RESUMEN
Cancer stem cells (CSC) appear to have increased metastatic potential, but mechanisms underlying this are poorly defined. Here we show that VEGFA induction of Sox2 promotes EMT and tumor metastasis. In breast lines and primary cancer culture, VEGFA rapidly upregulates SOX2 expression, leading to SNAI2 induction, EMT, increased invasion and metastasis. We show Sox2 downregulates miR-452, which acts as a novel metastasis suppressor to directly target the SNAI2 3'-untranslated region (3'-UTR). VEGFA stimulates Sox2- and Slug-dependent cell invasion. VEGFA increases lung metastasis in vivo, and this is abrogated by miR-452 overexpression. Furthermore, SNAI2 transduction rescues metastasis suppression by miR-452. Thus, in addition to its angiogenic action, VEGFA upregulates Sox2 to drive stem cell expansion, together with miR-452 loss and Slug upregulation, providing a novel mechanism whereby cancer stem cells acquire metastatic potential. Prior work showed EMT transcription factor overexpression upregulates CSC. Present work indicates that stemness and metastasis are a two-way street: Sox2, a major mediator of CSC self-renewal, also governs the metastatic process.
Asunto(s)
Neoplasias de la Mama/patología , Neoplasias Pulmonares/secundario , MicroARNs/genética , Células Madre Neoplásicas/patología , Factores de Transcripción SOXB1/metabolismo , Factores de Transcripción de la Familia Snail/metabolismo , Factor A de Crecimiento Endotelial Vascular/metabolismo , Animales , Neoplasias de la Mama/genética , Neoplasias de la Mama/metabolismo , Línea Celular Tumoral , Proliferación Celular , Femenino , Regulación Neoplásica de la Expresión Génica , Humanos , Neoplasias Pulmonares/genética , Neoplasias Pulmonares/metabolismo , Ratones , Ratones Endogámicos BALB C , Ratones Desnudos , Células Madre Neoplásicas/metabolismo , Factores de Transcripción SOXB1/genética , Factores de Transcripción de la Familia Snail/genética , Factor A de Crecimiento Endotelial Vascular/genéticaRESUMEN
Transgenic mice carrying multiple copies of a recoverable lambda phage shuttle vector carrying the supF mutation reporter gene (lambda supF) were constructed for the purpose of studying mutagenesis in a whole animal. Spontaneous mutations in rescued supF target genes from mouse liver and skin were analyzed. The mutation frequency was similar in both tissues (in the range of 2 x 10(-5)), but the spectrum of point mutations was distinct, with transitions common in the skin and transversions more prominent in the liver (P = 0.01). These results may help to elucidate pathways of endogenous mutagenesis in vivo, and they illustrate potentially important tissue-specific differences in genetic instability.
Asunto(s)
Bacteriófago lambda/genética , Ratones Transgénicos/genética , Especificidad de Órganos , Mutación Puntual , ARN de Transferencia/genética , Animales , Secuencia de Bases , Femenino , Genes Supresores , Hígado/fisiología , Ratones , Datos de Secuencia Molecular , Mutación , Análisis de Secuencia de ADN , Fenómenos Fisiológicos de la PielRESUMEN
Transgenic mice carrying multiple copies of a recoverable lambda phage shuttle vector (lambda supF) were constructed for the purpose of studying mutagenesis in a whole animal. Spontaneous mutations in rescued supF target genes from several different lines of transgenic mice were analyzed. One mouse line, 1139, was identified in which the frequency of spontaneous mutations was unusually high (3.15 x 10(-4)), 20-fold higher than in other transgenic mice carrying a similar number of copies of the lambda transgene (approximately 100). Over 75% of the spontaneous mutations from 1139 mice were found to be deletions, whereas mostly point mutations were recovered from the other mice. In 1139 no significant variation among adult tissues has been detected. However, embryonic tissue yielded a 3- to 4-fold lower frequency of mutations, most of which were point mutations rather than deletions. The frequency of mutations at another locus, the hypoxanthine phosphoribosyl transferase gene, was not elevated in fibroblast lines established in culture from the 1139 mice. Overall, these results suggest that the deletion mutagenesis affecting the transgene sequences in 1139 mice is a locus-specific effect occurring during growth and development. The increased mutagenesis could not be explained by the degree of methylation of the transgene sequences, since hypermethylation was seen in both 1139 mice and other mice with a low frequency of shuttle vector mutations. The integrated lambda vector DNA in 1139 mice was mapped to a single site on chromosome 7, but no mechanism for the mutagenesis was suggested by this localization. It is proposed that the lambda DNA may have either integrated into an unstable genomic site or created a newly unstable locus in the process of integration.
Asunto(s)
Ratones Transgénicos/genética , Eliminación de Secuencia , Animales , Bacteriófago lambda/genética , Secuencia de Bases , Mapeo Cromosómico , Análisis Mutacional de ADN , ADN Recombinante/química , ADN Recombinante/genética , Embrión de Mamíferos , Vectores Genéticos , Metilación , Ratones , Datos de Secuencia Molecular , Mutación PuntualRESUMEN
The tumor suppressor protein, p53, is proposed to have a critical role in maintaining the integrity of the genetic material. It has been established that p53 induces a cell cycle block in the G1 phase upon cellular DNA damage. Recent evidence also indicates the involvement of p53 directly and indirectly in nucleotide excision repair (NER). We have examined the role of p53 with respect to UV-induced mutagenesis. By gene transfer, we established a mouse fibroblast cell line overexpressing the val135 temperature-sensitive p53 allele. In this line, p53 activity can be modulated through temperature shift, as confirmed by Western blot and by cell cycle analysis. This cell line was also constructed to contain a recoverable lambda phage shuttle vector carrying the supF mutation reporter gene. Induction of p53 was found to enhance the clonogenic survival of the cells following UV-irradiation compared to the p53-deficient parental mouse cell line. The transfectant line also displayed a 4-fold reduction in the frequency of UV-induced mutations as measured in the chromosomally integrated supF reporter gene. Our results are consistent with a p53-induced cell cycle block at G1 allowing cells to repair chromosomal damage before DNA replication. However, our data may also reflect a more direct role of p53 in the repair of UV-induced lesions as suggested by studies showing that p53 can interact directly with repair factors.
Asunto(s)
Mutagénesis/efectos de la radiación , Proteína p53 Supresora de Tumor/biosíntesis , Rayos Ultravioleta , Animales , Bacteriófago lambda , Secuencia de Bases , Western Blotting , Ciclo Celular/efectos de la radiación , Línea Celular , Daño del ADN , Técnicas de Transferencia de Gen , Genes Supresores , Vectores Genéticos , Ratones , Datos de Secuencia Molecular , Mutación Puntual , ARN de Transferencia/biosíntesis , ARN de Transferencia/genética , Proteínas Recombinantes/análisis , Proteínas Recombinantes/biosíntesis , Proteína p53 Supresora de Tumor/análisisRESUMEN
Psoralens are used clinically in the treatment of several skin diseases, including psoriasis, vitiligo, and cutaneous T cell lymphoma. However, psoralen treatment has been associated with an increased risk of squamous cell carcinoma of the skin. To elucidate molecular events that may play a role in the psoralen-related carcinogenesis, we examined psoralen-induced mutagenesis in a mouse fibroblast cell line carrying a recoverable, chromosomally integrated lambda phage shuttle vector. Using the supF gene as a mutation reporter gene, we determined the spectrum of mutations induced by photoactivation of 8-methoxypsoralen and of 5-methylangelicin. Both psoralens generated predominately T:A to A:T and some T:A to G:C transversions. Most of the mutations occurred at either 5' TpA or 5' ApT sites, both of which are conducive to interstrand cross-link formation. However, 5-methylangelicin produces only monoadducts, whereas 8-methoxypsoralen generated 20% cross-links and 80% monoadducts under the conditions of our experiments, as measured by direct HPLC analysis of the DNA from the treated cells. Although most of the mutations occurred at potentially cross-linkable sites, these results implicate monoadducts, as well as cross-links, as critical premutagenic lesions in psoralen-treated mammalian cells. These findings may help in the identification of carcinogenic changes induced by psoralen, and they may aid in the improved design of psoralen-based treatment regimens in the future.
Asunto(s)
Furocumarinas/toxicidad , Metoxaleno/toxicidad , Mutágenos/toxicidad , Terapia PUVA/efectos adversos , Animales , Secuencia de Bases , Fibroblastos , Ratones , Datos de Secuencia Molecular , FotoquímicaRESUMEN
Ionizing radiation is a known carcinogen and teratogen. However, the point mutations produced by ionizing radiation in mammalian cells have not been fully characterized. Determination of a characteristic spectrum of X-ray-induced mutations in mammalian cells could provide clues to cellular repair processes and could serve as a marker of individual exposure to radiation. Mouse fibroblasts containing in their genome multiple copies of a recoverable lambda phage shuttle vector were used to detect and analyze radiation-induced point mutations in the supF mutation reporter gene. Following fractionated doses of ionizing radiation, a unique mutational spectrum notable for a high proportion of T:A-->G:C transversions (57%) was found. This pattern was distinct from the spectra of UV-induced and spontaneous mutations detected in the same mouse cell assay system (mainly C:G-->T:A transitions). The predominance of T:A-->G:C transversions and the pattern of mutation hot-spots are consistent with a possible role for polymerase beta in the repair of X-ray-damaged DNA. These results may also help to define a distinctive mutational signature of X-ray exposure in mammalian cells.