Tuncali, Serdar

Abstract Glioblastoma (GBM) is a highly lethal CNS malignancy in adults with a median survival of about 15 months. Effective therapeutic control of GBM is thwarted by the invasive nature of the tumor, which prevents complete surgical removal and results in tumor recurrence. Thus, there is a dire need to develop innovative approaches to target the invasive tumor cells for improved treatment of this disease. Expression of TROY, a member of the TNFR family, increases with glial tumor grade and inversely correlates with patient survival. Increased expression of TROY stimulates glioblastoma cell invasion and increases resistance to temozolomide (TMZ) and radiation treatment. We have demonstrated that TROY forms a novel complex with EGFR and modulates EGFR survival signaling. IHC analysis of GBM specimens showed that tumors with elevated TROY expression had a statistically positive correlation with increased EGFR expression. TROY expression enhanced EGFR phosphorylation, stabilized EGFR surface expression in the presence of ligand, and significantly increased EGF-stimulated GBM cell invasion. Consistent with invasion, co-expression of TROY with EGFR increased cell survival to TMZ. Moreover, we have shown that in cells treated with EGF, the TROY and ErbB4 receptor are recruited to the EGFR complex. Although the role of ErbB4 in GBM is not well defined, inhibition of ErbB4 expression suppressed tumor growth and invasion in multiple tumor subtypes, decreased EGFR surface retention, and limited EGF-induced cell migration. These data suggest that the TROY-EGFR-ErbB4 complex may represent an unappreciated therapeutic target to inhibit glioma invasion and decrease therapeutic resistance. Citation Format: Alison Roos, Zachary Mayo, Jean Kloss, Serdar Tuncali, Harshil Dhruv, Michael E. Berens, Joseph C. Loftus, Nhan L. Tran. TROY-EGFR signaling complex mediates glioblastoma cells invasion and survival. [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 506. doi:10.1158/1538-7445.AM2015-506

Abstract Glioblastoma multiforme (GBM) is the most common primary central nervous system tumor accounting for approximately 40% of all primary malignant brain tumors. The mechanism driving the development and recurrence of GBM is still largely unknown which greatly limits the successful treatment of this disease. The tumor necrosis factor receptor superfamily member TNFRSF19 (TROY) is a type I cell surface receptor protein containing the highly conserved TNFR cysteine-rich motifs in the extracellular domain and a tumor necrosis factor-receptor-associated factor (TRAF) - binding sequence in the cytoplasmic domain. We recently demonstrated that increased expression of TROY stimulated glioma cell migration in vitro and increased cell invasion in an organotypic brain slice model. Conversely, siRNA mediated knockdown of TROY expression inhibited glioma cell migration. In addition, profiling of TROY in brain tumor samples indicated that TROY mRNA expression was significantly increased in GBM samples, directly correlated with increasing glial tumor grade, and inversely correlated with patient outcome suggesting that TROY expression may play a role in GBM invasion and is a good indicator of survival outcome. In the current study, we investigated the role of TROY in therapeutic resistance and survival signaling. We report that TROY protein expression was significantly increased in patient GBM tumor samples with TROY mRNA exhibiting increased expression in the invasive cell population. Aberrant expression of TROY in mouse astrocytes in situ using glial-specific gene transfer in transgenic mice induced astrocyte migration within the brain supporting an important role for TROY in glioma cell migration. Notably, increased TROY expression did not increase cell proliferation but increased resistance of glioma cells to both radiation and temozolomide induced apoptosis while knockdown of TROY increased temozolomide sensitivity. TROY induced resistance to TMZ was dependent upon Akt and NF-κB activation. We also report that TROY induced NF-κB phosphorylation and stimulation of migration required the membrane proximal region of the TROY cytoplasmic domain and that knockdown of TROY expression increased survival in a xenograft model. The current results further support a role for TROY in GBM and suggest that targeting TROY and its signaling pathway represents a potential approach to increase tumor vulnerability and improve the therapeutic response of glioblastoma. Citation Format: Harshil D. Dhruv, Serdar Tuncali, Jean Kloss, Zhongbo Yang, Cassie Schumacher, Bart Williams, Julianna Ross, Nhan Tran, Joseph Loftus. TNFRSF19 (TROY) promotes glioma cell survival signaling and therapeutic resistance. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2621. doi:10.1158/1538-7445.AM2013-2621

Abstract Of the features that characterize glioblastoma, arguably none is more clinically relevant than the propensity of malignant glioma cells to aggressively invade into the surrounding normal brain tissue. These invasive cells render complete resection impossible, confer significant resistance to chemo- and radiation-therapy, and virtually assure tumor recurrence. Expression of TROY (TNFRSF19), a member of the TNF receptor superfamily, inversely correlates with patient survival and stimulates glioblastoma cell migration and invasion in vitro. In this study, we report that TROY is overexpressed in glioblastoma tumor specimens and TROY mRNA expression is increased in the invasive cell population in vivo. In addition, inappropriate expression of TROY in mouse astrocytes in vivo using glial-specific gene transfer in transgenic mice induces astrocyte migration within the brain, validating the importance of the TROY signaling cascade in glioblastoma cell migration and invasion. Knockdown of TROY expression in primary glioblastoma xenografts significantly prolonged survival in vivo. Moreover, TROY expression significantly increased resistance of glioblastoma cells to both IR- and TMZ-induced apoptosis via activation of Akt and NF-κB. Inhibition of either Akt or NF-κB activity suppressed the survival benefits of TROY signaling in response to TMZ treatment. These findings position aberrant expression and/or signaling by TROY as a contributor to the dispersion of glioblastoma cells and therapeutic resistance. Implications: Targeting of TROY may increase tumor vulnerability and improve therapeutic response in glioblastoma. Mol Cancer Res; 11(8); 865–74. ©2013 AACR.