Abstract 3324: A novel role for PAK4 in the regulation of EMT and stemness in glioblastoma

Abstract

Abstract Glioblastomas (GB) are the most aggressive of primary brain tumors with high rates of tumor recurrence and poor prognosis. Epithelial-mesenchymal transition (EMT) is the dynamic transdifferentiation process which leads to acquisition of invasiveness, stem-like characteristics and drug resistance in tumor cells. A small fraction of radio- and chemo-resistant cancer stem cells (CSC) with a capacity of self-renewal is considered to be crucial for tumor recurrence. Our previous studies indicated high levels of expression of p21-activated kinase 4 (PAK4) in GBs and confirmed its role in the regulation of proliferation, migration and invasion. Here, we aimed to determine whether PAK4-regulated invasiveness was associated with mesenchymal transition of glioma cells and to delineate the essential signaling events that governed EMT and maintenance of stemness in GBs. PAK4 overexpression in glioma cells resulted in loss of E-cadherin and Zo-1 and a significant increase in N-cadherin and vimentin levels. Conversely, shRNA-mediated PAK4 downregulation led to loss of mesenchymal phenotype and markers in glioma cell lines. Further, irradiation (IR, 8 Gy) treatments significantly elevated PAK4 expression and nuclear localization in correlation with increased EMT in glioma cells. FACS analysis and western blotting indicated an enrichment of CD133+ CSCs with high expression of CD133 and Nestin in IR-treated cells. In order to study the significance IR-induced EMT and stemness with PAK4 nuclear translocation, we performed a transcription factor (TF) interaction array with immunoprecipitated PAK4 as bait, which revealed nuclear-PAK4 association with PPARγ and other TFs. Moreover, immunoprecipitation, ChIP and re-ChIP experiments showed IR-induced PAK4 binding with PPARγ nuclear receptor complex and recruitment on the PPREs of NADPH oxidase-1 promoter and elevated Nox1 expression in IR-treated cells. PAK4-knockdown suppressed the IR-induced EMT and stemness in the glioma cells lines. In line with these in vitro results, mouse orthotopic intracranial xenograft experiments showed decreased tumor growth and N-cadherin expression in tumors from PAK4-shRNA expressing cells when compared with controls. These results strongly support a role for PAK4 in the regulation of IR-induced EMT and stemness via PPARγ/Nox1 signaling and provide a rationale for PAK4 as a new therapeutic target against glioblastoma and suggest a potential for overcoming radioresistance in these tumors. Citation Format: Divya Kesanakurti, Jihong Xu, Rao S. Jasti, Vinay K. Puduvalli. A novel role for PAK4 in the regulation of EMT and stemness 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 3324. doi:10.1158/1538-7445.AM2015-3324