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Jeongmin Hong

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    P1.02 - Biology/Pathology (ID 614)

    • Event: WCLC 2017
    • Type: Poster Session with Presenters Present
    • Track: Biology/Pathology
    • Presentations: 1
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      P1.02-071 - SFN Stabilizes Oncoproteins through Binding with SKP1 to Block SCF<Sup>FBW7</Sup> Ubiquiting Ligase (ID 9121)

      09:30 - 16:00  |  Presenting Author(s): Jeongmin Hong

      • Abstract
      • Slides

      Lung adenocarcinoma is the most common subtype of non-small cell lung cancer (NSCLC) and accounts for about 50% of them. Although EGFR or EML4-ALK has been identified as oncogenic driver mutation and translocation for advanced adenocarcinoma, trigger or mechanism of its early progression is still unclear. Previously, we revealed that stratifin (SFN, 14-3-3 sigma) has tissue-specific functions and regulate cell cycle progression in a positive manner in lung adenocarcinoma (Shiba-Ishii A et al. Mol Cancer 2015). Moreover, S-phase kinase-associated protein 1 (SKP 1) which is an adaptor part of SCF-type E3 ubiquitin ligase complex including SCF[FBW7], SCF[SKP2] and SCF[β][-TRCP] was identified as one of the SFN binding protein by pull-down assay and LC-MS/MS analysis. The aim of this study is to analyze the molecular mechanism of tumor progression in lung adenocarcinoma associated with SFN binding with SKP1. We have hypothesized that SFN binds with SKP1 among various SCF complexes and specifically blocks SCF[FBW7] function to ubiquitinate oncoproteins such as cyclin E1, c-Myc, c-Jun, and notch 1.

      Endogenous interaction of SKP1 and SFN or FBW7 was examined by co-immunoprecipitation using A549, lung adenocarcinoma cells. We performed ubiquitination assay under the treatment of proteosome inhibitor, MG132 to induce accumulation of ubiquitinated oncoproteins after siRNA-SFN transfection. Moreover, to investigate whether SFN regulates the localization of SKP1, we performed immunofluorescence staining of A549 after siRNA-SFN treatment.

      We found that SKP1 interacted with SFN and FBW7, respectively in lung adenocarcinoma cells. The binding activity of FBW7 with SKP1 increased after suppression of SFN, indicating that SFN and FBW7 might competitively bind with SKP1. Moreover, knockdown of SFN led to reduction of oncoproteins such as cyclin E1, c-Myc, c-Jun and notch 1 and showed accumulation of poly-ubiquitinated oncoproteins relative to the control by blocking proteosome degradation. However, p27[Kip1] (substrate of SCF[SKP2]) and IKB (substrate of SCF[β][-TRCP]) showed no expression change after knockdown of SFN. While SKP1 mainly localized in cytoplasm of A549, knockdown of SFN induced translocation of SKP1 to nucleus.

      SFN induces the stabilization of oncoproteins by blocking SCF[FBW7 ]ubiquitin ligase in lung adenocarcinoma and associated with its malignant progression. SFN will be a promising theraputic target for lung adenocarcinoma.

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