcohol. Liver sections were prepared from patients with alcoholic steatohepatitis. Changes in TG2 levels, Sp1 cross-linking and its activities, expression of hepatocyte growth factor receptor, c-Met, and hepatic apoptosis were measured.


RESULTS
Ethanol induced apoptosis in hepatic cells, enhanced activity and nuclear accumulation of TG2 as well as accumulation of cross-linked and inactivated Sp1, and reduced expression of the Sp1-responsive gene, c-Met. These effects were rescued by TG2 knockdown, restoration of functional Sp1, or addition of hepatocyte growth factor, whereas apoptosis was reproduced by Sp1 knockdown or TG2 overexpression. Compared with TG2+/+ mice, TG2-/- mice showed markedly reduced hepatocyte apoptosis and Sp1 cross-linking following ethanol or anti-Fas treatment. Treatment of TG2+/+ mice with the TG2 inhibitors putrescine or cystamine blocked anti-Fas-induced hepatic apoptosis and Sp1 silencing. Moreover, enhanced expression of cross-linked Sp1 and TG2 was evident in hepatocyte nuclei of patients with alcoholic steatohepatitis.


CONCLUSIONS
TG2 induces hepatocyte apoptosis via Sp1 cross-linking and inactivation, with resultant inhibition of the expression of c-Met required for hepatic cell viability.
Tatsukawa
Hideki
H
Molecular Ligand Biology Research Team, Chemical Genomics Research Group, Chemical Biology Department, RIKEN Advanced Science Institute, Wako, Saitama, Japan.
Fukaya
Yayoi
Y
Frampton
Gordon
G
Martinez-Fuentes
Antonio
A
Suzuki
Kenji
K
Kuo
Ting-Fang
TF
Nagatsuma
Keisuke
K
Shimokado
Kentaro
K
Okuno
Masataka
M
Wu
Jian
J
Iismaa
Siiri
S
Matsuura
Tomokazu
T
Tsukamoto
Hidekazu
H
Zern
Mark A
MA
Graham
Robert M
RM
Kojima
Soichi
S
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D002478:Cells, Cultured; D000431:Ethanol / Q000494:pharmacology*; D005235:Fatty Liver, Alcoholic / Q000378:metabolism* / Q000473:pathology; D019204:GTP-Binding Proteins / Q000378:metabolism*; D020868:Gene Silencing; D006168:Guinea Pigs; D022781:Hepatocytes / Q000378:metabolism; D006801:Humans; D051379:Mice; D008815:Mice, Inbred Strains; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D019859:Proto-Oncogene Proteins c-met / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D016329:Sp1 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation; D014162:Transfection; D011503:Transglutaminases / Q000378:metabolism*
D016329:Sp1 Transcription Factor; C000717609:Tgm2 protein, rat; D000431:Ethanol; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011503:Transglutaminases; D019859:Proto-Oncogene Proteins c-met; D019204:GTP-Binding Proteins