Abstract 754: Nuclear liaison between PAK4 and PPARγ regulates radiation-induced MOX-1-mediated epithelial-mesenchymal transition and cell migration via a ROS-dependent mechanism in glioblastoma.

Abstract

Abstract Despite the use of post-surgical radiation and chemotherapy, the mean survival rate is less than two years in glioblastoma (GBM), the most lethal human brain tumor. Augmented cell invasion and migration and increased tumor recurrence after ionizing radiation (IR) treatment is, in part, attributed to the IR-induced elevation in reactive oxygen species (ROS) levels and ROS-dependent signaling in tumors. Several reports, including our own studies, have confirmed the PAK4 oncogenic role in the regulation of tumor cell migration and invasion in GBM and various other tumors. However, the potential role of PAK4 in post-irradiated tumor malignancy and the underlying molecular mechanisms still remain unknown. Here, we show the significant PAK4 nuclear translocation in correlation with elevated ROS-mediated epithelial-mesenchymal transition (EMT) in IR-treated human glioma xenograft cells 4910 and 5310. Surprisingly, protein-transcription factor (TF) interaction arrays revealed a significant binding of nuclear-PAK4 with several TFs involved in tumor progression including AhR/ARNT, GATA1/2, FOXI1, Pax4, PPARα, PPARγ and TCF/LEF. We also observed that the nuclear co-localization of PAK4/PPARγ was elevated in correlation with increasing GBM grades. Most importantly, IR treatment elevated the PAK4/PPARγ nuclear interaction and increased MOX-1 expression, a PPARγ-target gene. In addition, EMSA and ChIP assays confirmed the presence of PAK4 in the PPARγ-DNA binding complex and recruitment onto MOX-1 promoter, which is further elevated in IR-treated cells. Stable shRNA-mediated knockdown of PPARγ or inhibition with a specific inhibitor, GW9662, abrogated IR-induced ROS levels, EMT and cell migration in vitro. siRNA-mediated PAK4 downregulation significantly decreased PPARγ DNA-binding activity and MOX-1 expression and inhibited EMT. On the other hand, PAK4 overexpression reversed GW9662-inhibited ROS levels, EMT and migration. In vivo experiments in nude mice showed the IR-induced PAK4/PPARγ nuclear co-localization in tumors. Furthermore, PAK4.si inhibited tumor growth and ROS-induced MOX-1 levels in IR-treated tumors. In summary, our studies not only demonstrate a prominent PAK4/PPARγ nuclear interaction but also suggest a novel regulation of PPARγ-mediated EMT by PAK4, thereby indicating the future therapeutic potential of targeting PAK4/PPARγ binding in glioma treatment. Citation Format: Divya Kesanakurti, Dilip Maddirela, Meena Gujrati, Sanjeeva Mohanam, Jasti S. Rao. Nuclear liaison between PAK4 and PPARγ regulates radiation-induced MOX-1-mediated epithelial-mesenchymal transition and cell migration via a ROS-dependent mechanism in glioblastoma. [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 754. doi:10.1158/1538-7445.AM2013-754