Abstract 4761: Regulation of TNFα-induced cell death of primary human brain microvessel endothelial cells by integrins

Abstract

Abstract TNFα induces cell death of primary human brain microvessel endothelial cells (MvEC) in a dose-dependent manner through TNF-R1 activation. To determine whether TNF-R1 was available to be therapeutically manipulated on tumor-associated endothelial cells in glioblastoma tumors, we evaluated its expression on the endothelial cells in 50 human glioblastoma and 38 normal brain samples by immunohistochemistry. A significantly increased expression of TNF-R1 and TNFα was detected on the endothelial cells in the tumor biopsies as compared to the normal brain samples. We then investigated whether integrins regulate TNF-R1 pro-apoptotic signaling in MvEC isolated from normal brain; these cells proliferate in culture and resemble reactive endothelial cells. TNFα stimulation readily induced cell death of the brain MvEC when plated on collagen or fibronectin (attachment mediated by integrins α2β1 and α5β1, respectively), but the cells were protected from this pro-death signal when plated on laminin (mediated by integrin α6β1). In the cells plated on collagen (not on laminin) a time-dependent increase in the phosphorylation of p38 MAP kinase was detected with TNFα stimulation and knockdown of p38 MAP kinase blocked the TNFα-induced cell death suggesting p38 MAP kinase is a downstream effector for TNFα-induced apoptosis. We then examined whether engagement of a particular integrin signaled for expression of an anti-apoptotic protein and found expression of cFLIP when the MvEC were plated on laminin, but not when the cells were plated on collagen. Furthermore, down-regulation of cFLIP using siRNA restored the pro-apoptotic signal of TNFα in MvEC plated on laminin. To substantiate the clinical relevance of these findings, we examined the effect of TNFα stimulation on endothelial cells isolated from two different glioblastoma tumors, and found that TNFα induced cell death was similarly regulated by the ECM or integrins. Our data suggest that TNF-R1 on tumor-associated endothelial cells in glioblastoma tumors is available to be therapeutically manipulated as part of an anti-angiogenic therapy, and that the effectiveness of such a therapy maybe in part dependent on the activity of specific integrins expressed on the tumor endothelial cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 4761. doi:10.1158/1538-7445.AM2011-4761