Role of Histone Deacetylase HDAC7 in B Lymphocyte Biology

• Autores: Lidia Román González
• Directores de la Tesis: Esteban Ballestar (dir. tes.), M. Isabel Parra Bola (dir. tes.)
• Lectura: En la Universitat de Barcelona ( España ) en 2014
• Idioma: inglés
• Tribunal Calificador de la Tesis: Carme Caelles Franch (presid.), Alejandro Vaquero García (secret.), Purificacion Muñoz Canoves (voc.)
• Materias:
  • Ciencias de la vida
    • Genética
    • Inmunología
  • Ciencias médicas
    • Medicina interna
      • Hematología
• Enlaces
  • Tesis en acceso abierto en:  TDX  Dipòsit Digital de la UB 
• Resumen

  • B lymphopoiesis is the result of several cell commitment, lineage choice and differentiation processes. Every differentiation step is characterized by the activation of a new, lineage specific, genetic program and the extinction of the previous one. To date, the central role of specific transcription factors in positively regulating these distinct differentiation processes to acquire a B cell specific genetic program is well established. However, the mechanisms by which B cell transcription factors mediate the process of gene silencing to acquire and maintain the cellular identity is poorly understood. The main goal of this PhD Project was to investigate the mechanisms of gene transcriptional repression during B lymphocyte development and maturation. Since histone deacetylases (HDACs) are known as important modulators of gene transcription and are associated with several proliferation and differentiation processes, we decided to study the potential contribution of class IIa HDACs in B lymphocyte Biology. Among all HDAC members, class IIa enzymes are potential candidates to participate in the gene transcriptional repression in B cell development for three reasons. First, they are expressed in a tissue-specific manner and are implicated in several differentiation and developmental processes. Second, they have an amino-terminal region that mediates their interaction with specific transcription factors, such as MEF2C, and this mediate their repression function. And third, this N-terminal domain is subject to phosphorylation and this mechanism is implicated in the regulation of their subcellular localization which in turn determines their function as transcriptional repressors. To achieve our principal objective, we have made use of two main experimental approaches: a biochemical-genome wide assay by using a highly efficient immune reprogramming system, and an in vivo approach by generating conditional knock-out mouse models. To study the potential contribution of class II HDACs in the reprogramming of B cells into macrophages, we have taken advantage of recently highly efficient cellular reprogramming system consisting by which a genetically modified B cell line can transdifferentiate to functional macrophages by addition of ß-estradiol (Bussmann, 2009). We have demonstrated that amon all class IIa HDACs, HDAC7 showed a lymphoid lineage specific expression pattern during cellular reprogramming. Importantly, re-expression of HDAC7 interfered with the macrophage gene transcriptional program, blocked the induction of key genes for macrophage function, (such as immune, inflammatory response and phagocytosis), and abolished crucial functions of macrophages, such as the ability to phagocytose bacteria and to respond to endotoxin by expressing major pro-inflammatory cytokines. Mechanistically, HDAC7 interacts with MEF2C and is recruited to the promoters of macrophage genes, leading to their transcriptional repression. Finally, to study the role of HDAC7 during B cell development, we generated conditional knock-out mouse models for a specific deletion of HDAC7 in the hematopoietic system. Our results demonstrated that HDAC7-deficient mice showed a highly relevant block in B cell development at pro-B cell stage, demonstrating that HDAC7 is a potential transcription factor implicated in B lymphopoiesis. Mechanistically, HDAC7 specifically interacts with MEF2C, resulting in the repression of non-lymphoid genes. Importantly, we showed that the absence of HDAC7 resulted in a highly significant up-regulation of relevant genes related to important biological processes and macrophage functions, such as ubiquitination, cell cycle and signal transduction, whereas no significant effects were seen on B master regulators, such as PAX5, E2A, EB1 and IKAROS. In conclusion, we have demonstrated that among class IIa HDACs, HDA7, through its interaction with other transcription factors, such as MEF2C, acts as a potential transcriptional repressor in B lymphocyte Biology by repressing lineage inappropriate genes, and thus allowing the appropriate development of B lymphocytes.