An E2F5-TFDP1-BRG1 Complex Mediates Transcriptional Activation of MYCN in Hepatocytes.

Zhiwen Fan,Longcheng Shang,Xiaolei Shi,Wei Zhu,Haozhen Ren,Hanyi Liu,Shuai Wang,Jinglin Wang,Ning Tang,Zhengyi Zhu,Xiulian Miao,Yan Guo,Ming Kong

doi:10.3389/fcell.2021.742319

Abstract

Liver regeneration is characterized by cell cycle reentrance of hepatocytes. N-Myc, encoded by MYCN, is a member of the Myc family of transcription factors. Elevation of MYCN expression has been noted in the course of liver regeneration whereas the underlying mechanism remains unclear. Here we describe that up-regulation of MYCN expression, as measured by quantitative PCR, Western blotting, and immunohistochemical staining, paralleled liver regeneration in animal and cell models. MYCN expression was up-regulated as a result of transcriptional activation. Ingenuity pathway analysis (IPA) revealed several up-stream transcriptional regulators for MYCN and RNA interference validated E2F5 and TFDP1 as essential for hepatocyte growth factor (HGF)-induced MYCN trans-activation. Further examination showed that deficiency of BRG1, a chromatin remodeling protein, attenuated MYCN induction during liver regeneration. BRG1 interacted with and was recruited by E2F5/TFDP1 to the MYCN promoter. Mechanistically, BRG1 might play a role regulating histone H3 acetylation and H3K4 trimethylation and facilitating/stabilizing the binding of RNA polymerase II surrounding the MYCN promoter. Over-expression of ectopic MYCN in BRG1-null hepatocytes overcame deficiency of proliferation. Importantly, a positive correlation between MYCN expression and BRG1/E2F5/TFDP1 expression was observed in human liver specimens. In conclusion, our data identify a novel epigenetic pathway where an E2F5-TFDP1-BRG1 complex regulates MYCN transcription to promote liver regeneration.

Highlights

Exposed to various injuries stimuli including surgical resection, pathogens, corrosive chemicals, toxins, and ischemia/anoxia, hepatocytes undergo necrosis or apoptosis leading to the loss of liver parenchyma and liver function
We examined the fluctuation of MYCN expression in the course of liver regeneration in two different animal models
Quantitative PCR showed that MYCN mRNA levels started to increase 12 h following APAP injection, peaked at 24 h, and declined at 48 h (Figure 1A); the pattern of MYCN expression tracked closely with hepatocyte proliferation as indicated by proliferating cell nuclear antigen (PCNA) expression

Summary

Introduction

Exposed to various injuries stimuli including surgical resection, pathogens, corrosive chemicals, toxins, and ischemia/anoxia, hepatocytes undergo necrosis or apoptosis leading to the loss of liver parenchyma and liver function. A regenerative response may ensue in which quiescent hepatocytes re-enter the cell cycle and resume proliferation to compensate for the loss of Transcriptional Regulation of MYCN liver mass and function (Fausto et al, 2006). Vigorous liver regeneration contributes to the normalization of liver function after injury and predicts better outcome in ESLD patients (Forbes and Newsome, 2016). During the process of liver regeneration, a complex hierarchy of regulatory factors, including growth factors, signaling molecules, and transcription factors, cooperate to enable quiescent hepatocytes to progress through different checkpoints of cell cycle, to re-acquire the ability to undergo mitosis and to replicate (Kurinna and Barton, 2010, 2011). E2F deletion impairs the spatiotemporal control of liver regeneration in mice whereas deficiency in E2F activity has been found to be responsible for aging-induced weakening of liver regenerative capacity (Trimarchi and Lees, 2002; Delgado et al, 2011)

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Conclusion