生物谷報道：研究人員在6月在線出版的《自然—免疫學》（Nature Immunology）期刊上報告說,，一種通常與B細胞淋巴瘤相關的蛋白質抑制了對"有用"B細胞的消滅,，否則，將隱含DNA損害的危機,。
     在絕大多數(shù)細胞中,，DNA的損害將觸發(fā)"感應器"中斷細胞的活動，直至DNA的損害獲得了修復,。生發(fā)中心細胞能產(chǎn)生抗體,，在一組選擇出來的名為生發(fā)中心細胞的B細胞組中，Ari Melnick和同事發(fā)現(xiàn)蛋白質Bcl—6能阻止DNA損傷感應器ATR的產(chǎn)生,。在這組B細胞中,，Bcl—6有益于受到外來抗原侵襲，并在抗原編碼的基因中經(jīng)歷DNA嚴重變異的B細胞,，通常情況下,，這一過程需要產(chǎn)生高效的抗體。然而,，這種DNA變異卻導致生發(fā)中心B細胞的死亡,，從而間接減少了了有用抗體的產(chǎn)生。
    Melnick小組的研究顯示,，Bcl—6能抑制ATR基因的活性,，這種基因能有效地關閉DNA損害感應器的機制，導致生發(fā)中心B細胞不再傾向于DAN損失所引導的死亡,。而且,，許多B細胞淋巴瘤顯示，解除管制的Bcl—6能表達和容忍過度的DNA變異,，包括由輻射治療引發(fā)的變異,。
    這項新研究推測，淋巴瘤細胞中Bcl—6的變異可能會讓它們對輻射更敏感,。

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).

原文出處：

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

相關基因：

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

作者簡介：
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.