CircSETD3 mediates acquired resistance to gefitinib in non-small lung cancer cells by FXR1/ECT2 pathway

BACKGROUND

Gefitinib is the first-line treatment for non-small cell lung cancer (NSCLC) harboring EGFR sensitive mutation. However, acquired resistance significantly limits its therapeutic efficacy. CircSETD3 has been reported to promote gefitinib resistance in NSCLC cells, however, its underlying mechanisms have not been fully clarified.

METHODS

The expression of circSETD3 were detected in NSCLC patients who received gefitinib as first-line treatment, including 20 gefitinib-sensitive patients and 20 acquired gefitinib-resistant patients. Cell viability were examined by CCK8 assay. The mRNA and protein levels were detected by qRT-PCR and western blot. Using RNA pull-down assay followed by mass spectrometry to identified proteins that interact with circSETD3. The interaction between circSETD3 and fragile X-related protein-1 (FXR1) were further validated by RNA immunoprecipitation (RIP) and pull-down analysis. Fuorescence in situ hybridization (FISH) and immunofluorescence (IF) assays was used for the identification of sub-location of circSETD3 and FXR1 in cells. The effect of circSETD3 overexpression and knockdown on NSCLC tumor growth to gefitinib sensitivity was detected using the mouse xenograft model.

RESULTS

CircSETD3 was significantly upregulated in gefitinib-resistant NSCLC cells, and decreased the gefitinib sensitivity in vitro and in vivo. Mechanically, circSETD3 facilitated FXR1 binding to its downstream mRNA target, epithelial cell-transforming sequence 2 (ECT2), promoting ECT2 mRNA decay, which further inhibited cellular apoptosis.

CONCLUSION

CircSETD3/FXR1/ECT2 axis plays a critical role in the acquired resistance to gefitinib in NSCLC. Our results highlight the potential of circSETD3 as a biomarker and therapeutic target for NSCLC patients with acquired gefitinib resistance.

CircSETD3 (Hsa_circ_0000567) Suppresses Hepatoblastoma Pathogenesis via Targeting the miR-423-3p/Bcl-2-Interacting Mediator of Cell Death Axis

Background: Up until now, the role of circSETD3 (Has_circ_0000567) in regulating cancer development has been reported in several tumors, but the role and regulatory mechanism of circSETD3 in hepatoblastoma (HB) remain unclear.

Methods: The qPCR and western blotting were used to determine the mRNA and protein levels in the present study. Stability of circular RNA was detected by RNA digested experiments. The gain-of-function and rescue experiments were used to explore the function and mechanism of circSETD3 in HB. Cell counting kit-8, colony formation, transwell assay, and xenograft mice model were used to detect effects and regulatory mechanism of circSETD3/miR-423-3p/Bim axis on cell aggressive phenotype in vitro and in vivo.

Results: Here, we identified that circSETD3 downregulated in both HB clinical tissues and cell lines, compared to that of normal tissues and cells. Further gain-of-function experiments validated that circSETD3 overexpression inhibited cell proliferation, viability, migration, epithelial-mesenchymal transition (EMT) and tumorigenesis, and induced cell apoptosis in HB cells. Next, we validated that miR-423-3p targeted both circSETD3 and 3′ untranslated region (3′UTR) of Bim, and circSETD3 positively regulated Bim in HB cells through sponging miR-423-3p in a competing endogenous RNA (ceRNA)-dependent manner. Furthermore, through conducting reversal experiments, we evidenced that the inhibiting effects of circSETD3 overexpression on HB development were abrogated by upregulating miR-423-3p and downregulating Bim.

Conclusion: Taken together, we evidenced that circSETD3 sponged miR-423-3p to upregulate Bim, resulting in the inhibition of HB development.

New biomarker for lung cancer - focus on circSETD3

In order to explore the mechanism of gefitinib-acquired resistance in lung cancer, a new biomarker has been developed for early clinical diagnosis and intervention; human NSCLC (Non-Small Cell Lung Cancer) cell lines H292 (denoted as H292S) and PC9 (denoted as PC9S) were used to establish gefitinib-resistant NSCLC cell lines H292 and PC9 models. CCK-8 (Cell Counting Kit-8) method was used to test the drug resistance of the cells. circRNAs (circular RNAs) that were differentially expressed before and after resistance were screened by RNA sequencing technology. The effects of circSETD3 overexpression and interference on the sensitivity of gefitinib was observed to analyze the nuclear localization of circSETD3 and verify the interaction between circSETD3-miR-520h-ABCG2. The results showed that the most significant change in differential expression of human NSCLC cell lines before and after drug resistance was hsa_circ_0000567, that is, circSETD3, which is mainly present in the cytoplasm. In H292S and PC9S, compared with the negative control group, the cell proliferation ability of the overexpression group was significantly increased, and the apoptosis ability was significantly decreased. In H292R and PC9R, compared with the negative control group, the proliferation ability of the interference group was significantly decreased, and the apoptosis ability was significantly increased. Overexpression of circSETD3 to H292S and PC9S, the expression of ABCG2 increased significantly. Also, the expression of ABCG2 decreased significantly after transfection with miR-520h mimics. H292R and PC9R interfered with circSETD3, the expression of ABCG2 decreased significantly. Moreover, the expression of ABCG2 increased significantly after transfection with miR-520h inhibitor. In conclusion, circSETD3 can be used as a novel biomarker for lung cancer. It relieves miR-520h degradation of the transporter ABCG2 by down-regulating the miR-520h expression, causing gefitinib to be pumped out of the cell.

circSETD3 Contributes to Acquired Resistance to Gefitinib in Non-Small-Cell Lung Cancer by Targeting the miR-520h/ABCG2 Pathway

Gefitinib is a first-line treatment for patients with non-small-cell lung cancer (NSCLC), but acquired resistance is a major obstacle to its therapeutic efficacy, and the underlying mechanisms are not fully elucidated. Recent studies have indicated that circular RNAs play a crucial role in chemoresistance, but their expression and function in NSCLC cells with acquired resistance to gefitinib are largely unknown. In this study, we determined that circSETD3 was significantly upregulated in gefitinib-resistant NSCLC cell lines and the plasma of gefitinib-resistant NSCLC patients. circSETD3 markedly decreased the gefitinib sensitivity of NSCLC cells both in vitro and in nude mice xenografts. It could directly bind to miR-520h and lead to the upregulation of ATP-binding cassette subfamily G member 2 (ABCG2), an efflux transporter of gefitinib, resulting in a reduced intracellular gefitinib concentration. Moreover, we reported that the downregulation of serine/arginine splicing factor 1 (SRSF1) contributed to, at least in part, the increased expression of circSETD3 in NSCLC cells with acquired resistance to gefitinib. Taken together, our findings indicated that circSETD3 may serve as a prognostic biomarker and a potential therapeutic target for acquired resistance to gefitinib in NSCLC.