ABSTRACT
Epidermal growth factor receptor (EGFR) family members play pivotal roles in cell proliferation, differentiation and survival. Overexpression and mutations of EGFRs, or aberrant EGFR signaling are commonly associated with the development of various cancers, where constitutive NF-κB activation is often found to promote the expression of various proteins involved in the proliferation, survival, migration and epithelial-to-mesenchymal transition of cancer cells. However, the mechanism of EGFR-induced NF-κB activation is not fully defined. Here, we used a Bimolecular Fluorescence Complementation-based functional genomics method to perform a high throughput screening and identified TMEM43/LUMA as a critical component in EGFR signaling network, mediating EGFR-induced NF-κB activation. Our data show that EGFR recruits TMEM43 following EGF stimulation. TMEM43 interacts with the scaffold protein CARMA3 and its associating complex to induce downstream NF-κB activation, and plays a critical role in controlling cell survival. TMEM43 deficiency significantly affects colony formation, survival of anoikis-induced cell death, migration and invasion of cancer cells in vitro, as well as tumor progression in vivo. Importantly, higher expression of TMEM43 closely correlates with brain tumor malignancy, and suppression of TMEM43 expression in brain tumor cells inhibited their growth both in vitro and in vivo. Altogether, our studies reveal a crucial link of EGF receptor to NF-κB activation and tumor progression.
Subject(s)
ErbB Receptors/metabolism , Membrane Proteins/metabolism , NF-kappa B/metabolism , Neoplasms/metabolism , Neoplasms/pathology , Signal Transduction , Animals , CARD Signaling Adaptor Proteins/metabolism , Cell Line, Tumor , Cell Movement/genetics , Cell Proliferation , Cell Survival , Disease Models, Animal , Disease Progression , Female , Gene Expression , Gene Knockdown Techniques , Genomics/methods , Heterografts , Humans , Membrane Proteins/genetics , Mice , Neoplasms/genetics , Neoplasms/mortality , Prognosis , Protein Binding , Tumor BurdenABSTRACT
Resistance and relapse are still primary causes that result in poor effectiveness of chemotherapy in malignant gliomas. Therefore, development of new therapeutic strategies requires the identification of key molecular pathways regulating chemoresistance. We previously found that abnormal high expression of the Tie2 receptor in gliomas was associated with tumor malignancy. Here, we studied the role of Tie2 activation in drug resistance by testing the cytotoxicity of several chemotherapeutic drugs in a panel of human glioma cell lines and brain tumor stem cells and found that Tie2 activation was significantly related to chemoresistance. The essential role of Tie2 in this phenotype was illustrated by silencing Tie2 using specific siRNA, and the subsequent abrogation of the angiopoietin 1 (Ang1)-mediated chemoresistance. Using quantitative real-time PCR and functional drug efflux studies, we observed that Tie2 activation resulted in increased expression of ATP-binding cassette (ABC) transporters. Consistent with these results, downmodulation of ABCG2 or ABCC2 resulted in the inability of Tie2 activation to induce a chemoresistant phenotype. Our results indicate that Tie2 activation may be important in modifying the evolution of gliomas during conventional chemotherapy regimens, and open new avenues for the search of more effective therapies to avoid the inevitable brain tumor recurrence.
