RESUMO
The histone methyltransferase EZH2 is frequently mutated in germinal center-derived diffuse large B-cell lymphoma and follicular lymphoma. To further characterize these EZH2 mutations in lymphomagenesis, we generated a mouse line where EZH2(Y641F) is expressed from a lymphocyte-specific promoter. Spleen cells isolated from the transgenic mice displayed a global increase in trimethylated H3K27, but the mice did not show an increased tendency to develop lymphoma. As EZH2 mutations often coincide with other mutations in lymphoma, we combined the expression of EZH2(Y641F) by crossing these transgenic mice with Eµ-Myc transgenic mice. We observed a dramatic acceleration of lymphoma development in this combination model of Myc and EZH2(Y641F). The lymphomas show histologic features of high-grade disease with a shift toward a more mature B-cell phenotype, increased cycling and gene expression, and epigenetic changes involving important pathways in B-cell regulation and function. Furthermore, they initiate disease in secondary recipients. In summary, EZH2(Y641F) can collaborate with Myc to accelerate lymphomagenesis demonstrating a cooperative role of EZH2 mutations in oncogenesis. This murine lymphoma model provides a new tool to study global changes in the epigenome caused by this frequent mutation and a promising model system for testing novel treatments.
Assuntos
Transformação Celular Neoplásica/genética , Linfoma/genética , Mutação , Complexo Repressor Polycomb 2/genética , Proteínas Proto-Oncogênicas c-myc/genética , Animais , Linfócitos B/metabolismo , Linfócitos B/patologia , Western Blotting , Células da Medula Óssea/metabolismo , Proliferação de Células , Transformação Celular Neoplásica/metabolismo , Modelos Animais de Doenças , Feminino , Citometria de Fluxo , Perfilação da Expressão Gênica , Histonas/metabolismo , Humanos , Estimativa de Kaplan-Meier , Linfoma/metabolismo , Linfoma/patologia , Linfoma de Células B/genética , Linfoma de Células B/metabolismo , Linfoma de Células B/patologia , Lisina/metabolismo , Masculino , Metilação , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Complexo Repressor Polycomb 2/metabolismo , Proteínas Proto-Oncogênicas c-myc/metabolismo , Baço/metabolismo , Baço/patologiaRESUMO
AIMS/HYPOTHESIS: Inflammation contributes to pancreatic beta cell dysfunction in type 2 diabetes. Toll-like receptor (TLR)-2 and -4 ligands are increased systemically in recently diagnosed type 2 diabetes patients, and TLR2- and TLR4-deficient mice are protected from the metabolic consequences of a high-fat diet. Here we investigated the role of macrophages in TLR2/6- and TLR4-mediated effects on islet inflammation and beta cell function. METHODS: Genetic and pharmacological approaches were used to determine the effects of TLR2/6 and TLR4 ligands on mouse islets, human islets and purified rat beta cells. Islet macrophages were depleted and sorted by flow cytometry and the effects of TLR2/6- and TLR4-activated bone-marrow-derived macrophages (BMDMs) on beta cell function were assessed. RESULTS: Macrophages contributed to TLR2/6- and TLR4-induced islet Il1a/IL1A and Il1b/IL1B mRNA expression in mouse and human islets and IL-1ß secretion from human islets. TLR2/6 and TLR4 ligands also reduced insulin gene expression; however, this occurred in a non-beta cell autonomous manner. TLR2/6- and TLR4-activated BMDMs reduced beta cell insulin secretion partly via reducing Ins1, Ins2, and Pdx1 mRNA expression. Antagonism of the IL-1 receptor and neutralisation of IL-6 completely reversed the effects of activated macrophages on beta cell gene expression. CONCLUSIONS/INTERPRETATION: We conclude that islet macrophages are major contributors to islet IL-1ß secretion in response to TLR2/6 and TLR4 ligands. BMDMs stimulated with TLR2/6 and TLR4 ligands reduce insulin secretion from pancreatic beta cells, partly via IL-1ß- and IL-6-mediated decreased insulin gene expression.