circHIPK3 (hsa_circ_0000284) Promotes Proliferation, Migration and Invasion of Breast Cancer Cells via miR-326

PURPOSE: circHIPK3 has carcinogenic or anti-tumor effects on different cancers. However, there is no relevant research showing whether circHIPK3 was involved in breast cancer (BCa). In this research, the aim was to analyze the function and possible molecular mechanism of circHIPK3 in BCa. METHODS: The expression of circHIPK3 in human BCa tissues and cells was detected by real-time quantitative PCR (RT-qPCR). CircInteractome and dual-luciferase assays were performed to detect circRNA–miRNA targeting relationship. Ribonuclease R treatment, RT-qPCR, Western blot and immunohistochemistry were performed to determine the stability, expressions, abundance of target genes. Loss-of-function or gain-of-function experiments were used to analyze the effects of circHIPK3 and miR-326 on BCa in vivo and in vitro. In vitro, MCF7 and BT20 cells were transfected with circHIPK3 or sicircHIPK3 or miR-326 mimic; in vivo, female BALB/c mice were subcutaneously injected with MCF7 cells (transfected with CirchipK3 or miR-326 mimic) to establish xenograft models. RESULTS: The circular structure of circHIPK3 was abundantly expressed in the cytoplasm and was up-regulated in BCa. Silenced circHIPK3 suppressed malignant phenotype of BCa cells. MiR-326 interacted with circHIPK3 and the two were negatively correlated. Overexpressed circHIPK3 promoted cell viability, proliferation, migration and invasion, but inhibited apoptosis. Moreover, overexpressed circHIPK3 promoted the expressions of EMT-related genes and antiapoptotic genes, but inhibited proapoptotic gene expressions. Overexpressed circHIPK3 promoted tumor growth and Ki-67 levels, inhibited apoptosis in vivo. The above mentioned effects of circHIPK3 were reversed by miR-326 in vitro or in vivo. CONCLUSION: circHIPK3 promoted proliferation, migration and invasion of BCa cells through regulating miR-326.