Exosomal circZFR promotes colorectal cancer progression via interacting with BCLAF1 and regulating the miR-3127-5p/RTKN2 axis

Background Circular RNAs (circRNAs) have gained attention as novel biomarkers for cancer diagnosis and prognosis. Aberrant expression of circRNAs is widely involved in cancer development, whereas the function and mechanism of novel circRNAs in colorectal cancer (CRC) remain unclear. Methods CircZFR was identified both in CRC tissues from the GEO database and in serum exosomes by competing endogenous RNA (ceRNA) microarray. The expression of circZFR was evaluated in CRC tissues and serum by qRT-PCR and in tissue microarray (TMA) by FISH. The functional roles were confirmed using a series of in vitro assays and tumor xenografts and pulmonary/hepatic metastasis mouse models. The mechanisms of circZFR were assessed through circRNA pulldown, RNA immunoprecipitation (RIP), dual-luciferase reporter assays and rescue experiments. Lastly, TCP1-CD-QDs nanocarrier was used to carry circZFR siRNA (si-circZFR) to exam the therapeutic potential of circZFR in patient-derived xenograft (PDX) models. Results CircZFR was upregulated in cancer tissues and serum exosomes of CRC patients and its level was positively associated to advanced TNM stages and poor prognosis. Serum circZFR was indicative of CRC incidence, advanced-stages and metastasis. Functional experiments demonstrated that circZFR promoted CRC proliferation and metastasis but inhibited apoptosis in vitro and in vivo, exosomes with upregulation of circZFR facilitated growth and migration of cocultured CRC cells. Mechanistically, the generation of circZFR could be improved by epithelial splicing regulatory protein 1 (ESRP1) in CRC cells. CircZFR bound to BCL2-associated transcription factor 1 (BCLAF1) and inhibited its ubiquitinated degradation. Moreover, circZFR sponged miR-3127-5p to increase the expression of rhotekin 2 (RTKN2). Our TCP1-CD-QDs nanocarrier was able to carry si-circZFR and delivered them to the vasculature of CRC tissues and cells, resulting in suppressive tumor growth without obvious adverse effects in PDX models. Conclusions Our findings indicate that ESRP1-mediated circZFR exerts oncogenic effects on CRC development and spread through suppressing BCLAF1 degradation and regulating the miR-3127-5P/RTKN2 axis. CircZFR is a promising serum biopsy marker for CRC diagnosis and an attractive target for further therapy.