| 摘要: | 肺部間質纖維化的特徵為慢性發炎、肌纖維母細胞的發生、和異常的組織修復。已經有文獻證明，在人類肺纖維化組織中會大量表達結締組織生長因子（connective tissue growth factor, CTGF）。過去的研究顯示，轉錄因子CCAAT/增強子結合蛋白β（CCAAT enhancer binding protein β, C/EBPβ）被認為是在調節肌纖維母細胞的關鍵因子，參與在急性期和炎症反應。最近研究證實，C/EBP β基因剔除會降低bleomycin誘導的肺間質纖維化。也有文獻證明，RSK (ribosomal S6 kinase) 誘導的C/EBPβ Thr217磷酸化可能導致的肺損傷和肝纖維化的發展。然而，C/EBPβ在肺間質纖維化中調控CTGF表達的作用仍然不清楚。目前已知，C/EBPβ的轉錄活性，可以透過調節基因的轉錄和轉錄後修飾 （post-translationaml modification, PTM），如磷酸化，乙醯化。例如:表皮生長因子 (EGF) 誘導COX-2基因啟動子的活化可以經由C/EBPβ的SUMO化及乙醯化的調控。然而，C/EBPβ轉錄後修飾的分子機制如何調控CTGF表現仍然不清楚。本篇論文將深入探討Akt、C/EBPβ、AP-1及STATS訊息傳遞在thrombin誘導人類纖維母細胞CTGF表現所扮演的角色。我們的結果顯示，C/EBPβ siRNA可以抑制thrombin誘導CTGF的表現。進一步發現，thrombin可以依時間相關性誘導C/EBPβ Thr235磷酸化及C/EBPβ-luciferase活性。Thrombin可以依時間相關性誘導磷酸化的C/EBPβ從細胞質轉位進入細胞核中，並促使C/EBPβ、AP-1與STAT3形成複合物。我們也觀察到，thrombin誘導Akt Ser473位置磷酸化，並且透過Akt DN可以抑制由thrombin誘導CTGF表現。綜合以上所有結果，我們發現在人類纖維母細胞中，thrombin經由活化Akt訊息傳導路徑，誘導C/EBPβ的活化且與下游轉錄因子AP-1和STAT3共同結合，啟動CTGF promoter並促使CTGF表現。
Pulmonary fibrosis is characterized by inflammation, genesis of myofibroblasts, and abnormal tissue repair. CTGF overexpression has been described in human fibrotic diseases. Previously, the transcription factor CCAAT/enhancer binding protein β (C/EBPβ) was found to be a key regulator of myofibroblast differentiation in vitro, and to be involved in the acute phase and inflammatory responses. Previous studies demonstrated that knockout of C/EBPβ were sufficiency attenuated bleomycin-induced pulmonary fibrosis in mice. Moreover, RSK-mediated C/EBPβ Thr 217 phosphorylation contribute to the development of lung injury and fibrosis. However, the role of C/EBPβ in regulating CTGF expression in pulmonary fibrosis remains unclear. Transcriptional activity of C/EBPβ can be regulated through gene transcription and post-translational modification (PTM), such as phosphorylation and acetylation. Previous reports showed that EGF-induced promoter activation of COX-2 gene is mediated by regulation of C/EBPβ SUMOylation and acetylation. Little is known, however, the molecular mechanism of C/EBPβ PTM codes in regulating CTGF expression. In this study, we investigated the roles of Akt, C/EBPβ, AP-1, and STAT3 in thrombin-indued CTGF expression in human lung fibroblasts. Thrombin-induced CTGF expression was inhibited by C/EBPβ siRNA. Thrombin caused a time-dependent increases in C/EBPβ Thr235 phosphorylation and C/EBPβ-luciferase activity. Furthermore, thrombin caused C/EBPβ translocation from the cytosol to the nucleus in time-dependent manner. Treatment of cells with thrombin induced C/EBPβ, AP-1, and STAT3 complex formation. Moreover, thrombin-induced increases in Akt Ser473 phosphorylation and CTGF expression was inhibited by cell transfection with AktDN. These results suggest that thrombin activates Akt signaling pathway, which in turn initiates C/EBPβ activation and recruitment of C/EBPβ interaction between AP-1 and STAT3 to CTGF promoter and ultimately indued CTGF expression in human lung fibroblasts. |
