Knockdown of DNA polymerase ζ relieved the chemoresistance of glioma via inhibiting the PI3K/AKT signaling pathway

Abstract

Previous reports suggest that DNA polymerase ζ is highly expressed in glioma tissues. The present study aimed to investigate the roles of the REV7 subunit of DNA polymerase ζ in glioma cell chemoresistance and its underlying mechanisms. The bioinformatics method was used to compare the expression of REV7 in glioma and normal tissues. The expression of REV7 in glioma tumor samples and the adjacent tissue was examined by reverse transcription polymerase chain reaction. Moreover, an in vitro analysis using glioma cells was used to test the effects of REV7 siRNA on the proliferation and apoptosis of glioma cell line U251 cells, and the effect of REV7 siRNA on the sensitivity of the U251 cells to cisplatin was also explored. The expression of REV7 in glioma tumors was significantly increased. Moreover, the knockdown of REV7 in glioma cells decreased the proliferation and increased the apoptosis of U251 cells; moreover, REV7 siRNA also increased the sensitivity of U251 cells to cisplatin. Finally, REV7 may regulate the proliferation, apoptosis, and chemosensitivity of U251 cells by affecting phosphoinositide 3-kinase signaling. Our data suggest that REV7 is involved in the chemosensitivity of glioma cells and provides a theoretical basis for targeting DNA polymerase ζ to improve the sensitivity of glioma cells to chemotherapy.

REV7 in Cancer Biology and Management

“…Although REV7 expression is low in most normal human tissues except for the testis, its expression is relatively high in various human tumor tissues, including colon, ovarian, breast, esophageal, lung, and skin cancers, gliomas, diffuse large B cell lymphomas, and testicular germ cell tumors (TGCTs) [ 85 , 86 , 87 , 88 , 89 , 90 , 91 , 92 , 93 ]. REV7 expression levels are correlated with cell proliferation ability represented by Ki-67 labeling indexes in small cell lung carcinomas and malignant melanomas, with metastases in breast and lung cancers, with tumor thickness in malignant melanomas, and with tumor sizes of gliomas [ 89 , 92 , 93 , 94 , 95 ]. There is a significant association between high levels of REV7 expression and poor prognosis in several tumors, including colon, breast, lung, gastric, and advanced ovarian cancers, diffuse large B cell lymphomas, and advanced bone and soft tissue sarcomas, suggesting the utility of REV7 as a biomarker for cancer prognosis [ 85 , 87 , 88 , 89 , 94 , 96 , 97 ].…”

“…The mechanisms for the upregulation of REV7 in tumor tissues have not been fully elucidated, although zinc finger protein with KRAB and SCAN domains 3 (ZKSCAN3), an oncogenic transcription factor, acts as a transcriptional repressor of REV7 in cultured tumor cells [ 98 ]. The contribution of REV7 to poor prognosis in various malignancies may be explained by the following: (1) REV7-high tumors exhibit the potential for high proliferation and tend to be more advanced [ 89 , 92 , 93 , 94 , 95 ]; and (2) REV7 expression affects cell mobility, intracellular signaling, EMT, and sensitivity to chemoradiotherapy, which will be discussed later. In support of this, a clinical study on advanced bone and soft tissue sarcomas demonstrated that REV7 expression is significantly high in non-responders to trabectedin and olaparib combination therapy [ 97 ].…”

“…The significance of REV7 in cancer cell biology has been studied using cultured cancer cells, most of which demonstrate the cancer-promoting effects of REV7, and a possible application of REV7 to cancer management has been proposed. Inactivation of REV7 with siRNA-mediated knockdown or CRISPR/Cas9 system-mediated gene silencing in a variety of cancer cells promotes the inhibition of cell growth, mobility, invasion, clonogenicity, and EMT in vitro, indicating that REV7 expression affects the nature of cancer cells [ 87 , 89 , 90 , 91 , 92 , 93 , 94 , 95 , 96 , 99 ]. Hypersensitivity to DNA-damaging agents such as cisplatin, carboplatin, melphalan, chlorethamine, doxorubicin, mitomycin c, or γ-irradiation, but not to H 2 O 2 , 5FU, taxol, or vincristine, decreased spontaneous and damage-induced mutation frequency, accumulation of DSBs and increased chromosomal aberrations after DNA damage, and suppressed cisplatin-induced SCE are promoted by REV7 depletion in nasopharyngeal carcinoma cells [ 61 ].…”

“…Consistently, the overexpression of REV7 promotes chemoresistance in lung cancer cells and radioresistance in esophageal SCC cells [ 90 , 94 ]. Mechanistically, REV7 activates intracellular signaling of the PI3K–AKT and RAS–MAPK pathways and promotes TGF-β1 expression, resulting in the acceleration of cell proliferation, migration, invasion, and EMT [ 89 , 93 , 95 ]. These results indicated that REV7 is involved in cell activity via modulating intracellular signaling and that its depletion promotes increased sensitivity to chemoradiotherapy, conceivably by abrogation of TLS-mediated DNA damage tolerance.…”

Insights into RNA transcriptome sequencing of retinal tissues in hypertensive retinopathy rat model

“…For instance, miRNAs, which are small ncRNAs that bind to the 3' untranslated region of target mRNAs to modulate gene expression, could regulate endothelial function, in ammation, and vascular remodeling in hypertensive retinopathy [7][8][9]. Similarly, lncRNAs that are longer than 200 nucleotides and could modulate gene expression through various mechanisms, have been shown to be differentially expressed within the retinas of hypertensive rats and may contribute to the pathogenesis of hypertensive retinopathy [10,11]. Furthermore, circRNAs, which are covalently closed circular RNAs that act as miRNA sponges, have recently been identi ed as potential regulators of gene expression in hypertensive retinopathy [12,13].…”