Introduction:
Aberrant circular RNA (circRNA) expression is associated with the development of breast cancer. In this study, we aimed to assess the anti-proliferative effect of circ_0119412 knockdown on breast cancer cells.

Material and methods:
Tumor and adjacent normal tissues were collected from 35 patients with invasive breast cancer (mean age: 56 years; mean tumor size: 2 cm; 46% patients with TNM I and II stages). The levels of circ_0119412, microRNA (miR)-1205, and N-acetylgalactosaminyltransferase 6 (GALNT6) were determined using reverse transcription-quantitative polymerase chain reaction. Cell proliferation and invasion were assessed using cell counting kit-8 and transwell assays, respectively. Cell apoptosis was assessed using flow cytometry. Moreover, the targeting relationships of miR-1205 with circ_0119412 and GALNT6 were determined using dual-luciferase reporter and RNA immunoprecipitation assays. Furthermore, tumor growth was observed in an animal model in vivo.

Results:
We found that circ_0119412 expression levels were upregulated in breast cancer tumor specimens and cell lines. Downregulation of circ _0119412 inhibited the invasion and proliferation, while enhancing the apoptosis of breast cancer cells. Furthermore, circ_0119412 knockdown suppressed tumor growth in vivo. Notably, miR-1205 was identified as a downstream target of circ_0119412. Downregulation of circ_0119412 suppressed the aggressive behavior of breast cancer cells by targeting miR-1205. Moreover, GALNT6 was the downstream target of miR-1205. Inhibition of miR-1205 aggravated the malignant behavior of breast cancer cells by increasing GALNT6 expression.

Conclusions:
Our findings suggest that the downregulation of circ_0119412 inhibits breast cancer progression, at least in part, by targeting the miR-1205/GALNT6 pathway.