Yan Zhang,1,* Mei Yang,1,2,* Yiping Wang,1 Junhao Zhao,1 Pei Yao Lee,1 Yuhua Ma,1 Shaohua Qu1 

1Department of Breast Surgery, The First Affiliated Hospital of Jinan University, Jinan University, Guangzhou, 510630, People’s Republic of China; 2Department of Breast Surgery, JiangMen Maternity and Child Health Care Hospital, Jiangmen, 529000, People’s Republic of China

*These authors contributed equally to this work

Correspondence: Yuhua Ma; Shaohua Qu, Email mayuhua2110@126.com; qushaohua2009@163.com

Background: Non-coding RNAs have received increasing attention in human tumors, with RNA interaction networks playing important roles in breast cancer. This study aims to explore novel circular RNAs and their mechanisms of biological function in breast cancer.
Methods: Six HER2-positive breast cancer tissues and paired normal tissues were obtained for the whole transcriptome RNA sequencing. Differentially expressed (DE) circRNAs, miRNAs and mRNAs were identified and Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses of DERNAs were performed. DECircRNAs- DEmiRNAs- DEmRNAs networks were constructed and further verified by bioinformatics database analyses, luciferase assays and RIP assays. The expression level of circDOCK1 in breast cancer specimens was measured using qRT-PCR. Functional rescue experiments were conducted to explore the role of circDOCK1/miR-138-5p/GRB7 axis in breast cancer cells. The correlation of circDOCK1 expression and clinicopathologic features of 102 HER2 positive breast cancer patients was analyzed.
Results: A total of 6960 DEmRNAs, 133 DE miRNAs and 1691 DE circRNAs were identified from HER2-positive breast cancer tissues and paracancerous tissues. Enrichment Analysis showed that the differential mRNAs were associated with cell division in biological processes and cell cycle and signaling pathways. GO and KEGG analysis demonstrated that DE circRNAs were mainly enriched in double-strand break repair, positive regulation of transcription by RNA polymerase II, nucleoplasma, nucleus, chromatin binding and protein binding. Forty networks of competing endogenous RNAs (ceRNAs) were constructed and circDOCK1/miR-138-5p/GRB7 axis was verified. Functional experiments revealed that the axis promotes migration and invasion of breast cancer cells. CircDOCK1 expression was elevated in breast cancer patients and correlated with adverse clinicopathologic parameters. Patients with high circDOCK1 level had poor outcomes.
Conclusion: A novel circDOCK1/miR-138-5p/GRB7 axis promotes HER2 positive breast cancer metastasis and progression, providing a potential therapeutic target in the treatment of breast cancer.

Keywords: circular DOCK1, ceRNA, breast cancer, progression, patient survival