Lethal-7 is down-regulated by the hepatitis B virus x protein and targets signal transducer and activator of transcription 3.
OBJECTIVE
The pleiotropic hepatitis B virus (HBV) x protein (HBx), associated with hepatocellular carcinoma (HCC), has been implicated in the deregulation of cellular gene expression at the transcriptional level. To date, it remains unknown if HBx regulates the expression of miRNAs which play important roles in gene-regulation at the post-transcriptional and/or translational level.


METHODS
miRNA microarrays were employed to compare the expression of cellular miRNAs in HBx-versus control-HepG2 cells. Reverse-transcription Taqman realtime-PCR was used to examine let-7a expression in normal liver as well as paired HCC-tumor and adjacent non-tumorous liver. Let-7a miRNA was functionally characterized in cells with transiently altered let-7a expression. The direct target of let-7a was identified in silico and validated using 3'UTR-reporter assay.


RESULTS
HBx up-regulates 7 and down-regulates 11 miRNAs, including the let-7 family. HBx expression was found to have a significant inverse correlation with the expression of the highly-expressed members of the let-7 family in HCC patients, highlighting the clinical relevance of our observations. Further characterization of let-7a, the most highly expressed let-7 family member, revealed that it negatively regulates cellular proliferation partly through targeting signal transducer and activator of transcription 3 (STAT3). HBx-mediated down-regulation of let-7a and up-regulation of STAT3 supports cell proliferation in HBx cells.


CONCLUSIONS
This study thus represents the first demonstration of HBx's ability to deregulate cellular miRNA expression. The deregulation of the expression of the let-7 family of miRNAs by HBx may represent a potential novel pathway through which HBx acts to deregulate cell proliferation leading to hepatocarcinogenesis.
Wang
Yu
Y
Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.
Lu
Yiwei
Y
Toh
Soo Ting
ST
Sung
Wing-Kin
WK
Tan
Patrick
P
Chow
Pierce
P
Chung
Alexander Y F
AY
Jooi
London L P
LL
Lee
Caroline G L
CG
D020413:3' Untranslated Regions; D017209:Apoptosis / Q000235:genetics / Q000502:physiology; D001483:Base Sequence; D006528:Carcinoma, Hepatocellular / Q000209:etiology / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D015536:Down-Regulation; D006515:Hepatitis B virus / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity; D006801:Humans; D008113:Liver Neoplasms / Q000209:etiology / Q000235:genetics / Q000378:metabolism; D035683:MicroRNAs / Q000235:genetics*; D034741:RNA, Small Interfering / Q000235:genetics; D050796:STAT3 Transcription Factor / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D054334:Viral Regulatory and Accessory Proteins
D020413:3' Untranslated Regions; D035683:MicroRNAs; D034741:RNA, Small Interfering; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D015534:Trans-Activators; D054334:Viral Regulatory and Accessory Proteins; C057628:hepatitis B virus X protein; C487931:mirnlet7 microRNA, human