RESUMEN
The naked mole rat (Heterocephalus glaber) is a long-lived and tumor-resistant rodent. Tumor resistance in the naked mole rat is mediated by the extracellular matrix component hyaluronan of very high molecular weight (HMW-HA). HMW-HA triggers hypersensitivity of naked mole rat cells to contact inhibition, which is associated with induction of the INK4 (inhibitors of cyclin dependent kinase 4) locus leading to cell-cycle arrest. The INK4a/b locus is among the most frequently mutated in human cancer. This locus encodes three distinct tumor suppressors: p15(INK4b), p16(INK4a), and ARF (alternate reading frame). Although p15(INK4b) has its own ORF, p16(INK4a) and ARF share common second and third exons with alternative reading frames. Here, we show that, in the naked mole rat, the INK4a/b locus encodes an additional product that consists of p15(INK4b) exon 1 joined to p16(INK4a) exons 2 and 3. We have named this isoform pALT(INK4a/b) (for alternative splicing). We show that pALT(INK4a/b) is present in both cultured cells and naked mole rat tissues but is absent in human and mouse cells. Additionally, we demonstrate that pALT(INK4a/b) expression is induced during early contact inhibition and upon a variety of stresses such as UV, gamma irradiation-induced senescence, loss of substrate attachment, and expression of oncogenes. When overexpressed in naked mole rat or human cells, pALT(INK4a/b) has stronger ability to induce cell-cycle arrest than either p15(INK4b) or p16(INK4a). We hypothesize that the presence of the fourth product, pALT(INK4a/b) of the INK4a/b locus in the naked mole rat, contributes to the increased resistance to tumorigenesis of this species.
Asunto(s)
Empalme Alternativo/fisiología , Puntos de Control del Ciclo Celular/fisiología , Inhibidor p15 de las Quinasas Dependientes de la Ciclina/biosíntesis , Inhibidor p16 de la Quinasa Dependiente de Ciclina/biosíntesis , Sitios Genéticos/fisiología , Animales , Línea Celular , Transformación Celular Neoplásica/genética , Transformación Celular Neoplásica/metabolismo , Senescencia Celular/fisiología , Inhibidor p15 de las Quinasas Dependientes de la Ciclina/genética , Inhibidor p16 de la Quinasa Dependiente de Ciclina/genética , Humanos , Ratones , Ratas Topo , Ratas , Especificidad de la EspecieRESUMEN
Cells of B-cell chronic lymphocytic leukemia (B-CLL) are characterized by short telomeres despite a low proliferative index. Because telomere length has been reported to be a valuable prognosis criteria, there is a great interest in a deep understanding of the origin and consequences of telomere dysfunction in this pathology. Cases of chromosome fusion involving extremely short telomeres have been reported at advanced stage. In the present study, we address the question of the existence of early telomere dysfunction during the B-CLL time course. In a series restricted to 23 newly diagnosed Binet stage A CLL patients compared with 12 healthy donors, we found a significant increase in recruitment of DNA-damage factors to telomeres showing telomere dysfunction in the early stage of the disease. Remarkably, the presence of dysfunctional telomeres did not correlate with telomere shortening or chromatin marks deregulation but with a down-regulation of 2 shelterin genes: ACD (coding for TPP1; P = .0464) and TINF2 (coding for TIN2; P = .0177). We propose that telomeric deprotection in the early step of CLL is not merely the consequence of telomere shortening but also of shelterin alteration.
Asunto(s)
Daño del ADN/fisiología , Leucemia Linfocítica Crónica de Células B/genética , Proteínas de Unión a Telómeros/genética , Telómero/patología , Secuencia de Bases , Estudios de Cohortes , Progresión de la Enfermedad , Regulación Leucémica de la Expresión Génica , Humanos , Leucemia Linfocítica Crónica de Células B/patología , Modelos Biológicos , Datos de Secuencia Molecular , ARN Mensajero/análisis , ARN Mensajero/metabolismo , Complejo Shelterina , Telómero/genética , Proteínas de Unión a Telómeros/metabolismoRESUMEN
The naked mole rat (NMR), a long-lived and cancer-resistant rodent, is highly resistant to hypoxia. Here, using robust cellular models wherein the mouse telomeric protein TRF1 is substituted by NMR TRF1 or its mutant forms, we show that TRF1 supports maximal glycolytic capacity under low oxygen, shows increased nuclear localization and association with telomeres, and protects telomeres from replicative stress. We pinpoint this evolutionary gain of metabolic function to specific amino acid changes in the homodimerization domain of this protein. We further find that NMR TRF1 accelerates telomere shortening. These findings reveal an evolutionary strategy to adapt telomere biology for metabolic control under an extreme environment.
RESUMEN
Dysfunctional telomeres suppress tumour progression by activating cell-intrinsic programs that lead to growth arrest. Increased levels of TRF2, a key factor in telomere protection, are observed in various human malignancies and contribute to oncogenesis. We demonstrate here that a high level of TRF2 in tumour cells decreased their ability to recruit and activate natural killer (NK) cells. Conversely, a reduced dose of TRF2 enabled tumour cells to be more easily eliminated by NK cells. Consistent with these results, a progressive upregulation of TRF2 correlated with decreased NK cell density during the early development of human colon cancer. By screening for TRF2-bound genes, we found that HS3ST4--a gene encoding for the heparan sulphate (glucosamine) 3-O-sulphotransferase 4--was regulated by TRF2 and inhibited the recruitment of NK cells in an epistatic relationship with TRF2. Overall, these results reveal a TRF2-dependent pathway that is tumour-cell extrinsic and regulates NK cell immunity.
Asunto(s)
Neoplasias de la Mama/prevención & control , Neoplasias del Colon/prevención & control , Células Asesinas Naturales/inmunología , Linfocitos Infiltrantes de Tumor/inmunología , Melanoma Experimental/prevención & control , Sulfotransferasas/metabolismo , Proteína 2 de Unión a Repeticiones Teloméricas/metabolismo , Animales , Apoptosis , Western Blotting , Neoplasias de la Mama/inmunología , Neoplasias de la Mama/metabolismo , Adhesión Celular , Proliferación Celular , Neoplasias del Colon/inmunología , Neoplasias del Colon/metabolismo , Cartilla de ADN/química , Receptor con Dominio Discoidina 1 , Femenino , Citometría de Flujo , Células HeLa , Humanos , Células Asesinas Naturales/metabolismo , Células Asesinas Naturales/patología , Linfocitos Infiltrantes de Tumor/patología , Melanoma Experimental/inmunología , Melanoma Experimental/metabolismo , Ratones , Ratones Desnudos , ARN Mensajero/genética , ARN Interferente Pequeño/genética , Reacción en Cadena en Tiempo Real de la Polimerasa , Proteínas Tirosina Quinasas Receptoras/genética , Proteínas Tirosina Quinasas Receptoras/metabolismo , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Sulfotransferasas/genética , Proteína 2 de Unión a Repeticiones Teloméricas/antagonistas & inhibidores , Proteína 2 de Unión a Repeticiones Teloméricas/genética , Células Tumorales CultivadasRESUMEN
The study of the proteins that bind to telomeric DNA in mammals has provided a deep understanding of the mechanisms involved in chromosome-end protection. However, very little is known on the binding of these proteins to nontelomeric DNA sequences. The TTAGGG DNA repeat proteins 1 and 2 (TRF1 and TRF2) bind to mammalian telomeres as part of the shelterin complex and are essential for maintaining chromosome end stability. In this study, we combined chromatin immunoprecipitation with high-throughput sequencing to map at high sensitivity and resolution the human chromosomal sites to which TRF1 and TRF2 bind. While most of the identified sequences correspond to telomeric regions, we showed that these two proteins also bind to extratelomeric sites. The vast majority of these extratelomeric sites contains interstitial telomeric sequences (or ITSs). However, we also identified non-ITS sites, which correspond to centromeric and pericentromeric satellite DNA. Interestingly, the TRF-binding sites are often located in the proximity of genes or within introns. We propose that TRF1 and TRF2 couple the functional state of telomeres to the long-range organization of chromosomes and gene regulation networks by binding to extratelomeric sequences.