DNAR-05. A ROLE FOR TAZ/YAP IN DNA DAMAGE REPAIR IN GLIOBLASTOMA

Abstract

Abstract Previous studies have shown that glioma stem-like cells (GSCs) evade conventional cytotoxic therapies and repopulate as recurrent tumors. A fuller understanding of the molecular mechanisms underlying the biology and therapy resistance of GSCs is required. Our group has shown that TAZ, a transcriptional co-factor is highly expressed in about 70% of glioblastomas (GBMs). TAZ and its paralog YAP are oncogenic drivers of brain tumor progression. GSCs overexpressing TAZ undergo a proneural (PN) to mesenchymal (MS) subtype transition, which is accompanied by aggressive phenotypes such as increased grade and treatment resistance in GSC xenografts. Although the oncogenic functions of TAZ/YAP are well established, the exact molecular mechanisms underlying TAZ/YAP mediated cell fate transition and therapy resistance in GBM are not fully understood. Here, we present novel functional interaction between TAZ/YAP and DNA-dependent protein kinase (DNA-PK) in response to exposure to ionizing radiation in GSCs. Mass-spectrometric analyses of TAZ-binding proteins showed that DNA-PK complex composed of the catalytic subunit (DNA-PKcs) and a Ku heterodimer of Ku70 and K80 interacted with TAZ. Immunoprecipitation of DNA-PK showed interaction of both YAP as well. Interaction of YAP/TAZ with DNA-PK complex and TEAD was enhanced by ionizing radiation. DNA-PKcs phosphorylated both YAP and TAZ, and phosphorylation level of these proteins were increased after irradiation, consistent with an increased interaction of these proteins. Intriguingly, siRNA knockdown of YAP and TAZ resulted in inactivation of DNA-PKcs, although protein stability of DNA-PKcs was not affected. Pharmacological inhibition of TAZ/YAPTEAD resulted in increased DNA damage and suppressed cell proliferation, and this effect was synergized by irradiation. We conclude that TAZ and YAP are integral components of DNA damage response and that pharmacological targeting of TAZ/YAP/TEAD pathway can overcome radiation resistance in GSCs.