Diehl A M, Yang S Q, Yin M, Lin H Z, Nelson S, Bagby G
Department of Medicine, Johns Hopkins University, Baltimore, MD 21205, USA.
Hepatology. 1995 Jul;22(1):252-61. doi: 10.1016/0270-9139(95)90379-8.
Injury-related cytokines, such as tumor necrosis factor-alpha (TNF), may preserve liver-specific gene expression during the subsequent regenerative response by modulating the activity of transcription factors, including CCAAT/enhancer binding proteins (C/EBPs), which regulate differentiated gene expression in hepatocytes. To test this theory, rats were treated with neutralizing antibody to TNF or nonimmune immunoglobulin before partial hepatectomy (PH) and regenerative changes in the messenger RNAs (mRNAs), proteins, and DNA-binding activities of C/EBP isoforms and the expression of a C/EBP-regulated gene, phosphoenol pyruvate carboxykinase (PEPCK), were compared. Before PH, the expressions of C/EBP-alpha, C/EBP-beta, and C/EBP-gamma were similar in the two treatment groups. Dimers containing C/EBP-alpha and C/EBP-beta accounted for virtually all of the C/EBP DNA binding activity and mRNA for PEPCK, the rate limiting hepatocyte enzyme for gluconeogenesis, was barely detected. After PH, in control rats, mRNA and nuclear protein concentrations of C/EBP-beta and C/EBP-gamma increased approximately fivefold by 3 hours after PH. This was accompanied by increased DNA binding activity of these C/EBP isoforms and decreased DNA binding activity of C/EBP-alpha. mRNA levels of PEPCK, a gene that is strongly transactivated by non-alpha C/EBP isoforms, increased fivefold. Pretreatment with anti-TNF antibodies prevented regenerative induction of C/EBP beta and gamma expression and DNA-binding activity. The nature of dimers binding to C/EBP cis-acting elements remained similar to that observed in liver before PH and increases in PEPCK mRNA were blunted. These results support the theory that TNF helps maintain liver-specific gene expression during liver regeneration by altering transcription factor complexes that regulate differentiated gene expression in hepatocytes.
与损伤相关的细胞因子，如肿瘤坏死因子-α（TNF），可能通过调节转录因子的活性来维持后续再生反应期间肝脏特异性基因的表达，这些转录因子包括CCAAT/增强子结合蛋白（C/EBP），其调节肝细胞中的分化基因表达。为了验证这一理论，在大鼠部分肝切除（PH）前用抗TNF中和抗体或非免疫免疫球蛋白进行处理，并比较C/EBP亚型的信使核糖核酸（mRNA）、蛋白质和DNA结合活性的再生变化以及C/EBP调节基因磷酸烯醇式丙酮酸羧激酶（PEPCK）的表达。在PH前，两个治疗组中C/EBP-α、C/EBP-β和C/EBP-γ的表达相似。几乎所有的C/EBP DNA结合活性都由含有C/EBP-α和C/EBP-β的二聚体构成，而PEPCK（糖异生的限速肝细胞酶）的mRNA几乎未被检测到。PH后，在对照大鼠中，C/EBP-β和C/EBP-γ的mRNA和核蛋白浓度在PH后3小时增加了约五倍。这伴随着这些C/EBP亚型的DNA结合活性增加以及C/EBP-α的DNA结合活性降低。PEPCK的mRNA水平增加了五倍，PEPCK是一个被非α C/EBP亚型强烈反式激活的基因。用抗TNF抗体预处理可阻止C/EBP β和γ表达及DNA结合活性的再生诱导。与C/EBP顺式作用元件结合的二聚体的性质仍与PH前肝脏中观察到的相似，并且PEPCK mRNA的增加受到抑制。这些结果支持了TNF通过改变调节肝细胞中分化基因表达的转录因子复合物来帮助维持肝脏再生期间肝脏特异性基因表达的理论。
