Platinum-based combination regimens are the standard of care to treat esophageal squamous cell carcinoma (ESCC) in both pre- and post-operative settings. Thus, resistance to cisplatin-based chemotherapies leads to worse survival outcomes in patients with ESCC. Therefore, there is an urgent need to understand aberrant mechanism driving cisplatin-resistance in ESCC. UBQLN4 is a proteasomal shuttle factor that interacts with ubiquitinated proteins and leads to proteasome-mediated protein degradation. We have recently demonstrated that UBQLN4 is highly expressed in solid aggressive tumors. However, the role of UBQLN4 in driving cisplatin-resistance in ESCC remains unknown. We hypothesize that UBQLN4 interacts with ubiquitinated-MRE11A, an essential component of the MRN complex and the DNA damage repairing pathway and thus, lead to cisplatin-resistance in ESCC tumors. In this study we demonstrated that MRE11A knockdown in ESCC cell lines reduced DNA damage and increased cisplatin-resistance, while MRE11A overexpression caused the opposite effects. MRE11A and UBQLN4 negatively correlated in TE-4, TE-8, and TE-10 cell lines. In established cisplatin-resistant ESCC cell lines (TE-8 and TE-10), MRE11A expression was significantly lower compared to their respective parental cell lines (p<0.01). UBQLN4 overexpression was associated with cisplatin-resistance in ESCC cell lines. Mechanistically, UBQLN4 bound to ubiquitinated MRE11A, enhanced MRE11A proteasomal degradation, and promoted cisplatin-resistance. Immunohistochemistry analysis was conducted in total 120 ESCC patients' specimens. In endoscopic core biopsies taken from 61 ESCC patients who underwent cisplatin-based neoadjuvant chemotherapy, low MRE11A and high UBQLN4 protein levels were associated with reduced pathological response to neoadjuvant chemotherapy (p<0.001 and p<0.001, respectively). Analysis of surgically-resected ESCC tissues from 59 patients who underwent upfront surgery and the following cisplatin-based adjuvant chemotherapy revealed that low MRE11A and high UBLQN4 expression were independent factors to predict shorter overall survival in multivariable analysis (p=0.02, HR=3.74, 95% C.I., 1.19-11.76; p=0.01, HR=5.11, 95% C.I., 1.45-18.03, respectively). In summary, UBQLN4 targets ubiquitinated-MRE11A to the proteasome for degradation during DNA damage induced by cisplatin in ESCC cell lines; thus, regulating MRE11A protein levels. MRE11A and UBQLN4 may serve as predictors for treatment response to cisplatin regimens and prognosis in ESCC patients.

Citation Format: Tomohiro Murakami, Yoshiaki Shoji, Tomohiko Nishi, Shu-Ching Chang, Ron D. Jachimowicz, Yosef Shiloh, Hiroya Takeuchi, Yuko Kitagawa, Dave S. Hoon, Matias A. Bustos. MRE11A expression regulated by UBQLN4 is related to cisplatin-resistance and survival in patients with esophageal squamous cell carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr LB218.