RESUMO
Cancer cells frequently depend on chromatin regulatory activities to maintain a malignant phenotype. Here, we show that leukemia cells require the mammalian SWI/SNF chromatin remodeling complex for their survival and aberrant self-renewal potential. While Brg1, an ATPase subunit of SWI/SNF, is known to suppress tumor formation in several cell types, we found that leukemia cells instead rely on Brg1 to support their oncogenic transcriptional program, which includes Myc as one of its key targets. To account for this context-specific function, we identify a cluster of lineage-specific enhancers located 1.7 Mb downstream from Myc that are occupied by SWI/SNF as well as the BET protein Brd4. Brg1 is required at these distal elements to maintain transcription factor occupancy and for long-range chromatin looping interactions with the Myc promoter. Notably, these distal Myc enhancers coincide with a region that is focally amplified in â¼3% of acute myeloid leukemias. Together, these findings define a leukemia maintenance function for SWI/SNF that is linked to enhancer-mediated gene regulation, providing general insights into how cancer cells exploit transcriptional coactivators to maintain oncogenic gene expression programs.
Assuntos
Proteínas de Ligação a DNA/metabolismo , Elementos Facilitadores Genéticos/fisiologia , Regulação Neoplásica da Expressão Gênica , Leucemia Mieloide Aguda/fisiopatologia , Proteínas Proto-Oncogênicas c-myc/genética , Fatores de Transcrição/metabolismo , Linhagem Celular Tumoral , Proliferação de Células , DNA Helicases/genética , DNA Helicases/metabolismo , Proteínas de Ligação a DNA/genética , Elementos Facilitadores Genéticos/genética , Técnicas de Silenciamento de Genes , Humanos , Proteínas Nucleares/genética , Proteínas Nucleares/metabolismo , Regiões Promotoras Genéticas/genética , Ligação Proteica , Proteínas Proto-Oncogênicas c-myc/metabolismo , Fatores de Transcrição/genéticaRESUMO
Representational difference analysis (RDA) of human breast cancer was used to discover a novel amplicon located at chromosomal region 8q24.3. We examined a series of breast cancer samples harboring amplification of this region and determined that KCNK9 is the sole overexpressed gene within the amplification epicenter. KCNK9 encodes a potassium channel that is amplified from 3-fold to 10-fold in 10% of breast tumors and overexpressed from 5-fold to over 100-fold in 44% of breast tumors. Overexpression of KCNK9 in cell lines promotes tumor formation and confers resistance to both hypoxia and serum deprivation, suggesting that its amplification and overexpression plays a physiologically important role in human breast cancer.
Assuntos
Amplificação de Genes , Canais de Potássio/genética , Canais de Potássio/metabolismo , Animais , Neoplasias da Mama/genética , Linhagem Celular , Transplante de Células , Cromossomos Humanos Par 8 , Sondas de DNA , Feminino , Regulação Neoplásica da Expressão Gênica , Genoma Humano , Humanos , Camundongos , Dados de Sequência Molecular , Oncogenes , Mapeamento Físico do Cromossomo , Sitios de Sequências Rotuladas , Transplante HeterólogoRESUMO
A previously uncharacterized gene, DBC2 (deleted in breast cancer), was cloned from a homozygously deleted region at human chromosome 8p21. DBC2 contains a highly conserved RAS domain and two putative protein interacting domains. Our analyses indicate that DBC2 is the best candidate tumor suppressor gene from this region. It lies within the epicenter of the deletions and is homozygously deleted in 3.5% (7/200) of breast tumors. Mutation analysis of DBC2 led to discovery of two instances of somatic missense mutations in breast tumor specimens, whereas no missense mutations were found in other candidates from the region. Unlike other genes in the region, expression of DBC2 is often extinguished in breast cancer cells or tissues. Moreover, our functional analysis revealed that DBC2 expression in breast cancer cells lacking DBC2 transcripts causes growth inhibition. By contrast, expression of a somatic mutant discovered in a breast cancer specimen does not suppress the growth of breast cancer cells.