Identification of a natural mutant of HBV X protein truncated 27 amino acids at the COOH terminal and its effect on liver cell proliferation.
OBJECTIVE
To identify mutants of the hepatitis B virus (HBV) X (HBx) gene and investigate the effect of the natural mutant on liver cell proliferation.


METHODS
We identified natural mutants of the HBx gene from 188 sera and 48 tissues of Chinese patients infected with HBV by PCR, respectively. Based on the identification of the mutants of HBx gene, we cloned the fragments of the mutants into the pcDNA3 vector. The biological activities of the mutants were investigated.


RESULTS
We identified a natural mutant of the HBx gene with deletion from 382 to 401 base pairs from 3 sera out of 188 patients, which resulted in the expression deletion of the HBx protein from the 128th amino acid at the COOH terminal. The similar mutant with deletion from 382 base pair at the COOH terminal was identified from 5 cases of genomes out of 48 hepatocellular carcinoma tissues. Regarding the biological activities of the mutant, we found that the mutant of the HBx protein failed to induce apoptosis by transient transfection, but promoted proliferation of human liver immortalized L-O2 cells by stable transfection, compared with the wild-type HBx protein. The data showed that the proliferation of the mutant stably-transfected L-O2-X-Sera cells and fragment stably-transfected L-O2-XDelta127 cells was enhanced by the BrdU incorporation assay and flow cytometry analysis. Luciferase reporter gene assay showed that the transcriptional activities of NF-kappaB, survivin, and human telomerase reverse transcriptase were upregulated, and Western blot analysis revealed that the expression levels of c-Myc and proliferating cell nuclear antigen (PCNA) were upregulated in the cells.


CONCLUSIONS
Our findings suggest that the natural HBx mutant truncated 27 amino acids at the COOH terminal promotes cell proliferation.
Zhang
Hang
H
Department of Cancer Research, Tianjin Key Laboratory of Microbial Function Genomics, Institute for Molecular Biology, Nankai University, Tianjin 300071, China.
Shan
Chang-liang
CL
Li
Nan
N
Zhang
Xuan
X
Zhang
Xue-zhi
XZ
Xu
Fu-qing
FQ
Zhang
Shuai
S
Qiu
Li-yan
LY
Ye
Li-Hong
LH
Zhang
Xiao-dong
XD
D000595:Amino Acid Sequence / Q000235:genetics; D000998:Antiviral Agents / Q000378:metabolism; D001973:Bromodeoxyuridine / Q000378:metabolism; D006528:Carcinoma, Hepatocellular / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D002461:Cell Line, Transformed; D049109:Cell Proliferation; D004396:Coloring Agents / Q000378:metabolism; D004279:DNA, Viral / Q000235:genetics / Q000302:isolation & purification; D017930:Genes, Reporter; D006515:Hepatitis B virus / Q000235:genetics*; D006801:Humans; D008113:Liver Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D008156:Luciferases / Q000378:metabolism; D008969:Molecular Sequence Data; D010957:Plasmids; D011419:Propidium / Q000378:metabolism; D017384:Sequence Deletion / Q000235:genetics*; D015534:Trans-Activators / Q000235:genetics*; D014162:Transfection; D054334:Viral Regulatory and Accessory Proteins / Q000235:genetics*
D000998:Antiviral Agents; D004396:Coloring Agents; D004279:DNA, Viral; D015534:Trans-Activators; D054334:Viral Regulatory and Accessory Proteins; C057628:hepatitis B virus X protein; D011419:Propidium; D008156:Luciferases; D001973:Bromodeoxyuridine