The incidence rate of breast cancer (BC) ranks first among female malignant tumors. Late-stage BC patients are at risk of death from distant metastasis. Circular RNAs (circRNAs) play an important function in cancer development. This study looked at the role of circMYH9 in BC. The nude mouse tumor-bearing experiment was used to verify the role of circMYH9 in regulating BC tumor growth in mice. Gene expression and protein amount were tested by qRT-PCR, western blot, and IHC. The pathological changes in tumor tissues were analyzed by HE staining. Cell viability, proliferation, migration, and invasion were assessed using CCK8, colony formation assay, wound healing assay, and Transwell assay, respectively. The interactions between circMYH9, SPAG6, and EIF4A3 were analyzed by RIP assay. CircMYH9 was significantly upregulated in BC, and its upregulated was related to poor prognosis. CircMYH9 silencing markedly impaired BC cell proliferation, migration, and invasion. Mechanistically, circMYH9 promoted the mRNA stability and expression of SPAG6 by recruiting EIF4A3. As expected, SPAG6 overexpression abrogated inhibition mediated by circMYH9 knockdown on BC cell malignant behaviors. In addition, circMYH9 knockdown inhibited PI3K/Akt signal pathway by increasing PTEN expression in BC cells, while was reversed by SPAG6 upregulation. PTEN inhibition abolished inhibition induced by circMYH9 downregulation on BC malignant progression. Moreover, circMYH9 silencing inhibited tumor growth in mice. CircMYH9 overexpression regulated the PTEN/PI3K/AKT pathway by increasing SPAG6 mRNA stability through recruiting EIF4A3, thereby promoting BC malignant progression.

Keywords: Breast cancer; EIF4A3; SPAG6; circMYH9; the PTEN/PI3K/AKT pathway.