Hepatitis B spliced protein (HBSP) promotes the carcinogenic effects of benzo [alpha] pyrene by interacting with microsomal epoxide hydrolase and enhancing its hydrolysis activity.
BACKGROUND
The risk of hepatocellular carcinoma (HCC) increases in chronic hepatitis B surface antigen (HBsAg) carriers who often have concomitant increase in the levels of benzo[alpha]pyrene-7,8-diol-9,10-epoxide(±) (BPDE)-DNA adduct in liver tissues, suggesting a possible co-carcinogenesis of Hepatitis B virus (HBV) and benzo[alpha]pyrene in HCC; however the exact mechanisms involved are unclear.


METHODS
The interaction between hepatitis B spliced protein (HBSP) and microsomal epoxide hydrolase (mEH) was confirmed using GST pull-down, co-immunoprecipitation and mammalian two-hybrid assay; the effects of HBSP on mEH-mediated B[alpha]P metabolism was examined by high performance liquid chromatography (HPLC); and the influences of HBSP on B[alpha]P carcinogenicity were evaluated by bromodeoxyuridine cell proliferation, anchorage-independent growth and tumor xenograft.


RESULTS
HBSP could interact with mEH in vitro and in vivo, and this interaction was mediated by the N terminal 47 amino acid residues of HBSP. HBSP could greatly enhance the hydrolysis activity of mEH in cell-free mouse liver microsomes, thus accelerating the metabolism of benzo[alpha]pyrene to produce more ultimate carcinnogen, BPDE, and this effect of HBSP requires the intact HBSP molecule. Expression of HBSP significantly increased the formation of BPDE-DNA adduct in benzo[alpha]pyrene-treated Huh-7 hepatoma cells, and this enhancement was blocked by knockdown of mEH. HBSP could enhance the cell proliferation, accelerate the G1/S transition, and promote cell transformation and tumorigenesis of B[alpha]P-treated Huh-7 hepatoma cells.


CONCLUSIONS
Our results demonstrated that HBSP could promote carcinogenic effects of B[alpha]P by interacting with mEH and enhancing its hydrolysis activity.
Jin-Yan
JY
Chen
Wan-Nan
WN
Chen
Bo-Yan
BY
Jiao
Wan-Song
WS
Lin
Yun-Li
YL
Wu
Ling-Ling
LL
Liu
Key Laboratory of Ministry of Education for Gastrointestinal Cancer, Research Center of Molecular Medicine, Fujian Medical University, Fuzhou, Fujian 350004, P,R, China. linxu@mail.fjmu.edu.cn.
Xu
X
Lin
D000818:Animals; D001580:Benzopyrenes / Q000633:toxicity; D063646:Carcinogenesis; D006528:Carcinoma, Hepatocellular / Q000235:genetics* / Q000473:pathology; D045744:Cell Line, Tumor; D018736:DNA Adducts / Q000378:metabolism; D004851:Epoxide Hydrolases / Q000235:genetics / Q000378:metabolism*; D015967:Gene Expression Regulation, Viral; D006515:Hepatitis B virus / Q000235:genetics / Q000472:pathogenicity; D006801:Humans; D006868:Hydrolysis / Q000187:drug effects; D008113:Liver Neoplasms / Q000235:genetics* / Q000473:pathology; D051379:Mice; D008861:Microsomes / Q000187:drug effects / Q000201:enzymology; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism*
D001580:Benzopyrenes; D018736:DNA Adducts; C478361:HBSP protein, Hepatitis B virus; D014764:Viral Proteins; D004851:Epoxide Hydrolases; C543485:EPHX1 protein, mouse