N6-methyladenosine-modified circ_0081069: an effective approach to modulate breast cancer's tumor immune microenvironment.

BACKGROUND: Circular RNA (circRNA) has been recognized as critical regulator in cancer progression. However, the mechanisms of circ_0081069 in breast cancer (BC) remain understood. The study was designed to elucidate the pathological significance and mechanism of circ_0081069 in BC. MATERIAL AND METHODS: The expression of circ_0081069 was investigated in BC tissues and cell via qRT-PCR. CCK-8 and Transwell were carried out for assessing cell viability and invasion. After transfection, the expression of circ_0081069, microRNA (miR)-1286 and E2F4 were manipulated, and the mechanism in BC were explored by bioinformatic predication, luciferase reporter assay and RIP assay. The m6A modification was confirmed via MeRIP assay. Granzyme, IFN-γ, TNF-α and PD-L1 levels were determined using ELISA and western blot. Xenograft tumor model was established to detect circ_0081069 functions in vivo. RESULTS: Circ_0081069 was markedly upregulated in BC tissues (n = 60) and cells, which was correlated with poor patient prognosis. Knockdown of circ_0081069 restrained MDA-MB-231 and BT549 cells viability and invasion. Moreover, Granzyme, TNF-α, IFN-γ and PD-L1 levels were elevated in the co-cultured BC and CD8+ T cells. Mechanistically, circ_0081069 was a sponge for miR-1286, leading to up-regulation of E2F4. The inhibitory functions of circ_0081069 knockdown in BC pathological behaviors and tumor microenvironment were reversed by miR-1286 inhibition. METTL3 silence inhibited cell viability, invasion and tumor microenvironment by stabilizing circ_0081069. Furthermore, circ_0081069 knockdown suppressed BC cell proliferation and regulated immune microenvironment in vivo. CONCLUSIONS: m6A-modified circ_0081069 facilitated BC progression and tumor microenvironment via the miR-1286/E2F4 regulatory axis.