IL-6–induced cGGNBP2 encodes a protein to promote cell growth and metastasis in intrahepatic cholangiocarcinoma

Abstract

Background and Aims: IL-6–induced tumor progression has been well established through the induction of antiapoptotic and proliferative genes. However, whether other mechanisms such as IL-6 regulation of circular RNAs (circRNAs) may also contribute to tumor development remains unknown. Approach and Results: High-throughput RNA sequencing was used to identify the differentially expressed circRNAs on IL-6 stimulation in intrahepatic cholangiocarcinoma (ICC) cells. CircRNA GGNBP2 (derived from ggnbp2 gene, termed as cGGNBP2) was up-regulated by IL-6 treatment in a time and concentration-dependent manner. The biogenesis of cGGNBP2 was regulated by RNA-binding protein DEx-H Box Helicase 9, which was also mediated by IL-6 exposure. Mass spectrometry and western blotting identified a protein cGGNBP2-184aa encoded by cGGNBP2. cGGNBP2-184aa promoted ICC cell proliferation and metastasis in vitro and in vivo. Mechanistically, cGGNBP2-184aa directly interacted with signal transducers and activators of transduction-3 (STAT3), phosphorylated STAT3Tyr705, and played a positive regulatory role in modulating IL-6/STAT3 signaling. IL-6/cGGNBP2-184aa/STAT3 formed a positive feedback loop to sustain constitutive activation of IL-6/STAT3 signaling. Elevated cGGNBP2 expression was correlated with poor prognosis of patients with ICC and was identified as an independent risk factor for patient prognosis. Conclusions: Our study demonstrates that cGGNBP2-184aa, a protein encoded by IL-6–induced cGGNBP2, formed a positive feedback loop to facilitate ICC progression and may serve as an auxiliary target for clinical IL-6/STAT3-targeting treatments in ICC.