Abstract 4706: Overexpression of the components of RNA-induced silencing complex: Contribution to hepatocellular carcinoma
Authors: Santhekadur Prasanna K. , Yoo Byoung Kwon , Gredler Rachel , Chen Dong , Bhutia Sujit K. , Fisher Paul B. , Sarkar Devanand 
Published: June 2012

Objectives: There is virtually no treatment for advanced hepatocellular carcinoma (HCC). As such novel targets need to be identified to develop effective therapies to combat this fatal disease. The oncogene Astrocyte elevated gene-1 (AEG-1) is overexpressed in more than 90% of human HCC patients and plays a seminal role in hepatocarcinogenesis. AEG-1 is localized on the cell membrane as well as in the cytoplasm, nucleus and endoplasmic reticulum. In each location AEG-1 interacts with specific proteins thereby modulating diverse intracellular processes which contributes pleotrophic oncogenic properties to AEG-1. Identification of AEG-1 interacting proteins would facilitate better understanding of AEG-1 function and help develop novel and targeted therapies for HCC.

Methods: Yeast two-hybrid assay and co-immunoprecipitation (co-ip) followed by mass spectrometry were used to identify AEG-1-interacting proteins. Co-ip and double immunofluorescence analyses were performed to confirm protein-protein interaction. A Renilla luciferase reporter plasmid containing a miRNA-recognition site in the 3’-untranslated region was used in a transfection based assay to monitor RNA-induced silencing complex (RISC) activity. Immunohistochemistry in tissue microarray was performed to check protein expression. Nude mice xenograft studies were done to check tumorigenesis.

Results: We identified Staphylococcal nuclease domain containing 1 (SND1), a nuclease functioning in the RNA-induced silencing complex (RISC), as an AEG-1 interacting protein. We documented that AEG-1 interacts with SND1 and Argonaute 2 (Ago2), the major nuclease in RISC, and thus AEG-1 itself is a component of RISC. Knocking down AEG-1 or SND1 abrogates and overexpression of AEG-1 or SND1 augments RISC activity in human HCC cells. 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 normal hepatocytes. We hypothesized that increased RISC activity, conferred by AEG-1 or SND1 overexpression, might facilitate function of oncomiRs resulting in increased degradation of tumor suppressor mRNAs. Indeed, overexpression of AEG-1 or SND1 downregulated while knockdown of AEG-1 or SND1 upregulated the mRNA level of tumor suppressor PTEN, a target of several oncomiRs overexpressed in HCC. Inhibition of SND1 enzymatic activity significantly abrogated cell growth and proliferation of human HCC cells. Stable overexpression of SND1 augmented while stable knockdown of SND1 inhibited tumor growth by human HCC cells in nude mice xenograft assay.

Conclusion: 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.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4706. doi:10.1158/1538-7445.AM2011-4706