37 results found
Schneiderman B, Barski M, Maertens G, 2022, Cabotegravir, the long-acting integrase strand transfer inhibitor, potently inhibits HTLV-1 transmission in vitro, Frontiers in Medicine, ISSN: 2296-858X
Human T cell Lymphotropic Virus Type 1 (HTLV-1) is a deltaretrovirus most prevalent in Southwestern Japan, sub-Saharan Africa, Australia, South America and the Carribean. Latest figures approximate 10 million people worldwide to be infected with HTLV-1. This is likely a significant underestimation due to lack of screening in endemic areas and absence of seroconversion symptoms. The two primary diseases associated with HTLV-1 infection are adult T cell leukaemia-lymphoma, a malignant and, sometimes, aggressive cancer; and HTLV-1 associated yelopathy/tropicalspastic paraparesis, a debilitating neurological degenerative disease. Unfortunately, despite the poor prognosis, there is currently no effective treatment for HTLV-1 infection. We previously showed that integrase strand transfer inhibitors (INSTIs) clinically used for HIV-1 prophylaxis and treatment are also effective against HTLV-1 transmission in vitro. In 2021 a new INSTI, cabotegravir, was approved by the FDA for HIV-1 treatment. We thus set out to evaluate its efficacy against HTLV-1 infection in vitro. Strand transfer assays performed using recombinant HTLV-1 integrase treated with increasing concentrations of cabotegravir, effectively inhibited strandtransfer activity, displaying an IC50 of 77.8 ± 22.4 nM. Furthermore, cabotegravir blocked HTLV-1 transmission in tissue culture; we determined an EC50 of 0.56 ±0.26 nM, similar to bictegravir. Alu-PCR confirmed the block in integration. Thus, there are 4 INSTIs and 1 reverse transcriptase inhibitor approved by the FDA for HIV-1 treatment, that potently block HTLV-1 infection in vitro. This should strongly encourage the establishment of a new standard of HTLV-1 treatment – particularly for pre-exposure prophylaxis and prevention of mother-to-child transmission.
Maertens GN, Engelman AN, Cherepanov P, 2022, Structure and function of retroviral integrase, Nature Reviews Microbiology, Vol: 20, Pages: 20-34, ISSN: 1740-1526
A hallmark of retroviral replication is establishment of the proviral state, wherein a DNA copy of the viral RNA genome is stably incorporated into a host cell chromosome. Integrase is the viral enzyme responsible for the catalytic steps involved in this process, and integrase strand transfer inhibitors are widely used to treat people living with HIV. Over the past decade, a series of X-ray crystallography and cryogenic electron microscopy studies have revealed the structural basis of retroviral DNA integration. A variable number of integrase molecules congregate on viral DNA ends to assemble a conserved intasome core machine that facilitates integration. The structures additionally informed on the modes of integrase inhibitor action and the means by which HIV acquires drug resistance. Recent years have witnessed the development of allosteric integrase inhibitors, a highly promising class of small molecules that antagonize viral morphogenesis. In this Review, we explore recent insights into the organization and mechanism of the retroviral integration machinery and highlight open questions as well as new directions in the field.
Barski MS, Vanzo T, Zhao XZ, et al., 2021, Structural basis for the inhibition of HTLV-1 integration inferred from cryo-EM deltaretroviral intasome structures (vol 12, 4996, 2021), NATURE COMMUNICATIONS, Vol: 12
Maertens G, Barski MS, Vanzo T, et al., 2021, Structural basis for the inhibition of HTLV-1 integration inferred from cryo-EM deltaretroviral intasome structures, Nature Communications, Vol: 12, Pages: 1-10, ISSN: 2041-1723
Between 10 and 20 million people worldwide are infected with the human T-celllymphotropic virus type 1 (HTLV-1). Despite causing life-threateningpathologies there is no therapeutic regimen for this deltaretrovirus. Here, wescreened a library of integrase strand transfer inhibitor (INSTI) candidates builtaround several chemical scaffolds to determine their effectiveness in limitingHTLV-1 infection. Naphthyridines with substituents in position 6 emerged as themost potent compounds against HTLV-1, with XZ450 having highest efficacy invitro. Using single-particle cryo-electron microscopy we visualised XZ450 aswell as the clinical HIV-1 INSTIs raltegravir and bictegravir bound to the activesite of the deltaretroviral intasome. The structures reveal subtle differences inthe coordination environment of the Mg2+ ion pair involved in the interactionwith the INSTIs. Our results elucidate the binding of INSTIs to the HTLV-1intasome and support their use for pre-exposure prophylaxis and possiblyfuture treatment of HTLV-1 infection.
Barski M, Minnell J, Maertens G, 2021, PP2A phosphatase as an emerging viral host factor, Frontiers in Cellular and Infection Microbiology, Vol: 11, ISSN: 2235-2988
Protein phosphatase 2A (PP2A) is one of the most ubiquitous cellular proteins and is responsible for the vast majority of Ser/Thr phosphatase activity in eukaryotes. PP2A is a heterotrimer, and its assembly, intracellular localization, enzymatic activity, and substrate specificity are subject to dynamic regulation. Each of its subunits can be targeted by viral proteins to hijack and modulate its activity and downstream signaling to the advantage of the virus. Binding to PP2A is known to be essential to the life cycle of many viruses and seems to play a particularly crucial role for oncogenic viruses, which utilize PP2A to transform infected cells through controlling the cell cycle and apoptosis. Here we summarise the latest developments in the field of PP2A viral targeting; in particular recent discoveries of PP2A hijacking through molecular mimicry of a B56-specific motif by several different viruses. We also discuss the potential as well as shortcomings for therapeutic intervention in the face of our current understanding of viral PP2A targeting.
Barski M, Minnell J, Pye V, et al., 2020, Cryo-EM structure of the deltaretroviral intasome in complex with the PP2A regulatory subunit B56γ, Nature Communications, Vol: 11, ISSN: 2041-1723
Human T-cell lymphotropic virus type 1 (HTLV-1) is a deltaretrovirus and the most oncogenic pathogen. Many of the ~20 million HTLV-1 infected people will develop severe leukaemia or an ALS-like motor disease, unless a therapy becomes available. A key step in the establishment of infection is the integration of viral genetic material into the host genome, catalysed by the retroviral integrase (IN) enzyme. Here, we use X-ray crystallography and single-particle cryo-electron microscopy to determine the structure of the functional deltaretroviral IN assembled on viral DNA ends and bound to the B56γ subunit of its human host factor, protein phosphatase 2 A. The structure reveals a tetrameric IN assembly bound to two molecules of the phosphatase via a conserved short linear motif. Insight into the deltaretroviral intasome and its interaction with the host will be crucial for understanding the pattern of integration events in infected individuals and therefore bears important clinical implications.
Barski MS, Minnell JJ, Maertens G, 2019, Inhibition of HTLV-1 infection by HIV-1 first- and second-generation integrase strand transfer inhibitors, Frontiers in Microbiology, Vol: 10, ISSN: 1664-302X
More than 10 million people worldwide are infected with the retrovirus human T-cell lymphotropic virus type 1 (HTLV-1). Infection phenotypes can range from asymptomatic to severe adult T-cell leukemia/lymphoma (ATLL) and HTLV-1-associated myelopathy. HTLV-1, like human immunodeficiency virus type 1 (HIV-1), is a blood-borne pathogen and viral infection happens in a similar fashion, with the major mode of transmission through breastfeeding. There is a strong correlation between time of infection and disease development, with a higher incidence of ATLL in patients infected during childhood. There is no successful therapeutic or preventative regimen for HTLV-1. It is therefore essential to develop therapies to inhibit transmission or block the onset/development of HTLV-1 associated diseases. Recently, we have seen the overwhelming success of integrase strand transfer inhibitors (INSTIs) in the treatment of HIV-1. Previously, raltegravir was shown to inhibit HTLV-1 infection. Here, we tested FDA-approved and two Phase II HIV-1 INSTIs in vitro and in a cell-to-cell infection model and show that they are highly active in blocking HTLV-1 infection, with bictegravir (EC50 = 0.30 ± 0.17 nM) performing best overall. INSTIs, in particular bictegravir, are more potent in blocking HTLV-1 transmission than tenofovir disproxil fumarate, an RT inhibitor. Our data suggest that HIV-1 INSTIs could present a good clinical strategy in HTLV-1 management and justifies the inclusion of INSTIs in clinical trials.
Stockum A, Snijders AP, Maertens GN, 2018, USP11 deubiquitinates RAE1 and plays a key role in bipolar spindle formation., PLoS ONE, Vol: 13, ISSN: 1932-6203
Correct segregation of the mitotic chromosomes into daughter cells is a highly regulated process critical to safeguard genome stability. During M phase the spindle assembly checkpoint (SAC) ensures that all kinetochores are correctly attached before its inactivation allows progression into anaphase. Upon SAC inactivation, the anaphase promoting complex/cyclosome (APC/C) E3 ligase ubiquitinates and targets cyclin B and securin for proteasomal degradation. Here, we describe the identification of Ribonucleic Acid Export protein 1 (RAE1), a protein previously shown to be involved in SAC regulation and bipolar spindle formation, as a novel substrate of the deubiquitinating enzyme (DUB) Ubiquitin Specific Protease 11 (USP11). Lentiviral knock-down of USP11 or RAE1 in U2OS cells drastically reduces cell proliferation and increases multipolar spindle formation. We show that USP11 is associated with the mitotic spindle, does not regulate SAC inactivation, but controls ubiquitination of RAE1 at the mitotic spindle, hereby functionally modulating its interaction with Nuclear Mitotic Apparatus protein (NuMA).
McCallin, 2016, The Regulation of HTLV-1 Integration by a Host Co-Factor
Kirk PDW, Huvet M, Melamed A, et al., 2016, Retroviruses integrate into a shared, non-palindromic DNA motif, Nature Microbiology, Vol: 2, Pages: 1-6, ISSN: 2058-5276
Many DNA-binding factors, such as transcription factors, form oligomeric complexes with structural symmetry that bind to palindromic DNA sequences1. Palindromic consensus nucleotide sequences are also found at the genomic integration sites of retroviruses2,3,4,5,6 and other transposable elements7,8,9, and it has been suggested that this palindromic consensus arises as a consequence of the structural symmetry in the integrase complex2,3. However, we show here that the palindromic consensus sequence is not present in individual integration sites of human T-cell lymphotropic virus type 1 (HTLV-1) and human immunodeficiency virus type 1 (HIV-1), but arises in the population average as a consequence of the existence of a non-palindromic nucleotide motif that occurs in approximately equal proportions on the plus strand and the minus strand of the host genome. We develop a generally applicable algorithm to sort the individual integration site sequences into plus-strand and minus-strand subpopulations, and use this to identify the integration site nucleotide motifs of five retroviruses of different genera: HTLV-1, HIV-1, murine leukaemia virus (MLV), avian sarcoma leucosis virus (ASLV) and prototype foamy virus (PFV). The results reveal a non-palindromic motif that is shared between these retroviruses.
Quinn K, Winston A, Kaye S, et al., 2016, Slow emergence of resistance to C34-PEG4-Chol; a novel HIV fusion inhibitor, 22nd Annual Conference of the British HIV Association (BHIVA), Publisher: Wiley, Pages: 29-29, ISSN: 1464-2662
Rice A, Wordsworth H, Moyle G, et al., 2016, An interim report of a study investigating longitudinal changes in sensory profiles in HIV-positive patients with and without HIV-associated sensory neuropathy, 22nd Annual Conference of the British HIV Association (BHIVA), Publisher: Wiley, Pages: 46-47, ISSN: 1464-2662
Maertens GNE, 2016, B'-protein phosphatase 2A is a functional binding partner of delta-retroviral integrase, Nucleic Acids Research, Vol: 44, Pages: 364-376, ISSN: 1362-4962
To establish infection, a retrovirus must insert a DNA copy of its RNA genome into host chromatin. This reaction is catalysed by the virally encoded enzyme integrase (IN) and is facilitated by viral genus-specific host factors. Herein, cellular serine/threonine protein phosphatase 2A (PP2A) is identified as a functional IN binding partner exclusive to δ-retroviruses, including human T cell lymphotropic virus type 1 and 2 (HTLV-1 and HTLV-2) and bovine leukaemia virus (BLV). PP2A is a heterotrimer composed of a scaffold, catalytic and one of any of four families of regulatory subunits, and the interaction is specific to the B′ family of the regulatory subunits. B′-PP2A and HTLV-1 IN display nuclear co-localization, and the B′ subunit stimulates concerted strand transfer activity of δ-retroviral INs in vitro. The protein–protein interaction interface maps to a patch of highly conserved residues on B′, which when mutated render B′ incapable of binding to and stimulating HTLV-1 and -2 IN strand transfer activity.
Kirk PDW, Huvet M, Melamed A, et al., 2015, Retroviruses integrate into a shared, non-palindromic motif
<jats:p>Palindromic consensus nucleotide sequences are found at the genomic integration sites of retroviruses and other transposable elements. It has been suggested that the palindromic consensus arises as a consequence of structural symmetry in the integrase complex, but the precise mechanism has yet to be elucidated. Here we perform a statistical analysis of large datasets of HTLV-1 and HIV-1 integration sites. The results show that the palindromic consensus sequence is not present in individual integration sites, but appears to arise in the population average as a consequence of the existence of a non-palindromic nucleotide motif that occurs in approximately equal proportions on the plus-strand and the minus-strand of the host genome. We demonstrate that palindromic probability position matrices are characteristic of such situations. We develop a generally applicable algorithm to sort the individual integration site sequences into plus-strand and minus-strand subpopulations. We apply this algorithm to identify the respective integration site nucleotide motifs of five retroviruses of different genera: HTLV-1, HIV-1, MLV, ASLV, and PFV}. The results reveal a non-palindromic motif that is shared between these retroviruses.</jats:p>
McCallin AJ, Maertens GN, Bangham CRM, 2015, Host determinants of HTLV-1 integration site preference, RETROVIROLOGY, Vol: 12, ISSN: 1742-4690
Serrao E, Ballandras-Colas A, Cherepanov P, et al., 2015, Key determinants of target DNA recognition by retroviral intasomes, Retrovirology, Vol: 12, ISSN: 1742-4690
Background: Retroviral integration favors weakly conserved palindrome sequences at the sites of viral DNA joiningand generates a short (4–6 bp) duplication of host DNA flanking the provirus. We previously determined two keyparameters that underlie the target DNA preference for prototype foamy virus (PFV) and human immunodeficiencyvirus type 1 (HIV-1) integration: flexible pyrimidine (Y)/purine (R) dinucleotide steps at the centers of the integrationsites, and base contacts with specific integrase residues, such as Ala188 in PFV integrase and Ser119 in HIV-1 integrase.Here we examined the dinucleotide preference profiles of a range of retroviruses and correlated these findings withrespect to length of target site duplication (TSD).Results: Integration datasets covering six viral genera and the three lengths of TSD were accessed from the literatureor generated in this work. All viruses exhibited significant enrichments of flexible YR and/or selection against rigid RYdinucleotide steps at the centers of integration sites, and the magnitude of this enrichment inversely correlated withTSD length. The DNA sequence environments of in vivo-generated HIV-1 and PFV sites were consistent with integrationinto nucleosomes, however, the local sequence preferences were largely independent of target DNA chromatinization.Integration sites derived from cells infected with the gammaretrovirus reticuloendotheliosis virus strain A (Rev-A),which yields a 5 bp TSD, revealed the targeting of global chromatin features most similar to those of Moloneymurine leukemia virus, which yields a 4 bp duplication. In vitro assays revealed that Rev-A integrase interacts withand is catalytically stimulated by cellular bromodomain containing 4 protein.Conclusions: Retroviral integrases have likely evolved to bend target DNA to fit scissile phosphodiester bondsinto two active sites for integration, and viruses that cut target DNA with a 6 bp stagger may not need to bendDNA as sharply as viruses tha
Foerster A, Maertens GN, Farrell PJ, et al., 2015, Dimerization of Matrix Protein Is Required for Budding of Respiratory Syncytial Virus, Journal of Virology, Vol: 89, Pages: 4624-4635, ISSN: 1098-5514
Respiratory syncytial virus (RSV) infects epithelial cells of the respiratory tract and is a major cause of bronchiolitis and pneumonia in children and the elderly. The virus assembles and buds through the plasma membrane, forming elongated membrane filaments, but details of how this happens remain obscure. Oligomerization of the matrix protein (M) is a key step in the process of assembly and infectious virus production. In addition, it was suggested to affect the conformation of the fusion protein, the major current target for RSV antivirals, in the mature virus. The structure and assembly of M are thus key parameters in the RSV antiviral development strategy. The structure of RSV M was previously published as a monomer. Other paramyxovirus M proteins have been shown to dimerize, and biochemical data suggest that RSV M also dimerizes. Here, using size exclusion chromatography-multiangle laser light scattering, we show that the protein is dimeric in solution. We also crystallized M in two crystal forms and show that it assembles into equivalent dimers in both lattices. Dimerization interface mutations destabilize the M dimer in vitro. To assess the biological relevance of dimerization, we used confocal imaging to show that dimerization interface mutants of M fail to assemble into viral filaments on the plasma membrane. Additionally, budding and release of virus-like particles are prevented in M mutants that fail to form filaments. Importantly, we show that M is biologically active as a dimer and that the switch from M dimers to higher-order oligomers triggers viral filament assembly and virus production.
Bajorek M, Caly L, Tran KC, et al., 2014, The Thr205 Phosphorylation Site within Respiratory Syncytial Virus Matrix (M) Protein Modulates M Oligomerization and Virus Production, JOURNAL OF VIROLOGY, Vol: 88, Pages: 6380-6393, ISSN: 0022-538X
Serrao E, Krishnan L, Shun M-C, et al., 2014, Integrase residues that determine nucleotide preferences at sites of HIV-1 integration: implications for the mechanism of target DNA binding, Nucleic Acids Research, Vol: 42, Pages: 5164-5176, ISSN: 0305-1048
Retroviruses favor target-DNA (tDNA) distortion and particular bases at sites of integration, but the mechanism underlying HIV-1 selectivity is unknown. Crystal structures revealed a network of prototype foamy virus (PFV) integrase residues that distort tDNA: Ala188 and Arg329 interact with tDNA bases, while Arg362 contacts the phosphodiester backbone. HIV-1 integrase residues Ser119, Arg231, and Lys258 were identified here as analogs of PFV integrase residues Ala188, Arg329 and Arg362, respectively. Thirteen integrase mutations were analyzed for effects on integrase activity in vitro and during virus infection, yielding a total of 1610 unique HIV-1 integration sites. Purine (R)/pyrimidine (Y) dinucleotide sequence analysis revealed HIV-1 prefers the tDNA signature (0)RYXRY(4), which accordingly favors overlapping flexible dinucleotides at the center of the integration site. Consistent with roles for Arg231 and Lys258 in sequence specific and non-specific binding, respectively, the R231E mutation altered integration site nucleotide preferences while K258E had no effect. S119A and S119T integrase mutations significantly altered base preferences at positions −3 and 7 from the site of viral DNA joining. The S119A preference moreover mimicked wild-type PFV selectivity at these positions. We conclude that HIV-1 IN residue Ser119 and PFV IN residue Ala188 contact analogous tDNA bases to effect virus integration.
Maertens GN, Cook NJ, Wang W, et al., 2014, Structural basis for nuclear import of splicing factors by human transportin 3, Proceedings of the National Academy of Sciences of the United States of America, Vol: 111, Pages: 2728-2733, ISSN: 0027-8424
Transportin 3 (Tnpo3, Transportin-SR2) is implicated in nuclear import of splicing factors and HIV-1 replication. Herein, we show that the majority of cellular Tnpo3 binding partners contain arginine-serine (RS) repeat domains and present crystal structures of human Tnpo3 in its free as well as GTPase Ran- and alternative splicing factor/splicing factor 2 (ASF/SF2)-bound forms. The flexible β-karyopherin fold of Tnpo3 embraces the RNA recognition motif and RS domains of the cargo. A constellation of charged residues on and around the arginine-rich helix of Tnpo3 HEAT repeat 15 engage the phosphorylated RS domain and are critical for the recognition and nuclear import of ASF/SF2. Mutations in the same region of Tnpo3 impair its interaction with the cleavage and polyadenylation specificity factor 6 (CPSF6) and its ability to support HIV-1 replication. Steric incompatibility of the RS domain and RanGTP engagement by Tnpo3 provides the mechanism for cargo release in the nucleus. Our results elucidate the structural bases for nuclear import of splicing factors and the Tnpo3–CPSF6 nexus in HIV-1 biology.
Gupta SS, Maetzig T, Maertens GN, et al., 2013, Bromo- and Extraterminal Domain Chromatin Regulators Serve as Cofactors for Murine Leukemia Virus Integration, JOURNAL OF VIROLOGY, Vol: 87, Pages: 12721-12736, ISSN: 0022-538X
Hare S, Maertens GN, Cherepanov P, 2012, 3 '-Processing and strand transfer catalysed by retroviral integrase in crystallo, The EMBO Journal, Vol: 31, Pages: 3020-3028, ISSN: 0261-4189
Retroviral integrase (IN) is responsible for two consecutive reactions, which lead to insertion of a viral DNA copy into a host cell chromosome. Initially, the enzyme removes di‐ or trinucleotides from viral DNA ends to expose 3′‐hydroxyls attached to the invariant CA dinucleotides (3′‐processing reaction). Second, it inserts the processed 3′‐viral DNA ends into host chromosomal DNA (strand transfer). Herein, we report a crystal structure of prototype foamy virus IN bound to viral DNA prior to 3′‐processing. Furthermore, taking advantage of its dependence on divalent metal ion cofactors, we were able to freeze trap the viral enzyme in its ground states containing all the components necessary for 3′‐processing or strand transfer. Our results shed light on the mechanics of retroviral DNA integration and explain why HIV IN strand transfer inhibitors are ineffective against the 3′‐processing step of integration. The ground state structures moreover highlight a striking substrate mimicry utilized by the inhibitors in their binding to the IN active site and suggest ways to improve upon this clinically relevant class of small molecules.
Cherepanov P, Maertens GN, Hare S, 2011, Structural insights into the retroviral DNA integration apparatus, CURRENT OPINION IN STRUCTURAL BIOLOGY, Vol: 21, Pages: 249-256, ISSN: 0959-440X
Maertens GN, Hare S, Cherepanov P, 2010, The mechanism of retroviral integration from X-ray structures of its key intermediates, Nature, Vol: 468, Pages: 326-U217, ISSN: 0028-0836
To establish productive infection, a retrovirus must insert a DNA replica of its genome into host cell chromosomal DNA1,2. This process is operated by the intasome, a nucleoprotein complex composed of an integrase tetramer (IN) assembled on the viral DNA ends3,4. The intasome engages chromosomal DNA within a target capture complex to carry out strand transfer, irreversibly joining the viral and cellular DNA molecules. Although several intasome/transpososome structures from the DDE(D) recombinase superfamily have been reported4,5,6, the mechanics of target DNA capture and strand transfer by these enzymes remained unclear. Here we report crystal structures of the intasome from prototype foamy virus in complex with target DNA, elucidating the pre-integration target DNA capture and post-catalytic strand transfer intermediates of the retroviral integration process. The cleft between IN dimers within the intasome accommodates chromosomal DNA in a severely bent conformation, allowing widely spaced IN active sites to access the scissile phosphodiester bonds. Our results resolve the structural basis for retroviral DNA integration and provide a framework for the design of INs with altered target sequences.
Maertens GN, El Messaoudi-Aubert S, Elderkin S, et al., 2010, Ubiquitin‐specific proteases 7 and 11 modulate Polycomb regulation of the INK4a tumour suppressor, EMBO Journal, Vol: 29, Pages: 2553-2565, ISSN: 0261-4189
An important facet of transcriptional repression by Polycomb repressive complex 1 (PRC1) is the mono‐ubiquitination of histone H2A by the combined action of the Posterior sex combs (Psc) and Sex combs extra (Sce) proteins. Here, we report that two ubiquitin‐specific proteases, USP7 and USP11, co‐purify with human PRC1‐type complexes through direct interactions with the Psc orthologues MEL18 and BMI1, and with other PRC1 components. Ablation of either USP7 or USP11 in primary human fibroblasts results in de‐repression of the INK4a tumour suppressor accompanied by loss of PRC1 binding at the locus and a senescence‐like proliferative arrest. Mechanistically, USP7 and USP11 regulate the ubiquitination status of the Psc and Sce proteins themselves, thereby affecting their turnover and abundance. Our results point to a novel function for USPs in the regulation and function of Polycomb complexes.
El Messaoudi-Aubert S, Nicholls J, Maertens GN, et al., 2010, Role for the MOV10 RNA helicase in Polycomb-mediated repression of the INK4a tumor suppressor, NATURE STRUCTURAL & MOLECULAR BIOLOGY, Vol: 17, Pages: 862-U112, ISSN: 1545-9993
Maertens GN, Messaoudi-Aubert SE, Racek T, et al., 2009, Several distinct polycomb complexes regulate and co-localize on the INK4a tumor suppressor locus, PLOS One, Vol: 4, ISSN: 1932-6203
Misexpression of Polycomb repressive complex 1 (PRC1) components in human cells profoundly influences the onset of cellular senescence by modulating transcription of the INK4a tumor suppressor gene. Using tandem affinity purification, we find that CBX7 and CBX8, two Polycomb (Pc) homologs that repress INK4a, both participate in PRC1-like complexes with at least two Posterior sex combs (Psc) proteins, MEL18 and BMI1. Each complex contains a single representative of the Pc and Psc families. In primary human fibroblasts, CBX7, CBX8, MEL18 and BMI1 are present at the INK4a locus and shRNA-mediated knockdown of any one of these components results in de-repression of INK4a and proliferative arrest. Sequential chromatin immunoprecipitation (ChIP) reveals that CBX7 and CBX8 bind simultaneously to the same region of chromatin and knockdown of one of the Pc or Psc proteins results in release of the other, suggesting that the binding of PRC1 complexes is interdependent. Our findings provide the first evidence that a single gene can be regulated by several distinct PRC1 complexes and raise important questions about their configuration and relative functions.
Barradas M, Anderton E, Acosta JC, et al., 2009, Histone demethylase JMJD3 contributes to epigenetic control of INK4a/ARF by oncogenic RAS, Genes Dev, Vol: 23, Pages: 1177-82
The INK4a/ARF tumor suppressor locus, a key executor of cellular senescence, is regulated by members of the Polycomb group (PcG) of transcriptional repressors. Here we show that signaling from oncogenic RAS overrides PcG-mediated repression of INK4a by activating the H3K27 demethylase JMJD3 and down-regulating the methyltransferase EZH2. In human fibroblasts, JMJD3 activates INK4a, but not ARF, and causes p16(INK4a)-dependent arrest. In mouse embryo fibroblasts, Jmjd3 activates both Ink4a and Arf and elicits a p53-dependent arrest, echoing the effects of RAS in this system. Our findings directly implicate JMJD3 in the regulation of INK4a/ARF during oncogene-induced senescence and suggest that JMJD3 has the capacity to act as a tumor suppressor.
Elderkin S, Maertens GN, Endoh M, et al., 2007, A phosphorylated form of mel-18 targets the Ring1B histone H2A ubliquitin ligase to chromatin, MOLECULAR CELL, Vol: 28, Pages: 107-120, ISSN: 1097-2765
Maertens GN, Cherepanov P, Engelman A, 2006, Transcriptional co-activator p75 binds and tethers the Myc-interacting protein JPO2 to chromatin, JOURNAL OF CELL SCIENCE, Vol: 119, Pages: 2563-2571, ISSN: 0021-9533
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