Leptin as a critical regulator of hepatocellular carcinoma development through modulation of human telomerase reverse transcriptase.
BACKGROUND
Numerous epidemiological studies have documented that obesity is associated with hepatocellular carcinoma (HCC). The aim of this study was to investigate the biological actions regulated by leptin, the obesity biomarker molecule, and its receptors in HCC and the correlation between leptin and human telomerase reverse transcriptase (hTERT), a known mediator of cellular immortalization.


METHODS
We investigated the relationship between leptin, leptin receptors and hTERT mRNA expression in HCC and healthy liver tissue samples. In HepG2 cells, chromatin immunoprecipitation assay was used to study signal transducer and activator of transcription-3 (STAT3) and myc/mad/max transcription factors downstream of leptin which could be responsible for hTERT regulation. Flow cytometry was used for evaluation of cell cycle modifications and MMP1, 9 and 13 expression after treatment of HepG2 cells with leptin. Blocking of leptin's expression was achieved using siRNA against leptin and transfection with liposomes.


RESULTS
We showed, for the first time, that leptin's expression is highly correlated with hTERT expression levels in HCC liver tissues. We also demonstrated in HepG2 cells that leptin-induced up-regulation of hTERT and TA was mediated through binding of STAT3 and Myc/Max/Mad network proteins on hTERT promoter. We also found that leptin could affect hepatocellular carcinoma progression and invasion through its interaction with cytokines and matrix mettaloproteinases (MMPs) in the tumorigenic microenvironment. Furthermore, we showed that histone modification contributes to leptin's gene regulation in HCC.


CONCLUSIONS
We propose that leptin is a key regulator of the malignant properties of hepatocellular carcinoma cells through modulation of hTERT, a critical player of oncogenesis.
Stefanou
Nikolaos
N
University of Thessaly, Medical School, Department of Biology, Larissa, Greece.
Papanikolaou
Vassilis
V
Furukawa
Yoichi
Y
Nakamura
Yusuke
Y
Tsezou
Aspasia
A
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D006528:Carcinoma, Hepatocellular / Q000188:drug therapy / Q000201:enzymology / Q000473:pathology*; D002453:Cell Cycle; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D047369:Chromatin Immunoprecipitation; D005260:Female; D005434:Flow Cytometry; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007124:Immunoenzyme Techniques; D020738:Leptin / Q000494:pharmacology*; D008099:Liver / Q000378:metabolism / Q000473:pathology*; D008113:Liver Neoplasms / Q000188:drug therapy / Q000201:enzymology / Q000473:pathology*; D008297:Male; D008875:Middle Aged; D011401:Promoter Regions, Genetic / Q000235:genetics; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering / Q000494:pharmacology; D054411:Receptors, Leptin / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050796:STAT3 Transcription Factor / Q000235:genetics / Q000378:metabolism; D019098:Telomerase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D015854:Up-Regulation
D020738:Leptin; D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D054411:Receptors, Leptin; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; C509186:TERT protein, human; D019098:Telomerase