Abstract 2127: p53-independent Noxa induction by cisplatin is regulated by ATF3/ATF4 in HNSCC cells
Authors: Sharma Kanika , Vu Thien-Trang , Naseri Mitra , Nakajima Wataru , Zhan Kevin , Harada Hisashi 
Published: July 2017

Abstract
Head and neck cancer is the sixth leading cancer worldwide and head and neck squamous cell carcinoma (HNSCC) accounts for more than 90% of incident cases. The long-term prognosis of patients with advanced HNSCC has shown little improvement over the last three decades. Induction chemotherapy with platinum-based compounds, taxanes, and 5-fluorouracil is beneficial for head and neck cancer patients, but the prolonged use of chemotherapeutic drugs is limited by their toxicity and by the development of resistance. Tumor cell death induced by both conventional and targeted chemotherapy is often mediated by the BCL-2 family-dependent mitochondrial apoptotic pathway. However, initiators of this apoptotic pathway, such as p53, are frequently mutated or deleted in HNSCC rendering it refractory to treatment. To counter such resistance, direct therapeutic targeting of the BCL-2 family is conceptually appealing. We have investigated the cytotoxic effects of a DNA damaging agent, cisplatin that is used for a standard therapy for locally advanced HNSCC. Cisplatin produces anticancer effects mainly by generating DNA lesions and activating DNA damage response followed by inducing BCL-2 family-dependent mitochondrial apoptosis. Cisplatin induces the expression of a pro-apoptotic BH3-only protein, Noxa that binds to the pro-survival BCL-2 family protein, MCL-1 to inactivate its function and induces cell death. To examine the contribution of Noxa in cisplatin-induced apoptosis, shRNA for Noxa was introduced in p53-null HNSCC cells, since p53 is mutated or deleted in more than 50% of HNSCC. We found that the up-regulation of Noxa is critical for cisplatin-induced apoptosis in p53-independent HNSCC cells. This Noxa induction is regulated at the transcriptional level. Thus, we examined the regulation of the Noxa promoter with a series of luciferase reporter assays. We found that the CRE (cAMP responsive element located at -66~-59 from the transcription start site) on the promoter plays a critical role in Noxa induction. The CRE is known to be regulated by ATF/CREB transcription factors. Downregulation of ATF3 or ATF4 by shRNAs clearly reduced Noxa induction. Furthermore, the binding of these transcription factors to the CRE on the Noxa promoter was increased by cisplatin treatment, determined by chromatin-immunoprecipitation assays. In conclusion, ATF3 and ATF4 are important regulators for cisplatin-induced Noxa in a p53-independent pathway. The results suggest that modulation of the signaling pathways that activate ATF3/ATF4 could be an alternative approach to induce Noxa followed by apoptosis in HNSCC.
Citation Format: Kanika Sharma, Thien-Trang Vu, Mitra Naseri, Wataru Nakajima, Kevin Zhan, Hisashi Harada. p53-independent Noxa induction by cisplatin is regulated by ATF3/ATF4 in HNSCC cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2127. doi:10.1158/1538-7445.AM2017-2127