Glutathione peroxidase 4 (GPX4) utilizes glutathione (GSH) to detoxify lipid peroxidation and plays an essential role in inhibiting ferroptosis. As a selenoprotein, GPX4 protein synthesis is highly ...inefficient and energetically costly. How cells coordinate GPX4 synthesis with nutrient availability remains unclear. In this study, we perform integrated proteomic and functional analyses to reveal that SLC7A11-mediated cystine uptake promotes not only GSH synthesis, but also GPX4 protein synthesis. Mechanistically, we find that cyst(e)ine activates mechanistic/mammalian target of rapamycin complex 1 (mTORC1) and promotes GPX4 protein synthesis at least partly through the Rag-mTORC1-4EBP signaling axis. We show that pharmacologic inhibition of mTORC1 decreases GPX4 protein levels, sensitizes cancer cells to ferroptosis, and synergizes with ferroptosis inducers to suppress patient-derived xenograft tumor growth in vivo. Together, our results reveal a regulatory mechanism to coordinate GPX4 protein synthesis with cyst(e)ine availability and suggest using combinatorial therapy of mTORC1 inhibitors and ferroptosis inducers in cancer treatment.
Recent epidemiological and clinical studies have suggested the benefit of aspirin for patients with cancer, which inspired increasing efforts to demonstrate the anticancer ability of aspirin and ...reveal the molecular mechanisms behind. Nevertheless, the anticancer activity and related mechanisms of aspirin remain largely unknown. This study aimed to confirm this observation, and more importantly, to investigate the potential target contributed to the anticancer of aspirin.
A homogeneous time-resolved fluorescence (HTRF) assay was used to examine the impact of aspirin on heparanase. Streptavidin pull-down, surface plasmon resonance (SPR) assay, and molecular docking were performed to identify heparanase as an aspirin-binding protein. Transwell, rat aortic rings, and chicken chorioallantoic membrane model were used to evaluate the antimetastasis and anti-angiogenesis effects of aspirin, and these phenotypes were tested in a B16F10 metastatic model, MDA-MB-231 metastatic model, and MDA-MB-435 xenograft model.
This study identified heparanase, an oncogenic extracellular matrix enzyme involved in cancer metastasis and angiogenesis, as a potential target of aspirin. We had discovered that aspirin directly binds to Glu225 region of heparanase and inhibits the enzymatic activity. Aspirin impeded tumor metastasis, angiogenesis, and growth in heparanase-dependent manner.
In summary, this study has illustrated heparanase as a target of aspirin for the first time. It provides insights for a better understanding of the mechanisms of aspirin in anticancer effects, and offers a direction for the development of small-molecule inhibitors of heparanase.
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Mechanistic understanding of how ionizing radiation induces type I interferon signaling and how to amplify this signaling module should help to maximize the efficacy of radiotherapy. In the current ...study, we report that inhibitors of the DNA damage response kinase ATR can significantly potentiate ionizing radiation‐induced innate immune responses. Using a series of mammalian knockout cell lines, we demonstrate that, surprisingly, both the cGAS/STING‐dependent DNA‐sensing pathway and the MAVS‐dependent RNA‐sensing pathway are responsible for type I interferon signaling induced by ionizing radiation in the presence or absence of ATR inhibitors. The relative contributions of these two pathways in type I interferon signaling depend on cell type and/or genetic background. We propose that DNA damage‐elicited double‐strand DNA breaks releases DNA fragments, which may either activate the cGAS/STING‐dependent pathway or—especially in the case of AT‐rich DNA sequences—be transcribed and initiate MAVS‐dependent RNA sensing and signaling. Together, our results suggest the involvement of two distinct pathways in type I interferon signaling upon DNA damage. Moreover, radiation plus ATR inhibition may be a promising new combination therapy against cancer.
Synopsis
Type I interferon signaling plays key roles in cancer radiotherapy with ionizing radiation (IR). Here, exploration of combinatory effects of IR and DNA damage kinase inhibitors reveals surprising involvement of distinct cytosolic nucleic acid‐sensing pathways in interferon response induction.
Inhibition of DNA damage response kinase ATR (ATRi) significantly potentiates IR‐induced type I interferon response in multiple human and murine cancer cells.
MAVS‐dependent RNA sensing pathway is indispensable for interferon signaling induced by combined IR+ATRi in some human cells.
Both cGAS/STING‐dependent cytosolic DNA‐ and MAVS‐dependent cytosolic RNA‐sensing pathways contribute to IR+ATRi‐induced interferon signaling to varying extent in different cell lines.
DNA damage‐elicited AT‐rich DNA mediates type I interferon signaling in a subset of human cells.
Surprisingly, both cGAS/STING‐dependent DNA‐ and MAVS‐dependent RNA‐sensing pathways contribute to the effects of combined radiotherapy and blocked DNA damage signaling, depending on cellular context.
Abstract
In response to DNA double-strand breaks (DSBs), repair proteins are recruited to the damaged sites. Ubiquitin signaling plays a critical role in coordinating protein recruitment during the ...DNA damage response. Here, we find that the microRNA biogenesis factor DGCR8 promotes tumor resistance to X-ray radiation independently of its Drosha-binding ability. Upon radiation, the kinase ATM and the deubiquitinase USP51 mediate the activation and stabilization of DGCR8 through phosphorylation and deubiquitination. Specifically, radiation-induced ATM-dependent phosphorylation of DGCR8 at serine 677 facilitates USP51 to bind, deubiquitinate, and stabilize DGCR8, which leads to the recruitment of DGCR8 and DGCR8’s binding partner RNF168 to MDC1 and RNF8 at DSBs. This, in turn, promotes ubiquitination of histone H2A, repair of DSBs, and radioresistance. Altogether, these findings reveal the non-canonical function of DGCR8 in DSB repair and suggest that radiation treatment may result in therapy-induced tumor radioresistance through ATM- and USP51-mediated activation and upregulation of DGCR8.
Type 2 diabetes (T2D) is a major chronic healthcare concern worldwide. Emerging evidence suggests that a histone-modification-mediated epigenetic mechanism underlies T2D. Nevertheless, the dynamics ...of histone marks in T2D have not yet been carefully analyzed. Using a mass spectrometry-based label-free and chemical stable isotope labeling quantitative proteomic approach, we systematically profiled liver histone post-translational modifications (PTMs) in a prediabetic high-fat diet-induced obese (DIO) mouse model. We identified 170 histone marks, 30 of which were previously unknown. Interestingly, about 30% of the histone marks identified in DIO mouse liver belonged to a set of recently reported lysine acylation modifications, including propionylation, butyrylation, malonylation, and succinylation, suggesting possible roles of these newly identified histone acylations in diabetes and obesity. These histone marks were detected without prior affinity enrichment with an antibody, demonstrating that the histone acylation marks are present at reasonably high stoichiometry. Fifteen histone marks differed in abundance in DIO mouse liver compared with liver from chow-fed mice in label-free quantification, and six histone marks in stable isotope labeling quantification. Analysis of hepatic histone modifications from metformin-treated DIO mice revealed that metformin, a drug widely used for T2D, could reverse DIO-stimulated histone H3K36me2 in prediabetes, suggesting that this mark is likely associated with T2D development. Our study thus offers a comprehensive landscape of histone marks in a prediabetic mouse model, provides a resource for studying epigenetic functions of histone modifications in obesity and T2D, and suggest a new epigenetic mechanism for the physiological function of metformin.
Poly(ADP-ribose)ylation or PARylation by PAR polymerase 1 (PARP1) and dePARylation by poly(ADP-ribose) glycohydrolase (PARG) are equally important for the dynamic regulation of DNA damage response. ...PARG, the most active dePARylation enzyme, is recruited to sites of DNA damage via pADPr-dependent and PCNA-dependent mechanisms. Targeting dePARylation is considered an alternative strategy to overcome PARP inhibitor resistance. However, precisely how dePARylation functions in normal unperturbed cells remains elusive. To address this challenge, we conducted multiple CRISPR screens and revealed that dePARylation of S phase pADPr by PARG is essential for cell viability. Loss of dePARylation activity initially induced S-phase-specific pADPr signaling, which resulted from unligated Okazaki fragments and eventually led to uncontrolled pADPr accumulation and PARP1/2-dependent cytotoxicity. Moreover, we demonstrated that proteins involved in Okazaki fragment ligation and/or base excision repair regulate pADPr signaling and cell death induced by PARG inhibition. In addition, we determined that PARG expression is critical for cellular sensitivity to PARG inhibition. Additionally, we revealed that PARG is essential for cell survival by suppressing pADPr. Collectively, our data not only identify an essential role for PARG in normal proliferating cells but also provide a potential biomarker for the further development of PARG inhibitors in cancer therapy.
Protein lysine malonylation is a recently identified post-translational modification (PTM), which is evolutionarily conserved from bacteria to mammals. Although analysis of lysine malonylome in ...mammalians suggested that this modification was related to energy metabolism, the substrates and biological roles of malonylation in prokaryotes are still poorly understood. In this study, we performed qualitative and quantitative analyses to globally identify lysine malonylation substrates in Escherichia coli. We identified 1745 malonylation sites in 594 proteins in E. coli, representing the first and largest malonylome data set in prokaryotes up to date. Bioinformatic analyses showed that lysine malonylation was significantly enriched in protein translation, energy metabolism pathways and fatty acid biosynthesis, implying the potential roles of protein malonylation in bacterial physiology. Quantitative proteomics by fatty acid synthase inhibition in both auxotrophic and prototrophic E. coli strains revealed that lysine malonylation is closely associated with E. coli fatty acid metabolism. Protein structural analysis and mutagenesis experiment suggested malonylation could impact enzymatic activity of citrate synthase, a key enzyme in citric acid (TCA) cycle. Further comparative analysis among lysine malonylome, succinylome and acetylome data showed that these three modifications could participate in some similar enriched metabolism pathways, but they could also possibly play distinct roles such as in fatty acid synthesis. These data expanded our knowledge of lysine malonylation in prokaryotes, providing a resource for functional study of lysine malonylation in bacteria.
Etoposide (ETO) is an anticancer drug that targets topoisomerase II (TOP2). It stabilizes a normally transient TOP2-DNA covalent complex (TOP2cc), thus leading to DNA double-strand breaks (DSBs). ...Tyrosyl-DNA phosphodiesterases two (TDP2) is directly involved in the repair of TOP2cc by removing phosphotyrosyl peptides from 5'-termini of DSBs. Recent studies suggest that additional factors are required for TOP2cc repair, which include the proteasome and the zinc finger protein associated with TDP2 and TOP2, named ZATT. ZATT may alter the conformation of TOP2cc in a way that renders the accessibility of TDP2 for TOP2cc removal. In this study, our genome-wide clustered regularly interspaced short palindromic repeats (CRISPR) screens revealed that ZATT also has a TDP2-independent role in promoting cell survival following ETO treatment. ZATT KO cells showed relatively higher ETO sensitivity than TDP2-KO cells, and ZATT/TDP2 DKO cells displayed additive hypersensitivity to ETO treatment. The study using a series of deletion mutants of ZATT determined that the N-terminal 1-168 residues of ZATT are required for interaction with TOP2 and this interaction is critical to ETO sensitivity. Moreover, depletion of ZATT resulted in accelerated TOP2 degradation after ETO or cycloheximide (CHX) treatment, suggesting that ZATT may increase TOP2 stability and likely participate in TOP2 turnover. Taken together, this study suggests that ZATT is a critical determinant that dictates responses to ETO treatment and targeting. ZATT is a promising strategy to increase ETO efficacy for cancer therapy.
Mechanisms and functions of protein ubiquitylation and LPS ubiquitylation. LPS ubiquitylation serves as a scaffold to recruit E3 ligases for the ubiquitylation of the membrane of bacteria. ...Polyubiquitin coat on the bacterial cell surface is one type of “eat‐me” signal recognized by the host cells. The abbreviations used in the figure are Pro, Protein; Ub, Ubiquitin; E1, Ubiquitin‐activating enzymes; E2, Ubiquitin‐conjugating enzymes; E3, Ubiquitin‐ligating enzymes; LPS, lipopolysaccharide; RNF213, Ring Finger Protein 213; and LUBAC, linear ubiquitin chain assembly complex.
Although the conserved AAA ATPase and bromodomain factor, ATAD2, has been described as a transcriptional co-activator upregulated in many cancers, its function remains poorly understood. Here, using ...a combination of ChIP-seq, ChIP-proteomics, and RNA-seq experiments in embryonic stem cells where Atad2 is normally highly expressed, we found that Atad2 is an abundant nucleosome-bound protein present on active genes, associated with chromatin remodelling, DNA replication, and DNA repair factors. A structural analysis of its bromodomain and subsequent investigations demonstrate that histone acetylation guides ATAD2 to chromatin, resulting in an overall increase of chromatin accessibility and histone dynamics, which is required for the proper activity of the highly expressed gene fraction of the genome. While in exponentially growing cells Atad2 appears dispensable for cell growth, in differentiating ES cells Atad2 becomes critical in sustaining specific gene expression programmes, controlling proliferation and differentiation. Altogether, this work defines Atad2 as a facilitator of general chromatin-templated activities such as transcription.
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