Pin1 interacts with a specific serine-proline motif of hepatitis B virus X-protein to enhance hepatocarcinogenesis.
OBJECTIVE
The peptidyl prolyl isomerase Pin1 frequently is overexpressed in hepatocellular carcinoma (HCC). Hepatitis B virus (HBV) is the most common etiologic agent in HCC, and its encoded X-protein (HBx) is oncogenic and possesses a serine-proline motif that may bind Pin1. The role of Pin1 in hepatocarcinogenesis, particularly in HBV-related HCC, was investigated.


METHODS
Immunohistochemical staining was performed to evaluate the prevalence of Pin1 overexpression in HCCs of different etiologies. Glutathione S-transferase pull-down and co-immunoprecipitation experiments were used to validate the physical interaction between Pin1 and HBx. Reporter assay, cell proliferation assay, and xenotransplantation experiments were used to show the functional consequence and importance of Pin1-HBx interaction in hepatocarcinogenesis.


RESULTS
We showed preferential Pin1 overexpression in HBV-related tumors and confirmed the interaction between Pin1 and HBx at the specific serine-proline motif. Pin1 overexpression increased the protein stability of HBx. Furthermore, HBx-mediated transactivation was enhanced by co-expression of Pin1. HepG2 expressing Pin1 and HBx showed a synergistic increase in cellular proliferation, as compared with cells expressing Pin1 or HBx alone. Furthermore, concomitant expression of Pin1 and HBx in the nontumorigenic human hepatocyte cell line MIHA led to a synergistic increase in tumor growth. Finally, in Hep3B cells with suppressed Pin1 expression, HBx-enhanced tumor growth in nude mice was abrogated.


CONCLUSIONS
Pin1 binds HBx to enhance hepatocarcinogenesis in HBV-infected hepatocytes. The discovery of an interaction between Pin1 and HBx will further our understanding of the molecular pathogenic mechanism of HBV-related HCC in human beings.
Pang
Roberta
R
Department of Medicine, The University of Hong Kong, Queen Mary Hospital, Hong Kong.
Lee
Terence K W
TK
Poon
Ronnie T P
RT
Fan
Sheung T
ST
Wong
Kam B
KB
Kwong
Yok-Lam
YL
Tse
Eric
E
D020816:Amino Acid Motifs; D000818:Animals; D006528:Carcinoma, Hepatocellular / Q000235:genetics / Q000378:metabolism* / Q000473:pathology / Q000821:virology; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002471:Cell Transformation, Neoplastic / Q000235:genetics / Q000378:metabolism*; D006509:Hepatitis B / Q000150:complications* / Q000235:genetics / Q000378:metabolism / Q000473:pathology / Q000821:virology; D006801:Humans; D008113:Liver Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology / Q000821:virology; D008114:Liver Neoplasms, Experimental / Q000378:metabolism / Q000473:pathology / Q000821:virology; D051379:Mice; D008819:Mice, Nude; D000072340:NIMA-Interacting Peptidylprolyl Isomerase; D019696:Peptidylprolyl Isomerase / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D011392:Proline; D011485:Protein Binding; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D015203:Reproducibility of Results; D012694:Serine; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D051996:Transcription Factor RelA / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014162:Transfection; D014183:Transplantation, Heterologous; D015854:Up-Regulation; D054334:Viral Regulatory and Accessory Proteins; D051020:bcl-X Protein / Q000235:genetics / Q000378:metabolism
D000072340:NIMA-Interacting Peptidylprolyl Isomerase; D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger; D015534:Trans-Activators; D051996:Transcription Factor RelA; D054334:Viral Regulatory and Accessory Proteins; D051020:bcl-X Protein; C057628:hepatitis B virus X protein; D012694:Serine; D011392:Proline; C000606846:PIN1 protein, human; D019696:Peptidylprolyl Isomerase; C000606850:Pin1 protein, mouse