Background: Radiation therapy is the primary method of treatment for glioblastoma (GBM). Therefore, the suppression of radioresistance in GBM cells is of enormous significance. Ribophorin II (RPN2), a protein component of an N-oligosaccharyl transferase complex, has been associated with chemotherapy drug resistance in multiple cancers, including GBM. However, it remains unclear whether this also plays a role in radiation therapy resistance in GBM. Methods: We conducted a bioinformatic analysis of RPN2 expression using the UCSC Cancer Genomics Browser and GEPIA database and performed an immunohistochemical assessment of RPN2 expression in biopsy specimens from 34 GBM patients who had received radiation-based therapy. We also studied the expression and function of RPN2 in radiation-resistant GBM cells. Results: We found that RPN2 expression was upregulated in GBM tumors and correlated with poor survival. The expression of RPN2 was also higher in GBM patients with tumor recurrence, who were classified to be resistant to radiation therapy. In the radiation-resistant GBM cells, the expression of RPN2 was also higher than in the parental cells. Depletion of RPN2 in resistant cells can sensitize these cells to radiation-induced apoptosis, and overexpression of RPN2 had the reverse effect. Myeloid cell leukemia 1 (MCL1) was found to be the downstream target of RPN2, and contributed to radiation resistance in GBM cells. Furthermore, STAT3 was found to be the regulator of MCL1, which can be activated by RPN2 dysregulation. Conclusion: Our study has revealed a novel function of RPN2 in radiation-resistant GBM, and has shown that MCL1 depletion or suppression could be a promising method of therapy to overcome the resistance promoted by RPN2 dysregulation.

Background Glioma is the most frequent, highly aggressive primary intracranial malignant tumor. Circular RNA (circRNA) circ_0037655 has been reported to be a vital regulator in glioma. The different functional mechanism behind circ_0037655 was investigated in the current study. Methods The expression of circ_0037655, microRNA-1229-3p (miR-1229-3p) and integrin beta-8 (ITGB8) was detected via the quantitative reverse transcription-polymerase chain reaction (qRT-PCR). Cellular research was performed via colony formation assay for cell proliferation, flow cytometry for cell cycle and cell apoptosis, scratch assay for cell migration, as well as transwell assay for cell migration and invasion. Western blot was used for detection of ITGB8 protein and epithelial–mesenchymal transition (EMT) process. Dual-luciferase reporter assay was implemented for the binding analysis of potential targets. In vivo assay was administered via xenograft in mice. Results Upregulation of circ_0037655 was affirmed in glioma samples and cells. Tumor formation and metastasis of glioma were inhibited after circ_0037655 was downregulated. miR-1229-3p acted as a target of circ_0037655, and its upregulation was responsible for the function of si-circ_0037655 in glioma cells. miR-1229-3p functioned as a tumor inhibitor in glioma progression by targeting ITGB8. circ_0037655 modulated the ITGB8 expression by targeting miR-1229-3p. In vivo knockdown of circ_0037655 also suppressed glioma tumorigenesis by acting on the miR-1229-3p/ITGB8 axis. Conclusion This study showed that downregulation of the expression of circ_0037655 could inhibit glioma progression by acting on the miR-1229-3p/ITGB8 axis. The specific circ_0037655/miR-1229-3p/ITGB8 axis was disclosed in glioma research.