Circular RNA circ-ERBB2 Elevates the Warburg Effect and Facilitates Triple-Negative Breast Cancer Growth by the MicroRNA 136-5p/Pyruvate Dehydrogenase Kinase 4 Axis

Triple-negative breast cancer (TNBC) is an aggressive histological subtype of breast cancer. It has been reported that the circular RNA (circRNA) circ-ERBB2 (circBase identifier hsa_circ_0007766) is mainly distributed in the cytoplasm of TNBC cells and promotes the proliferation and invasion of TNBC cells. This study aimed to explore the molecular mechanism of circ-ERBB2 regulating the progression of TNBC. The expression of circ-ERBB2 was detected by quantitative real-time PCR (qRT-PCR). Loss-of-function experiments were performed to investigate the function of circ-ERBB2 in TNBC cells in vitro and in vivo. The regulatory mechanism of circ-ERBB2 was surveyed by bioinformatics analysis and dual-luciferase reporter and RNA immunoprecipitation (RIP) or RNA pulldown assays. We observed that circ-ERBB2 was overexpressed in TNBC, and TNBC patients with high circ-ERBB2 expression levels had a poor prognosis. Functionally, circ-ERBB2 knockdown constrained TNBC growth in vivo, reduced the Warburg effect, accelerated apoptosis, and repressed the proliferation, migration, and invasion of TNBC cells in vitro. Mechanically, circ-ERBB2 sponged microRNA 136-5p (miR-136-5p) to elevate pyruvate dehydrogenase kinase 4 (PDK4) expression. In conclusion, circ-ERBB2 facilitated the Warburg effect and malignancy of TNBC cells by the miR-136-5p/PDK4 pathway, at least in part. This study supports circ-ERBB2 as a prognostic indicator for TNBC.