Abstract 4158: Novel PAK4-mediated regulation of endothelial CXCL1/CXCR2 signaling and angiogenesis in glioblastoma

Abstract

Abstract Increased endothelial cell proliferation and aberrant neovascularization are pathological hallmarks of glioblastoma that correlate with clinical outcome. Recent studies have also implicated ionizing radiation (IR)-induced angiogenesis as a potential cause for tumor recurrence and metastases in several malignancies. Its impact in gliomas has not been characterized. Factors that drive endothelial proliferation, angiogenesis and interaction of endothelial cells with tumor cells in the context of radiotherapy are potentially novel targets for glioma therapy. Our previous studies demonstrated high levels of expression of p21-activated kinase 4 (PAK4) in gliomas; analyses of tumor cell medium (CM) prepared from shRNA-mediated PAK4-knockdown cells using an angiogenesis antibody array showed a significant decrease in key angiogenic factors including CXCL1. Treatment of human brain microvascular endothelial cells (HBMECs) with CM from PAK4-knockdown cells (PAK4-kd CM) significantly inhibited proliferation, migration and microtubule formation compared with CM from control and scrambled vector-expressing glioma cells. PAK4-kd CM treatment also suppressed CXCR2 activation and decreased the expression levels of p-STAT3, VEGF, MMP-2 and cyclinD1 in HBMECs. Additionally, treatment with CM from ionizing radiation (IR, 8 Gy)-treated cells resulted in elevated CXCL1, MMP-2 and VEGF levels in HBMECs, and induced high levels of endothelial capillary network formation on matrigel, indicating an IR-induced angiogenesis in these cells. Conversely, PAK4-kd inhibited IR-induced angiogenesis and decreased p-STAT3, VEGF and MMP-2 levels in IR-treated HBMECS. Further, in vivo experiments with orthotopic intracranial tumors in nude mice showed growth suppression in PAK4-knockdown tumors compared to control tumors. Immunohistochemical analyses of brain tumor sections revealed a significant decrease in CXCL1, VEGF and MMP-2 in PAK4.sh tumors. In summary, our studies emphasize a novel regulation of angiogenic switch and endothelial CXCL1/CXCR2 signaling by PAK4 in tumor cells, thereby, suggests the role of PAK4 as a critical mediator of tumor-endothelial cell interactions in glioblastoma. Abrogation of key angiogenic signaling after IR treatment and inhibition of in vivo tumor growth by PAK4 suppression indicates its therapeutic potential in the treatment of glioma. Citation Format: Divya Kesanakurti, Jihong Xu, Alessandro Canella, Prabhakaran Nagarajan, Balveen Kaur, Vinay K. Puduvalli. Novel PAK4-mediated regulation of endothelial CXCL1/CXCR2 signaling and angiogenesis in glioblastoma. [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 4158. doi:10.1158/1538-7445.AM2015-4158