PURPOSE

The oncogenic role of circular RNAs (circRNA) has been well studied in cancers including colorectal cancer. However, tumor-suppressive circRNAs and the mechanism through which they exert their antitumor effects remain largely unknown. We aim to find out the critical tumor-suppressive circRNAs and their possibility to serve as gene therapy targets.

EXPERIMENTAL DESIGN

circRNA sequencing, gain-of-function and loss-of-function experiments, and transcriptomic analysis were performed to find tumor-suppressive and antitumor immunity effects of circRERE. Molecular biology experiments were conducted for mechanism exploration. Finally, we conducted adeno-associated virus (AAV) to deliver circRERE (circRERE-AAV) and evaluated circRERE-AAV alone and in combination with anti-PD-1 antibody in C57BL/6J mice bearing subcutaneous MC38 tumors.

RESULTS

circRERE is lowly expressed in colorectal cancer. Overexpression of circRERE inhibits the malignant behaviors of colorectal cancer in vitro and in vivo, while knockdown exhibits the opposite effects. The expression of circRERE is regulated by EP300, a histone acetyltransferase downregulated in colorectal cancer as well. Mechanistically, circRERE acts as a competitive endogenous RNA to sponge miR-6837-3p to upregulate MAVS expression, thereby activating type I IFN signaling and promoting antitumor immunity. Delivery of circRERE-AAV elicits significant antitumor effects, and combination treatment with circRERE-AAV and anti-PD-1 antibody exhibits synergistic effects on tumor growth in preclinical models of colorectal cancer.

CONCLUSIONS

These results uncover modulatory axis constituting of EP300/circRERE/miR-6837-3p/MAVS and its essential roles in antitumor immunity, and demonstrate that circRERE-AAV might represent a new therapeutic avenue to prime immune responses and boost the effects of immunotherapy in clinic.