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End Processing Factor APLF Promotes NHEJ Efficiency and Contributes to TMZ- and Ionizing Radiation-Resistance in Glioblastoma Cells.

ABSTRACT: Purpose:Glioblastoma (GBM) is the most commonly diagnosed primary brain tumor in adults. Despite a variety of advances in the understanding of GBM cancer biology during recent decades, very few of them were applied into treatment, and the survival rate of GBM patients has not been improved majorly due to the low chemosensitivity to temozolomide (TMZ) or low radiosensitivity. Therefore, it is urgent to elucidate mechanisms of TMZ- and IR-resistance and develop novel therapeutic strategies to improve GBM treatment. Methods:TMZ- and IR-resistant cell lines were acquired by continuous exposing parental GBM cells to TMZ or IR for 3 months. Cell viability was determined by using Sulforhodamine B (SRB) assay. Protein and mRNA expression were examined by Western blotting assay and quantitative polymerase chain reaction (qPCR) assay, respectively. Homologous recombination (HR) and nonhomologous end joining (NHEJ) efficiency were measured by HR and NHEJ reporter assay. Cell apoptosis was determined by Caspase3/7 activity. Autophagy was analyzed using CYTO-ID® Autophagy detection kit. Tumor growth was examined by U87 xenograft mice model. Results:DNA repair efficiency of non-homologous end joining (NHEJ) pathway is significantly increased in TMZ- and IR-resistant GBM cells. Importantly, APLF, which is one of the DNA end processing factors in NHEJ, is upregulated in TMZ- and IR-resistant GBM cells and patients. APLF deficiency significantly decreases NHEJ efficiency and improves cell sensitivity to TMZ and IR both in vitro and in vivo. Conclusion:Our study provides evidence for APLF serving as a promising, novel target in GBM chemo- and radio-therapy.

SUBMITTER: Dong W

PROVIDER: S-EPMC7584509 | biostudies-literature | 2020

REPOSITORIES: biostudies-literature

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End Processing Factor APLF Promotes NHEJ Efficiency and Contributes to TMZ- and Ionizing Radiation-Resistance in Glioblastoma Cells.

Dong Wei W Li Lanlan L Teng Xuepeng X Yang Xinhua X Si Shujing S Chai Jie J

OncoTargets and therapy 20201019

<h4>Purpose</h4>Glioblastoma (GBM) is the most commonly diagnosed primary brain tumor in adults. Despite a variety of advances in the understanding of GBM cancer biology during recent decades, very few of them were applied into treatment, and the survival rate of GBM patients has not been improved majorly due to the low chemosensitivity to temozolomide (TMZ) or low radiosensitivity. Therefore, it is urgent to elucidate mechanisms of TMZ- and IR-resistance and develop novel therapeutic strategies ...[more]

PMID: 33116637

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Project description:BackgroundBladder cancer progression has been associated with dysfunctional repair of double-strand breaks (DSB), a deleterious type of DNA lesions that fuel genomic instability. Accurate DSB repair relies on two distinct pathways, homologous recombination (HR) and classical non-homologous end-joining (c-NHEJ). The transcription factor E2F1 supports HR-mediated DSB repair and protects genomic stability. However, invasive bladder cancers (BC) display, in contrast to non-invasive stages, genomic instability despite their high E2F1 levels. Hence, E2F1 is either inefficient in controlling DSB repair in this setting, or rewires the repair apparatus towards alternative, error-prone DSB processing pathways.MethodsRT-PCR and immunoblotting, in combination with bioinformatics tools were applied to monitor c-NHEJ factors status in high-E2F1-expressing, invasive BC versus low-E2F1-expressing, non-invasive BC. In vivo binding of E2F1 on target gene promoters was demonstrated by ChIP assays and E2F1 CRISPR-Cas9 knockdown. MIR888-dependent inhibition of APLF by E2F1 was demonstrated using overexpression and knockdown experiments, in combination with luciferase assays. Methylation status of MIR888 promoter was monitored by methylation-specific PCR. The changes in invasion potential and the DSB repair efficiency were estimated by Boyden chamber assays and pulse field electrophoresis, correspondingly.ResultsHerein, we show that E2F1 directly transactivates the c-NHEJ core factors Artemis, DNA-PKcs, ligase IV, NHEJ1, Ku70/Ku80 and XRCC4, but indirectly inhibits APLF, a chromatin modifier regulating c-NHEJ. Inhibition is achieved by miR-888-5p, a testis-specific, X-linked miRNA which, in normal tissues, is often silenced via promoter methylation. Upon hypomethylation in invasive BC cells, MIR888 is transactivated by E2F1 and represses APLF. Consequently, E2F1/miR-888/APLF rewiring is established, generating conditions of APLF scarcity that compromise proper c-NHEJ function. Perturbation of the E2F1/miR-888/APLF axis restores c-NHEJ and ameliorates cell invasiveness. Depletion of miR-888 can establish a 'high E2F1/APLF/DCLRE1C' signature, which was found to be particularly favorable for BC patient survival.ConclusionSuppression of the 'out-of-context' activity of miR-888 improves DSB repair and impedes invasiveness by restoring APLF.

Project description:Despite optimal clinical treatment, glioblastoma multiforme (GBM) inevitably recurs. Standard treatment of GBM, exposes patients to radiation which kills tumor cells, but also modulates the molecular fingerprint of any surviving tumor cells and the cross-talk between those cells and the host. Considerable investigation of short-term (hours to days) post-irradiation tumor cell response has been undertaken, yet long-term responses (weeks to months) which are potentially even more informative of recurrence, have been largely overlooked. To better understand the potential of these processes to reshape tumor regrowth, molecular studies in conjunction with in silico modeling were used to examine short- and long-term growth dynamics. Despite survival of 2.55% and 0.009% following 8 or 16Gy, GBM cell populations in vitro showed a robust escape from cellular extinction and a return to pre-irradiated growth rates with no changes in long-term population doublings. In contrast, these same irradiated GBM cell populations injected in vivo elicited tumors which displayed significantly suppressed growth rates compared to their pre-irradiated counterparts. Transcriptome analysis days to weeks after irradiation revealed, 281 differentially expressed genes with a robust increase for cytokines, histones and C-C or C-X-C motif chemokines in irradiated cells. Strikingly, this same inflammatory signature in vivo for IL1A, CXCL1, IL6 and IL8 was increased in xenografts months after irradiation. Computational modeling of tumor cell dynamics indicated a host-mediated negative pressure on the surviving cells was a source of inhibition consistent with the findings resulting in suppressed tumor growth. Thus, tumor cells surviving irradiation may shift the landscape of population doubling through inflammatory mediators interacting with the host in a way that impacts tumor recurrence and affects the efficacy of subsequent therapies. Clues to more effective therapies may lie in the development and use of pre-clinical models of post-treatment response to target the source of inflammatory mediators that significantly alter cellular dynamics and molecular pathways in the early stages of tumor recurrence.

Dataset Information

End Processing Factor APLF Promotes NHEJ Efficiency and Contributes to TMZ- and Ionizing Radiation-Resistance in Glioblastoma Cells.

Publications

End Processing Factor APLF Promotes NHEJ Efficiency and Contributes to TMZ- and Ionizing Radiation-Resistance in Glioblastoma Cells.

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