title: Functional characterization of glycine N-methyltransferase and its interactive protein DEPDC6/DEPTOR in hepatocellular carcinoma.
abstract: Glycine N-methyltransferase (GNMT) is a tumor suppressor for hepatocellular carcinoma (HCC). High rates of Gnmt knockout mice developed HCC. Epigenetic alteration and dysregulation of several pathways including wingless-type MMTV integration site (Wnt), mitogen-activated protein kinase (MAPK) and Janus kinase and signal transducer and activator of transcription (JAK-STAT) are associated with HCC development in Gnmt knockout mice. We hypothesized that GNMT may regulate signal transduction through interacting with other proteins directly. In this report, we identified a mammalian target of rapamycin (mTOR) inhibitor (DEP domain containing MTOR-interacting protein [DEPDC6/DEPTOR]) as a GNMT-binding protein by using yeast two-hybrid screening. Fluorescence resonance energy transfer assay demonstrated that the C-terminal half of GNMT interact with the PSD-95/Dlg1/ZO-1 (PDZ) domain of DEPDC6/DEPTOR. Immunohistochemical staining showed that 27.5% (14/51) of HCC patients had higher expression levels of DEPDC6/DEPTOR in the tumorous tissues than in tumor-adjacent tissues, especially among HCC patients with hepatitis B viral infection (odds ratio 10.3, 95% confidence interval [CI] 1.05-11.3) or patients with poor prognosis (death hazard ratio 4.51, 95% CI 1.60-12.7). In terms of molecular mechanism, knockdown of DEPDC6/DEPTOR expression in HuH-7 cells caused S6K and 4E-BP activation, but suppressed Akt. Overexpression of DEPDC6/DEPTOR activated Akt and increased survival of HCC cells. Overexpression of GNMT caused activation of mTOR/raptor downstream signaling and delayed G2/M cell cycle progression, which altogether resulted in cellular senescence. Furthermore, GNMT reduced proliferation of HuH-7 cells and sensitized them to rapamycin treatment both in vitro and in vivo. In conclusion, GNMT regulates HCC growth in part through interacting with DEPDC6/DEPTOR and modulating mTOR/raptor signaling pathway. Both GNMT and DEPDC6/DEPTOR are potential targets for developing therapeutics for HCC.
authors.affiliation: AIDS Prevention and Research Center, National Yang-Ming University, Shih-Pai, Taipei, Taiwan.
authors.forename: Chia-Hung
authors.initials: CH
authors.lastname: Yen
authors.forename: Yao-Cheng
authors.initials: YC
authors.lastname: Lu
authors.forename: Chung-Hsien
authors.initials: CH
authors.lastname: Li
authors.forename: Cheng-Ming
authors.initials: CM
authors.lastname: Lee
authors.forename: Chia-Yen
authors.initials: CY
authors.lastname: Chen
authors.forename: Ming-Yuan
authors.initials: MY
authors.lastname: Cheng
authors.forename: Shiu-Feng
authors.initials: SF
authors.lastname: Huang
authors.forename: Kuen-Feng
authors.initials: KF
authors.lastname: Chen
authors.forename: Ann-Lii
authors.initials: AL
authors.lastname: Cheng
authors.forename: Li-Ying
authors.initials: LY
authors.lastname: Liao
authors.forename: Yan-Hwa Wu
authors.initials: YH
authors.lastname: Lee
authors.forename: Yi-Ming Arthur
authors.initials: YM
authors.lastname: Chen
mesh_terms: D000328:Adult; D000368:Aged; D000818:Animals; D006528:Carcinoma, Hepatocellular / Q000188:drug therapy / Q000378:metabolism* / Q000473:pathology; D045744:Cell Line, Tumor; D000068338:Everolimus; D005260:Female; D050938:Glycine N-Methyltransferase / Q000378:metabolism*; D057809:HEK293 Cells; D006509:Hepatitis B / Q000150:complications / Q000378:metabolism; D006526:Hepatitis C / Q000150:complications / Q000378:metabolism; D006801:Humans; D007166:Immunosuppressive Agents / Q000627:therapeutic use; D047908:Intracellular Signaling Peptides and Proteins; D008113:Liver Neoplasms / Q000378:metabolism*; D008297:Male; D051379:Mice; D016513:Mice, SCID; D008875:Middle Aged; D020123:Sirolimus / Q000031:analogs & derivatives / Q000627:therapeutic use; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*; D020798:Two-Hybrid System Techniques; D023041:Xenograft Model Antitumor Assays
chemical_list: D007166:Immunosuppressive Agents; D047908:Intracellular Signaling Peptides and Proteins; D000068338:Everolimus; C494510:GNMT protein, human; D050938:Glycine N-Methyltransferase; C556139:DEPTOR protein, human; C546842:MTOR protein, human; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus