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E. Lang

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    MA 19 - Mesothelioma: Bench to Bedside (ID 680)

    • Event: WCLC 2017
    • Type: Mini Oral
    • Track: Mesothelioma
    • Presentations: 1
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      MA 19.07 - Does Loss of Smad7 Lead to Increased Aggressiveness of Malignant Pleural Mesothelioma? (ID 8459)

      11:00 - 12:30  |  Author(s): E. Lang

      • Abstract
      • Presentation
      • Slides

      Malignant pleural mesothelioma (MPM) is characterized by aggressive growth, limited therapeutic options and rapid recurrence following treatment. A better understanding of biological factors underlying MPM aggressiveness offers the chance to improve therapeutic strategies. Growth factors of the TGF-beta superfamily including TGF-beta itself, activins and BMPs have been repeatedly linked to MPM growth. In the current study, we focus on the role of Smad7, a key intracellular antagonist of TGF-beta and activin signaling, in MPM.

      A panel of 17 human MPM cell lines was screened for tumorigenicity in SCID mice. Comparative genomic hybridization and whole genome gene expression arrays were used for identification of genes correlating with tumorigenicity. Immunoblotting and qPCR were used to detect Smad7 expression levels in cell lines. For ectopic overexpression of Smad7 in MPM cells, a retroviral expression system was used. Various in vitro assays, immunoblotting and reporter gene assays were employed to characterize the effect of Smad7 overexpression on MPM cell proliferation, migration, signal transduction and drug response.

      When human MPM cell lines were dichotomized into tumorigenic ones and non-tumorigenic ones based on their ability to form tumors in SCID mice, loss of Smad7 was one of the most conspicuous associations with tumorigenicity identified in CGH arrays. The tumorigenic group also showed a reduced Smad7 transcript expression in gene expression microarrays. Based on these data we screened a larger panel of MPM cell lines for Smad7 mRNA and protein expression and identified cell lines with high, medium and low Smad7 expression. We generated a retroviral expression construct and established an isogenic subline overexpressing Smad7 from the MPM cell line VMC33 that shows low endogenous Smad7 expression. Compared to parental VMC33 cells or VMC33-RFP cells, which overexpress red fluorescent protein and were used as control, VMC33-Smad7 cells showed a reduced growth rate and diminished clone forming capacity in vitro. VMC33-Smad7 also showed reduced cell migration, but no difference in invasion could be detected. Since Smad7 was described as antagonist of TGF-beta, we tested its effect on TGF-beta signaling with a reporter gene assay and indeed found a blunted response to TGF-b in Smad7 overexpressing cells. With respect to sensitivity against kinase inhibitors targeting TGF-beta receptors, VMC33-Smad7 showed a decreased response to galunisertib and SB-431542 compared to VMC33-RFP.

      Taken together, these data suggest that Smad7 may have a growth limiting function in MPM, possibly by antagonizing growth-promoting TGF-beta and/or activin signals.

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