CircPLK1 Acts as a Carcinogenic Driver to Promote the Development of Malignant Pleural Mesothelioma by Governing the miR-1294/HMGA1 Pathway.

The deregulation of circular RNAs (circRNAs) is involved in cancer development. CircRNA polo-like kinase 1 (circPLK1) was reported to promote breast cancer development. However, the role of circPLK1 in malignant pleural mesothelioma (MPM) is unclear. The expression of circPLK1, miR-1294, and high mobility group AT-hook 1 (HMGA1) mRNA was measured by quantitative real-time PCR (qPCR). Cell viability was detected by CCK-8 assay. Colony formation ability was monitored by colony formation assay. Cell proliferation was detected by EdU assay. Cell migration and cell invasion were monitored by transwell assay. Cancer cell stemness was investigated by sphere formation assay. The protein levels of marker proteins and HMGA1 expression were measured by western blot analysis. The binding relationship between miR-1294 and circPLK1 or HMGA1 was validated by pull-down assay, dual-luciferase reporter assay or RIP assy. Animal study was performed to disclose the role of circPLK1 in vivo. Exosomes were identified by transmission electron microscopy (TEM) and nanoparticle tracking analysis (NTA). CircPLK1 was upregulated in MPM tumor tissues and cell lines. CircPLK1 knockdown suppressed the proliferation, migration, invasion and stemness of MPM cells. CircPLK1 contained a binding site for miR-1294 and thus bound to miR-1294 to sequester its expression. Inhibition of miR-1294 reversed the effects of circPLK1 knockdown. HMGA1 was a target of miR-1294, and circPLK1 bound to miR-1294 to increase the expression of HMGA1. MiR-1294 restoration also suppressed the proliferation, migration, invasion and stemness of MPM cells, while these effects were abolished by HMGA1 overexpression. In addition, circPLK1 knockdown inhibited tumor growth in vivo. CircPLK1 was overexpressed in exosomes derived from serum of MPM patients. CircPLK1 knockdown inhibited MPM cell proliferation, migration, invasion and stemness by targeting the miR-1294/HMGA1 pathway.