Abstract 1263: UCHL1 modulates uterine papillary serous cancer progression through interaction with cyclin B1

Introduction: Uterine papillary serous carcinoma (UPSC) comprises less than 10% of all endometrial cancers but is the most aggressive subtype of endometrial carcinoma. Few prospective studies focus solely on this rare subtype, making it difficult to determine optimal treatment strategies. The purpose of this study was to identify novel therapeutic targets that could aid in the management of UPSC. Methods: Clinical and RNA sequencing data from The Cancer Genome Atlas (TCGA) was used to identify differentially expressed genes between the more benign endometrioid endometrial carcinoma (EEC) and UPSC that also correlated with overall patient survival. Ubiquitin C-terminal hydrolase 1 (UCHL1) upregulation and survival correlation was validated by immunohistochemical staining of an independent cohort of paraffin samples. UCHL1 silencing by siRNA in UPSC cell lines ARK1, ARK2 and HEC50 was performed to measure changes in cell proliferation, migration, and apoptosis. Luciferase-expressing ARK1 cells transduced with lentiviral doxycycline-inducible control shRNA or anti-UCHL1 shRNA were injected intraperitoneally into nude mice and monitored by in vivo bioluminescent imaging over time. The effect of UCHL1 silencing on cyclin B1 RNA and protein levels was measured, and the effect on cell cycle progression was analyzed by flow cytometry. ARK1 and ARK2 cells were treated with a drug combination of the UCHL1 inhibitor LDN-57444 and paclitaxel; synergistic effect was evaluated using CompuSyn. Results: RNA and protein expression of UCHL1 was significantly higher in UPSC than EEC. Kaplan-Meier analysis and cox regression of TCGA samples and an independent cohort of patient samples confirmed that UCHL1 expression correlated significantly with poorer overall survival in UPSC. siRNA-mediated silencing did not affect cell migration or apoptosis, but reduced cell proliferation in vitro. Following intraperitoneal injection of ARK1 cells in nude mice, control shRNA tumours exhibited significantly higher bioluminescence by week 10 than UCHL1-knockdown tumours. UCHL1 RNA expression correlated positively with cyclin B1 protein levels in the TCGA data set. UCHL1 silencing reduced cyclin B1 protein levels in ARK1, ARK2 and HEC50; this change was not due to reduced RNA expression. Cell cycle analysis after UCHL1 silencing showed a reduction in the percentage of cells in the S and G2/M phases, and inhibition by LDN-57444 delayed the entry of synchronized cells into G2/M. Combination treatment in vitro with LDN-57444 and paclitaxel was synergistic across a range of dose levels. Conclusions: These findings indicate that UCHL1 contributes to the aggressiveness of UPSC by stabilizing cyclin B1 and increasing tumor cell proliferation. Inhibition of UCHL1 alone or in combination with paclitaxel may be useful in the management of UPSC. Citation Format: Suet Ying Kwan, Samuel C. Mok, Rosemarie E. Schmandt, Kwong-Kwok Wong, Karen H. Lu. UCHL1 modulates uterine papillary serous cancer progression through interaction with cyclin B1. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1263.