title: Increased RNA-induced silencing complex (RISC) activity contributes to hepatocellular carcinoma.
abstract: There is virtually no effective treatment for advanced hepatocellular carcinoma (HCC) and novel targets need to be identified to develop effective treatment. We recently documented that the oncogene Astrocyte elevated gene-1 (AEG-1) plays a seminal role in hepatocarcinogenesis. Employing yeast two-hybrid assay and coimmunoprecipitation followed by mass spectrometry, we identified staphylococcal nuclease domain containing 1 (SND1), a nuclease in the RNA-induced silencing complex (RISC) facilitating RNAi-mediated gene silencing, as an AEG-1 interacting protein. Coimmunoprecipitation and colocalization studies confirmed that AEG-1 is also a component of RISC and both AEG-1 and SND1 are required for optimum RISC activity facilitating small interfering RNA (siRNA) and micro RNA (miRNA)-mediated silencing of luciferase reporter gene. In 109 human HCC samples SND1 was overexpressed in ≈74% cases compared to normal liver. Correspondingly, significantly higher RISC activity was observed in human HCC cells compared to immortal normal hepatocytes. Increased RISC activity, conferred by AEG-1 or SND1, resulted in increased degradation of tumor suppressor messenger RNAs (mRNAs) that are target of oncomiRs. Inhibition of enzymatic activity of SND1 significantly inhibited proliferation of human HCC cells. As a corollary, stable overexpression of SND1 augmented and siRNA-mediated inhibition of SND1 abrogated growth of human HCC cells in vitro and in vivo, thus revealing a potential role of SND1 in hepatocarcinogenesis.
  
  
  CONCLUSIONS
  We unravel a novel mechanism that overexpression of AEG-1 and SND1 leading to increased RISC activity might contribute to hepatocarcinogenesis. Targeted inhibition of SND1 enzymatic activity might be developed as an effective therapy for HCC.
authors.affiliation: Department of Human and Molecular Genetics, Virginia Commonwealth University, School of Medicine, Richmond, VA, USA.
authors.forename: Byoung Kwon
authors.initials: BK
authors.lastname: Yoo
authors.forename: Prasanna K
authors.initials: PK
authors.lastname: Santhekadur
authors.forename: Rachel
authors.initials: R
authors.lastname: Gredler
authors.forename: Dong
authors.initials: D
authors.lastname: Chen
authors.forename: Luni
authors.initials: L
authors.lastname: Emdad
authors.forename: Sujit
authors.initials: S
authors.lastname: Bhutia
authors.forename: Lewis
authors.initials: L
authors.lastname: Pannell
authors.forename: Paul B
authors.initials: PB
authors.lastname: Fisher
authors.forename: Devanand
authors.initials: D
authors.lastname: Sarkar
mesh_terms: D000818:Animals; D006528:Carcinoma, Hepatocellular / Q000209:etiology*; D015815:Cell Adhesion Molecules / Q000502:physiology*; D004720:Endonucleases; D006801:Humans; D008113:Liver Neoplasms / Q000209:etiology*; D008565:Membrane Proteins; D051379:Mice; D009687:Nuclear Proteins / Q000502:physiology*; D016601:RNA-Binding Proteins; D034743:RNA-Induced Silencing Complex / Q000502:physiology*; D014407:Tumor Cells, Cultured
chemical_list: D015815:Cell Adhesion Molecules; C483039:MTDH protein, human; D008565:Membrane Proteins; D009687:Nuclear Proteins; D016601:RNA-Binding Proteins; D034743:RNA-Induced Silencing Complex; D004720:Endonucleases; C095221:SND1 protein, human