Presence Of DNA Damage Research Articles

PPM1D activity promotes cellular transformation by preventing senescence and cell death

Cell cycle checkpoints, oncogene-induced senescence and programmed cell death represent intrinsic barriers to tumorigenesis. Protein phosphatase magnesium-dependent 1 (PPM1D) is a negative regulator of the tumour suppressor p53 and has been implicated in termination of the DNA damage response. Here, we addressed the consequences of increased PPM1D activity resulting from the gain-of-function truncating mutations in exon 6 of the PPM1D. We show that while control cells permanently exit the cell cycle and reside in senescence in the presence of DNA damage caused by ionising radiation or replication stress induced by the active RAS oncogene, RPE1-hTERT and BJ-hTERT cells carrying the truncated PPM1D continue proliferation in the presence of DNA damage, form micronuclei and accumulate genomic rearrangements revealed by karyotyping. Further, we show that increased PPM1D activity promotes cell growth in the soft agar and formation of tumours in xenograft models. Finally, expression profiling of the transformed clones revealed dysregulation of several oncogenic and tumour suppressor pathways. Our data support the oncogenic potential of PPM1D in the context of exposure to ionising radiation and oncogene-induced replication stress.

Effects of PCNA Stability on the Formation of Mutations.

The fidelity of replication, especially in the presence of DNA damage, is essential for the proper function of cells. Mutations that inactivate genes involved in DNA damage repair or bypass are enriched in several types of cancer cells. Thus, it is important to further our understanding of the mechanisms governing replication fidelity. PCNA is a ring-shaped complex that encircles DNA at the front of the replication fork, at the double-stranded/single-stranded DNA junction. It serves as a processivity factor for the different DNA replication polymerases, allowing them to replicate longer stretches of DNA by physically tethering them to the DNA and preventing their detachment. In addition, PCNA also regulates and coordinates different DNA damage bypass pathways meant to allow DNA replication in the presence of DNA damage. Due to its essentiality and the numerous functions it has in the cell, much is still unclear about PCNA. Here, we utilize PCNA mutants that lower the stability of the PCNA complex on the chromatin, and thus tend to disassociate and fall from the DNA. Using these mutants, we show that PCNA's physical presence on the DNA can prevent DNA misalignment at repetitive sequences, leading to increased mutation formation. We also show that PCNA-interacting proteins play an important role in strengthening the ring's stability on the chromatin. Such repetitive sequence-induced mutations are common in several human diseases and it is important to study their formation and the mechanisms guarding against them.

EXO1 and DNA2-mediated ssDNA gap expansion is essential for ATR activation and to maintain viability in BRCA1-deficient cells.

DNA replication faces challenges from DNA lesions originated from endogenous or exogenous sources of stress, leading to the accumulation of single-stranded DNA (ssDNA) that triggers the activation of the ATR checkpoint response. To complete genome replication in the presence of damaged DNA, cells employ DNA damage tolerance mechanisms that operate not only at stalled replication forks but also at ssDNA gaps originated by repriming of DNA synthesis downstream of lesions. Here, we demonstrate that human cells accumulate post-replicative ssDNA gaps following replicative stress induction. These gaps, initiated by PrimPol repriming and expanded by the long-range resection factors EXO1 and DNA2, constitute the principal origin of the ssDNA signal responsible for ATR activation upon replication stress, in contrast to stalled forks. Strikingly, the loss of EXO1 or DNA2 results in synthetic lethality when combined with BRCA1 deficiency, but not BRCA2. This phenomenon aligns with the observation that BRCA1 alone contributes to the expansion of ssDNA gaps. Remarkably, BRCA1-deficient cells become addicted to the overexpression of EXO1,DNA2 or BLM. This dependence on long-range resection unveils a new vulnerability of BRCA1-mutant tumors, shedding light on potential therapeutic targets for these cancers.

Material basis revelation of anti-hepatoma effect of Huachansu (Cinobufacini) through down-regulation of thymidylate synthase

ObjectiveHepatocellular carcinoma (HCC) is a leading cause of mortality worldwide. Huachansu (Cinobufacini) is active extract isolated from the dry skin of Bufo Bufo gargarizans. It has now been widely used in clinical treatment of cancer, this study is to clarify the material basis of down-regulation of thymidylate synthase (TYMS) induced by Huachansu. MethodsOur study utilized UPLC-MS/MS to identify major bioactive components from Huachansu. Cell Counting Kit 8 (CCK-8) assay and clone formation assay were used to examine the cell viability of tumor cells. TYMS and γ-H2AX level were detected by using quantitative real-time RT-PCR and/or western blotting. Small interfering RNA (siRNA) transfection was used to explore whether inhibition of TYMS could enhance the suppressive effect of Huachansu on cell growth of HCC cells. ResultsIn our study, firstly, we identify 21 major bioactive components from Huachansu. CCK-8 assay results showed that Huachansu and its bioactive bufadienolides (Bufalin, Bufotalin, Cinobufotalin, Desacetylcinobufagin, Arenobufagin, Telocinobufagin, and Resibufogenin) significantly inhibited the proliferation of HepG2 and SK-HEP-1 cells in a dose- and time-dependent manner. Further molecular mechanistic investigation demonstrates that Huachansu significantly suppresses thymidylate synthase (TYMS), the enzyme which provides the sole de novo source of thymidylate for DNA synthesis. The inhibition of TYMS could lead to cell-cycle block and DNA damage of HCC cells. Furthermore, we identified that Huachansu markedly increased γ-H2AX expression, which indicated the presence of DNA damage. Moreover, we confirmed that transfection of cells with small interfering RNA specific to TYMS could increase the suppressive effects of Huachansu on the HCC cells proliferation. Quantitative RT-PCR analysis showed that Huachansu treatment had no effect on the transcription level of TYMS. Furthermore, proteasomal inhibitor MG132 could block TYMS inhibition induced by Huachansu, and concomitant administration of protein synthesis inhibitor cycloheximide (CHX) with Huachansu could further suppress the protein level of TYMS, indicating that Huachansu promotes proteasome-dependent degradation of TYMS in liver cancer cells. More importantly, the bioactive bufadienolides of Huachansu such as Bufalin, Bufotalin, Cinobufotalin, Desacetylcinobufagin, Arenobufagin, Telocinobufagin, and Resibufogenin could also significantly restrain the protein level of TYMS, revealing the material basis of inhibition of TYMS exposed to Huachansu. 5-fluorouracil (5-FU) is a TYMS inhibitor, we also evaluate the effects of the combined treatment of Huachansu with 5-FU, the results show that interactions between Huachansu and 5-FU are synergistic or antagonistic. Thus, in clinical, attention should be paid to the dosage of Huachansu in combination with 5-FU. ConclusionHuachansu inhibits the growth and induces DNA damage of human HCC cells through proteasome-dependent degradation of TYMS, bioactive bufadienolides are the material basis of down-regulation of TYMS induced by Huachansu.

Aberrant repair of 8-oxoguanine in short DNA bulges

The presence of DNA damage can increase the likelihood of DNA replication errors and promote mutations. In particular, pauses of DNA polymerase at the site of damage can lead to polymerase slippage and the formation of 1–2 nucleotide bulges. Repair of such structures using an undamaged DNA template leads to small deletions. One of the most abundant oxidative DNA lesions, 8-oxoguanine (oxoG), has been shown to induce small deletions but the mechanism of this phenomenon is currently unknown. We have studied the aberrant repair of oxoG, located in one- and two-nucleotide bulges, by the Escherichia coli and human base excision repair systems. Our results indicate that the repair in such substrates can serve as a mechanism for fixing small deletions in bacteria but not in humans.

Myxococcus xanthus translesion DNA synthesis protein ImuA is an ATPase enhanced by DNA.

Translesion DNA synthesis pathways are necessary to ensure bacterial replication in the presence of DNA damage. Translesion DNA synthesis carried out by the PolV mutasome is well-studied in Escherichia coli, but ~one third of bacteria use a functionally homologous protein complex, consisting of ImuA, ImuB, and ImuC (also called DnaE2). Numerous in vivo studies have shown that all three proteins are required for translesion DNA synthesis and that ImuC is the error-prone polymerase, but the roles of ImuA and ImuB are unclear. Here we carry out biochemical characterization of ImuA and a truncation of ImuB from Myxococcus xanthus. We find that ImuA is an ATPase, with ATPase activity enhanced in the presence of DNA. The ATPase activity is likely regulated by the C-terminus, as loss of the ImuA C-terminus results in DNA-independent ATP hydrolysis. We also find that ImuA binds a variety of DNA substrates, with DNA binding affinity affected by the addition of ADP or adenylyl-imidodiphosphate. An ImuB truncation also binds DNA, with lower affinity than ImuA. In the absence of DNA, ImuA directly binds ImuB with moderate affinity. Finally, we show that ImuA and ImuB self-interact, but that ImuA is predominantly a monomer, while truncated ImuB is a trimer in vitro. Together, with our findings and the current literature in the field, we suggest a model for translesion DNA synthesis, where a trimeric ImuB would provide sufficient binding sites for DNA, the β-clamp, ImuC, and ImuA, and where ImuA ATPase activity may regulate assembly and disassembly of the translesion DNA synthesis complex.

Comparative analysis of basal and etoposide-induced alterations in gene expression by DNA-PKcs kinase activity.

Background: Maintenance of the genome is essential for cell survival, and impairment of the DNA damage response is associated with multiple pathologies including cancer and neurological abnormalities. DNA-PKcs is a DNA repair protein and a core component of the classical nonhomologous end-joining pathway, but it also has roles in modulating gene expression and thus, the overall cellular response to DNA damage. Methods: Using cells producing either wild-type (WT) or kinase-inactive (KR) DNA-PKcs, we assessed global alterations in gene expression in the absence or presence of DNA damage. We evaluated differential gene expression in untreated cells and observed differences in genes associated with cellular adhesion, cell cycle regulation, and inflammation-related pathways. Following exposure to etoposide, we compared how KR versus WT cells responded transcriptionally to DNA damage. Results: Downregulated genes were mostly involved in protein, sugar, and nucleic acid biosynthesis pathways in both genotypes, but enriched biological pathways were divergent, again with KR cells manifesting a more robust inflammatory response compared to WT cells. To determine what major transcriptional regulators are controlling the differences in gene expression noted, we used pathway analysis and found that many master regulators of histone modifications, proinflammatory pathways, cell cycle regulation, Wnt/β-catenin signaling, and cellular development and differentiation were impacted by DNA-PKcs status. Finally, we have used qPCR to validate selected genes among the differentially regulated pathways to validate RNA sequence data. Conclusion: Overall, our results indicate that DNA-PKcs, in a kinase-dependent fashion, decreases proinflammatory signaling following genotoxic insult. As multiple DNA-PK kinase inhibitors are in clinical trials as cancer therapeutics utilized in combination with DNA damaging agents, understanding the transcriptional response when DNA-PKcs cannot phosphorylate downstream targets will inform the overall patient response to combined treatment.

Brain pathology and symptoms linked to concussion history: beyond chronic traumatic encephalopathy.

Repeated head trauma acquired through sports injuries has been associated with the development of long-term disabling symptoms that negatively impact the quality of life. In this retrospective case series, 52 male former professional athletes involved in contact sports and with a history of multiple concussions were evaluated for chronic clinical symptoms and post-mortem neuropathological diagnoses. The clinical symptoms of 19 cases were examined in greater detail for symptom type, severity and duration. Information on neurological, psychiatric and physical symptoms, substance use profiles and concussion histories was obtained from the athletes' next of kin and assessed in relation to post-mortem neuropathological diagnoses. Cases were categorized into three different neuropathological groups: no major neuropathological findings, the presence of only chronic traumatic encephalopathy (CTE) and the diagnosis(es) of other neurodegenerative diseases. Age at death and the presence of DNA damage in the post-mortem brains were analysed for correlation with the clinical symptoms. In this case series, 14/52 (26.9%) cases (mean age 48.2 ± 11.4) had neuropathological evidence of low-stage/low-burden CTE. A total of 11/52 (21.2%) cases (mean age 38.7 ± 12.7) presented a similar profile and severity of behavioural symptoms to those with CTE, despite the lack of significant post-mortem neuropathological findings. A total of 27/52 (51.9%) cases (mean age 75.5 ± 8.7) presented with complex post-mortem neurodegenerative diagnoses, including Alzheimer's disease and other mixed pathologies, and clinical symptoms associated with language, memory and sensory dysfunction. The presence of DNA damage in the brain was found in all neuropathological groups, predominantly in the ependymal lining of ventricles, and phosphorylated histone H2AX staining was correlated with higher age at death (r = 0.59) and symptoms of language dysfunction (r = 0.56). Findings from our case series suggest that post-concussive symptoms are not driven by CTE. Our findings show that proteinopathies alone may not account for the complexity of the clinical manifestations and suggest the possibility of other drivers, such as DNA damage, as potentially useful markers of brain trauma. Broadening the search for biological markers that reflect the effects of brain injury, even when proteinopathy is not observed, and taking a symptom-driven approach are therefore advised.

The global RNA–RNA interactome of Klebsiella pneumoniae unveils a small RNA regulator of cell division

The ubiquitous RNA chaperone Hfq is involved in the regulation of key biological processes in many species across the bacterial kingdom. In the opportunistic human pathogen Klebsiella pneumoniae, deletion of the hfq gene affects the global transcriptome, virulence, and stress resistance; however, the ligands of the major RNA-binding protein in this species have remained elusive. In this study, we have combined transcriptomic, co-immunoprecipitation, and global RNA interactome analyses to compile an inventory of conserved and species-specific RNAs bound by Hfq and to monitor Hfq-mediated RNA-RNA interactions. In addition to dozens of RNA-RNA pairs, our study revealed an Hfq-dependent small regulatory RNA (sRNA), DinR, which is processed from the 3' terminal portion of dinI mRNA. Transcription of dinI is controlled by the master regulator of the SOS response, LexA. As DinR accumulates in K. pneumoniae in response to DNA damage, the sRNA represses translation of the ftsZ transcript by occupation of the ribosome binding site. Ectopic overexpression of DinR causes depletion of ftsZ mRNA and inhibition of cell division, while deletion of dinR antagonizes cell elongation in the presence of DNA damage. Collectively, our work highlights the important role of RNA-based gene regulation in K. pneumoniae and uncovers the central role of DinR in LexA-controlled division inhibition during the SOS response.

The putative RNA helicase DDX1 associates with the nuclear RNA exosome and modulates RNA/DNA hybrids (R-loops)

The RNA exosome is a ribonuclease complex that mediates both RNA processing and degradation. This complex is evolutionarily conserved, ubiquitously expressed, and required for fundamental cellular functions, including rRNA processing. The RNA exosome plays roles in regulating gene expression and protecting the genome, including modulating the accumulation of RNA-DNA hybrids (R-loops). The function of the RNA exosome is facilitated by cofactors, such as the RNA helicase MTR4, which binds/remodels RNAs. Recently, missense mutations in RNA exosome subunit genes have been linked to neurological diseases. One possibility to explain why missense mutations in genes encoding RNA exosome subunits lead to neurological diseases is that the complex may interact with cell- or tissue-specific cofactors that are impacted by these changes. To begin addressing this question, we performed immunoprecipitation of the RNA exosome subunit, EXOSC3, in a neuronal cell line (N2A) followed by proteomic analyses to identify novel interactors. We identified the putative RNA helicase, DDX1, as an interactor. DDX1 plays roles in double-strand break repair, rRNA processing, and R-loop modulation. To explore the functional connections between EXOSC3 and DDX1, we examined the interaction following double-strand breaks, and analyzed changes in R-loops in N2A cells depleted for EXOSC3 or DDX1 by DNA/RNA immunoprecipitation followed by sequencing (DRIP-Seq). We find that EXOSC3 interaction with DDX1 is decreased in the presence of DNA damage and that loss of EXOSC3 or DDX1 alters R-loops. These results suggest EXOSC3 and DDX1 interact during events of cellular homeostasis and potentially suppress unscrupulous expression of genes promoting neuronal projection.

Aberrant Repair of 8-Oxoguanine in Short DNA Bulges.

The presence of DNA damage can increase the likelihood of DNA replication errors and promote mutations. In particular, pauses of DNA polymerase at the site of damage can lead to polymerase slippage and the formation of 1-2-nucleotide bulges. Repair of such structures using an undamaged DNA template leads to small deletions. One of the most abundant oxidative DNA lesions, 8-oxoguanine (oxoG), was shown to induce small deletions, but the mechanism of this phenomenon is currently unknown. We studied the aberrant repair of oxoG located in one- and two-nucleotide bulges by the Escherichia coli and human base excision repair systems. Our results indicate that the repair in such substrates can serve as a mechanism for fixing small deletions in bacteria but not in humans.

The FAM104 proteins VCF1/2 promote the nuclear localization of p97/VCP.

The ATPase p97 (also known as VCP, Cdc48) has crucial functions in a variety of important cellular processes such as protein quality control, organellar homeostasis, and DNA damage repair, and its de-regulation is linked to neuromuscular diseases and cancer. p97 is tightly controlled by numerous regulatory cofactors, but the full range and function of the p97-cofactor network is unknown. Here, we identify the hitherto uncharacterized FAM104 proteins as a conserved family of p97 interactors. The two human family members VCP nuclear cofactor family member 1 and 2 (VCF1/2) bind p97 directly via a novel, alpha-helical motif and associate with p97-UFD1-NPL4 and p97-UBXN2B complexes in cells. VCF1/2 localize to the nucleus and promote the nuclear import of p97. Loss of VCF1/2 results in reduced nuclear p97 levels, slow growth, and hypersensitivity to chemical inhibition of p97 in the absence and presence of DNA damage, suggesting that FAM104 proteins are critical regulators of nuclear p97 functions.

The FHA domain protein ArnA functions as a global DNA damage response repressor in the hyperthermophilic archaeon Saccharolobus islandicus.

Forkhead-associated (FHA) domain proteins specifically recognize phosphorylated threonine via the FHA domain and are involved in signal transduction in various processes especially DNA damage response (DDR) and cell cycle regulation in eukaryotes. Although FHA domain proteins are found in prokaryotes, archaea, and bacteria, their functions are far less clear as compared to the eukaryotic counterparts, and it has not been studied whether archaeal FHA proteins play a role in DDR. Here, we have characterized an FHA protein from the hyperthermophilic Crenarchaeon Saccharolobus islandicus (SisArnA) by genetic, biochemical, and transcriptomic approaches. We find that ΔSisarnA exhibits higher resistance to DNA damage agent 4-nitroquinoline 1-oxide (NQO). The transcription of ups genes, encoding the proteins for pili-mediated cell aggregation and cell survival after DDR, is elevated in ΔSisarnA. The interactions of SisArnA with two predicted partners, SisvWA1 (SisArnB) and SisvWA2 (designated as SisArnE), were enhanced by phosphorylation in vitro. ΔSisarnB displays higher resistance to NQO than the wild type. In addition, the interaction between SisArnA and SisArnB, which is reduced in the NQO-treated cells, is indispensable for DNA binding in vitro. These indicate that SisArnA and SisArnB work together to inhibit the expression of ups genes in vivo. Interestingly, ΔSisarnE is more sensitive to NQO than the wild type, and the interaction between SisArnA and SisArnE is strengthened after NQO treatment, suggesting a positive role of SisArnE in DDR. Finally, transcriptomic analysis reveals that SisArnA represses a number of genes, implying that archaea apply the FHA/phospho-peptide recognition module for extensive transcriptional regulation. IMPORTANCE Cellular adaption to diverse environmental stresses requires a signal sensor and transducer for cell survival. Protein phosphorylation and its recognition by forkhead-associated (FHA) domain proteins are widely used for signal transduction in eukaryotes. Although FHA proteins exist in archaea and bacteria, investigation of their functions, especially those in DNA damage response (DDR), is limited. Therefore, the evolution and functional conservation of FHA proteins in the three domains of life is still a mystery. Here, we find that an FHA protein from the hyperthermophilic Crenarchaeon Saccharolobus islandicus (SisArnA) represses the transcription of pili genes together with its phosphorylated partner SisArnB. SisArnA derepression facilitates DNA exchange and repair in the presence of DNA damage. The fact that more genes including a dozen of those involved in DDR are found to be regulated by SisArnA implies that the FHA/phosphorylation module may serve as an important signal transduction pathway for transcriptional regulation in archaeal DDR.

The Role of Annexin A1 in DNA Damage Response in Placental Cells: Impact on Gestational Diabetes Mellitus.

The functions of annexin A1 (ANXA1), which is expressed on membranes and in cytoplasmic granules, have been fully described. Nonetheless, the role of this protein in protecting against DNA damage in the nucleus is still emerging and requires further investigation. Here, we investigated the involvement of ANXA1 in the DNA damage response in placental cells. Placenta was collected from ANXA1 knockout mice (AnxA1-/-) and pregnant women with gestational diabetes mellitus (GDM). The placental morphology and ANXA1 expression, which are related to the modulation of cellular response markers in the presence of DNA damage, were analyzed. The total area of AnxA1-/- placenta was smaller due to a reduced labyrinth zone, enhanced DNA damage, and impaired base excision repair (BER) enzymes, which resulted in the induction of apoptosis in the labyrinthine and junctional layers. The placentas of pregnant women with GDM showed reduced expression of AnxA1 in the villous compartment, increased DNA damage, apoptosis, and a reduction of enzymes involved in the BER pathway. Our translational data provide valuable insights into the possible involvement of ANXA1 in the response of placental cells to oxidative DNA damage and represent an advancement in investigations into the mechanisms involved in placental biology.

The Cross Talk between Cellular Senescence and Melanoma: From Molecular Pathogenesis to Target Therapies.

Melanoma is a malignant skin tumor that originates from melanocytes. The pathogenesis of melanoma involves a complex interaction that occurs between environmental factors, ultraviolet (UV)-light damage, and genetic alterations. UV light is the primary driver of the skin aging process and development of melanoma, which can induce reactive oxygen species (ROS) production and the presence of DNA damage in the cells, and results in cell senescence. As cellular senescence plays an important role in the relationship that exists between the skin aging process and the development of melanoma, the present study provides insight into the literature concerning the topic at present and discusses the relationship between skin aging and melanoma, including the mechanisms of cellular senescence that drive melanoma progression, the microenvironment in relation to skin aging and melanoma factors, and the therapeutics concerning melanoma. This review focuses on defining the role of cellular senescence in the process of melanoma carcinogenesis and discusses the targeting of senescent cells through therapeutic approaches, highlighting the areas that require more extensive research in the field.

A RAD51 functional assay as a candidate test for homologous recombination deficiency in ovarian cancer

RationaleHomologous recombination deficiency (HRD), defined as BRCA1/2 mutation (BRCAmut) or high genomic instability, is used to identify ovarian cancer (OC) patients most likely to benefit from PARP inhibitors. While these tests are useful, they are imperfect. Another approach is to measure the capacity of tumor cells to form RAD51 foci in the presence of DNA damage using an immunofluorescence assay (IF). We aimed to describe for the first time this assay in OC and correlate it to platinum response and BRCAmut. MethodsTumor samples were prospectively collected from the randomized CHIVA trial of neoadjuvant platinum +/− nintedanib. IF for RAD51, GMN and gH2AX was performed on FFPE blocks. Tumors were considered RAD51-low if ≤10% of GMN-positive tumor cells had ≥5 RAD51 foci. BRCAmut were identified by NGS. Results155 samples were available. RAD51 assay was contributive for 92% of samples and NGS available for 77%. gH2AX foci confirmed the presence of significant basal DNA damage. 54% of samples were considered HRD by RAD51 and presented higher overall response rates to neoadjuvant platinum (P = 0.04) and longer progression-free survival (P = 0.02). In addition, 67% of BRCAmut were HRD by RAD51. Among BRCAmut, RAD51-high tumors seem to harbor poorer response to chemotherapy (P = 0.02). ConclusionsWe evaluated a functional assay of HR competency. OC demonstrate high levels of DNA damage, yet 54% fail to form RAD51 foci. These RAD51-low OC tend to be more sensitive to neoadjuvant platinum. The RAD51 assay also identified a subset of RAD51-high BRCAmut tumors with unexpected poor platinum response.

Dynamics of endogenous PARP1 and PARP2 during DNA damage revealed by live-cell single-molecule imaging

PARP1 contributes to genome architecture and DNA damage repair through its dynamic association with chromatin. PARP1 and PARP2 (PARP1/2) recognize damaged DNA and recruit the DNA repair machinery. Using single-molecule microscopy in live cells, we monitored the movement of PARP1/2 on undamaged and damaged chromatin. We identify two classes of freely diffusing PARP1/2 and two classes of bound PARP1/2. The majority (>60%) of PARP1/2 diffuse freely in both undamaged and damaged nuclei and in the presence of inhibitors of PARP1/2 used for cancer therapy (PARPi). Laser-induced DNA damage results in a small fraction of slowly diffusing PARP1 and PARP2 to become transiently bound. Treatment of cells with PARPi in the presence of DNA damage causes subtle changes in the dynamics of bound PARP1/2, but not the high levels of PARP1/2 trapping seen previously. Our results imply that next-generation PARPi could specifically target the small fraction of DNA-bound PARP1/2.

Targeting PIP4K2 Lipid Kinases through Thz-P1-2 Reveals Vulnerabilities Related to Mitochondrial Homeostasis and Autophagy in Acute Leukemia

Mitochondrial metabolism plays an important role in the therapeutic response of acute myeloid leukemia (AML) cell subsets and affects treatment outcome. Of not, leukemia stem cells (LSC) were shown to have increased sensitivity to disruptions of the oxidative phosphorylation process. These vulnerabilities may be specifically targeted with the BCL2 inhibitor venetoclax, which suppresses the tricarboxylic acid cycle by inhibiting amino acid metabolism. Additionally, autophagy and lysosomal biosynthesis have emerged as potential targets to improve the therapeutic response to these diseases. Genetic models of phosphatidylinositol-5-phosphate 4-kinase type 2 proteins (PIP4K2s) inhibition demonstrated the relevance of these enzymes in mitochondrial homeostasis and autophagic flux. High PIP4K2A and PIP4K2C transcript levels were associated with adverse cytogenetic risk and poor clinical outcomes in AML. Taking together, these data suggest that PIP4K2s inhibitors may have antileukemic effects and may synergize with venetoclax. Here, we uncover the cellular and molecular effects of THZ-P1-2, a pan-inhibitor of PIP4K2s, in acute leukemia cells and tested aforementioned hypothesis. Using a panel of 21 commonly used human myeloid and lymphoid leukemic cell lines, THZ-P1-2 caused a dose-dependent decrease in viability in these leukemia cells. Our results indicated cytostatic effects associated with a reduction of cells in S and G2/M phases when THZ-P1-2 was administrated at low concentrations (1.6 or 3.2 µM). Conversely, when THZ-P1-2 was administrated at high concentrations (6.4 µM), we observed cytotoxic effects linked with an increased accumulation of cells in the subG1 (all p < 0.05). The presence of DNA damage after exposure to THZ-P1-2 in leukemia cells was confirmed by the comet assay (all p < 0.05). An increase in apoptosis was detected in all cellular models upon the treatment with THZ-P1-2 in leukemia cells (all p < 0.05). Notably, acidic vesicular organelles levels were substantially elevated upon THZ-P1-2 exposure, particularly at concentrations that induced lower levels of apoptosis. At the molecular level, THZ-P1-2 induced the expression of apoptosis markers (PARP1 cleavage) and DNA damage (γH2AX) at levels compatible with those observed in previous cellular assays. Furthermore, LC3BII and SQSTM1/p62 levels were increased, which indicates a failure to complete the autophagic flow. In addition, exposure to THZ-P1-2 reduced basal and maximal cellular respiration capacity as well as glycolytic flux. The combined treatment showed synergistic effects, reducing the IC50 of venetoclax and strongly increasing the induction of apoptosis in leukemia cells [apoptosis rates (mean, SD); vehicle: 3.8, 0.7%, 6.4 µM venetoclax: 33.3, 4.8%, 6.4 µM THZ-P1-2: 18.5, 2.8%, 12.5 µM THZ-P1-2: 64.3, 4.3%, 6.4 µM venetoclax plus 6.4 µM THZ-P1-2: 78.3, 1.2%, 6.4 µM venetoclax plus 12.5 µM THZ-P1-2: 97.4, 0.3%, all p < 0.05]. Similar to what was observed in the cell line model, THZ-P1-2 reduced the viability of primary leukemic cells (AML, n = 45; ALL, n = 20) in a dose-dependent manner, which was correlated with a more metabolically active phenotype (oxygen consumption and extracellular acidification) of the leukemic blasts. Proteome analysis was performed on samples from patients considered sensitive and resistant to THZ-P1-2, which presented distinct protein signatures. A gene enrichment analysis identified multiple processes and signaling pathways associated with mitochondrial metabolism, cell cycle stage, leukemic cell-of-origin, and TP53 pathway (all FDR q-value < 0.05). Minimal effects of THZ-P1-2 observed in healthy CD34+ cells suggested a favorable therapeutic window. Our study provides insight into pharmacological inhibition of PIP4Ks targeting mitochondrial homeostasis and autophagy shedding light on a new class of drugs for acute leukemias. Supported by FAPESP, CNPq and CAPES.

Abstract 9727: Reduced Bmpr2 Causes a Decrease in Foxf1 That Links Unrepaired DNA Damage to Persistent Pulmonary Hypertension

Introduction: B MPR2 mutation is the most common genetic cause of pulmonary arterial hypertension (PAH). Loss of BMPR2 causes pulmonary arterial (PA) endothelial cell (EC) dysfunction and impairs EC-mediated suppression of smooth muscle cells proliferation. These are characteristic features of PAH vascular cells as is the presence of DNA damage that can be induced by oxidative stress. We previously showed that EC- Bmpr2 -/- mice have persistent pulmonary hypertension (PH) with reoxygenation after hypoxia. However, the role of DNA damage in causing persistent PH related to loss of BMPR2 and oxidative stress is unknown. Hypothesis: We hypothesize that loss of BMPR2 causes unrepaired DNA damage and persistent PH by altering the expression of genes that maintain EC homeostasis. Methods and Results: DNA damage assessed by γH2AX foci was observed in PAEC of EC- Bmpr2 -/- mice in room air, that was more extensive after reoxygenation (10% hypoxia for 3 weeks followed by recovery in room-air for 4 weeks). Deletion of the DNA damage sensor ataxia-telangiectasia mutated (ATM) in EC of mice (EC- Atm -/- ) also resulted in persistent DNA damage and PH. RNA sequencing of PAEC after reoxygenation in EC- Bmpr2 -/- and EC- Atm -/- mice vs. controls showed downregulated EC differentiation and development genes enriched in biding motifs for Foxf1, a transcription factor associated with DNA repair and angiogenesis. Foxf1 expression was reduced in PAEC with loss of BMPR2 or ATM. Loss of Foxf1 decreased angiogenic genes Cldn5 and Vegfr2 , and DNA damage response genes Atm and p53 , and impaired PAEC migration and tube formation. Foxf1 overexpression increased these genes in PAEC. Immunohistochemistry showed decreased FOXF1 in PAEC of human pulmonary vascular lesions. Delivery of Foxf1 to EC- Bmpr2 -/- mice with an AAV2-peptide targeting the PA endothelium attenuated DNA damage in PAEC, restored angiogenesis genes and completely reversed persistent PH returning right ventricular systolic pressure to normal levels. Conclusions: We link loss of BMPR2 and DNA damage sensing in PAEC to persistent DNA damage and PAH and show that both are mediated by reduced FOXF1 . In EC- Bmpr2 -/- mice, Foxf1 gene therapy attenuated DNA damage restored angiogenesis genes, and prevented persistent PH.

Replication stalling activates SSB for recruitment of DNA damage tolerance factors

Translesion synthesis (TLS) polymerases bypass DNA lesions that block replicative polymerases, allowing cells to tolerate DNA damage encountered during replication. It is well known that most bacterial TLS polymerases must interact with the sliding-clamp processivity factor to carry out TLS, but recent work in Escherichia coli has revealed that single-stranded DNA-binding protein (SSB) plays a key role in enriching the TLS polymerase Pol IV at stalled replication forks in the presence of DNA damage. It remains unclear how this interaction with SSB enriches Pol IV in a stalling-dependent manner given that SSB is always present at the replication fork. In this study, we use single-molecule imaging in live E. coli cells to investigate this SSB-dependent enrichment of Pol IV. We find that Pol IV is enriched through its interaction with SSB in response to a range of different replication stresses and that changes in SSB dynamics at stalled forks may explain this conditional Pol IV enrichment. Finally, we show that other SSB-interacting proteins are likewise selectively enriched in response to replication perturbations, suggesting that this mechanism is likely a general one for enrichment of repair factors near stalled replication forks.