Tatsukawa Hideki, Fukaya Yayoi, Frampton Gordon, Martinez-Fuentes Antonio, Suzuki Kenji, Kuo Ting-Fang, Nagatsuma Keisuke, Shimokado Kentaro, Okuno Masataka, Wu Jian, Iismaa Siiri, Matsuura Tomokazu, Tsukamoto Hidekazu, Zern Mark A, Graham Robert M, Kojima Soichi
Molecular Ligand Biology Research Team, Chemical Genomics Research Group, Chemical Biology Department, RIKEN Advanced Science Institute, Wako, Saitama, Japan.
Gastroenterology. 2009 May;136(5):1783-95.e10. doi: 10.1053/j.gastro.2009.01.007. Epub 2009 Jan 14.
BACKGROUND & AIMS: 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.
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.
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.
TG2 induces hepatocyte apoptosis via Sp1 cross-linking and inactivation, with resultant inhibition of the expression of c-Met required for hepatic cell viability.
尽管全球范围内酒精性肝病的发病率和死亡率都很高，但酒精诱导肝细胞死亡的分子机制尚未完全明确。转谷氨酰胺酶2（TG2）是一种与细胞凋亡有关的交联酶。TG2的水平和活性会随着各种类型的肝损伤而升高。然而，TG2如何诱导肝脏细胞凋亡尚不清楚。
用乙醇处理人肝细胞、大鼠原代肝细胞或TG2+/+和TG2-/-小鼠。给小鼠注射抗Fas抗体或酒精。制备酒精性脂肪性肝炎患者的肝组织切片。检测TG2水平、Sp1交联及其活性、肝细胞生长因子受体c-Met的表达以及肝脏细胞凋亡的变化。
乙醇诱导肝细胞凋亡，增强TG2的活性和核内蓄积以及交联和失活的Sp1的蓄积，并降低Sp1反应性基因c-Met的表达。通过敲低TG2、恢复功能性Sp1或添加肝细胞生长因子可挽救这些效应，而敲低Sp1或过表达TG2则会重现细胞凋亡。与TG2+/+小鼠相比，TG2-/-小鼠在乙醇或抗Fas处理后肝细胞凋亡和Sp1交联明显减少。用TG2抑制剂腐胺或胱胺处理TG2+/+小鼠可阻断抗Fas诱导的肝脏细胞凋亡和Sp1沉默。此外，在酒精性脂肪性肝炎患者的肝细胞核中，交联的Sp1和TG2的表达明显增强。
TG2通过Sp1交联和失活诱导肝细胞凋亡，从而抑制肝细胞存活所需的c-Met的表达。
