生物谷报道：研究人员在6月在线出版的《自然—免疫学》（Nature Immunology）期刊上报告说，一种通常与B细胞淋巴瘤相关的蛋白质抑制了对"有用"B细胞的消灭，否则，将隐含DNA损害的危机。
在绝大多数细胞中，DNA的损害将触发"感应器"中断细胞的活动，直至DNA的损害获得了修复。生发中心细胞能产生抗体，在一组选择出来的名为生发中心细胞的B细胞组中，Ari Melnick和同事发现蛋白质Bcl—6能阻止DNA损伤感应器ATR的产生。在这组B细胞中，Bcl—6有益于受到外来抗原侵袭，并在抗原编码的基因中经历DNA严重变异的B细胞，通常情况下，这一过程需要产生高效的抗体。然而，这种DNA变异却导致生发中心B细胞的死亡，从而间接减少了了有用抗体的产生。
Melnick小组的研究显示，Bcl—6能抑制ATR基因的活性，这种基因能有效地关闭DNA损害感应器的机制，导致生发中心B细胞不再倾向于DAN损失所引导的死亡。而且，许多B细胞淋巴瘤显示，解除管制的Bcl—6能表达和容忍过度的DNA变异，包括由辐射治疗引发的变异。
这项新研究推测，淋巴瘤细胞中Bcl—6的变异可能会让它们对辐射更敏感。
Figure 1 - ATR is a direct target gene of Bcl-6.
(a) Quantitative PCR of the abundance of ATR mRNA in Ly1 cells exposed for 5 h to 4 mM recombinant BPI or mutant control peptide (Ctrl), presented as the 'fold change' relative to that of cells treated with mutant BPI. (b) Chromatin immunoprecipitation on a chip with anti-Bcl-6 and irrelevant anti-actin (IgG), presented as 'fold enrichment' of Bcl-6 or actin relative to input, starting at 2.5-fold enrichment, our cutoff for relevant data. Horizontal axis, location in the ATR genomic sequence at chromosome 3, positions 143,755,777–143,791,000. Arrows and bar below peak indicate positions of primers and amplicon used for single-locus confirmation of Bcl-6 binding; boxes indicate exon-intron structure of ATR along horizontal axis (transcribed from right to left). BS, binding site. (c) Quantitative chromatin immunoprecipitation with anti-Bcl-6, anti-N-CoR or anti-actin at the ATR binding site in b in the presence of BPI or control peptide, presented as percent enrichment relative to input. Data (error bars (a,c), s.d.) represent three independent experiments (a) or samples done in triplicate (b) or three times (c).
原文出处：
Nature Immunology 8, 705 - 714 (2007)
Published online: 10 June 2007 | doi:10.1038/ni1478
Bcl-6 mediates the germinal center B cell phenotype and lymphomagenesis through transcriptional repression of the DNA-damage sensor ATR
Stella Maris Ranuncolo, Jose M Polo, Jamil Dierov, Michael Singer, Tracy Kuo, John Greally, Roland Green, Martin Carroll, Ari Melnick
Abstract | Full Text | PDF | phenotype%20and%20lymphomagenesis%20through%20transcriptional%20repression%20of%20the%20DNA-damage%20sensor%20ATR&author=Stella%20Maris%20Ranuncolo,%20Jose%20M%20Polo,%20Jamil%20Dierov,%20Michael%20Singer,%20Tracy%20Kuo,%20John%20Greally,%20Roland%20Green,%20Martin%20Carroll,%20Ari%20Melnick&contentID=10.1038/ni1478&publicationDate=01%20Jul%202007">Rights and permissions | Save this link
相关基因：
ATR
Official Symbol ATR and Name: ataxia telangiectasia and Rad3 related [Homo sapiens]
Other Aliases: FRP1, MEC1, SCKL, SCKL1
Other Designations: FRAP-related protein-1; MEC1, mitosis entry checkpoint 1, homolog; Rad3 related protein; Seckel syndrome; ataxia telangiectasia and Rad3 related protein; protein kinase ATR
Chromosome: 3; Location: 3q22-q24
Annotation: Chromosome 3, NC_000003.10 (143780340..143650768, complement)
MIM: 601215
GeneID: 545
作者简介：
Dr. Ari Melnick
Department of Developmental and Molecular Biology
Ari Melnick's Laboratory personnel
The Role of Chromatin Remodeling and Epigenetics in Hematopoiesis and Hematologic Malignancies
Overview: We are interested in molecular mechanisms that direct gene expression during the development of normal and malignant blood cells. We focus in particular on silencing mechanisms used by transcription factors that play master regulatory roles in these processes. The ordered repression of certain genes is as important for cell differentiation and proliferation as is the process of gene activation, yet far less is known about these silencing mechanisms. In general, mechanisms of transcriptional repression are highly complex and involve multiple effects on chromatin. Such effects include modifications of histone tails by methylation and acetylation, remodeling of nucleosomes by helicases and direct methylation of DNA. Furthermore, regulatory proteins form chromatin-associated complexes that directly shut down gene expression. All of these events are coordinated by binding of sequence-specific transcriptional repressors to their target DNA, in response to multiple signaling and developmental pathways.
BTB transcription factors: A major class of transcriptional repressor proteins involved in hematopoiesis is characterized by the presence of an N-terminal BTB/POZ domain. We found that the BTB domain was required for both dimerization and transcriptional repression by these proteins. In a detailed structure function analysis we observed that the repression, dimerization and oligomerization could be mapped to different regions of the BTB domain. We found that the repression motif of the BTB domain directly recruits co-repressor proteins that serve as a scaffold for histone deacetylases (HDACs). In the absence of this motif, proteins that play important roles in leukemias and lymphomas such as PLZF and Bcl-6 fail to repress their target genes and fail to mediate their biological effects. On the basis of these results, and in collaboration with structural biology colleagues, we are using crystallographic analysis coupled with molecular biology techniques, to develop a novel form of specific therapy for cancers where BTB proteins play a prominent role.
Transcriptional repression and common pathways of aberrant gene expression in hematologic malignancies: Hematologic malignancies are characterized by an extensive number of nonrandom mutations. Such mutations most often lead to de-regulation of transcription factors that lead to aberrant patterns of gene expression and malignancy transformation. The large number of these mutations makes a concerted approach towards these diseases difficult. We hypothesize however that many of these targeted transcription factors might in fact be part of common complexes. This is in fact the case since we found that the ETO protein involved in the M2 form of acute myeloid leukemia (AML) is part of repression complex by the PLZF protein that is involved in the M3 form of AML. In fact, ETO enhances the repression effects of PLZF through recruitment of histone deacetylases. Interestingly, the fusion protein of ETO with AML-1, which is characteristic of AML with the 8;21 translocation, acts as a dominant anti-corepressor that abrogates PLZF repression. In this way, leukemia cells that express this fusion protein are able to escape the growth suppressive effects of PLZF and grow indefinitely. We are currently exploring the interactions of several other leukemia and lymphoma oncoproteins. These studies are allowing us to define networks of hematopoietic transcription factor networks in blood development and differentiation, as well as opportunities for molecular targeted therapeutics.
Chromatin, epigenetics and leukemia: Recent data indicate that covalent modifications of nucleosomal histone tails regulate the transcriptional status of gene expression. These changes, along with alterations in the relationship between DNA and core histones mediated by chromatin remodeling machines, are coordinated by DNA binding transcription factors. We are interested in how these different machineries and their effects are choreographed by transcriptional factors such as the BTB family of repressors mentioned above. To this end we are establishing in vitro models of these regulatory events using chromatinized templates and correlating these findings in appropriate vivo systems. The combination of the approaches outlined in these paragraphs are designed to collectively facilitate a comprehensive analysis of gene silencing and contribute to the understanding of normal and malignant hematopoiesis.
Selected References:
Transcriptional signature with differential expression of BCL6 target genes accurately identifies BCL6-dependent diffuse large B cell lymphomas. Polo JM, Juszczynski P, Monti S, Cerchietti L, Ye K, Greally JM, Shipp M, Melnick A. 2007 Proc Natl Acad Sci U S A. 104(9):3207-12.
Targeting APL fusion proteins by peptide interference. Melnick A. 2007 Curr Top Microbiol Immunol. 313:221-43.
Comparative isoschizomer profiling of cytosine methylation: the HELP assay.. Khulan B, Thompson RF, Ye K, Fazzari MJ, Suzuki M, Stasiek E, Figueroa ME, Glass JL, Chen Q, Montagna C, Hatchwell E, Selzer RR, Richmond TA, Green RD, Melnick A, Greally JM. 2006 Genome Res. 16(8):1046-55.
Specific peptides for the therapeutic targeting of oncogenes. Prive GG, Melnick A. 2006 Curr Opin Genet Dev. 16(1):71-7.
Kaiso-deficient mice show resistance to intestinal cancer. Prokhortchouk A, Sansom O, Selfridge J, Caballero IM, Salozhin S, Aithozhina D, Cerchietti L, Meng FG, Augenlicht LH, Mariadason JM, Hendrich B, Melnick A, Prokhortchouk E, Clarke A, Bird A. 2006 Mol Cell Biol. 26(1):199-208
Predicting the effect of transcription therapy in hematologic malignancies. Melnick A. 2005 Leukemia 19(7):1109-17.
Reprogramming specific gene expression pathways in B-cell lymphomas. Melnick A. 2005 Cell Cycle. 4(2):239-41.
Specific peptide interference reveals BCL6 transcriptional and oncogenic mechanisms in B-cell lymphoma cells. Polo JM, Dell'Oso T, Ranuncolo SM, Cerchietti L, Beck D, Da Silva GF, Prive GG, Licht JD, Melnick A. 2004 Nat Med. 10(12):1329-35
Mechanism of SMRT corepressor recruitment by the BCL6 BTB domain. Ahmad KF, Melnick A, Lax S, Bouchard D, Liu J, Kiang CL, Mayer S, Takahashi S, Licht JD, Prive GG. 2003 Mol Cell. 12(6):1551-64.
ETO protein of t(8;21) AML is a corepressor for Bcl-6 B-cell lymphoma oncoprotein. Chevallier N, Corcoran CM, Lennon C, Hyjek E, Chadburn A, Bardwell VJ, Licht JD, Melnick A. 2004 Blood. 103(4):1454-63.
