ALKBH1 promotes HIF-1α-mediated glycolysis by inhibiting N-glycosylation of LAMP2A.

ALKBH1 is a typical demethylase of nucleic acids, which is correlated with multiple types of biological processes and human diseases. Recent studies are focused on the demethylation of ALKBH1, but little is known about its non-demethylase function. Here, we demonstrate that ALKBH1 regulates the glycolysis process through HIF-1α signaling in a demethylase-independent manner. We observed that depletion of ALKBH1 inhibits glycolysis flux and extracellular acidification, which is attributable to reduced HIF-1α protein levels, and it can be rescued by reintroducing HIF-1α. Mechanistically, ALKBH1 knockdown enhances chaperone-mediated autophagy (CMA)-mediated HIF-1α degradation by facilitating the interaction between HIF-1α and LAMP2A. Furthermore, we identify that ALKBH1 competitively binds to the OST48, resulting in compromised structural integrity of oligosaccharyltransferase (OST) complex and subsequent defective N-glycosylation of LAMPs, particularly LAMP2A. Abnormal glycosylation of LAMP2A disrupts lysosomal homeostasis and hinders the efficient degradation of HIF-1α through CMA. Moreover, NGI-1, a small-molecule inhibitor that selectively targets the OST complex, could inhibit the glycosylation of LAMPs caused by ALKBH1 silencing, leading to impaired CMA activity and disruption of lysosomal homeostasis. In conclusion, we have revealed a non-demethylation role of ALKBH1 in regulating N-glycosylation of LAMPs by interacting with OST subunits and CMA-mediated degradation of HIF-1α.

Research progress of N1-methyladenosine RNA modification in cancer.

N1-methyladenosine (m1A) is a post-transcriptionally modified RNA molecule that plays a pivotal role in the regulation of various biological functions and activities. Especially in cancer cell invasion, proliferation and cell cycle regulation. Over recent years, there has been a burgeoning interest in investigating the m1A modification of RNA. Most studies have focused on the regulation of m1A in cancer enrichment areas and different regions. This review provides a comprehensive overview of the methodologies employed for the detection of m1A modification. Furthermore, this review delves into the key players in m1A modification, known as the "writers," "erasers," and "readers." m1A modification is modified by the m1A methyltransferases, or writers, such as TRMT6, TRMT61A, TRMT61B, TRMT10C, NML, and, removed by the demethylases, or erasers, including FTO and ALKBH1, ALKBH3. It is recognized by m1A-binding proteins YTHDF1, TYHDF2, TYHDF3, and TYHDC1, also known as "readers". Additionally, we explore the intricate relationship between m1A modification and its regulators and their implications for the development and progression of specific types of cancer, we discuss how m1A modification can potentially facilitate the discovery of novel approaches for cancer diagnosis, treatment, and prognosis. Our summary of m1A methylated adenosine modification detection methods and regulatory mechanisms in various cancers provides useful insights for cancer diagnosis, treatment, and prognosis. Video Abstract.

ALYREF (Aly/REF export factor): A potential biomarker for predicting cancer occurrence and therapeutic efficacy.

5-Methylcytosine (m5C) methylation is present in almost all types of RNA as an essential epigenetic modification. It is dynamically modulated by its associated enzymes, including m5C methyltransferases (NSUN, DNMT and TRDMT family members), demethylases (TET family and ALKBH1) and binding proteins (YTHDF2, ALYREF and YBX1). Among them, aberrant expression of the RNA-binding protein ALYREF can facilitate a variety of malignant phenotypes such as maintenance of proliferation, malignant heterogeneity, metastasis, and drug resistance to cell death through different regulatory mechanisms, including pre-mRNA processing, mRNA stability, and nuclear-cytoplasmic shuttling. The induction of these cellular processes by ALYREF results in treatment resistance and poor outcomes for patients. However, there are currently few reports of clinical applications or drug trials related to ALYREF. In addition, the looming observations on the role of ALYREF in the mechanisms of carcinogenesis and disease prognosis have triggered considerable interest, but critical evidence is not available. For example, animal experiments and ALYREF small molecule inhibitor trials. In this review, we, therefore, revisit the literature on ALYREF and highlight its importance as a prognostic biomarker for early prevention and as a therapeutic target.

Chemoproteomic Approaches to Studying RNA Modification-Associated Proteins.

The function of cellular RNA is modulated by a host of post-transcriptional chemical modifications installed by dedicated RNA-modifying enzymes. RNA modifications are widespread in biology, occurring in all kingdoms of life and in all classes of RNA molecules. They regulate RNA structure, folding, and protein-RNA interactions, and have important roles in fundamental gene expression processes involving mRNA, tRNA, rRNA, and other types of RNA species. Our understanding of RNA modifications has advanced considerably; however, there are still many outstanding questions regarding the distribution of modifications across all RNA transcripts and their biological function. One of the major challenges in the study of RNA modifications is the lack of sequencing methods for the transcriptome-wide mapping of different RNA-modification structures. Furthermore, we lack general strategies to characterize RNA-modifying enzymes and RNA-modification reader proteins. Therefore, there is a need for new approaches to enable integrated studies of RNA-modification chemistry and biology.In this Account, we describe our development and application of chemoproteomic strategies for the study of RNA-modification-associated proteins. We present two orthogonal methods based on nucleoside and oligonucleotide chemical probes: 1) RNA-mediated activity-based protein profiling (RNABPP), a metabolic labeling strategy based on reactive modified nucleoside probes to profile RNA-modifying enzymes in cells and 2) photo-cross-linkable diazirine-containing synthetic oligonucleotide probes for identifying RNA-modification reader proteins.We use RNABPP with C5-modified cytidine and uridine nucleosides to capture diverse RNA-pyrimidine-modifying enzymes including methyltransferases, dihydrouridine synthases, and RNA dioxygenase enzymes. Metabolic labeling facilitates the mechanism-based cross-linking of RNA-modifying enzymes with their native RNA substrates in cells. Covalent RNA-protein complexes are then isolated by denaturing oligo(dT) pulldown, and cross-linked proteins are identified by quantitative proteomics. Once suitable modified nucleosides have been identified as mechanism-based proteomic probes, they can be further deployed in transcriptome-wide sequencing experiments to profile the substrates of RNA-modifying enzymes at nucleotide resolution. Using 5-fluorouridine-mediated RNA-protein cross-linking and sequencing, we analyzed the substrates of human dihydrouridine synthase DUS3L. 5-Ethynylcytidine-mediated cross-linking enabled the investigation of ALKBH1 substrates. We also characterized the functions of these RNA-modifying enzymes in human cells by using genetic knockouts and protein translation reporters.We profiled RNA readers for N6-methyladenosine (m6A) and N1-methyladenosine (m1A) using a comparative proteomic workflow based on diazirine-containing modified oligonucleotide probes. Our approach enables quantitative proteome-wide analysis of the preference of RNA-binding proteins for modified nucleotides across a range of affinities. Interestingly, we found that YTH-domain proteins YTHDF1/2 can bind to both m6A and m1A to mediate transcript destabilization. Furthermore, m6A also inhibits stress granule proteins from binding to RNA.Taken together, we demonstrate the application of chemical probing strategies, together with proteomic and transcriptomic workflows, to reveal new insights into the biological roles of RNA modifications and their associated proteins.

Predicting response of immunotherapy and targeted therapy and prognosis characteristics for renal clear cell carcinoma based on m1A methylation regulators.

In recent years, RNA methylation modification has been found to be related to a variety of tumor mechanisms, such as rectal cancer. Clear cell renal cell carcinoma (ccRCC) is most common in renal cell carcinoma. In this study, we get the RNA profiles of ccRCC patients from ArrayExpress and TCGA databases. The prognosis model of ccRCC was developed by the least absolute shrinkage and selection operator (LASSO) regression analysis, and the samples were stratified into low-high risk groups. In addition, our prognostic model was validated through the receiver operating characteristic curve (ROC). "pRRophetic" package screened five potential small molecule drugs. Protein interaction networks explore tumor driving factors and drug targeting factors. Finally, polymerase chain reaction (PCR) was used to verify the expression of the model in the ccRCC cell line. The mRNA matrix in ArrayExpress and TCGA databases was used to establish a prognostic model for ccRCC through LASSO regression analysis. Kaplan Meier analysis showed that the overall survival rate (OS) of the high-risk group was poor. ROC verifies the reliability of our model. Functional enrichment analysis showed that there was a obviously difference in immune status between the high-low risk groups. "pRRophetic" package screened five potential small molecule drugs (A.443654, A.770041, ABT.888, AG.014699, AMG.706). Protein interaction network shows that epidermal growth factor receptor [EGRF] and estrogen receptor 1 [ESR1] are tumor drivers and drug targeting factors. To further analyze the differential expression and pathway correlation of the prognosis risk model species. Finally, polymerase chain reaction (PCR) showed the expression of YTHN6-Methyladenosine RNA Binding Protein 1[YTHDF1], TRNA Methyltransferase 61B [TRMT61B], TRNA Methyltransferase 10C [TRMT10C] and AlkB Homolog 1[ALKBH1] in ccRCC cell lines. To sum up, the prognosis risk model we created not only has good predictive value, but also can provide guidance for accurately predicting the prognosis of ccRCC.

A DNA adenine demethylase impairs PRC2-mediated repression of genes marked by a specific chromatin signature.

BACKGROUND: The Fe (II)- and α-ketoglutarate-dependent AlkB family dioxygenases are implicated in nucleotide demethylation. AlkB homolog1 (ALKBH1) is shown to demethylate DNA adenine methylation (6mA) preferentially from single-stranded or unpaired DNA, while its demethylase activity and function in the chromatin context are unclear. RESULTS: Here, we find that loss-of-function of the rice ALKBH1 gene leads to increased 6mA in the R-loop regions of the genome but has a limited effect on the overall 6mA level. However, in the context of mixed tissues, rather than on individual loci, the ALKBH1 mutation or overexpression mainly affects the expression of genes with a specific combination of chromatin modifications in the body region marked with H3K4me3 and H3K27me3 but depleted of DNA CG methylation. In the similar context of mixed tissues, further analysis reveals that the ALKBH1 protein preferentially binds to genes marked by the chromatin signature and has a function to maintain a high H3K4me3/H3K27me3 ratio by impairing the binding of Polycomb repressive complex 2 (PRC2) to the targets, which is required for both the basal and stress-induced expression of the genes. CONCLUSION: Our findings unravel a function of ALKBH1 to control the balance between the antagonistic histone methylations for gene activity and provide insight into the regulatory mechanism of PRC2-mediated H3K27me3 deposition within the gene body region.

Sirtuin4 impacts mitochondrial homeostasis in pancreatic cancer cells by reducing the stability of AlkB homolog 1 via deacetylation of the HRD1-SEL1L complex.

Pancreatic ductal adenocarcinoma (PDAC) is a highly malignant tumor with a poor prognosis. As a tumor inhibitor, the specific tumor suppressor mechanism of Sirtuin4(SIRT4) in PDAC remains elusive. In this study, SIRT4 was found to inhibit PDAC by impacting mitochondrial homeostasis. SIRT4 deacetylated lysine 547 of SEL1L and increased the protein level of an E3 ubiquitin ligase HRD1. As a central member of ER-associated protein degradation (ERAD), HRD1-SEL1L complex is recently reported to regulate the mitochondria, though the mechanism is not fully delineated. Here, we found the increase in SEL1L-HRD1 complex decreased the stability of a mitochondrial protein, ALKBH1. Downregulation of ALKBH1 subsequently blocked the transcription of mitochondrial DNA-coded genes, and resulted in mitochondrial damage. Lastly, a putative SIRT4 stimulator, Entinostat, was identified, which upregulated the expression of SIRT4 and effectively inhibited pancreatic cancer in vivo and in vitro.

Xiao Chai Hu Tang alleviates the pancreatic tumorigenesis via improving the mtDNA N6-Methyladenine modification mediated mitochondrial dysfunction in Syrian hamster model.

BACKGROUND: Pancreatic intraepithelial neoplasia (PanIN) is the most common precursor lesion of pancreatic ductal adenocarcinoma (PDAC), which is a highly malignant tumor and lack of effective treatment. Although Xiao Chai Hu Tang (XCHT) has a good therapeutic effect on pancreatic cancer patients with advanced stage, the effect and mechanism of XCHT remains unclear in pancreatic tumorigenesis. PURPOSE: To assess the therapeutic effects of XCHT on the malignant transformation from PanIN to PDAC and to reveal its mechanisms of pancreatic tumorigenesis. METHODS: Syrian golden hamster were induced by N-Nitrosobis (2-oxopropyl) amine (BOP) to establish the pancreatic tumorigenesis model. The morphological changes of pancreatic tissue were observed by H&E and Masson staining; the Gene ontology (GO) analysis the transcriptional profiling changes; the mitochondrial ATP generation, mitochondrial redox status, mitochondrial DNA (mtDNA) N6-methyladenine (6mA) level and relative mtDNA genes expressions were examined. In addition, immunofluorescence detect the cell localization of 6mA in human pancreatic cancer PANC1 cell. Using the TCGA database, the prognostic effect of mtDNA 6mA demethylation ALKBH1 expression on pancreatic cancer patients was analyzed. RESULTS: We confirmed the mtDNA 6mA levels were gradually increased with the mitochondrial dysfunction in PanINs progression. XCHT showed the effect to inhibit the occurrence and development of pancreatic cancer in Syrian hamster pancreatic tumorigenesis model. In addition, the lack of ALKBH1 mediated mtDNA 6mA increase, mtDNA coded genes down-expression and abnormal redox status were rescued by XCHT. CONCLUSIONS: ALKBH1/mtDNA 6mA mediated mitochondrial dysfunction to induce the occurrence and progression of pancreatic cancer. XCHT can improve ALKBH1 expression and mtDNA 6mA level, regulate the oxidative stress and expression of mtDNA coded genes. This study investigated a new molecular mechanism of pancreatic tumorigenesis, and revealed the therapeutic efficacy of XCHT in pancreatic tumorigenesis for the first time.

U-shaped association between serum IGF2BP3 and T2DM: A cross-sectional study in Chinese population.

OBJECTIVE: To clarify the expression of N6-methyladenosine (m6 A) modulators involved in the pathogenesis of type 2 diabetes mellitus (T2DM). We further explored the association of serum insulin-like growth factor 2 mRNA-binding proteins 3 (IGF2BP3) levels and odds of T2DM in a high-risk population. METHODS: The gene expression data set GSE25724 was obtained from the Gene Expression Omnibus, and a cluster heatmap was generated by using the R package ComplexHeatmap. Differential expression analysis for 13 m6 A RNA methylation regulators between nondiabetic controls and T2DM subjects was performed using an unpaired t test. A cross-sectional design, including 393 subjects (131 patients with newly diagnosed T2DM, 131 age- and sex-matched subjects with prediabetes, and 131 healthy controls), was carried out. The associations between serum IGF2BP3 concentrations and T2DM were modeled by restricted cubic spline and logistic regression models. RESULTS: Two upregulated (IGF2BP2 and IGF2BP3) and 5 downregulated (methyltransferase-like 3 [METTL3], alkylation repair homolog protein 1 [ALKBH1], YTH domain family 2 [YTHDF2], YTHDF3, and heterogeneous nuclear ribonucleoprotein [HNRNPC]) m6 A-related genes were found in islet samples of T2DM patients. A U-shaped association existed between serum IGF2BP3 levels and odds of T2DM according to cubic natural spline analysis models, after adjustment for body mass index, waist circumference, diastolic blood pressure, total cholesterol, and triglyeride. Multivariate logistic regression showed that progressively higher odds of T2DM were observed when serum IGF2BP3 levels were below 0.62 ng/mL (odds ratio 3.03 [95% confidence interval 1.23-7.47]) in model 4. CONCLUSION: Seven significantly altered m6 A RNA methylation genes were identified in T2DM. There was a U-shaped association between serum IGF2BP3 levels and odds of T2DM in the general Chinese adult population. This study provides important evidence for further examination of the role of m6 A RNA methylation, especially serum IGF2BP3 in T2DM risk assessment.

DNA 6mA demethylase ALKBH1 regulates DDX18 expression to promote proliferation of human head and neck squamous cell carcinoma.

PURPOSE: Human head and neck squamous cell carcinoma (HNSCC) is the sixth most common malignancy worldwide. Currently, surgical resection plus a combination of chemotherapy and radiotherapy is the standard treatment for HNSCC, and the 5-year survival rate of patients with HNSCC remains very low because of the higher incidence of metastasis with consequent recurrence. Here, we aimed to investigate the potential role of DNA N6-methyladenine (6mA) demethylase ALKBH1 in tumor cell proliferation in HNSCC. METHODS: The expression of ALKBH1 in 10 pairs of HNSCC/normal tissues and 3 HNSCC cell lines were measured by qRT‒PCR and western blotting. Colony formation, flow cytometry, patient-derived HNSCC organoid assays were used to assess the role of ALKBH1 in HNSCC cell proliferation in cell lines and human HNSCC patients. MeDIP-seq, RNA sequencing, Dot blotting and western blotting were used to evaluate the regulatory effect of ALKBH1 on the expression of DEAD-box RNA helicase DDX18. A dual-luciferase reporter assay was used to assess the putative effect of DNA 6mA levels on DDX18 transcription. RESULTS: ALKBH1 was highly expressed in HNSCC cells and patient tissues. Functional experiments revealed that ALKBH1 knockdown in SCC9, SCC25, and CAL27 cells inhibited their proliferation in vitro. Using patient-derived HNSCC organoid assay, we found that knockdown of ALKBH1 inhibited the proliferation and colony formation of HNSCC patients-derived organoids. Moreover, we found that ALKBH1 can enhance DDX18 expression by erasing DNA 6mA level and regulating its promoter activity. ALKBH1 deficiency blocked tumor cell proliferation by inhibiting DDX18 expression. Exogenous overexpression of DDX18 rescued the cell proliferation arrest caused by ALKBH1 knockdown. CONCLUSION: Our data reveal the important role of ALKBH1 in regulating proliferation of HNSCC.

The N6-methyladenine DNA demethylase ALKBH1 promotes gastric carcinogenesis by disrupting NRF1 binding capacity.

DNA N6-methyladenine (6mA) is an epigenetic modification that regulates various biological processes. Here, we show that gastric cancer (GC) cells and tumors display a marked reduction in 6mA levels compared with normal gastric tissues and cells. 6mA is abundant in the surrounding transcription start sites and occurs at consensus motifs. Among the 6mA regulators, ALKBH1, a demethylase, is significantly overexpressed in GC tissues compared with adjacent normal tissues. Moreover, high ALKBH1 expression is associated with poor survival of patients with GC. ALKBH1 knockout in mice impairs chemically induced gastric carcinogenesis. Mechanistically, ALKBH1 mediates DNA 6mA demethylation to repress gene expression. In particular, the 6mA sites are enriched in NRF1 binding sequences and targeted for demethylation by ALKBH1. ALKBH1-induced 6mA demethylation inhibits NRF1-driven transcription of downstream targets, including multiple genes involved in the AMP-activated protein kinase (AMPK) signaling pathway. Accordingly, ALKBH1 suppresses AMPK signaling, causing a metabolic shift toward the Warburg effect, which facilitates tumorigenesis.

ALKBH1 contributes to renal cell carcinoma progression by reducing N6-methyladenine of GPR137.

BACKGROUND: Renal cell carcinoma (RCC) accounts for approximately 4% of all adult malignancies with high mortality worldwide. Although conventional chemotherapy and radiotherapy treatment has been applied for RCC in clinic, the mortality rate of patients is increasing each year, and patients with metastatic RCC are still suffering from poor prognosis. Thus, further investigation of the molecular mechanisms responsible for the development and progression of RCC is of particular importance. METHODS: Total of 10 pairs of RCC tissues and adjacent nontumor tissues were collected for examination of ALKBH1 and GPR137 expression. The correlations between ALKBH1 and GPR137 expression in RCC patient were assessed by GEPIA online tool and were analyzed using auto best cutoff. The human RCC cell lines Caki-1, 786-O, ACHN, Osrc2, A498, and 769-P, were used for mechanistic investigation. RESULTS: Here, we report that the expression of AlkB homologue 1 (ALKBH1) is upregulated in RCC tissues, which is correlated with G-protein-coupled receptor 137 (GPR137) expression. The elevated expression of ALKBH1 is associated with RCC cell malignant characteristics, including cell proliferation and movement (migration and invasion). Mechanistic investigation further reveals that ALKBH1 reduces m6 A levels of GPR137 mRNA in RCC cells, which upregulates GPR137 mRNA levels, resulting in the increased GPR137 protein expression subsequently and the enhanced RCC cell biological actions consequently. In contrast, the suppression of GPR137 effectively alleviates the ALKBH1-induced malignancies of RCC cells. CONCLUSION: Our results indicate that ALKBH1-GPR137 axis might be used as a potential therapeutic target in RCC, contributing to finding new prognostic biomarkers for RCC at an early stage.

ALKBH1-mediated m1 A demethylation of METTL3 mRNA promotes the metastasis of colorectal cancer by downregulating SMAD7 expression.

Colorectal cancer (CRC) is one of the most common malignancies, and the main cause of death from CRC is tumor metastasis. m1 A RNA modification plays critical role in many biological processes. However, the role of m1 A modification in CRC remains unclear. Here, we find that the m1 A demethylase alkB homolog 1, histone H2A dioxygenase (ALKBH1) is overexpressed in CRC and is associated with metastasis and poor prognosis. Upregulation of ALKBH1 expression promotes CRC metastasis in vitro and in vivo. Mechanistically, knockdown of ALKBH1 results in a decrease in methyltransferase 3, N6-adenosine-methyltransferase complex catalytic subunit (METTL3) expression, probably due to m1 A modification of METTL3 mRNA, followed by m6 A demethylation of SMAD family member 7 (SMAD7) mRNA. In addition, downregulation of SMAD7 establishes an aggressive phenotype. More importantly, the cell migration and invasion defects caused by ALKBH1 depletion or METTL3 depletion are significantly reversed by SMAD7 silencing. Considering these results collectively, we propose that ALKBH1 promotes CRC metastasis by destabilizing SMAD7 through METTL3.

Expression of m6A Methylation Regulator in Osteoarthritis and Its Prognostic Markers.

OBJECTIVE: Osteoarthritis (OA) is a multifactorial disorder, in which genetic factors are strongly associated with its development. However, the pathogenesis of OA is still unclear, and recently it has been observed that epigenetic modifications are also involved in the pathogenesis of OA. This study aims to study the potential role of m6A-related genes in the occurrence and development of OA. DESIGN: We downloaded the OA expression profile data (GSE55235) from the Gene Expression Omnibus database. First, function enrichment analysis of 17 representative m6A methylation regulatory factors was performed using the DAVID database and Metascape online tool. Then, we analyzed the expression of 17 m6A methylation regulatory factors in OA and the correlation between regulatory factors using Perl software. Finally, receiver operating characteristic (ROC) curve analysis and the area under the ROC curve were used to evaluate the diagnostic effectiveness of m6A-related genes for discriminating patients with OA and healthy. RESULTS: We first identified that 12 of the 17 genes were differentially expressed in OA. ALKBH1, EIF3, IGF2BP3, WTAP, and YTHDC1 were associated with early diagnosis and prognosis of OA. CONCLUSIONS: m6A RNA methylation regulator factors are key players in the progression of OA and have potential role in the stratification of prognosis and the formulation of treatment strategies.

Selected ALKBH dioxygenases are overexpressed in salivary gland tumours.

Salivary gland tumours (SGTs) are a heterogeneous group of benign tumours of various origins and pathologies, showing a number of DNA modifications. Previously, in malignant head and neck cancer (HNSCC), we found overexpression of ALKBH proteins, the homologs of Escherichia coli AlkB 2-oxoglutarate and Fe(II) dependent dioxygenase. Moreover, we proved the connection of some of these dioxygenases with cancer development. Here, we studied the expression of five of these ALKBH dioxygenases: 1, 3, 4, 5, and FTO in benign SGTs. Using Western blot analysis, we found overexpression of three proteins: ALKBH1, 4, and FTO in SGT as compared to the surrounding, unaffected tissue. ALKBH4 was overexpressed in 76% of patient samples, whereas ALKBH1 and FTO in 65% of the samples. These results differ from those obtained in HNSCC, where FTO overexpression has been observed in 90% of patient samples. We also investigated the relationships between ALKBHs' expression levels in normal and SGT tissues and identified two correlated pairs: ALKBH1-ALKBH3 and ALKBH1-ALKBH5. Additionally, in tumour tissue ALKBHs: ALKBH1, ALKBH3, ALKBH4, and ALKBH5 levels were correlated with each other. Together, these findings show that the ALKBH proteins exhibit pro cancerogenic action in SGT, even though the levels ALKBHs are generally lower in benign SGT than in malignant HNSCC. We suggest that the overexpression of the ALKBHs, especially FTO, may be used as a cancer marker and for its grading.

DNA 6mA Demethylase ALKBH1 Orchestrates Fatty Acid Metabolism and Suppresses Diet-Induced Hepatic Steatosis.

BACKGROUND & AIMS: Nonalcoholic fatty liver disease (NAFLD) is a major cause of liver-related morbidity and mortality whereas the pathogenic mechanism remains largely elusive. DNA N6-methyladenosine (6mA) modification is a recently identified epigenetic mark indicative of transcription in eukaryotic genomes. Here, we aimed to investigate the role and mechanism of DNA 6mA modification in NAFLD progression. METHODS: Dot blot and immunohistochemistry were used to detect DNA 6mA levels. Liver-specific AlkB homolog 1 (ALKBH1)-knockout mice and mice with ALKBH1 overexpression in liver were subjected to a high-fat diet or methionine choline-deficient diet to evaluate the critical role of ALKBH1-demethylated DNA 6mA modification in the pathogenesis of hepatic steatosis during NAFLD. RNA sequencing and chromatin immunoprecipitation sequencing were performed to investigate molecular mechanisms underlying this process. RESULTS: The DNA 6mA level was increased significantly with hepatic steatosis, while ALKBH1 expression was down-regulated markedly in both mouse and human fatty liver. Deletion of ALKBH1 in hepatocytes increased genomic 6mA levels and accelerated diet-induced hepatic steatosis and metabolic dysfunction. Comprehensive analyses of transcriptome and chromatin immunoprecipitation sequencing data indicated that ALKBH1 directly bound to and exclusively demethylated 6mA levels of genes involved in fatty acid uptake and lipogenesis, leading to reduced hepatic lipid accumulation. Importantly, ALKBH1 overexpression was sufficient to suppress lipid uptake and synthesis, and alleviated diet-induced hepatic steatosis and insulin resistance. CONCLUSIONS: Our findings show an indispensable role of ALKBH1 as an epigenetic suppressor of DNA 6mA in hepatic fatty acid metabolism and offer a potential therapeutic target for NAFLD treatment.

Tyrosyl-DNA phosphodiesterase 1 excises the 3'-DNA-ALKBH1 cross-link and its application for 3'-DNA-ALKBH1 cross-link characterization by LC-MS/MS.

The apurinic/apyrimidinic (abasic, AP) site is one of the most abundant DNA lesions. Previous studies by others demonstrated that human AlkB homologue 1 (ALKBH1) catalyzes the DNA strand incision at an AP site, resulting in suicidal cross-linking of the enzyme to the 3'-DNA end. Prior site-directed mutagenesis experiments had reported that Cys129 of ALKBH1 is the predominant nucleophile that conjugates to the C3' position of the incised AP site, 3'-phospho-α,ß-unsaturated aldehyde (3'-PUA), to form a 3'-PUA-ALKBH1 cross-link. However, direct evidence to support this mechanism was lacking. The 3'-PUA-ALKBH1 cross-link is so far the only adduct that has been found to form via a Michael addition reaction between a protein and 3'-PUA. It is unclear whether and how this type of cross-link is repaired. In this study, we first demonstrated that the 3'-PUA-ALKBH1 cross-link is fairly stable under physiological temperature and pH as only ~10% of the adduct decomposed after a 3-day incubation. Using a gel-based assay with an aldehyde-reacting probe, we demonstrated that the 3'-PUA-ALKBH1 cross-link has a free aldehyde group that is in line with the Michael addition mechanism. Moreover, we found that the 3'-PUA-ALKBH1 cross-link can be excised by human tyrosyl-DNA phosphodiesterase 1 (TDP1) and the removal efficiency is significantly enhanced if the adduct is pre-digested by trypsin. Notably, we employed TDP1 as a molecular tool to homogeneously release the cross-linked peptides from DNA to facilitate liquid chromatography tandem mass spectrometry analysis, and demonstrated that Cys129 and Cys371 of ALKBH1 cross-link to 3'-PUA.

ALKBH family members as novel biomarkers and prognostic factors in human breast cancer.

Breast cancer is the most common lethal carcinoma worldwide and better targeted therapies are still worthy of exploration, having had some great successes already. Abnormal expression of ALKBH members were found in various cancers, and the roles played by it were the focus of attention. The ALKBH gene family encodes nine homologous enzymes (ALKBH1-8 and FTO) to repair DNA or RNA depending on Fe2+ and α-ketoglutarate (α-KG), which is related to carcinogenesis. In this study, we applied several databases to explore the roles of ALKBHs in breast cancer. We found that ALKBH members were abnormal expression in breast cancer and associated with tumor stage and subclasses. Higher alteration rates of ALKBH family were found in breast cancer. Function enrichment revealed that several cancer-associated signal pathways were related to ALKBH family such as PI3K-Akt signaling pathway and axon guidance. Infiltration of immune cells (Eosinophiles, NK CD56bright cells, mast cells, T helper cells and so on) were strongly related to ALKBHs. Moreover, we further found that there was strong correlation between ALKBH7 and higher age, later T stage, ER/PR positive and post-menopause of breast cancer patients, and patients with higher ALKBH7 expression had shorter overall survival (OS) and post progression survival (PPS). In conclusion, our findings may provide novel insights into ALKBH-targeted therapy for breast cancer patients, and ALKBH7 may be a potential prognostic biomarker.

Reactivity-dependent profiling of RNA 5-methylcytidine dioxygenases.

Epitranscriptomic RNA modifications can regulate fundamental biological processes, but we lack approaches to map modification sites and probe writer enzymes. Here we present a chemoproteomic strategy to characterize RNA 5-methylcytidine (m5C) dioxygenase enzymes in their native context based upon metabolic labeling and activity-based crosslinking with 5-ethynylcytidine (5-EC). We profile m5C dioxygenases in human cells including ALKBH1 and TET2 and show that ALKBH1 is the major hm5C- and f5C-forming enzyme in RNA. Further, we map ALKBH1 modification sites transcriptome-wide using 5-EC-iCLIP and ARP-based sequencing to identify ALKBH1-dependent m5C oxidation in a variety of tRNAs and mRNAs and analyze ALKBH1 substrate specificity in vitro. We also apply targeted pyridine borane-mediated sequencing to measure f5C sites on select tRNA. Finally, we show that f5C at the wobble position of tRNA-Leu-CAA plays a role in decoding Leu codons under stress. Our work provides powerful chemical approaches for studying RNA m5C dioxygenases and mapping oxidative m5C modifications and reveals the existence of novel epitranscriptomic pathways for regulating RNA function.

The enhanced genomic 6 mA metabolism contributes to the proliferation and migration of TSCC cells.

In contrast to the well-established genomic 5-methylcytosine (5mC), the existence of N6-methyladenine (6 mA) in eukaryotic genomes was discovered only recently. Initial studies found that it was actively regulated in cancer cells, suggesting its involvement in the process of carcinogenesis. However, the contribution of 6 mA in tongue squamous cell carcinoma (TSCC) still remains uncharacterized. In this study, a pan-cancer type analysis was first performed, which revealed enhanced 6 mA metabolism in diverse cancer types. The study was then focused on the regulation of 6 mA metabolism, as well as its effects on TSCC cells. To these aspects, genome 6 mA level was found greatly increased in TSCC tissues and cultured cells. By knocking down 6 mA methylases N6AMT1 and METTL4, the level of genomic 6 mA was decreased in TSCC cells. This led to suppressed colony formation and cell migration. By contrast, knockdown of 6 mA demethylase ALKBH1 resulted in an increased 6 mA level, enhanced colony formation, and cell migration. Further study suggested that regulation of the NF-κB pathway might contribute to the enhanced migration of TSCC cells. Therefore, in the case of TSCC, we have shown that genomic 6 mA modification is involved in the proliferation and migration of cancer cells.