RESUMEN
In this issue of Molecular Cell, Razew et al.1 and Sabath et al.2 assign function to an unexplored module of the Integrator (INT) complex, expanding the toolbox of this genome-wide attenuator of RNA polymerase II (RNAPII) transcription.
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ARN Polimerasa II , Transcripción Genética , ARN Polimerasa II/metabolismo , ARN Polimerasa II/genéticaRESUMEN
The PP2A-B55 phosphatase regulates a plethora of signaling pathways throughout eukaryotes. How PP2A-B55 selects its substrates presents a severe knowledge gap. By integrating AlphaFold modelling with comprehensive high resolution mutational scanning, we show that α-helices in substrates bind B55 through an evolutionary conserved mechanism. Despite a large diversity in sequence and composition, these α-helices share key amino acid determinants that engage discrete hydrophobic and electrostatic patches. Using deep learning protein design, we generate a specific and potent competitive peptide inhibitor of PP2A-B55 substrate interactions. With this inhibitor, we uncover that PP2A-B55 regulates the nuclear exosome targeting complex by binding to an α-helical recruitment module in RBM7. Collectively, our findings provide a framework for the understanding and interrogation of PP2A-B55 in health and disease.
RESUMEN
The nuclear cap-binding complex (CBC) coordinates co-transcriptional maturation, transport, or degradation of nascent RNA polymerase II (Pol II) transcripts. CBC with its partner ARS2 forms mutually exclusive complexes with diverse "effectors" that promote either productive or destructive outcomes. Combining AlphaFold predictions with structural and biochemical validation, we show how effectors NCBP3, NELF-E, ARS2, PHAX, and ZC3H18 form competing binary complexes with CBC and how PHAX, NCBP3, ZC3H18, and other effectors compete for binding to ARS2. In ternary CBC-ARS2 complexes with PHAX, NCBP3, or ZC3H18, ARS2 is responsible for the initial effector recruitment but inhibits their direct binding to the CBC. We show that in vivo ZC3H18 binding to both CBC and ARS2 is required for nuclear RNA degradation. We propose that recruitment of PHAX to CBC-ARS2 can lead, with appropriate cues, to competitive displacement of ARS2 and ZC3H18 from the CBC, thus promoting a productive rather than a degradative RNA fate.
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Complejo Proteico Nuclear de Unión a la Caperuza , ARN , Unión Competitiva , Complejo Proteico Nuclear de Unión a la Caperuza/química , ARN/genética , ARN Polimerasa II/metabolismo , ARN NuclearRESUMEN
The RNA exosome is a versatile ribonuclease. In the nucleoplasm of mammalian cells, it is assisted by its adaptors the nuclear exosome targeting (NEXT) complex and the poly(A) exosome targeting (PAXT) connection. Via its association with the ARS2 and ZC3H18 proteins, NEXT/exosome is recruited to capped and short unadenylated transcripts. Conversely, PAXT/exosome is considered to target longer and adenylated substrates via their poly(A) tails. Here, mutational analysis of the core PAXT component ZFC3H1 uncovers a separate branch of the PAXT pathway, which targets short adenylated RNAs and relies on a direct ARS2-ZFC3H1 interaction. We further demonstrate that similar acidic-rich short linear motifs of ZFC3H1 and ZC3H18 compete for a common ARS2 epitope. Consequently, while promoting NEXT function, ZC3H18 antagonizes PAXT activity. We suggest that this organization of RNA decay complexes provides co-activation of NEXT and PAXT at loci with abundant production of short exosome substrates.
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ARN Nuclear , Proteínas de Unión al ARN , Animales , Núcleo Celular/metabolismo , Complejo Multienzimático de Ribonucleasas del Exosoma/metabolismo , Mamíferos , Estabilidad del ARN/genética , ARN Mensajero/genética , ARN Nuclear/genética , Proteínas de Unión al ARN/genéticaRESUMEN
The RNA-binding ARS2 protein is centrally involved in both early RNA polymerase II (RNAPII) transcription termination and transcript decay. Despite its essential nature, the mechanisms by which ARS2 enacts these functions have remained unclear. Here, we show that a conserved basic domain of ARS2 binds a corresponding acidic-rich, short linear motif (SLiM) in the transcription restriction factor ZC3H4. This interaction recruits ZC3H4 to chromatin to elicit RNAPII termination, independent of other early termination pathways defined by the cleavage and polyadenylation (CPA) and Integrator (INT) complexes. We find that ZC3H4, in turn, forms a direct connection to the nuclear exosome targeting (NEXT) complex, hereby facilitating rapid degradation of the nascent RNA. Hence, ARS2 instructs the coupled transcription termination and degradation of the transcript onto which it is bound. This contrasts with ARS2 function at CPA-instructed termination sites where the protein exclusively partakes in RNA suppression via post-transcriptional decay.
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Proteínas Nucleares , Transcripción Genética , Proteínas Nucleares/metabolismo , Factores de Transcripción/metabolismo , ARN Polimerasa II/genética , ARN Polimerasa II/metabolismo , Estabilidad del ARN/genética , Proteínas de Unión al ARN/genética , Proteínas de Unión al ARN/metabolismo , ARNRESUMEN
In mammalian cells, spurious transcription results in a vast repertoire of unproductive non-coding RNAs, whose deleterious accumulation is prevented by rapid decay. The nuclear exosome targeting (NEXT) complex plays a central role in directing non-functional transcripts to exosome-mediated degradation, but the structural and molecular mechanisms remain enigmatic. Here, we elucidated the architecture of the human NEXT complex, showing that it exists as a dimer of MTR4-ZCCHC8-RBM7 heterotrimers. Dimerization preconfigures the major MTR4-binding region of ZCCHC8 and arranges the two MTR4 helicases opposite to each other, with each protomer able to function on many types of RNAs. In the inactive state of the complex, the 3' end of an RNA substrate is enclosed in the MTR4 helicase channel by a ZCCHC8 C-terminal gatekeeping domain. The architecture of a NEXT-exosome assembly points to the molecular and regulatory mechanisms with which the NEXT complex guides RNA substrates to the exosome.
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Exosomas , ARN , Núcleo Celular/genética , Núcleo Celular/metabolismo , ARN Helicasas DEAD-box/metabolismo , ADN Helicasas/metabolismo , Complejo Multienzimático de Ribonucleasas del Exosoma/metabolismo , Exosomas/genética , Exosomas/metabolismo , Humanos , Unión Proteica , ARN/genética , ARN/metabolismo , ARN Helicasas/metabolismo , Estabilidad del ARN/genéticaRESUMEN
Transposable elements (TEs) are widespread genetic parasites known to be kept under tight transcriptional control. Here, we describe a functional connection between the mouse-orthologous "nuclear exosome targeting" (NEXT) and "human silencing hub" (HUSH) complexes, involved in nuclear RNA decay and the epigenetic silencing of TEs, respectively. Knocking out the NEXT component ZCCHC8 in embryonic stem cells results in elevated TE RNA levels. We identify a physical interaction between ZCCHC8 and the MPP8 protein of HUSH and establish that HUSH recruits NEXT to chromatin at MPP8-bound TE loci. However, while NEXT and HUSH both dampen TE RNA expression, their activities predominantly affect shorter non-polyadenylated and full-length polyadenylated transcripts, respectively. Indeed, our data suggest that the repressive action of HUSH promotes a condition favoring NEXT RNA decay activity. In this way, transcriptional and post-transcriptional machineries synergize to suppress the genotoxic potential of TE RNAs.
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Complejo Multienzimático de Ribonucleasas del Exosoma , Exosomas , Animales , Cromatina/genética , Cromatina/metabolismo , Elementos Transponibles de ADN/genética , Complejo Multienzimático de Ribonucleasas del Exosoma/genética , Exosomas/metabolismo , Humanos , Ratones , Proteínas Nucleares/metabolismo , ARN/metabolismo , Estabilidad del ARNRESUMEN
ID proteins are helix-loop-helix (HLH) transcriptional regulators frequently overexpressed in cancer. ID proteins inhibit basic-HLH transcription factors often blocking differentiation and sustaining proliferation. A small-molecule, AGX51, targets ID proteins for degradation and impairs ocular neovascularization in mouse models. Here we show that AGX51 treatment of cancer cell lines impairs cell growth and viability that results from an increase in reactive oxygen species (ROS) production upon ID degradation. In mouse models, AGX51 treatment suppresses breast cancer colonization in the lung, regresses the growth of paclitaxel-resistant breast tumors when combined with paclitaxel and reduces tumor burden in sporadic colorectal neoplasia. Furthermore, in cells and mice, we fail to observe acquired resistance to AGX51 likely the result of the inability to mutate the binding pocket without loss of ID function and efficient degradation of the ID proteins. Thus, AGX51 is a first-in-class compound that antagonizes ID proteins, shows strong anti-tumor effects and may be further developed for the management of multiple cancers.
RESUMEN
Recruitment of the human ribonucleolytic RNA exosome to nuclear polyadenylated (pA+) RNA is facilitated by the Poly(A) Tail eXosome Targeting (PAXT) connection. Besides its core dimer, formed by the exosome co-factor MTR4 and the ZFC3H1 protein, the PAXT connection remains poorly defined. By characterizing nuclear pA+-RNA bound proteomes as well as MTR4-ZFC3H1 containing complexes in conditions favoring PAXT assembly, we here uncover three additional proteins required for PAXT function: ZC3H3, RBM26 and RBM27 along with the known PAXT-associated protein, PABPN1. The zinc-finger protein ZC3H3 interacts directly with MTR4-ZFC3H1 and loss of any of the newly identified PAXT components results in the accumulation of PAXT substrates. Collectively, our results establish new factors involved in the turnover of nuclear pA+ RNA and suggest that these are limiting for PAXT activity.
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Proteínas de Unión al ADN/metabolismo , Exosomas/metabolismo , Poli A/metabolismo , Estabilidad del ARN , ARN Nuclear/metabolismo , Proteínas de Unión al ARN/metabolismo , Células HEK293 , Células HeLa , Humanos , Unión Proteica , Proteoma/metabolismo , Ribonucleoproteínas/metabolismoRESUMEN
The majority of the mammalian genome is transcribed by RNA polymerase II, yielding a vast amount of noncoding RNA (ncRNA) in addition to the standard production of mRNA. The typical nuclear biogenesis of mRNA relies on the tightly controlled coupling of co- and post-transcriptional processing events, which ultimately results in the export of transcripts into the cytoplasm. These processes are subject to surveillance by nuclear RNA decay pathways to prevent the export of aberrant, or otherwise "non-optimal," transcripts. However, unlike mRNA, many long ncRNAs are nuclear retained and those that maintain enduring functions must employ precautions to evade decay. Proper sorting and localization of RNA is therefore an essential activity in eukaryotic cells and the formation of ribonucleoprotein complexes during early stages of RNA synthesis is central to deciding such transcript fate. This review details our current understanding of the pathways and factors that direct RNAs towards a particular destiny and how transcripts combat the adverse conditions of the nucleus. This article is categorized under: RNA Export and Localization > Nuclear Export/Import RNA Turnover and Surveillance > Turnover/Surveillance Mechanisms RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications.
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Núcleo Celular/metabolismo , ARN/metabolismo , Animales , Humanos , ARN/genéticaRESUMEN
Pluripotent embryonic stem cells (ESCs) constitute an essential cellular niche sustained by epigenomic and transcriptional regulation. Any role of post-transcriptional processes remains less explored. Here, we identify a link between nuclear RNA levels, regulated by the poly(A) RNA exosome targeting (PAXT) connection, and transcriptional control by the polycomb repressive complex 2 (PRC2). Knockout of the PAXT component ZFC3H1 impairs mouse ESC differentiation. In addition to the upregulation of bona fide PAXT substrates, Zfc3h1-/- cells abnormally express developmental genes usually repressed by PRC2. Such de-repression is paralleled by decreased PRC2 binding to chromatin and low PRC2-directed H3K27 methylation. PRC2 complex stability is compromised in Zfc3h1-/- cells with elevated levels of unspecific RNA bound to PRC2 components. We propose that excess RNA hampers PRC2 function through its sequestration from DNA. Our results highlight the importance of balancing nuclear RNA levels and demonstrate the capacity of bulk RNA to regulate chromatin-associated proteins.
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Células Madre Embrionarias de Ratones/metabolismo , Complejo Represivo Polycomb 2/metabolismo , Estabilidad del ARN , ARN Nuclear/metabolismo , Transcripción Genética , Animales , Cromatina/genética , Cromatina/metabolismo , Ratones , Ratones Noqueados , Células Madre Embrionarias de Ratones/citología , Complejo Represivo Polycomb 2/genética , ARN Nuclear/genética , Factores de Transcripción/genética , Factores de Transcripción/metabolismoRESUMEN
Id helix-loop-helix (HLH) proteins (Id1-4) bind E protein bHLH transcription factors, preventing them from forming active transcription complexes that drive changes in cell states. Id proteins are primarily expressed during development to inhibit differentiation, but they become re-expressed in adult tissues in diseases of the vasculature and cancer. We show that the genetic loss of Id1/Id3 reduces ocular neovascularization in mouse models of wet age-related macular degeneration (AMD) and retinopathy of prematurity (ROP). An in silico screen identifies AGX51, a small-molecule Id antagonist. AGX51 inhibits the Id1-E47 interaction, leading to ubiquitin-mediated degradation of Ids, cell growth arrest, and reduced viability. AGX51 is well-tolerated in mice and phenocopies the genetic loss of Id expression in AMD and ROP models by inhibiting retinal neovascularization. Thus, AGX51 is a first-in-class compound that antagonizes an interaction formerly considered undruggable and that may have utility in the management of multiple diseases.
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Factores de Transcripción con Motivo Hélice-Asa-Hélice Básico/metabolismo , Neovascularización Patológica/tratamiento farmacológico , Bibliotecas de Moléculas Pequeñas/farmacología , Animales , Línea Celular , Línea Celular Tumoral , Proliferación Celular/efectos de los fármacos , Femenino , Células HCT116 , Células HEK293 , Células Endoteliales de la Vena Umbilical Humana , Humanos , Proteína 1 Inhibidora de la Diferenciación/metabolismo , Masculino , Ratones , Ratones Endogámicos BALB C , Ratones Endogámicos C57BL , Ratones Desnudos , Neovascularización Patológica/metabolismoRESUMEN
Rrp6 is a conserved catalytic subunit of the eukaryotic nuclear exosome ribonuclease complex that functions in the productive 3' end maturation of stable RNAs, the degradation of transiently expressed noncoding transcripts and in discard pathways that eradicate the cell of incorrectly processed or assembled RNAs. The function of Rrp6 in these pathways is at least partially dependent upon its interaction with a small nuclear protein called Rrp47/Lrp1, but the underlying mechanism(s) by which Rrp47 functions in concert with Rrp6 are not established. Previous work on yeast grown in rich medium has suggested that Rrp6 expression is not markedly reduced in strains lacking Rrp47. Here we show that Rrp6 expression in rrp47∆ mutants is substantially reduced during growth in minimal medium through effects on both transcript levels and protein stability. Exogenous expression of Rrp6 enables normal levels to be attained in rrp47∆ mutants. Strikingly, exogenous expression of Rrp6 suppresses many, but not all, of the RNA processing and maturation defects observed in an rrp47∆ mutant and complements the synthetic lethality of rrp47∆ mpp6∆ and rrp47∆ rex1∆ double mutants. Increased Rrp6 expression in the resultant rrp47∆ rex1∆ double mutant suppresses the defect in the 3' maturation of box C/D snoRNAs. In contrast, increased Rrp6 expression in the rrp47∆ mpp6∆ double mutant diminishes the block in the turnover of CUTs and in the degradation of the substrates of RNA discard pathways. These results demonstrate that a principal function of Rrp47 is to facilitate appropriate expression levels of Rrp6 and support the conclusion that the Rrp6/Rrp47 complex and Rex1 provide redundant exonuclease activities for the 3' end maturation of box C/D snoRNAs.
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Proteínas de Unión al ADN/metabolismo , Complejo Multienzimático de Ribonucleasas del Exosoma/metabolismo , Proteínas Nucleares/metabolismo , Proteínas de Unión al ARN/metabolismo , Proteínas de Saccharomyces cerevisiae/metabolismo , Saccharomyces cerevisiae/metabolismo , Proteínas de Unión al ADN/genética , Complejo Multienzimático de Ribonucleasas del Exosoma/genética , Proteínas Nucleares/genética , Estabilidad Proteica , Proteínas de Unión al ARN/genética , Saccharomyces cerevisiae/genética , Proteínas de Saccharomyces cerevisiae/genéticaRESUMEN
The eukaryotic exosome exoribonuclease Rrp6 forms a complex with Rrp47 that functions in nuclear RNA quality control mechanisms, the degradation of cryptic unstable transcripts (CUTs), and in the 3' end maturation of stable RNAs. Stable expression of Rrp47 is dependent upon its interaction with the N-terminal domain of Rrp6 (Rrp6NT). To address the function of Rrp47 independently of Rrp6, we developed a DECOID (decreased expression of complexes by overexpression of interacting domains) strategy to resolve the Rrp6/Rrp47 complex in vivo and employed mpp6Δ and rex1Δ mutants that are synthetic lethal with loss-of-function rrp47 mutants. Strikingly, Rrp47 was able to function in mpp6Δ and rex1Δ mutants when separated from the catalytic and exosome-binding domains of Rrp6, whereas a truncated Rrp47 protein lacking its C-terminal region caused a block in cell growth. Northern analyses of the conditional mutants revealed a specific block in the 3' maturation of box C/D snoRNAs in the rex1 rrp47 mutant and widespread inhibition of Rrp6-mediated RNA surveillance processes in the mpp6 rrp47 mutant. In contrast, growth analyses and RNA northern blot hybridization analyses showed no effect on the rrp47Δ mutant upon overexpression of the Rrp6NT domain. These findings demonstrate that Rrp47 and Rrp6 have resolvable functions in Rrp6-mediated RNA surveillance and processing pathways. In addition, this study reveals a redundant requirement for Rrp6 or Rex1 in snoRNA maturation and demonstrates the effective use of the DECOID strategy for the resolution and functional analysis of protein complexes.
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Proteínas de Unión al ADN/fisiología , Complejo Multienzimático de Ribonucleasas del Exosoma/metabolismo , Complejo Multienzimático de Ribonucleasas del Exosoma/fisiología , Proteínas Nucleares/fisiología , Proteínas de Unión al ARN/fisiología , Proteínas de Saccharomyces cerevisiae/metabolismo , Proteínas de Saccharomyces cerevisiae/fisiología , Saccharomyces cerevisiae/enzimología , Unión Competitiva , Dominio Catalítico , Proteínas de Unión al ADN/química , Exorribonucleasas/genética , Exorribonucleasas/metabolismo , Complejo Multienzimático de Ribonucleasas del Exosoma/química , Complejo Multienzimático de Ribonucleasas del Exosoma/genética , Expresión Génica , Proteínas Nucleares/química , Unión Proteica , Dominios y Motivos de Interacción de Proteínas , Procesamiento Postranscripcional del ARN , Estabilidad del ARN , ARN de Hongos/metabolismo , Proteínas de Unión al ARN/química , Proteínas de Unión al ARN/genética , Proteínas de Unión al ARN/metabolismo , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/crecimiento & desarrollo , Proteínas de Saccharomyces cerevisiae/química , Proteínas de Saccharomyces cerevisiae/genética , Eliminación de SecuenciaRESUMEN
CONTEXT: Pain associated with superficial procedures, including intravenous (IV) access procedures, should be prevented when possible, especially in children. OBJECTIVES: To evaluate a topical local anesthetic patch containing lidocaine 70 mg/tetracaine 70 mg with a heating element designed to warm the skin and facilitate rapid delivery of local anesthetics into the skin. The pilot study was designed to provide data to inform the design of the definitive study to evaluate the impact of controlled heat on the efficacy of the lidocaine/tetracaine patch (patch) when applied before IV cannulation. METHODS: Subjects in the pilot study were randomized to eight groups that varied by heated vs. unheated patch, 20 vs. 30 minute application, and 16 vs. 18 G catheter. Subjects in the definitive study were randomized in a double-blind manner to receive either the heated or unheated patch, 20 minutes before vascular access, using a 16 G catheter in the antecubital space of the arm. In both studies, the primary efficacy measure was subject-reported pain intensity using a visual analog scale. RESULTS: Pilot study: Subjects who received the heated patch (n=43) vs. the unheated patch (n=37) had lower mean pain intensity scores (14.7 vs. 23.5mm, P=0.04). Pain intensity scores did not differ significantly by application time, but the difference between the 16 and 18 G catheter groups approached statistical significance (22.8 vs. 14.9 mm, P=0.05). Definitive study: Mean pain intensity scores for the heated patch group (n=124) vs. the unheated patch group (n=126) were 14.2 and 20.5mm, respectively (P=0.006). CONCLUSION: Heated patches provided significantly better pain relief compared with unheated patches. All the subjects tolerated the patches well, with few adverse effects.
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Analgesia/métodos , Calor/uso terapéutico , Dolor/prevención & control , Flebotomía/efectos adversos , Administración Cutánea , Adolescente , Adulto , Anciano , Anestésicos Locales/administración & dosificación , Anestésicos Locales/uso terapéutico , Método Doble Ciego , Femenino , Humanos , Lidocaína/administración & dosificación , Lidocaína/uso terapéutico , Masculino , Persona de Mediana Edad , Dolor/etiología , Dimensión del Dolor , Proyectos Piloto , Resultado del TratamientoRESUMEN
The efficacy of novel monoclonal antibodies that neutralize the pro-angiogenic mediator, sphingosine-1-phosphate (S1P), were tested using in vitro and in vivo angiogenesis models, including choroidal neovascularization (CNV) induced by laser disruption of Bruch's membrane. S1P receptor levels in human brain choroid plexus endothelial cells (CPEC), human lung microvascular endothelial cells, human retinal vascular endothelial cells, and circulating endothelial progenitor cells were examined by semi-quantitative PCR. The ability of murine or humanized anti-S1P monoclonal antibodies (mAbs) to inhibit S1P-mediated microvessel tube formation by CPEC on Matrigel was evaluated and capillary density in subcutaneous growth factor-loaded Matrigel plugs was determined following anti-S1P treatment. S1P promoted in vitro capillary tube formation in CPEC consistent with the presence of cognate S1P(1-5) receptor expression by these cells and the S1P antibody induced a dose-dependent reduction in microvessel tube formation. In a murine model of laser-induced rupture of Bruch's membrane, S1P was detected in posterior cups of mice receiving laser injury, but not in uninjured controls. Intravitreous injection of anti-S1P mAbs dramatically inhibited CNV formation and sub-retinal collagen deposition in all treatment groups (p<0.05 compared to controls), thereby identifying S1P as a previously unrecognized mediator of angiogenesis and subretinal fibrosis in this model. These findings suggest that neutralizing S1P with anti-S1P mAbs may be a novel method of treating patients with exudative age-related macular degeneration by reducing angiogenesis and sub-retinal fibrosis, which are responsible for visual acuity loss in this disease.
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Inhibidores de la Angiogénesis/uso terapéutico , Anticuerpos Monoclonales/uso terapéutico , Neovascularización Coroidal/prevención & control , Lisofosfolípidos/inmunología , Esfingosina/análogos & derivados , Inhibidores de la Angiogénesis/farmacología , Animales , Neovascularización Coroidal/etiología , Neovascularización Coroidal/patología , Colágeno , Modelos Animales de Enfermedad , Combinación de Medicamentos , Evaluación Preclínica de Medicamentos/métodos , Femenino , Fibrosis/prevención & control , Expresión Génica , Laminina , Rayos Láser , Lisofosfolípidos/análisis , Lisofosfolípidos/farmacología , Ratones , Ratones Endogámicos C57BL , Neovascularización Fisiológica/efectos de los fármacos , Proteoglicanos , ARN Mensajero/genética , Conejos , Receptores de Lisoesfingolípidos/biosíntesis , Receptores de Lisoesfingolípidos/genética , Retina/patología , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa/métodos , Esfingosina/análisis , Esfingosina/inmunología , Esfingosina/farmacología , Cuerpo Vítreo/químicaRESUMEN
S1P has been proposed to contribute to cancer progression by regulating tumor proliferation, invasion, and angiogenesis. We developed a biospecific monoclonal antibody to S1P to investigate its role in tumorigenesis. The anti-S1P mAb substantially reduced tumor progression and in some cases eliminated measurable tumors in murine xenograft and allograft models. Tumor growth inhibition was attributed to antiangiogenic and antitumorigenic effects of the antibody. The anti-S1P mAb blocked EC migration and resulting capillary formation, inhibited blood vessel formation induced by VEGF and bFGF, and arrested tumor-associated angiogenesis. The anti-S1P mAb also neutralized S1P-induced proliferation, release of proangiogenic cytokines, and the ability of S1P to protect tumor cells from apoptosis in several tumor cell lines, validating S1P as a target for therapy.