Division of Gastroenterology and Liver Diseases, University of Southern California Research Center for Liver Diseases, Keck School of Medicine USC, Los Angeles, CA 90033, USA.
Hepatology. 2010 Dec;52(6):2096-108. doi: 10.1002/hep.23919. Epub 2010 Oct 1.
Prohibitin 1 (PHB1) is a highly conserved, ubiquitously expressed protein that participates in diverse processes including mitochondrial chaperone, growth and apoptosis. The role of PHB1 in vivo is unclear and whether it is a tumor suppressor is controversial. Mice lacking methionine adenosyltransferase 1A (MAT1A) have reduced PHB1 expression, impaired mitochondrial function, and spontaneously develop hepatocellular carcinoma (HCC). To see if reduced PHB1 expression contributes to the Mat1a knockout (KO) phenotype, we generated liver-specific Phb1 KO mice. Expression was determined at the messenger RNA and protein levels. PHB1 expression in cells was varied by small interfering RNA or overexpression. At 3 weeks, KO mice exhibit biochemical and histologic liver injury. Immunohistochemistry revealed apoptosis, proliferation, oxidative stress, fibrosis, bile duct epithelial metaplasia, hepatocyte dysplasia, and increased staining for stem cell and preneoplastic markers. Mitochondria are swollen and many have no discernible cristae. Differential gene expression revealed that genes associated with proliferation, malignant transformation, and liver fibrosis are highly up-regulated. From 20 weeks on, KO mice have multiple liver nodules and from 35 to 46 weeks, 38% have multifocal HCC. PHB1 protein levels were higher in normal human hepatocytes compared to human HCC cell lines Huh-7 and HepG2. Knockdown of PHB1 in murine nontransformed AML12 cells (normal mouse hepatocyte cell line) raised cyclin D1 expression, increased E2F transcription factor binding to cyclin D1 promoter, and proliferation. The opposite occurred with PHB1 overexpression. Knockdown or overexpression of PHB1 in Huh-7 cells did not affect proliferation significantly or sensitize cells to sorafenib-induced apoptosis.
Hepatocyte-specific PHB1 deficiency results in marked liver injury, oxidative stress, and fibrosis with development of HCC by 8 months. These results support PHB1 as a tumor suppressor in hepatocytes.
阻抑蛋白 1（PHB1）是一种高度保守的、广泛表达的蛋白质，参与多种过程，包括线粒体伴侣、生长和凋亡。PHB1 在体内的作用尚不清楚，它是否是肿瘤抑制因子也存在争议。缺乏蛋氨酸腺苷转移酶 1A（MAT1A）的小鼠表达的 PHB1 减少，线粒体功能受损，并且自发性地发展为肝细胞癌（HCC）。为了观察 PHB1 表达减少是否导致 Mat1a 敲除（KO）表型，我们生成了肝脏特异性 Phb1 KO 小鼠。在信使 RNA 和蛋白质水平上确定表达。通过小干扰 RNA 或过表达来改变细胞中的 PHB1 表达。在 3 周时，KO 小鼠表现出生化和组织学肝损伤。免疫组织化学显示凋亡、增殖、氧化应激、纤维化、胆管上皮化生、肝细胞发育不良和干细胞和前肿瘤标志物的染色增加。线粒体肿胀，许多线粒体没有明显的嵴。差异基因表达显示与增殖、恶性转化和肝纤维化相关的基因高度上调。从 20 周开始，KO 小鼠有多个肝结节，从 35 周到 46 周，有 38%的小鼠有多发性 HCC。与人类 HCC 细胞系 Huh-7 和 HepG2 相比，PHB1 蛋白水平在正常人类肝细胞中更高。在鼠非转化 AML12 细胞（正常小鼠肝细胞系）中敲低 PHB1 会增加细胞周期蛋白 D1 的表达，增加 E2F 转录因子与细胞周期蛋白 D1 启动子的结合，并促进增殖。而 PHB1 过表达则相反。在 Huh-7 细胞中敲低或过表达 PHB1 对增殖没有显著影响，也不能使细胞对索拉非尼诱导的凋亡敏感。
肝细胞特异性 PHB1 缺乏导致明显的肝损伤、氧化应激和纤维化，并在 8 个月时发展为 HCC。这些结果支持 PHB1 作为肝细胞中的肿瘤抑制因子。
