Hepatitis C virus NS5A drives a PTEN-PI3K/Akt feedback loop to support cell survival.
OBJECTIVE
Decreased levels of phosphatase and tensin homologue (PTEN) are associated with hepatocellular carcinoma (HCC) pathogenesis and poor prognosis in hepatitis C virus (HCV)-infected HCC patients. The molecular processes governing the reduction in PTEN and outcome of PTEN dysfunction in hepatocytes are poorly understood.


METHODS
The levels of proteins and mRNA were assessed by real time PCR and immunoblot. PTEN promoter activity was measured by reporter assay. Signalling pathways were perturbed using siRNAs or pharmacological inhibitors.


RESULTS
Here, we report that HCV down-regulates PTEN expression at the transcriptional level by decreasing its promoter activity, mRNA transcription, and protein levels. We further identify NS5A protein as a key determinant of PTEN reduction among HCV proteins. NS5A-mediated down-regulation of PTEN occurs through a cooperation of reactive oxygen species (ROS)-dependent Nuclear Factor- kappa B (NF-κB) and ROS-independent phosphoinositol-3-kinase (PI3K) pathways. Moreover, NS5A protects cells against apoptosis. In addition, we found that down-regulation of PTEN relieves its inhibitory effect on PI3K-Akt pathway and triggers cumulative activation of Akt. This PTEN-PI3K/Akt feedback network mediates the suppression of cell apoptosis caused by NS5A.


CONCLUSIONS
These data demonstrate that HCV NS5A down-regulates PTEN expression through a cooperation of ROS-dependent and -independent pathways that subsequently drives a PTEN-PI3K/Akt feedback loop to support cell survival. Our findings provide new insights suggesting that NS5A contributes to HCV-related hepatocarcinogenesis.
Department of Gastroenterology, Renmin Hospital, Wuhan University, Wuhan, China.|Liver Center, Gastrointestinal Division, Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA.|Liver Diseases Center, Department of Infectious Diseases, The Second Xiangya Hospital, Central South University, Changsha, China.
Du
D
Cheng
Liver Center, Gastrointestinal Division, Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA.|MOH Key Laboratory of Systems Biology of Pathogens, Institute of Pathogen Biology, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing, China.
Leiliang
L
Zhang
MOH Key Laboratory of Systems Biology of Pathogens, Institute of Pathogen Biology, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing, China.
Guangbo
G
Yang
Liver Center, Gastrointestinal Division, Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA.
Lei
L
Zhao
Liver Diseases Center, Department of Infectious Diseases, The Second Xiangya Hospital, Central South University, Changsha, China.
Feng
F
Peng
Liver Diseases Center, Department of Infectious Diseases, The Second Xiangya Hospital, Central South University, Changsha, China.
Yi
Y
Tian
Liver Diseases Center, Department of Infectious Diseases, The Second Xiangya Hospital, Central South University, Changsha, China.
Xinqiang
X
Xiao
Liver Center, Gastrointestinal Division, Department of Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA.
Raymond T
RT
Chung
Liver Diseases Center, Department of Infectious Diseases, The Second Xiangya Hospital, Central South University, Changsha, China.
Guozhong
G
Gong
D017209:Apoptosis; D045744:Cell Line, Tumor; D002470:Cell Survival; D015536:Down-Regulation; D016174:Hepacivirus; D022781:Hepatocytes / Q000166:cytology; D006801:Humans; D016328:NF-kappa B / Q000378:metabolism*; D051059:PTEN Phosphohydrolase / Q000235:genetics / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D015398:Signal Transduction; D014158:Transcription, Genetic; D017361:Viral Nonstructural Proteins / Q000235:genetics / Q000378:metabolism*; D012324:RNA-Dependent RNA Polymerase
D016328:NF-kappa B; D051059:PTEN Phosphohydrolase; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D012333:RNA, Messenger; D017361:Viral Nonstructural Proteins; C087036:NS-5 protein, hepatitis C virus; D012324:RNA-Dependent RNA Polymerase; C494929:PTEN protein, human
HCV; NF-κB; NS5A; PTEN; ROS