Overexpression of Jab1 in hepatocellular carcinoma and its inhibition by peroxisome proliferator-activated receptor{gamma} ligands in vitro and in vivo.
OBJECTIVE
Jun activation domain-binding protein 1 (Jab1) is the fifth subunit of the COP9 signalosome and exhibits oncogenic activity. We investigated Jab1 expression in hepatocellular carcinoma (HCC) tissues and cell lines and tested the effect of peroxisome proliferator-activated receptor gamma (PPARgamma) ligands on Jab1 expression.


METHODS
Jab1 expression in HCC tissues and cell lines was studied by real-time reverse transcription-PCR, immunohistochemical staining, and Western blotting. Promoter activity and chromatin immunoprecipitation assays were done to address the inhibition of Jab1 promoter by PPARgamma ligands. RNA interference was used to clarify PPARgamma ligand-induced inhibition of Jab1. Anticancer and Jab1-suppressing activity of PPARgamma ligands was tested in nude mice.


RESULTS
Jab1 was detected in the nucleus and cytoplasm of HCC tissues and 37% (37 of 99) of tissues exhibited Jab1 overexpression. Jab1 expression correlated with sex and hepatitis C virus infection, whereas it was negatively associated with hepatitis B virus infection. Additionally, Jab1 was overexpressed in HCC cell lines. PPARgamma ligands troglitazone and rosiglitazone down-regulated Jab1 expression in HCC cells, and troglitazone directly suppressed Jab1 promoter activity by inhibiting Sp1- and Tcf4-mediated transcription. This suppression was mediated via both PPARgamma-dependent and PPARgamma-independent mechanisms. Ectopic expression of Jab1 counteracted troglitazone-induced growth inhibition. Animal studies verified that intratumor or i.p. injection of troglitazone attenuated HCC growth and reduced Jab1 expression in tumor tissues.


CONCLUSIONS
Our results indicate that Jab1 is overexpressed in HCC and PPARgamma ligands may suppress Jab1 to inhibit the proliferation of HCC cells.
Hsu
Ming-Chuan
MC
Graduate Institute of Medicine, College of Medicine, Kaohsiung Medical University, Taiwan, People's Republic of China.
Huang
Chao-Cheng
CC
Chang
Hui-Chiu
HC
Hu
Tsung-Hui
TH
Hung
Wen-Chun
WC
D000328:Adult; D000368:Aged; D000818:Animals; D000075686:COP9 Signalosome Complex; D006528:Carcinoma, Hepatocellular / Q000378:metabolism*; D005260:Female; D015971:Gene Expression Regulation, Enzymologic; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D066298:In Vitro Techniques; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D008024:Ligands; D008113:Liver Neoplasms / Q000378:metabolism*; D008297:Male; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D008875:Middle Aged; D009368:Neoplasm Transplantation; D047495:PPAR gamma / Q000378:metabolism*; D010447:Peptide Hydrolases / Q000378:metabolism*
D047908:Intracellular Signaling Peptides and Proteins; D008024:Ligands; D047495:PPAR gamma; D010447:Peptide Hydrolases; C501488:COPS5 protein, human; D000075686:COP9 Signalosome Complex