Circ-LAMP1 contributes to the growth and metastasis of cholangiocarcinoma via miR-556-5p and miR-567 mediated YY1 activation.

Dysregulation of circular RNAs (circRNAs) executes important regulatory roles in carcinogenesis. Nonetheless, few studies focused on the mechanisms of circRNAs in cholangiocarcinoma (CCA). qRT-PCR was applied to verify the dysregulated circRNAs in CCA. Fisher's exact test, Kaplan-Meier analysis and Cox regression model were utilized to investigate the clinical implications of circ-LAMP1 in the patients with CCA. The viability, apoptosis, migration and invasion of CCA cells were detected after silencing/overexpression of circ-LAMP1. Xenograft and lung metastasis assays were performed to verify the in vitro results. The regulatory networks of circ-LAMP1 were unveiled by bioinformatic analysis, RNA immunoprecipitation (RIP), RNA pulldown and luciferase reporter assays. Up-regulation of circ-LAMP1 was found in CCA tissue samples and cell lines. Enhanced level of circ-LAMP1 was linked to clinical severity, high post-operative recurrence and poor prognosis for the patients with CCA. Gain/loss-of-function assays confirmed the oncogenic role of circ-LAMP1 in mediating cell growth, apoptosis, migration and invasion. Nevertheless, the level of circ-LAMP1 had no effect on normal biliary epithelium proliferation and apoptosis. Animal study further verified the in vitro data. Mechanistically, circ-LAMP1 directly sponged miR-556-5p and miR-567, thereby releasing their suppression on YY1 at post-transcriptional level. Rescue assay indicated that the oncogenic role of circ-LAMP1 is partially dependent on its modulation of YY1 in CCA. In summary, this study suggested that circ-LAMP1 might be used as a promising biomarker/therapeutic target for CCA.