RESUMEN
BACKGROUND: Spi-B and PU.1 are highly related members of the E26-transformation-specific (ETS) family of transcription factors that have similar, but not identical, roles in B cell development. PU.1 and Spi-B are both expressed in B cells, and have been demonstrated to redundantly activate transcription of genes required for B cell differentiation and function. It was hypothesized that Spi-B and PU.1 occupy a similar set of regions within the genome of a B lymphoma cell line. RESULTS: To compare binding regions of Spi-B and PU.1, murine WEHI-279 lymphoma cells were infected with retroviral vectors encoding 3XFLAG-tagged PU.1 or Spi-B. Anti-FLAG chromatin immunoprecipitation followed by next generation sequencing (ChIP-seq) was performed. Analysis for high-stringency enriched genomic regions demonstrated that PU.1 occupied 4528 regions and Spi-B occupied 3360 regions. The majority of regions occupied by Spi-B were also occupied by PU.1. Regions bound by Spi-B and PU.1 were frequently located immediately upstream of genes associated with immune response and activation of B cells. Motif-finding revealed that both transcription factors were predominantly located at the ETS core domain (GGAA), however, other unique motifs were identified when examining regions associated with only one of the two factors. Motifs associated with unique PU.1 binding included POU2F2, while unique motifs in the Spi-B regions contained a combined ETS-IRF motif. CONCLUSIONS: Our results suggest that complementary biological functions of PU.1 and Spi-B may be explained by their interaction with a similar set of regions in the genome of B cells. However, sites uniquely occupied by PU.1 or Spi-B provide insight into their unique functions.
Asunto(s)
Secuenciación de Nucleótidos de Alto Rendimiento , Linfoma/genética , Proteínas Proto-Oncogénicas c-ets/genética , Proteínas Proto-Oncogénicas/genética , Transactivadores/genética , Secuencia de Aminoácidos , Animales , Linfocitos B/metabolismo , Linfocitos B/patología , Sitios de Unión/genética , Línea Celular Tumoral , Proteínas de Unión al ADN/genética , Genoma , Linfoma/patología , Ratones , Regiones Promotoras Genéticas , Proteínas Proto-Oncogénicas/metabolismo , Proteínas Proto-Oncogénicas c-ets/metabolismo , Transactivadores/metabolismoRESUMEN
B cell acute lymphoblastic leukemia (B-ALL) is frequently associated with mutations or chromosomal translocations of genes encoding transcription factors. Conditional deletion of genes encoding the E26-transformation-specific transcription factors, PU.1 and Spi-B, in B cells (ΔPB mice) leads to B-ALL in mice at 100% incidence rate and with a median survival of 21 wk. We hypothesized that PU.1 and Spi-B may redundantly activate transcription of genes encoding tumor suppressors in the B cell lineage. Characterization of aging ΔPB mice showed that leukemia cells expressing IL-7R were found in enlarged thymuses. IL-7R-expressing B-ALL cells grew in culture in response to IL-7 and could be maintained as cell lines. Cultured ΔPB cells expressed reduced levels of B cell linker protein (BLNK), a known tumor suppressor gene, compared with controls. The Blnk promoter contained a predicted PU.1 and/or Spi-B binding site that was required for promoter activity and occupied by PU.1 and/or Spi-B as determined by chromatin immunoprecipitation. Restoration of BLNK expression in cultured ΔPB cells opposed IL-7-dependent proliferation and induced early apoptosis. We conclude that the tumor suppressor BLNK is a target of transcriptional activation by PU.1 and Spi-B in the B cell lineage.