Abstract 758: Loss of USP1 translational control as a targetable cisplatin resistance mechanism in non-small cell lung cancer (NSCLC)

Abstract

Abstract Backgroung : Cisplatin is part of standard therapy for a number of solid tumors including lung cancer. The initial response to this antineoplastic agent is in most cases only transient and tumors quickly become resistant to the drug. The mechanisms of resistance have been intensively explored, mostly by functional high throughput screening methods or by genomic and transcriptomic approaches. Our aim was to analyze the translational reprogramming following cisplatin treatment in order to identify candidates that mediate cisplatin resistance. Material and methods: Here we explored the response of a sensitive and of a matched resistant NSCLC cell line to cisplatin at the level of the nascent proteome by performing polysome profiling. Cellular mRNAs were resolved on a linear sucrose gradient. The heavily translated mRNAs that are associated with ribosome particles (the so-called polysomes) could be isolated and competitively hybridized on a cDNA microarray against the total mRNA fraction. This approach enabled us to identify the mRNAs whose translation is modified upon cisplatin treatment in the resistant cells. Results : Amongst the 200 candidate genes identified by this approach, we focused on the Ubiquitin-Specific Peptidase 1 (USP1) gene regulation. We found that while the transcription of the gene remains unaffected in both the sensitive and the resistant cell lines, the translation of USP1 is modulated by cisplatin in the sensitive cells. The immediate response (4h after treatment) results in a decrease of USP1 mRNA translation, followed by a stimulation of the translation at a later time point (16h). Importantly, this translational regulation of USP1 is lost in the resistant cells which instead show a constitutively high translation rate for USP1. Inhibition of cell growth by cisplatin was potentiated when USP 1 expression was suppressed by siRNA. Similarly, ML323, a specific inhibitor of the USP1-UAF1 deubiquitinase complex, dramatically increased cell sensitivity to cisplatin. Thus interfering with USP1 activity in resistant cells by both an siRNA approach and the use of a small molecule inhibitor re-sensitized the resistant cells to cisplatin. Conclusion: Our original approach led to the identification of USP1 as a potential determinant of cisplatin resistance of a lung cancer cell line. USP1 protein levels in tumor samples could potentially serve as a predictive marker of the response to cisplatin. We suggest that small molecule inhibitors of USP1 should be tested as cisplatin-sensitizers. The analysis of the ‘nascent proteome’ by polysome profiling could enable the identification of additional candidates mediating cisplatin-resistance. Citation Format: Carole Helissey, Tony Sourisseau, Hélène Mahieu, Céline Lefebvre, Stephan Vagner, Jean-Charles Soria, Ken Olaussen. Loss of USP1 translational control as a targetable cisplatin resistance mechanism in non-small cell lung cancer (NSCLC). [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 758. doi:10.1158/1538-7445.AM2015-758