Downregulation of transcription factor E4F1 in hepatocarcinoma cells: HBV-dependent effects on autophagy, proliferation and metabolism

Abstract

The multifunctional E4F1 protein is a cellular target of the E1A adenoviral oncoprotein. Interaction between E4F1 and the hepatitis B virus (HBV) protein HBx has been demonstrated in vitro. In this study, RNA interference has been used to downregulate E4F1 in the hepatocellular carcinoma (HCC) cell line HepG2 (HBV negative) and its derivative, HBV expressing HepG2/2.2.15. Reduction of E4F1 levels induced hepatocyte vacuolation (formation of large cytoplasmic vesicles), increased autophagy and caused mitochondrial defects and metabolism changes in HepG2/2.2.15, but not in HepG2. Moreover, downregulation of E4F1 reduced DNA synthesis with partial cell cycle arrest in G1 in both cell types and this effect was more marked in HepG2/2.2.15 than in HepG2. These effects were partially prevented by RNA interference directed to either HBx or to p53. Coprecipitation and western blot experiments detected complexes between E4F1 and HBx in several HCC cell lines. Although a review of mutation and gene expression public databases did not support that E4F1 is specifically altered in liver cancer, our results suggest that E4F1 may neutralize the capacity of HBx to activate a p53-dependent, metabolic and growth arrest phenotype in liver cells, thus possibly contributing to the viability and proliferation of HBV-infected cells.

Metabolic profiling of normal hepatocyte and hepatocellular carcinoma cells via 1H nuclear magnetic resonance spectroscopy

“…Cultured HCC cell lines are more pure than primary cancer cells which usually contain more than one cell type, and during isolation these cells are probably mixed with fibroblasts or other miscellaneous cells. The HepG2 cell line is frequently used in many researches as HCC cell line (Benarbia Mel et al, ; Kang et al, ; Dai et al, ). We wanted to investigate the metabolic profile differences between these two cell lines and then achieve preliminary results for further exploration.…”

MicroRNA-33-3p Regulates Vein Endothelial Cell Apoptosis in Selenium-Deficient Broilers by Targeting E4F1

“…Moreover, relative studies indicate that E4F1 deficiency results in increasing levels of intracellular ROS, leading to oxidative stress [33, 44, 45]. And E4F1 may contribute to the viability and proliferation of HBV-infected cells [46]. In addition, E4F1 also decreases expression of the cyclin A promoter and downregulates cell cycle progression.…”

HBx induced AFP receptor expressed to activate PI3K/AKT signal to promote expression of Src in liver cells and hepatoma cells

“…HBx emerged transcriptional activity on a variety of viral and cellular promoters [ 4 - 6 ]. HBx does not directly bind to genomic DNA of host cells, but has been shown to interact with components of basal transcription machinery [ 7 , 8 ] and several transcription factors, such as p53, HIF-1α and E4F1 [ 9 - 11 ]. However, documents evidenced that the localization of HBx predominantly in the cytoplasm, HBx harbors a function to activate signal transduction cascades, including phosphatidylinositol 3-kinase(PI3K)/protein kinase B(AKT) [ 12 , 13 ] and mitogen-activated protein kinase(MAPK) [ 14 ].…”