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RNA (New York, N.Y.) Jun 2024Telomere replication is essential for continued proliferation of human cells, such as stem cells and cancer cells. Telomerase lengthens the telomeric G-strand, while...
Telomere replication is essential for continued proliferation of human cells, such as stem cells and cancer cells. Telomerase lengthens the telomeric G-strand, while C-strand replication is accomplished by CST-polymerase α -primase (CST-PP). Replication of both strands is inhibited by formation of G-quadruplex (GQ) structures in the G-rich single-stranded DNA. TMPyP4 and pyridostatin (PDS), which stabilize GQ structures in both DNA and RNA, inhibit telomerase in vitro, and they cause telomere shortening in human cells that has been attributed to telomerase inhibition. Here, we show that TMPyP4 and PDS also inhibit C-strand synthesis by stabilizing DNA secondary structures and thereby preventing CST-PP from binding to telomeric DNA. We also show that these small molecules inhibit CST-PP binding to a DNA sequence containing no consecutive guanine residues, which is unlikely to form GQs. Thus, while these "telomerase inhibitors" indeed inhibit telomerase, they are also robust inhibitors of telomeric C-strand synthesis. Furthermore, given their limited specificity for GQ structures, they may disrupt many other protein-nucleic acid interactions in human cells.
PubMed: 38918043
DOI: 10.1261/rna.080043.124 -
BioRxiv : the Preprint Server For... Jun 2024The cellular enzyme poly (ADP-ribose) polymerase-1 (PARP-1) regulates multiple processes that are potentially implicated in HIV-1 infection. However, the role of PARP-1...
UNLABELLED
The cellular enzyme poly (ADP-ribose) polymerase-1 (PARP-1) regulates multiple processes that are potentially implicated in HIV-1 infection. However, the role of PARP-1 in HIV-1 infection remains controversial, with reports indicating or excluding that PARP-1 influence early steps of the HIV-1 life cycle. Most of these studies have been conducted with Vesicular Stomatitis virus Glycoprotein G (VSV-G)-pseudotyped, single-round infection HIV-1; limiting our understanding of the role of PARP-1 in HIV-1 replication. Therefore, we evaluated the effect of PARP-1 deficiency or inhibition in HIV-1 replication in human CD4+ T cells. Our data showed that PARP-1 knockout increased viral replication in SUP-T1 cells. Similarly, a PARP-1 inhibitor that targets PARP-1 DNA-binding activity enhanced HIV-1 replication. In contrast, inhibitors affecting the catalytic activity of the enzyme were inactive. In correspondence with the pharmacological studies, mutagenesis analysis indicated that the DNA-binding domain was required for the PARP-1 anti-HIV-1 activity, but the poly-ADP-ribosylation activity was dispensable. Our results also demonstrated that PARP-1 acts at the production phase of the viral life cycle since HIV-1 produced in cells lacking PARP-1 was more infectious than control viruses. The effect of PARP-1 on HIV-1 infectivity required Env, as PARP-1 deficiency or inhibition did not modify the infectivity of Env-deleted, VSV-G-pseudotyped HIV-1. Furthermore, virion-associated Env was more abundant in sucrose cushion-purified virions produced in cells lacking the enzyme. However, PARP-1 did not affect Env expression or processing in the producer cells. In summary, our data indicate that PARP-1 antagonism enhances HIV-1 infectivity and increases levels of virion-associated Env.
IMPORTANCE
Different cellular processes counteract viral replication. A better understanding of these interfering mechanisms will enhance our ability to control viral infections. We have discovered a novel, antagonist effect of the cellular enzyme poly (ADP-ribose) polymerase-1 (PARP-1) in HIV-1 replication. Our data indicate that PARP-1 deficiency or inhibition augment HIV-1 infectivity in human CD4+ T cells, the main HIV-1 target cell . Analysis of the mechanism of action suggested that PARP-1 antagonism increases in the virus the amounts of the viral protein mediating viral entry to the target cells. These findings identify for the first time PARP-1 as a host factor that regulates HIV-1 infectivity, and could be relevant to better understand HIV-1 transmission and to facilitate vaccine development.
PubMed: 38915699
DOI: 10.1101/2024.06.11.598467 -
BioRxiv : the Preprint Server For... Jun 2024Stalled replication forks can be processed by several distinct mechanisms collectively called post-replication repair which includes homologous recombination, fork...
Stalled replication forks can be processed by several distinct mechanisms collectively called post-replication repair which includes homologous recombination, fork regression, and translesion DNA synthesis. However, the regulation of the usage between these pathways is not fully understood. The Rad51 protein plays a pivotal role in maintaining genomic stability through its roles in HR and in protecting stalled replication forks from degradation. We report the isolation of separation-of-function mutations in Rad51 that retain their recombination function but display a defect in fork protection leading to a shift in post-replication repair pathway usage from HR to alternate pathways including mutagenic translesion synthesis. Rad51-E135D and Rad51-K305N show normal and recombination despite changes in their DNA binding profiles, in particular to dsDNA, with a resulting effect on their ATPase activities. The mutants lead to a defect in Rad51 recruitment to stalled forks as well as a defect in the protection of dsDNA from degradation by Dna2-Sgs1 and Exo1 . A high-resolution cryo-electron microscopy structure of the Rad51-ssDNA filament at 2.4 Å resolution provides a structural basis for a mechanistic understanding of the mutant phenotypes. Together, the evidence suggests a model in which Rad51 binding to duplex DNA is critical to control pathway usage at stalled replication forks.
PubMed: 38915629
DOI: 10.1101/2024.06.14.599120 -
BioRxiv : the Preprint Server For... Jun 2024Lipid nanoparticles (LNPs) have transformed genetic medicine, recently shown by their use in COVID-19 mRNA vaccines. While loading LNPs with mRNA has many uses, loading...
Lipid nanoparticles (LNPs) have transformed genetic medicine, recently shown by their use in COVID-19 mRNA vaccines. While loading LNPs with mRNA has many uses, loading DNA would provide additional advantages such as long-term expression and availability of promoter sequences. However, here we show that plasmid DNA (pDNA) delivery via LNPs (pDNA-LNPs) induces acute inflammation in naïve mice which we find is primarily driven by the cGAS-STING pathway. Inspired by DNA viruses that inhibit this pathway for replication, we co-loaded endogenous lipids that inhibit STING into pDNA-LNPs. Specifically, loading nitro-oleic acid (NOA) into pDNA-LNPs (NOA-pDNA-LNPs) ameliorates serious inflammatory responses enabling prolonged transgene expression (at least 1 month). Additionally, we demonstrate the ability to iteratively optimize NOA-pDNA-LNPs' expression by performing a small LNP formulation screen, driving up expression 50-fold . Thus, NOA-pDNA-LNPs, and pDNA-LNPs co-loaded with other bioactive molecules, will provide a major new tool in the genetic medicine toolbox, leveraging the power of DNA's long-term and promoter-controlled expression.
PubMed: 38915627
DOI: 10.1101/2024.06.11.598533 -
BioRxiv : the Preprint Server For... Jun 2024In eukaryotic post-replicative mismatch repair, MutS homologs (MSH) detect mismatches and recruit MLH complexes to nick the newly replicated DNA strand upon activation...
In eukaryotic post-replicative mismatch repair, MutS homologs (MSH) detect mismatches and recruit MLH complexes to nick the newly replicated DNA strand upon activation by the replication processivity clamp, PCNA. This incision enables mismatch removal and DNA repair. Biasing MLH endonuclease activity to the newly replicated DNA strand is crucial for repair. In reconstituted assays, PCNA is loaded at pre-existing discontinuities and orients the major MLH endonuclease Mlh1-Pms1/MLH1-PMS2 (yeast/human) to nick the discontinuous strand. newly replicated DNA transiently contains discontinuities which are critical for efficient mismatch repair. How these discontinuities are preserved as strand discrimination signals during the window of time where mismatch repair occurs is unknown. Here, we demonstrate that yeast Mlh1-Pms1 uses ATP binding to recognize DNA discontinuities. This complex does not efficiently interact with PCNA, which partially suppresses ATPase activity, and prevents dissociation from the discontinuity. These data suggest that in addition to initiating mismatch repair by nicking newly replicated DNA, Mlh1-Pms1 protects strand discrimination signals, aiding in maintaining its own strand discrimination signposts. Our findings also highlight the significance of Mlh1-Pms1's ATPase activity for inducing DNA dissociation, as mutant proteins deficient in this function become immobilized on DNA post-incision, explaining phenotypes.
PubMed: 38915520
DOI: 10.1101/2024.06.13.598860 -
Frontiers in Oncology 2024Homologous recombination (HR) comprises series of interrelated pathways that repair double-stranded DNA breaks and inter-strand crosslinks. It provides support for DNA...
The prognostic and predictive value of homologous recombination deficiency status in patients with advanced stage epithelial ovarian carcinoma after first-line platinum-based chemotherapy.
OBJECTIVE
Homologous recombination (HR) comprises series of interrelated pathways that repair double-stranded DNA breaks and inter-strand crosslinks. It provides support for DNA replication to recover stalled or broken replication forks. Compared with homologous recombination proficiency (HRP), cancers with homologous recombination deficiency (HRD) are more likely to undergo cell death when treated with DNA-damaging agents, such as platinum agents, and have better disease control.
METHODS
Patients diagnosed with stage III/IV ovarian cancer, early stages with recurrence, who received adjuvant chemotherapy after debulking surgery, and who also had known HR status were eligible.
RESULTS
Forty-four patients were included, with 21 in the HRD group (including 8 with germline mutations) and 23 in the HRP group. The HRD group was composed predominantly of serous carcinoma (95.2%), while mucinous (n=3) and clear cell (n=1) cases were all found in the HRP group. Stage III/IV disease was 66.7% and 91.3% in HRD and HRP groups, respectively (p=0.064). Patients who were optimally debulked to no residual disease was 90.0% and 72.7% (p=0.243), respectively. Late line use of PARP inhibitors was 33.3% and 17.4% (p=0.303). Median PFS was 22.5 months (95% CI, 18.5 - 66.6) and 21.5 months (95% CI, 18.3-39.5) (p=0.49) in HRD and HRP respectively. Median platinum free interval (PFI) was 15.8 months (95% CI 12.4-60.4) and 15.9 months (95% CI 8.3-34.1) (p=0.24), respectively. Median OS was 88.2 months (95% CI 71.2-NA) and 49.7 months (95% CI 35.1-NA) (p=0.21). The PFS of the patients with germline mutations (n=5) was 54.3 months (95% CI 23.1-NA) and 21.5 months (95% CI 18.3-39.5) in the HRP group (p=0.095); the PFI difference was 47.7 months (95% CI 17.6-NA) in the mutation group, and 15.9 months (95% CI 12.4-60.4) in HRP, showing statistical significance (p=0.039); while the median OS was NA and 49.7 months (95% CI 35.1-NA) respectively (p=0.051). When adding two additional patients with somatic mutations to the germline mutation carriers, the median OS is NA (95% CI 73, NA) versus 49.7 months (95% CI 35.1, NA) for HRP (p=0.045).
CONCLUSIONS
HRD status was not associated with longer PFS or PFI in advanced ovarian cancer who received first line adjuvant platinum-based chemotherapy. Its role as a prognostic marker for overall survival is suggested, particularly in the subgroup with germline and somatic mutations.
PubMed: 38915363
DOI: 10.3389/fonc.2024.1372482 -
Cell Discovery Jun 2024Mpox virus (MPXV) can cause mpox in humans. Due to its quick and wide spread in the past two years, mpox has turned into a significant public health concern. Helicase E5...
Mpox virus (MPXV) can cause mpox in humans. Due to its quick and wide spread in the past two years, mpox has turned into a significant public health concern. Helicase E5 is a multi-domain protein; its primer synthesis and DNA unwinding activity are required for genome uncoating and DNA replication of MPXV. However, the in vitro DNA unwinding activity has never been demonstrated. Here, we report the structural and biochemical studies of MPXV E5, showing that the full-length protein adopts an auto-inhibited conformation. Truncation of the N-terminus can recover the in vitro unwinding activity of E5 towards the forked DNA. Further structural analysis reveals that MPXV E5 shares a conserved mechanism in DNA unwinding and primer synthesis with the homologous proteins. These findings not only advance our understanding on the function of MPXV E5, but also provide a solid basis for the development of anti-poxvirus drugs.
PubMed: 38914567
DOI: 10.1038/s41421-024-00680-1 -
MBio Jun 2024We have investigated the function of inositol hexakisphosphate (IP6) and inositol pentakisphosphate (IP5) in the replication of murine leukemia virus (MLV). While IP6 is...
We have investigated the function of inositol hexakisphosphate (IP6) and inositol pentakisphosphate (IP5) in the replication of murine leukemia virus (MLV). While IP6 is known to be critical for the life cycle of HIV-1, its significance in MLV remains unexplored. We find that IP6 is indeed important for MLV replication. It significantly enhances endogenous reverse transcription (ERT) in MLV. Additionally, a pelleting-based assay reveals that IP6 can stabilize MLV cores, thereby facilitating ERT. We find that IP5 and IP6 are packaged in MLV particles. However, unlike HIV-1, MLV depends upon the presence of IP6 and IP5 in target cells for successful infection. This IP6/5 requirement for infection is reflected in impaired reverse transcription observed in IP6/5-deficient cell lines. In summary, our findings demonstrate the importance of capsid stabilization by IP6/5 in the replication of diverse retroviruses; we suggest possible reasons for the differences from HIV-1 that we observed in MLV.IMPORTANCEInositol hexakisphosphate (IP6) is crucial for the assembly and replication of HIV-1. IP6 is packaged in HIV-1 particles and stabilizes the viral core enabling it to synthesize viral DNA early in viral infection. While its importance for HIV-1 is well established, its significance for other retroviruses is unknown. Here we report the role of IP6 in the gammaretrovirus, murine leukemia virus (MLV). We found that like HIV-1, MLV packages IP6, and as in HIV-1, IP6 stabilizes the MLV core thus promoting reverse transcription. Interestingly, we discovered a key difference in the role of IP6 in MLV versus HIV-1: while HIV-1 is not dependent upon IP6 levels in target cells, MLV replication is significantly reduced in IP6-deficient cell lines. We suggest that this difference in IP6 requirements reflects key differences between HIV-1 and MLV replication.
PubMed: 38912776
DOI: 10.1128/mbio.01158-24 -
Cell Reports. Physical Science May 2024Recreating tissue environments with precise control over mechanical, biochemical, and cellular organization is essential for next-generation tissue models for drug...
Recreating tissue environments with precise control over mechanical, biochemical, and cellular organization is essential for next-generation tissue models for drug discovery, development studies, and the replication of disease environments. However, controlling these properties at cell-scale lengths remains challenging. Here, we report the development of printing approaches that leverage polyethylene glycol diacrylate (PEGDA) hydrogels containing photocaged oligonucleotides to spatially program material characteristics with non-destructive, non-ultraviolet light. We further integrate this system with a perfusion chamber to allow us to alter the composition of PEGDA hydrogels while retaining common light-activatable photocaged DNAs. We demonstrate that the hydrogels can capture DNA functionalized materials, including cells coated with complementary oligonucleotides with spatial control using biocompatible wavelengths. Overall, these materials open pathways to orthogonal capture of any DNA functionalized materials while not changing the sequences of the DNA.
PubMed: 38911357
DOI: 10.1016/j.xcrp.2024.101922 -
Nature Communications Jun 2024Despite extensive studies on DNA replication, the exchange mechanisms of DNA polymerase during replication remain unclear. Existing models propose that this exchange is...
Despite extensive studies on DNA replication, the exchange mechanisms of DNA polymerase during replication remain unclear. Existing models propose that this exchange is facilitated by protein partners like helicase. Here we present data, employing a combination of mechanical DNA manipulation and single fluorescent protein observation, that reveal DNA polymerase undergoing rapid and autonomous exchange during replication not coordinated by other proteins. The DNA polymerase shows fast unbinding and rebinding dynamics, displaying a preference for either exonuclease or polymerase activity, or pausing events, during each brief binding event. We also observed a 'memory effect' in DNA polymerase rebinding, i.e., the enzyme tends to preserve its prior activity upon reassociation. This effect, potentially linked to the ssDNA/dsDNA junction's conformation, might play a role in regulating binding preference enabling high processivity amidst rapid protein exchange. Taken together, our findings support an autonomous replication model that includes rapid protein exchange, burst of activity, and a 'memory effect' while moving processively forward.
Topics: DNA Replication; DNA-Directed DNA Polymerase; DNA; Escherichia coli; DNA, Single-Stranded; Protein Binding
PubMed: 38909023
DOI: 10.1038/s41467-024-49612-3