CircGAK inhibits cell growth, migration, invasion, and angiogenesis of hepatocellular carcinoma via miR-1323/HHIP axis

Increasing evidence demonstrates that circular RNA (circRNA) plays a pivotal role in the development of disease, especially in Cancer. A previous circRNA microarray study showed that circGAK (hsa_circ_0005830) was remarkably down-regulated in hepatocellular carcinoma (HCC) tissues. However, the role of circGAK in HCC remains largely unclear. The candidate circRNAs were screened via integrating the Gene Expression Omnibus (GEO) database (GSE164803) analysis with the online program GEO2R. Quantitative real-time PCR (qRT-PCR) was employed to measure the expression of circGAK miR-1323, and hedgehog-interacting protein (HHIP) in HCC tissues and cells. The biological function of circGAK in HCC was examined using colony formation assay, 5-ethynyl-2'-deoxyuridine (EdU) assay, wound healing assay, transwell cell invasion assay, endothelial tubular formation assay, western blot assay, and xenograft mouse model. Bioinformatics analysis, RNA immunoprecipitation (RIP) assay, and dual-luciferase reporter assay were utilized to test the interaction between miR-1323, and circGAK or HHIP. The expression of circGAK was abnormally down-regulated in HCC tissues and was associated with the tumor-node-metastasis (TNM) stage. Overexpression of circGAK remarkably impeded HCC cell proliferation, migration, invasion, and endothelial tube formation in vitro, and tumor growth in vivo. Bioinformatics predicted that circGAK interacted with miR-1323, which targeted the HHIP mRNA 3'untranslated regions (UTR). Furthermore, upregulation of miR-1323 or shRNA-mediated HHIP suppression could recover circGAK-mediated malignant behaviors of HCC cells and tube formation of endothelial cells. Taken together, the circGAK/miR-1323/HHIP axis could suppress the progression of HCC and may provide potential new targets for the diagnosis and therapy of HCC.