Transformed astrocytes confer temozolomide resistance on glioblastoma via delivering ALKBH7 to enhance APNG expression after educating by glioblastoma stem cells-derived exosomes.

BACKGROUND: Glioblastoma is the most malignant primary brain tumor in adults. Temozolomide (TMZ) stands for the first-line chemotherapeutic agent against glioblastoma. Nevertheless, the therapeutic efficacy of TMZ appears to be remarkably limited, because of low cytotoxic efficiency against glioblastoma. Besides, various mechanical studies and the corresponding strategies fail to enhancing TMZ curative effect in clinical practice. Our previous studies have disclosed remodeling of glial cells by GSCs, but the roles of these transformed cells on promoting TMZ resistance have never been explored. METHODS: Exosomes were extracted from GSCs culture through standard centrifugation procedures, which can activate transformation of normal human astrocytes (NHAs) totumor-associated astrocytes (TAAs) for 3 days through detect the level of TGF-ß, CD44 and tenascin-C. The secretive protein level of ALKBH7 of TAAs was determined by ELISA kit. The protein level of APNG and ALKBH7 of GBM cells were determined by Western blot. Cell-based assays of ALKBH7 and APNG triggered drug resistance were performed through flow cytometric assay, Western blotting and colony formation assay respectively. A xenograft tumor model was applied to investigate the function of ALKBH7 in vivo. Finally, the effect of the ALKBH7/APNG signaling on TMZ resistance were evaluated by functional experiments. RESULTS: Exosomes derived from GSCs can activate transformation of normal human astrocytes (NHAs)to tumor-associated astrocytes (TAAs), as well as up-regulation of ALKBH7expression in TAAs. Besides, TAAs derived ALKBH7 can regulate APNG gene expression of GBM cells. After co-culturing with TAAs for 5 days, ALKBH7 and APNG expression in GBM cells were elevated. Furthermore, Knocking-down of APNG increased the inhibitory effect of TMZ on GBM cells survival. CONCLUSION: The present study illustrated a new mechanism of glioblastoma resistance to TMZ, which based on GSCs-exo educated TAAs delivering ALKBH7 to enhance APNG expression of GBM cells, which implied that targeting on ALKBH7/APNG regulation network may provide a new strategy of enhancing TMZ therapeutic effects against glioblastoma.

Base-resolution quantitative DAMM-seq for mapping RNA methylations in tRNA and mitochondrial polycistronic RNA.

The human AlkB family proteins, such as FTO and ALKBH5, are known to mediate RNA m6A demethylation. However, although ALKBH7 localizes in mitochondria and affects metabolism, the detailed biological function and mechanism have remained unknown for years. We developed Demethylation-Assisted Multiple Methylation sequencing (DAMM-seq) to simultaneously detect N1-methyladenosine (m1A), N3-methylcytidine (m3C), N1-methylguanosine (m1G) and N2,N2-dimethylguanosine (m22G) methylations in both steady-state RNA and nascent RNA, and discovered that human ALKBH7 demethylates m22G and m1A within mt-Ile and mt-Leu1 pre-tRNA regions, respectively, in mitochondrial polycistronic RNA. DAMM-seq quantitatively and sensitively monitors the methylation stoichiometry change at pre-tRNA junctions within nascent mt-RNA, revealing the target region where ALKBH7 regulates RNA processing and local structural switch of polycistronic mt-RNAs. A new RNA demethylase in human cells was characterized through the base-resolution quantification of multiple RNA methylations in nascent mt-RNA, resolving the long-standing question about the functional substrate of ALKBH7.

N1-methyladenosine modification in cancer biology: Current status and future perspectives.

Post-transcriptional modifications in RNAs regulate their biological behaviors and functions. N1-methyladenosine (m1A), which is dynamically regulated by writers, erasers and readers, has been found as a reversible modification in tRNA, mRNA, rRNA and long non-coding RNA (lncRNA). m1A modification has impacts on the RNA processing, structure and functions of targets. Increasing studies reveal the critical roles of m1A modification and its regulators in tumorigenesis. Due to the positive relevance between m1A and cancer development, targeting m1A modification and m1A-related regulators has been of attention. In this review, we summarized the current understanding of m1A in RNAs, covering the modulation of m1A modification in cancer biology, as well as the possibility of targeting m1A modification as a potential target for cancer diagnosis and therapy.

PRMT5 regulates RNA m6A demethylation for doxorubicin sensitivity in breast cancer.

Cancer cells respond to various stressful conditions through the dynamic regulation of RNA m6A modification. Doxorubicin is a widely used chemotherapeutic drug that induces DNA damage. It is interesting to know whether cancer cells regulate the DNA damage response and doxorubicin sensitivity through RNA m6A modification. Here, we found that doxorubicin treatment significantly induced RNA m6A methylation in breast cancer cells in both a dose- and a time-dependent manner. However, protein arginine methyltransferase 5 (PRMT5) inhibited RNA m6A modification under doxorubicin treatment by enhancing the nuclear translocation of the RNA demethylase AlkB homolog 5 (ALKBH5), which was previously believed to be exclusively localized in the nucleus. Then, ALKBH5 removed the m6A methylation of BRCA1 for mRNA stabilization and further enhanced DNA repair competency to decrease doxorubicin efficacy in breast cancer cells. Importantly, we identified the approved drug tadalafil as a novel PRMT5 inhibitor that could decrease RNA m6A methylation and increase doxorubicin sensitivity in breast cancer. The strategy of targeting PRMT5 with tadalafil is a promising approach to promote breast cancer sensitivity to doxorubicin through RNA methylation regulation.

A Pan-Cancer Analysis Reveals the Prognostic and Immunotherapeutic Value of ALKBH7.

Recent studies have identified a role for ALKBH7 in the occurrence and progression of cancer, and this protein is related to cellular immunity and immune cell infiltration. However, the prognostic and immunotherapeutic value of ALKBH7 in different cancers have not been explored. In this study, we observed high ALKBH7 expression in 17 cancers and low expression in 5 cancers compared to paired normal tissues. Although ALKBH7 expression did not correlate relatively significantly with the clinical parameters of age (6/33), sex (3/33) and stage (3/27) in the cancers studied, the results of the survival analysis reflect the pan-cancer prognostic value of ALKBH7. In addition, ALKBH7 expression was significantly correlated with the TMB (7/33), MSI (13/33), mDNAsi (12/33) and mRNAsi (13/33) in human cancers. Moreover, ALKBH7 expression was associated and predominantly negatively correlated with the expression of immune checkpoint (ICP) genes in many cancers. Furthermore, ALKBH7 correlated with infiltrating immune cells and ESTIMATE scores, especially in PAAD, PRAD and THCA. Finally, the ALKBH7 gene coexpression network is involved in the regulation of cellular immune, oxidative, phosphorylation, and metabolic pathways. In conclusion, ALKBH7 may serve as a potential prognostic pan-cancer biomarker and is involved in the immune response. Our pan-cancer analysis provides insight into the role of ALKBH7 in different cancers.

The interactome and proteomic responses of ALKBH7 in cell lines by in-depth proteomics analysis.

BACKGROUND: ALKBH7 is a mitochondrial protein, involved in programmed necrosis, fatty acid metabolism, cell cycle regulation, and prostate cancer disease. However, the exact roles of ALKBH7 and the underlying molecular mechanisms remain mysterious. Thus, investigations of the interactome and proteomic responses of ALKBH7 in cell lines using proteomics strategies are urgently required. METHODS: In the present study, we investigated the interactome of ALKBH7 in mitochondria through immunoprecipitation-mass spectrometry/mass spectrometry (IP-MS/MS). Additionally, we established the ALKBH7 knockdown and overexpression cell lines and further identified the differentially expressed proteins (DEPs) in these cell lines by TMT-based MS/MS. Two DEPs (UQCRH and HMGN1) were validated by western blotting analysis. RESULTS: Through bioinformatic analysis the proteomics data, we found that ALKBH7 was involved in protein homeostasis and cellular immunity, as well as cell proliferation, lipid metabolism, and programmed necrosis by regulating the expression of PTMA, PTMS, UQCRH, HMGN1, and HMGN2. Knockdown of ALKBH7 resulted in upregulation of UQCRH and HMGN1 expression, and the opposite pattern of expression was detected in ALKBH7 overexpression cell lines; these results were consistent with our proteomics data. CONCLUSION: Our findings indicate that the expression of UQCRH and HMGN1 is regulated by ALKBH7, which provides potential directions for future studies of ALKBH7. Furthermore, our results also provide comprehensive insights into the molecular mechanisms and pathways associated with ALKBH7.

Metabolism and DNA repair shape a specific modification pattern in mitochondrial DNA.

The mitochondrial DNA (mtDNA) resides in the vicinity of energy-rich reactions. Thus, chemical modifications of mtDNA might mirror mitochondrial processes and could serve as biomarkers of metabolic processes in the mitochondria. This hypothesis was tested by assessing modifications at 17 different sites in the mtDNA as a function of cell type, oxidative stress and mitochondrial activity. Two mouse mutants with a metabolic phenotype were compared to wild-type (WT) mice: the ogg1-/- mouse that lacks the 8-oxoguanine DNA glycosylase (OGG1), and the alkbh7-/- mouse missing the ALKBH7 protein that has been implicated in fatty acid oxidation. It was found that cell type, oxidative stress and mitochondrial complex activity shaped distinct modification patterns in mtDNA, and that OGG1 and ALKBH7 independently modulated these modification patterns. The modifications included ribonucleotides, which also accumulated in mtDNA with age. Interestingly, this age-dependent accumulation most likely involves DNA repair, as mtDNA from ogg1-/- mice did not accumulate modifications with age. On the other hand, alkbh7-/- mtDNA accumulated more modifications with age than WT mtDNA. Our results show that mtDNA is dynamically modified with metabolic activity and imply a novel synergy between metabolism and mtDNA repair proteins.

The atomic resolution structure of human AlkB homolog 7 (ALKBH7), a key protein for programmed necrosis and fat metabolism.

ALKBH7 is the mitochondrial AlkB family member that is required for alkylation- and oxidation-induced programmed necrosis. In contrast to the protective role of other AlkB family members after suffering alkylation-induced DNA damage, ALKBH7 triggers the collapse of mitochondrial membrane potential and promotes cell death. Moreover, genetic ablation of mouse Alkbh7 dramatically increases body weight and fat mass. Here, we present crystal structures of human ALKBH7 in complex with Mn(II) and α-ketoglutarate at 1.35 Å or N-oxalylglycine at 2.0 Å resolution. ALKBH7 possesses the conserved double-stranded ß-helix fold that coordinates a catalytically active iron by a conserved HX(D/E) … Xn … H motif. Self-hydroxylation of Leu-110 was observed, indicating that ALKBH7 has the potential to catalyze hydroxylation of its substrate. Unlike other AlkB family members whose substrates are DNA or RNA, ALKBH7 is devoid of the "nucleotide recognition lid" which is essential for binding nucleobases, and thus exhibits a solvent-exposed active site; two loops between ß-strands ß6 and ß7 and between ß9 and ß10 create a special outer wall of the minor ß-sheet of the double-stranded ß-helix and form a negatively charged groove. These distinct features suggest that ALKBH7 may act on protein substrate rather than nucleic acids. Taken together, our findings provide a structural basis for understanding the distinct function of ALKBH7 in the AlkB family and offer a foundation for drug design in treating cell death-related diseases and metabolic diseases.

Human ALKBH7 is required for alkylation and oxidation-induced programmed necrosis.

Programmed necrosis has emerged as a crucial modulator of cell death in response to several forms of cellular stress. In one form of programmed necrotic cell death, induced by cytotoxic alkylating agents, hyperactivation of poly-ADP-ribose polymerase (PARP) leads to cellular NAD and ATP depletion, mitochondrial dysfunction, reactive oxygen species formation, and ensuing cell death. Here, we show that the protein encoded by the human AlkB homolog 7 (ALKBH7) gene plays a pivotal role in DNA-damaging agent-induced programmed necrosis by triggering the collapse of mitochondrial membrane potential and large-scale loss of mitochondrial function that lead to energy depletion and cellular demise. Depletion of ALKBH7 suppresses necrotic cell death induced by numerous alkylating and oxidizing agents while having no effect on apoptotic cell death. Like wild-type cells, ALKBH7-depleted cells undergo PARP hyperactivation and NAD depletion after severe DNA damage but, unlike wild-type cells, exhibit rapid recovery of intracellular NAD and ATP levels. Consistent with the recovery of cellular bioenergetics, ALKBH7-depleted cells maintain their mitochondrial membrane potential, plasma membrane integrity, and viability. Our results uncover a novel role for a mammalian AlkB homolog in programmed necrosis, presenting a new target for therapeutic intervention in cancer cells that are resistant to apoptotic cell death.

Deletion of mouse Alkbh7 leads to obesity.

Mammals have nine homologues of the Escherichia coli AlkB repair protein: Alkbh1-8, and the fat mass and obesity associated protein FTO. In this report, we describe the first functional characterization of mouse Alkbh7. We show that the Alkbh7 protein is located in the mitochondrial matrix and that an Alkbh7 deletion dramatically increases body weight and body fat. Our data indicate that Alkbh7, directly or indirectly, facilitates the utilization of short-chain fatty acids, which we propose is the likely cause for the obesity phenotype observed in the Alkbh7(-/-) mice. Collectively, our data provide the first direct demonstration that murine Alkbh7 is a mitochondrial resident protein involved in fatty acid metabolism and the development of obesity.