A novel NF-κB regulator encoded by circPLCE1 inhibits colorectal carcinoma progression by promoting RPS3 ubiquitin-dependent degradation

Background: Constitutive activation of nuclear factor-kappa B (NF-kappa B) signaling plays a key role in the development and progression of colorectal carcinoma (CRC). However, the underlying mechanisms of excessive activation of NF-kappa B signaling remain largely unknown. Methods: We used high throughput RNA sequencing to identify differentially expressed circular RNAs (circRNAs) between normal human intestinal epithelial cell lines and CRC cell lines. The identification of protein encoded by circPLCE1 was performed using LC-MS. The function of novel protein was validated in vitro and in vivo by gain or loss of function assays. Mechanistic results were concluded by immunoprecipitation analyses. Results: A novel protein circPLCE1-411 encoded by circular RNA circPLCE1 was identified as a crucial player in the NF-kappa B activation of CRC. Mechanistically, circPLCE1-411 promoted the ubiquitin-dependent degradation of the critical NF-kappa B regulator RPS3 via directly binding the HSP90 alpha/RPS3 complex to facilitate the dissociation of RPS3 from the complex, thereby reducing NF-kappa B nuclear translocation in CRC cells. Functionally, circPLCE1 inhibited tumor proliferation and metastasis in CRC cells, as well as patient-derived xenograft and orthotopic xenograft tumor models. Clinically, circPLCE1 was downregulated in CRC tissues and correlated with advanced clinical stages and poor survival. Conclusions: circPLCE1 presents an epigenetic mechanism which disrupts NF-kappa B nuclear translocation and serves as a novel and promising therapeutic target and prognostic marker.