Abstract 4098: Musashi-2 (MSI2) activates TGF-β signaling and inhibits CLDN7 to promote non-small cell lung cancer (NSCLC) metastasis
Authors: Kudinov Alexander , Deneka Alexander Deneka , Nikonova Anna , Ahn Young-Ho , Liu Xin Liu , Serebriiskii Ilya , Efimov Andrey , Yang Dong-Hua , Andrake Mark Andrake , Nicolas Emmanuelle , Egleston Brian , Borghaei Hossein , Gibbons Don , Kurie Jonathan , Golemis Erica , Boumber Yanis 
Published: August 2015

Abstract
Approximately 220,000 new patients were diagnosed with lung cancer and ∼160,000 died from this disease in the United States in 2014. Non-small cell lung cancer (NSCLC) has a 5 year survival rate of approximately 16%, with most deaths associated with distant metastasis. To gain a better insight into the regulation of metastasis, we studied metastasis-competent versus low metastasis-potential cell lines derived from NSCLC tumors of KrasLA1/+; P53R172HG/+ (KP) mice. Initial screening showed consistent and statistically significant upregulation of Musashi-2 (MSI2) in highly metastatic cells on both mRNA and protein level. Furthermore, we established statistically significant elevation of MSI2 protein expression in 123 human NSCLC tumor specimens versus normal lung tissue (p&lt;0.0001).
MSI2 is an RNA binding protein that regulates mRNA translation and is upregulated and functionally important in hematologic malignancies including CML and AML. MSI2 knockdown in four independent metastatic murine and human NSCLC cell lines very significantly decreased invasion in vitro but did not significantly change cell proliferation or survival. In orthotropic lung injection of mouse NSCLC cells into the lungs of immunocompetent 129Sv mice, MSI2 depletion dramatically decreased invasion of mediastinal lymph nodes and abrogated metastasis. Reverse-phase protein array (RPPA) screening indicated that Msi2 depletion significantly affected the expression of multiple proteins associated with epithelial-mesenchymal transition (EMT) and control of cell-cell attachments, including the extracellular matrix component fibronectin (FN1) and the tight junction protein claudin-7 (CLDN7). These and additional targets were validated in all four NSCLC model systems. MSI2 dependent control of FN1 expression was mediated at the level of mRNA induction, while CLDN7 expression was strikingly upregulated (10-fold) at the protein but not mRNA level, nominating CLDN7 as a putative direct MSI2 target. Parallel evaluation of a series of candidate direct MSI2 translational targets indicated MSI2 depletion downregulated translation of TGF-β receptor (TGF-βRI) and SMAD3. Morphologically, MSI2 depleted cells were marked by a greater degree of cell-cell attachment, potentially explaining their decreased invasive capacity. Based on this work, we propose that MSI2 supports TGF-βRI dependent EMT signaling and downregulates tight junction controls in a subset of metastatic NSCLC, and may influence tumor response to inhibitors targeting the TGF-β pathway.
Citation Format: Alexander Kudinov, Alexander Deneka Deneka, Anna Nikonova, Young-Ho Ahn, Xin Liu Liu, Ilya Serebriiskii, Andrey Efimov, Dong-Hua Yang, Mark Andrake Andrake, Emmanuelle Nicolas, Brian Egleston, Hossein Borghaei, Don Gibbons, Jonathan Kurie, Erica Golemis, Yanis Boumber. Musashi-2 (MSI2) activates TGF-β signaling and inhibits CLDN7 to promote non-small cell lung cancer (NSCLC) metastasis. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4098. doi:10.1158/1538-7445.AM2015-4098