Overexpressed BCL6 (LAZ3) oncoprotein triggers apoptosis, delays S phase progression and associates with replication foci

One of the most frequent genetic abnormalities associated with non Hodgkin lymphoma is the structural alteration of the 5′ non coding/regulatory region of the BCL6 (LAZ3) protooncogene. BCL6 encodes a POZ/Zn finger protein, a structure similar to that of many Drosophila developmental regulators and to another protein involved in a human hematopoietic malignancy, PLZF. BCL6 is a sequence specific transcriptional repressor controlling germinal center formation and T cell dependent immune response. Although the expression of BCL6 negatively correlates with cellular proliferation in different cell types, the influence of BCL6 on cell growth and survival is currently unknown so that the way its deregulation may contribute to cancer remains elusive. To directly address this issue, we used a tetracycline-regulated system in human U2OS osteosarcoma cells and thus found that BCL6 mediates growth suppression associated with impaired S phase progression and apoptosis. Interestingly, overexpressed BCL6 can colocalize with sites of ongoing DNA synthesis, suggesting that it may directly interfere with S phase initiation and/or progression. In contrast, the isolated Zn finger region of BCL6, which binds BCL6 target sequence but lacks transcriptional repression activity, slows, but does not suppress, U2OS cell growth, is less efficient at delaying S phase progression, and does not trigger apoptosis. Thus, for a large part, the effects of BCL6 overexpression on cell growth and survival depend on its ability to engage protein/protein interactions with itself and/or its transcriptional corepressors. That BCL6 restricts cell growth suggests that its deregulation upon structural alterations may alleviate negative controls on the cell cycle and cell survival.

[1]  S. Mori,et al.  Regulation of BCL-6 gene expression in human myeloid/monocytoid leukemic cells , 1997, Leukemia.

[2]  C Gélinas,et al.  c-Rel arrests the proliferation of HeLa cells and affects critical regulators of the G1/S-phase transition , 1997, Molecular and cellular biology.

[3]  V. Bardwell,et al.  The BCL-6 POZ domain and other POZ domains interact with the co-repressors N-CoR and SMRT , 1998, Oncogene.

[4]  P. Pandolfi,et al.  The BCL-6 proto-oncogene controls germinal-centre formation and Th2-type inflammation , 1997, Nature Genetics.

[5]  N. Aoki,et al.  Gene involved in the 3q27 translocation associated with B-cell lymphoma, BCL5, encodes a Krüppel-like zinc-finger protein. , 1994, Blood.

[6]  L. Staudt,et al.  BCL-6 expression during B-cell activation. , 1996, Blood.

[7]  C. Pinset,et al.  Increased expression of the LAZ3 (BCL6) proto-oncogene accompanies murine skeletal myogenesis. , 1998, Differentiation; research in biological diversity.

[8]  Chi-Wai Wong,et al.  Histone deacetylase associated with mSin3A mediates repression by the acute promyelocytic leukemia-associated PLZF protein , 1998, Oncogene.

[9]  J. Wang,et al.  Inhibition of DNA synthesis by RB: effects on G1/S transition and S-phase progression. , 1998, Genes & development.

[10]  P. Rao,et al.  The t(2;3)(q21;q27) translocation in non-Hodgkin's lymphoma displays BCL6 mutations in the 5′ regulatory region and chromosomal breakpoints distant from the gene , 1998, Oncogene.

[11]  David Newsome,et al.  Gene Dosage–Dependent Embryonic Development and Proliferation Defects in Mice Lacking the Transcriptional Integrator p300 , 1998, Cell.

[12]  K Offit,et al.  Alterations of a zinc finger-encoding gene, BCL-6, in diffuse large-cell lymphoma. , 1993, Science.

[13]  S. Baylin,et al.  p53 activates expression of HIC-1, a new candidate tumour suppressor gene on 17p13.3 , 1995, Nature Genetics.

[14]  S. Inoue,et al.  Role of the histone deacetylase complex in acute promyelocytic leukaemia , 1998, Nature.

[15]  M. Pearson,et al.  Cell death induction by the acute promyelocytic leukemia-specific PML/RARalpha fusion protein. , 1997, Proceedings of the National Academy of Sciences of the United States of America.

[16]  J. Girault,et al.  Histone acetyltransferase activity of CBP is controlled by cycle-dependent kinases and oncoprotein E1A , 1998, Nature.

[17]  C. Mello,et al.  A CBP/p300 homolog specifies multiple differentiation pathways in Caenorhabditis elegans. , 1998, Genes & development.

[18]  H. Leonhardt,et al.  Reversal of terminal differentiation and control of DNA replication: Cyclin A and cdk2 specifically localize at subnuclear sites of DNA replication , 1993, Cell.

[19]  R. Evans,et al.  The LAZ3(BCL-6) oncoprotein recruits a SMRT/mSIN3A/histone deacetylase containing complex to mediate transcriptional repression. , 1998, Nucleic acids research.

[20]  H. Leonhardt,et al.  A targeting sequence directs DNA methyltransferase to sites of DNA replication in mammalian nuclei , 1992, Cell.

[21]  S. Fukuhara,et al.  Significance of rearrangement of the BCL6 gene in B-cell lymphoid neoplasms. , 1997, Leukemia & lymphoma.

[22]  H. Tilly,et al.  LAZ3, a novel zinc–finger encoding gene, is disrupted by recurring chromosome 3q27 translocations in human lymphomas , 1993, Nature Genetics.

[23]  S. Okabe,et al.  The BCL6 gene is predominantly expressed in keratinocytes at their terminal differentiation stage. , 1996, Biochemical and biophysical research communications.

[24]  T. Akiyama,et al.  BCL-6 is phosphorylated at multiple sites in its serine- and proline-clustered region by mitogen-activated protein kinase (MAPK) in vivo , 1997, Oncogene.

[25]  H. Perlman,et al.  Cell cycle exit upon myogenic differentiation. , 1997, Current opinion in genetics & development.

[26]  D. Dean,et al.  Rb Interacts with Histone Deacetylase to Repress Transcription , 1998, Cell.

[27]  G. Carmichael,et al.  An alternative pathway for gene regulation by Myc , 1997, The EMBO journal.

[28]  R. Eisenman,et al.  Targeted disruption of the MYC antagonist MAD1 inhibits cell cycle exit during granulocyte differentiation , 1998, The EMBO journal.

[29]  D. Leprince,et al.  Small deletions occur in highly conserved regions of the LAZ3/BCL6 major translocation cluster in one case of non-Hodgkin's lymphoma without 3q27 translocation , 1997, Oncogene.

[30]  L. Magnaghi-Jaulin,et al.  Retinoblastoma protein represses transcription by recruiting a histone deacetylase , 1998, Nature.

[31]  S. Minucci,et al.  Fusion proteins of the retinoic acid receptor-α recruit histone deacetylase in promyelocytic leukaemia , 1998, Nature.

[32]  L. Staudt,et al.  Control of inflammation, cytokine expression, and germinal center formation by BCL-6. , 1997, Science.

[33]  M. Gossen,et al.  Tight control of gene expression in mammalian cells by tetracycline-responsive promoters. , 1992, Proceedings of the National Academy of Sciences of the United States of America.

[34]  R. Dalla‐Favera,et al.  Antigen receptor signaling induces MAP kinase-mediated phosphorylation and degradation of the BCL-6 transcription factor. , 1998, Genes & development.

[35]  M. Koken,et al.  PML induces a novel caspase-independent death process , 1998, Nature Genetics.

[36]  C. Allis,et al.  Histone Acetylation and Chromatin Assembly: A Single Escort, Multiple Dances? , 1996, Cell.

[37]  A. Lima-de-faria,et al.  Late DNA Synthesis in Heterochromatin , 1968, Nature.

[38]  N. Zeleznik-Le,et al.  BCL6 can repress transcription from the human immunodeficiency virus type I promoter/enhancer region , 1997, Genes, chromosomes & cancer.

[39]  A. Zelent,et al.  Reduced retinoic acid-sensitivities of nuclear receptor corepressor binding to PML- and PLZF-RARalpha underlie molecular pathogenesis and treatment of acute promyelocytic leukemia. , 1998, Blood.

[40]  K. Vousden,et al.  Cell cycle arrest and DNA endoreduplication following p21Waf1/Cip1 expression , 1998, Oncogene.

[41]  G. G. Stokes.  "J." , 1890, The New Yale Book of Quotations.

[42]  K. Offit,et al.  BCL-6 protein is expressed in germinal-center B cells. , 1995, Blood.

[43]  M. Bartelmann,et al.  APM‐1, a novel human gene, identified by aberrant co‐transcription with papillomavirus oncogenes in a cervical carcinoma cell line, encodes a BTB/POZ‐zinc finger protein with growth inhibitory activity , 1998, The EMBO journal.

[44]  P. Pandolfi,et al.  Pml is essential for multiple apoptotic pathways , 1998, Nature Genetics.

[45]  A. Dejean,et al.  SMRT corepressor interacts with PLZF and with the PML-retinoic acid receptor α (RARα) and PLZF-RARα oncoproteins associated with acute promyelocytic leukemia , 1997 .

[46]  D. Leprince,et al.  Corepressor SMRT binds the BTB/POZ repressing domain of the LAZ3/BCL6 oncoprotein. , 1997, Proceedings of the National Academy of Sciences of the United States of America.

[47]  M. Privalsky,et al.  Components of the SMRT Corepressor Complex Exhibit Distinctive Interactions with the POZ Domain Oncoproteins PLZF, PLZF-RARα, and BCL-6* , 1998, The Journal of Biological Chemistry.

[48]  K. Offit,et al.  Frequent somatic hypermutation of the 5' noncoding region of the BCL6 gene in B-cell lymphoma. , 1995, Proceedings of the National Academy of Sciences of the United States of America.

[49]  Tony Kouzarides,et al.  Retinoblastoma protein recruits histone deacetylase to repress transcription , 1998, Nature.

[50]  R. Chaganti,et al.  Chromosomal translocations cause deregulated BCL6 expression by promoter substitution in B cell lymphoma. , 1995, The EMBO journal.

[51]  D. Haber,et al.  WT1 suppresses synthesis of the epidermal growth factor receptor and induces apoptosis. , 1995, The EMBO journal.

[52]  R S Chaganti,et al.  BCL-6, a POZ/zinc-finger protein, is a sequence-specific transcriptional repressor. , 1996, Proceedings of the National Academy of Sciences of the United States of America.

[53]  D. Leprince,et al.  The BTB/POZ domain: a new protein-protein interaction motif common to DNA- and actin-binding proteins. , 1995, Cell growth & differentiation : the molecular biology journal of the American Association for Cancer Research.

[54]  R. Treisman,et al.  The POZ domain: a conserved protein-protein interaction motif. , 1994, Genes & development.

[55]  J. Licht,et al.  The Promyelocytic Leukemia Zinc Finger Protein Affects Myeloid Cell Growth, Differentiation, and Apoptosis , 1998, Molecular and Cellular Biology.

[56]  K. Kamiya,et al.  Over‐expressed ZF5 Gene Product, a c‐myc‐binding Protein Related to GL1‐Kruppel Protein, Has a Growth‐suppressive Activity in Mouse Cell Lines , 1995, Japanese journal of cancer research : Gann.

[57]  D. Leprince,et al.  Multiple domains participate in distance-independent LAZ3/BCL6-mediated transcriptional repression. , 1996, Biochemical and biophysical research communications.

[58]  S. Mittnacht,et al.  pRB phosphorylation mutants reveal role of pRB in regulating S phase completion by a mechanism independent of E2F , 1998, Oncogene.

[59]  M. Ebara,et al.  BAZF, a Novel Bcl6 Homolog, Functions as a Transcriptional Repressor , 1998, Molecular and Cellular Biology.

[60]  M. Hatano,et al.  Disruption of the Bcl6 Gene Results in an Impaired Germinal Center Formation , 1997, The Journal of experimental medicine.

[61]  U. Storb,et al.  Mutation of BCL-6 gene in normal B cells by the process of somatic hypermutation of Ig genes. , 1998, Science.

[62]  L. Pasqualucci,et al.  BCL-6 mutations in normal germinal center B cells: evidence of somatic hypermutation acting outside Ig loci. , 1998, Proceedings of the National Academy of Sciences of the United States of America.