RESUMEN
BACKGROUND/AIMS: To investigate the clinical significance and functional mechanisms of deubiquitinase USP33 in papillary thyroid carcinoma (PTC). METHODS: Immunohistochemistry staining was conducted to explore the expression of USP33 in PTC tissues and adjacent normal thyroid tissues. Patients' prognosis was evaluated by disease-free survival. The prognostic role of USP33 was tested by univariate and multivariate analyses. To confirm the effect of USP33 in cell proliferation and invasion, overexpression and knockdown of USP33 were performed in two PTC cell lines. Besides, cell cycle, immunoprecipitation, and apoptosis experiments were conducted to further explore the signaling pathways. RESULTS: By analyzing series of 158 PTC tissues, we found that USP33 was down-regulated in tumor tissue compared with normal thyroid tissues, which was closely associated with lymph node metastasis (P<0.001). In particular, univariate and multivariate analyses indicated that USP33 was an independent prognostic biomarker for PTC, low USP33 expression indicated high recurrence risk. Cellular studies with TPC-1 and BCPAP cells demonstrated that USP33 can attenuate the cell capacities of proliferation, migration and invasion. Fluorescence-activated cell sorting experiment found no significant effect of USP33 on cell cycle, whereas the apoptotic caspase proteins were activated by USP33-overexpression. Moreover, the interaction between USP33 and Robo1 protein was identified, and knockdown of Robo1 enhancing the oncogenic effect upon USP33-knockdown, suggesting that USP33 may inhibit tumor progression through Robo1 signaling. CONCLUSIONS: Our data demonstrated that USP33 downregulation in PTC tissues was correlated with poor clinical outcome, which may serve as a novel biomarker and potential therapeutic target.