RESUMO
Pax4 and MafA (v-maf musculoaponeurotic fibrosarcoma oncogene homolog A) are two transcription factors crucial for normal functions of islet beta cells in the mouse. Intriguingly, recent studies indicate the existence of notable difference between human and rodent islet in terms of gene expression and functions. To better understand the biological role of human PAX4 and MAFA, we investigated their expression in normal and diseased human islets, using validated antibodies. PAX4 was detected in 43.0±5.0% and 39.1±4.0% of normal human alpha and beta cells respectively. We found that MAFA, detected in 88.3±6.3% insulin(+)cells as in the mouse, turned out to be also expressed in 61.2±6.4% of human glucagons(+) cells with less intensity than in insulin(+) cells, whereas MAFB expression was found not only in the majority of glucagon(+) cells (67.2±7.6%), but also in 53.6±10.5% of human insulin(+) cells. Interestingly, MAFA nuclear expression in both alpha and beta cells, and the percentage of alpha cells expressing PAX4 were found altered in a substantial proportion of patients with type 2 diabetes. Both MAFA and PAX4 display, therefore, a distinct expression pattern in human islet cells, suggesting more potential plasticity of human islets as compared with rodent islets.
Assuntos
Diabetes Mellitus Tipo 2/metabolismo , Células Secretoras de Glucagon/metabolismo , Proteínas de Homeodomínio/metabolismo , Fatores de Transcrição Maf Maior/metabolismo , Fatores de Transcrição Box Pareados/metabolismo , Adolescente , Adulto , Idoso , Animais , Estudos de Casos e Controles , Núcleo Celular/metabolismo , Células Cultivadas , Diabetes Mellitus Tipo 2/patologia , Feminino , Expressão Gênica , Regulação da Expressão Gênica , Proteínas de Homeodomínio/genética , Humanos , Células Secretoras de Insulina/metabolismo , Fatores de Transcrição Maf Maior/genética , Masculino , Camundongos , Pessoa de Meia-Idade , Obesidade/metabolismo , Fatores de Transcrição Box Pareados/genética , Pâncreas/metabolismo , Pâncreas/patologiaRESUMO
OBJECTIVE: In multiple myeloma (MM), seven primary recurrent translocations involving the immunoglobulin heavy chain locus have been identified. One of the partner loci maps to 20q12 and involves the MAFB gene resulting in its ectopic expression. We attempt here to identify MAFB target genes in MM. MATERIALS AND METHODS: We used an inducible system to upregulate MAFB in MM cell lines not carrying the t(14;20). Microarray expression analysis was used to detect gene expression changes upon MAFB expression. These genes were further evaluated comparatively with gene expression profiles obtained from MM or plasma cell leukemia tumors carrying an activated MAFB gene. Functional implications of these upregulated genes were studied by testing their promoter activity in reporter assays. C-MAF was included comparatively as well. RESULTS: The inducible cell lines identified a total of 284 modulated transcripts. After further evaluation using ex vivo data 14 common upregulated genes were found, common to the C-MAF pathway as well. The promoter activity of some of these secondary genes proved a functional relationship with MAFB. In connection with one of these secondary genes (NOTCH2), even tertiary upregulated genes were found. Functional studies indicated that inducible MAFB expression conferred antiapoptotic effects. CONCLUSION: We identified 14 upregulated genes, and their downstream consequences in the combined MAFB/C-MAF pathway. Eleven of these genes are novel in the C-MAF pathway as well. These direct target genes may be responsible for the oncogenic transformation of MAF expressing myeloma cells.
Assuntos
Regulação Neoplásica da Expressão Gênica , Fator de Transcrição MafB/metabolismo , Mieloma Múltiplo/metabolismo , Linhagem Celular , Cromossomos Humanos Par 21/genética , Cromossomos Humanos Par 21/metabolismo , Perfilação da Expressão Gênica , Regulação Neoplásica da Expressão Gênica/genética , Humanos , Cadeias Pesadas de Imunoglobulinas/genética , Cadeias Pesadas de Imunoglobulinas/metabolismo , Fator de Transcrição MafB/genética , Mieloma Múltiplo/genética , Análise de Sequência com Séries de Oligonucleotídeos , Proteínas Proto-Oncogênicas c-maf/genética , Proteínas Proto-Oncogênicas c-maf/metabolismo , Locos de Características Quantitativas/genética , Translocação Genética/genéticaRESUMO
Chromosomal translocations of the immunoglobulin heavy chain (IgH) gene region at 14q32 are regularly involved in B lymphoid malignancies; they may initiate transformation either by deregulation of existing (proto) oncogenes or creation of new hybrid genes with transforming properties. Previously, we reported a reciprocal novel translocation, t(14;20)(q32;q12), found in the myeloma cell line UM3. In this cell line, the t(14;20) is the only translocation involving the IgH locus. Using double colour immunofluorescence in situ hybridization, the t(14;20) was also found in the diagnostic bone marrow sample, excluding a possible in vitro artefact. We also have found this recurrent t(14;20) in four other cell lines and in additional patient material. We cloned the regions containing the breakpoints in the der(14) and der(20) chromosomes from UM3, and analysed ectopic mRNA expression of genes in the breakpoint regions of both derivative chromosomes. Ectopic gene expression was observed for the transcription factor MAFB in der(14). The breakpoint scatter in the five cell lines with a t(14;20)--all expressing MAFB--is comprised within a region of 0.8 Mb. Provisional data indicate that this t(14;20) is associated with an adverse prognosis. Aberrant expression of MAFB may be involved in the oncogenic transformation of myeloma cells that harbour the t(14;20).