Abstract 2466: The tumor suppressor Merlin decreases TGFβ/Smad signaling in metastatic breast cancer cells

Abstract

Abstract Background: Merlin is a tumor suppressor protein encoded by the NF2 gene. Mutations in NF2 have been implicated in neurofibromas, schwannomas, and mesothelioma. While the mutation rate of NF2 is low in breast cancer, our lab has previously demonstrated a loss of the Merlin protein in advanced stage breast cancers. We have shown that the matricellular metastasis-promoting protein osteopontin activates Akt which then marks Merlin for targeted proteasomal degradation. In the context of other cancers, Merlin has been shown to play a role in sensitization to contact inhibition, cell proliferation, inhibiting invasion, and the negative regulation of focal adhesion kinase. Merlin is also an upstream regulator of the Hippo pathway. However, the implications of the loss of Merlin in the context of breast cancer signaling pathways that promote tumor progression and metastasis have not been fully explored. Here we demonstrate a Merlin-dependent decrease in TGFβ signaling in metastatic breast cancer cells. Methods: Using Ingenuity Pathway Analysis we analyzed a gene expression array comparing the triple-negative metastatic SUM159 breast cancer cells and their counterparts that were stably restored for Merlin expression. TGFβ was identified as a significant upstream regulator. TGFβ signaling was analyzed in these cells via a SBE4-luc luciferase assay. Signaling was further analyzed by Western blots for SMAD and phospho-SMAD proteins. Results and Conclusions: Re-expression of Merlin in metastatic breast cancer cells with low-levels of endogenous Merlin decreases TGFβ signaling, demonstrated by decreased luciferase assay activity, decreased rSMAD expression, decreased coSMAD expression and increased iSMAD protein levels. Future studies will explore the nature of this Merlin-dependent decrease in TGFβ signaling. Acknowledgments: R01CA138850 to L. A. Shevde Citation Format: William P. Jackson, Kelly M. Kreitzburg, Shamik Das, Sarah K. Bailey, Brandon J. Metge, Rajeev S. Samant, Lalita R. Shevde-Samant. The tumor suppressor Merlin decreases TGFβ/Smad signaling in metastatic breast cancer cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2466. doi:10.1158/1538-7445.AM2014-2466