Attachment of telomeres to the nuclear envelope (NE) and their clustering in a chromosomal bouquet during meiotic prophase I is an evolutionary conserved event that promotes chromosome pairing and ...recombination. In fission yeast, bouquet formation fails when the telomeric protein Rap1 is absent or when the telomeric protein Taz1 fails to recruit Rap1 to telomeres. The mammalian Rap1 orthologue is a component of the shelterin complex and localises to telomeres through an interaction with a Taz1-like telomeric DNA binding factor, TRF2. Here, we investigated the role of mammalian Rap1 in meiotic telomere attachment and clustering by analysing spermatogenesis in Rap1-deficient mice. The results establish that the meiotic three-dimensional nuclear architecture and recombination are not affected by the absence of Rap1. Furthermore, Rap1-deficient meiotic telomeres assemble the SUN1 nuclear membrane protein, attach to the NE, and undergo bouquet formation indistinguishable from the wild-type setting. Thus, the role of Rap1 in meiosis is not conserved between fission yeast and mammals, suggesting that mammals have alternative modes for connecting telomeres to SUN proteins on the meiotic nuclear envelope.
Support for basic science has been eclipsed by initiatives aimed at specific medical problems. The latest example is the dismantling of the Skirball Institute at NYU School of Medicine. Here, we ...reflect on the achievements and mission underlying the Skirball to gain insight into the dividends of maintaining a basic science vision within the academic enterprises.
Support for basic science has been eclipsed by initiatives aimed at specific medical problems. The latest example is the dismantling of the Skirball Institute at NYU School of Medicine. Here, we reflect on the achievements and mission underlying the Skirball to gain insight into the dividends of maintaining a basic science vision within the academic enterprises.
DNA polymerase theta (Polθ) is an attractive synthetic lethal target for drug discovery, predicted to be efficacious against breast and ovarian cancers harboring BRCA-mutant alleles. Here, we ...describe our hit-to-lead efforts in search of a selective inhibitor of human Polθ (encoded by POLQ). A high-throughput screening campaign of 350,000 compounds identified an 11 micromolar hit, giving rise to the N2-substituted fused pyrazolo series, which was validated by biophysical methods. Structure-based drug design efforts along with optimization of cellular potency and ADME ultimately led to the identification of RP-6685: a potent, selective, and orally bioavailable Polθ inhibitor that showed in vivo efficacy in an HCT116 BRCA2–/– mouse tumor xenograft model.
Abstract
Recent genomic characterization of PDA reveals that between 20-25 % of PDA harbor recurrent mutations in genes, including BRCA1/2, PALB2, and ATM, which are critical for homologous ...recombination (HR), an important form of DNA repair. In many patients, these may be germline mutations. This subgroup of PDAs, termed HR-deficient PDA, has emerged as a defined biological entity associated with increased chemoresistance and a more aggressive disease course. The defects in HR observed in these tumors impart cells with a specific vulnerability to PARP inhibitors and platinum-containing therapy. Still, as observed in the case of many other targeted therapies, only a fraction of HR-defective patient tumors respond to PARP inhibition. More so, many patients that initially respond eventually often develop resistance and progress. Therefore, novel therapies which can be effective against HR-defective PDA, alone or in combination with PARP inhibitors or other combinatorial regimens, are urgently needed. We have recently determined that inactivation of the HR pathway is associated with overexpression of polymerase theta (PolO–, also known as POLQ) in PDA. POLQ is a key enzyme that regulates an alternative pathway of DNA repair, known as the alternative non-homologous end-joining (Alt-NHEJ) pathway. In the setting of defective HR, Alt-NHEJ becomes a critical pathway responsible for the repair of DNA breaks and POLQ inhibition in HR-defective tumor cells demonstrates a synthetic lethality phenotype, not observed in cells with intact HR. Furthermore, POLQ knockdown significantly upregulated the cGAS-STING pathway in HR-deficient PDAs linking the DNA damage response to the immune response. Overall, targeting POLQ may represent a novel and in a valuable therapeutic strategy in HR-defective pancreatic cancer, as POLQ inhibitors are currently in development for clinical use.
Citation Format: Annie Wang, Andrea Zamperone, Mohammad Sohail, Lidong Wang, Fiyinfolu Balogun, Jiufeng Li, Ende Zhao, Daniel Diolaiti, Agnel Sfeir, Diane M. Simeone. Polymerase theta synthetic lethal interaction in homologous recombination-deficient pancreatic ductal adenocarcinoma abstract. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2019 Sept 6-9; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2019;79(24 Suppl):Abstract nr I14.
Mammalian telomeres end in single-stranded, G-rich 3' overhangs resulting from both the "end-replication problem" (the inability of DNA polymerase to replicate the very end of the telomeres) and ...postreplication processing. Telomeric G-rich overhangs are precisely defined in ciliates; the length and the terminal nucleotides are fixed. Human telomeres have very long overhangs that are heterogeneous in size (35-600 nt), indicating that their processing must differ in some respects from model organisms. We developed telomere-end ligation protocols that allowed us to identify the terminal nucleotides of both the C-rich and the G-rich telomere strands. Up to approximately 80% of the C-rich strands terminate in CCAATC-5', suggesting that after replication a nuclease with high specificity or constrained action acts on the C strand. In contrast, the G-terminal nucleotide was less precise than Tetrahymena and Euplotes but still had a bias that changed as a function of telomerase expression.
Next-generation sequencing technology is used to show that the error-prone polymerase theta (Poltheta) is needed to promote alternative non-homologous end joining at telomeres, and during chromosomal ...translocations, while counteracting homologous recombination; inhibition of Poltheta represents a potential therapeutic strategy for tumours that have mutations in homology-directed repair genes.
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DOBA, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, SBMB, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract
Pancreatic ductal adenocarcinoma (PDAC) is a highly lethal malignancy that harbors mutations in homologous recombination (HR) repair genes in up to 25% of cases. Defects in HR impart to ...tumor cells a specific vulnerability to poly-ADP ribose polymerase inhibitors and platinum-based chemotherapy. However, not all patients respond, and some who initially respond develop resistance and progress. Thus, new therapies that are effective against HR-deficient PDAC are needed. Here, we show that inactivation of the HR pathway in PDAC is associated with overexpression of polymerase theta (Polθ, or POLQ), a key enzyme that regulates the alternative non-homologous end-joining (alt-NHEJ) pathway of double-strand break (DSB) DNA repair. Using both human and murine HR-deficient PDAC models, we find that POLQ knockdown is synthetically lethal with mutations in HR genes (BRCA1, BRCA2, and PALB2) as well as the DNA damage repair gene ATM. Further, we present the first findings that POLQ knockdown enhances cytosolic micronucleus formation and activates cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) signaling. In an in vivo murine model, POLQ inhibition also leads to STING-dependent recruitment of immune cells and enhanced CD8+ T cell infiltration in the BRCA2-deficient tumor microenvironment (TME). Through its role in the alt-NHEJ pathway, we thus find that POLQ is critical for DSB repair in HR-deficient PDAC, and its inhibition presents a novel synthetic lethal approach to suppress tumor growth while simultaneously stimulating an immune response in the PDAC TME.
Citation Format: Grace Oh, Annie Wang, Lidong Wang, Jiufeng Li, Gregor Werba, Daniel Weissinger, Ende Zhao, Surajit Dhara, Rosmel Hernandez, Amanda Ackermann, Despoina Kalfakakou, Emily A. Kawaler, Talia Golan, Theodore H. Welling, Agnel Sfeir, Diane M. Simeone. Polymerase theta inhibition activates the cGAS-STING signaling pathway and elicits an immune response in homologous recombination-deficient pancreatic adenocarcinoma abstract. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr B065.
Telomeres protect chromosome ends through the interaction of telomeric repeats with shelterin, a protein complex that represses DNA damage signaling and DNA repair reactions. The telomeric repeats ...are maintained by telomerase, which solves the end replication problem. We report that the TTAGGG repeat arrays of mammalian telomeres pose a challenge to the DNA replication machinery, giving rise to replication-dependent defects that resemble those of aphidicolin-induced common fragile sites. Gene deletion experiments showed that efficient duplication of telomeres requires the shelterin component TRF1. Without TRF1, telomeres activate the ATR kinase in S phase and show a fragile-site phenotype in metaphase. Single-molecule analysis of replicating telomeres showed that TRF1 promotes efficient replication of TTAGGG repeats and prevents fork stalling. Two helicases implicated in the removal of G4 DNA structures, BLM and RTEL1, were required to repress the fragile-telomere phenotype. These results identify a second telomere replication problem that is solved by the shelterin component TRF1.
The mammary gland reaches a fully differentiated phenotype at lactation, a stage characterized by the abundant expression of beta-casein. We have investigated the expression and regulation of gap ...junction proteins (connexins, Cx) during the various developmental stages of mouse mammary gland. Immunohistochemical analysis, with specific antibodies, reveals that Cx26 and Cx32 are expressed and confined to the cell borders of luminal epithelial cells in all developmental stages of the gland. Cx26 and Cx32 expression, at the mRNA and protein levels, increases in pregnancy and peaks in lactation. Whereas Cx43 mRNA decreases in pregnancy and lactation, the functional activity of Cx43 protein, which has been localized to myoepithelial cells, is regulated (through phosphorylation) during pregnancy and peaks during lactation. Cx30 mRNA and proteins have, for the first time, been detected in mammary gland epithelia. Using reverse transcription/polymerase chain reaction and sequencing techniques, we show that Cx30 is abundant in pregnant and lactating mammary gland. Cx30 protein levels have not been detected in the mammary gland prior to day 15 of pregnancy, whereas maximum expression occurs at the onset of lactation. In mouse mammary cells in culture, Cx30 is epithelial-cell-specific and is induced by lactogenic hormones. These data identify a novel player in mammary differentiation and suggest a potential role for Cx30 in the fully differentiated gland.
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