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

Background & aims Interleukin (IL)-6 induced tumor progression has been well established via the induction of anti-apoptotic 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 & results High-throughput RNA-seq was used to identify the differentially expressed circRNAs upon IL-6 stimulation in intrahepatic cholangiocarcinoma (ICC) cells. CircRNA GGNBP2 (derived from ggnbp2 gene, termed as cGGNBP2) was upregulated by IL-6 treatment in a time and concentration-dependent manner. The biogenesis of cGGNBP2 was regulated by RNA-binding protein DHX9, which was also mediated by IL-6 exposure. Mass spectrometry and western blotting identified a novel 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 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 ICC patients and was identified as an independent risk factor for patient prognosis. Conclusions Our study demonstrates that cGGNBP2-184aa, a novel protein encoded by IL-6 induced cGGNBP2, formed a positive feedback loop to facilitate ICC progression and may serves as an auxiliary target for clinical IL-6/STAT3-targeting treatments in ICC.