circUSP42 Is Downregulated in Triple-Negative Breast Cancer and Associated With Poor Prognosis

We previously showed that microRNA-182 (miR-182) might promote cell proliferation and migration in triple-negative breast cancer (TNBC). This study aimed to investigate circular RNAs (circRNAs) that interact with miR-182 and play important roles in TNBC. Thirty patients with TNBC were enrolled. One pair of tumor and adjacent tissue samples (control) were submitted for circRNA sequencing to establish the expression profile of circRNAs. Concomitantly, circRNAs aberrantly expressed between TNBC and control groups were identified, and these differentially expressed circRNAs (DEcircRNAs) were subjected to Gene Ontology and KEGG pathway enrichment analyses, as well as prediction of interactions with miRNAs. The expression levels of 5 circRNAs interacting with miR-182 were validated using qRT-PCR. Associations between the expression of circUSP42 and clinicopathological features and prognosis were evaluated. A total of 825 upregulated and 1127 downregulated DEcircRNAs were identified between tumor and control groups. Upregulated DEcircRNAs were significantly involved in proteoglycans in cancer, and endocytosis. Downregulated DEcircRNAs were involved in the pathway of resistance to EGFR tyrosine kinase inhibitors. Prediction of circRNA-miRNA interactions showed that hsa_circ_0002032, chr6:131973682-132047340+, hsa_circ_0005982, hsa_circ_0007823 (circUSP42), and hsa_circ_0001777 might act as miRNA sponges for miR-182. qRT-PCR showed consistent results with circRNA sequencing data (P < 0.05). Downregulation of circUSP42 was significantly associated with lymph node metastasis (P = 0.005) and advanced clinical stage (P = 0.032). Furthermore, Kaplan-Meier plots showed that low expression of circUSP42 was closely associated with poor outcome (log-rank test, P < 0.001). Our data suggested that dysregulation of circUSP42 might contribute to the development and progression of TNBC.