RESUMO
The PAX-5 gene codes for the transcription factor BSAP, which is expressed throughout B-cell development. Although loss-of-function mutation in the mouse showed an essential role for Pax-5 in early B lymphopoiesis, gain-of-function mutations have implicated the human PAX-5 gene in the control of late B-cell differentiation. PAX-5 (on 9p13) has been involved together with the immunoglobulin heavy-chain (IgH) gene (on 14q32) in the recurring t(9;14)(p13;q32) translocation that is characteristic of small lymphocytic lymphoma with plasmacytoid differentiation. Here we have characterized a complex t(2;9;14)(p12;p13;q32) translocation present in a closely related non-Hodgkin's lymphoma referred to as splenic marginal zone lymphoma (MZL). In this MZL-1 translocation, the two promoters of PAX-5 were replaced on the derivative chromosome 14 by an immunoglobulin switch Smicro promoter that was linked to the structural PAX-5 gene upstream of its translation initiation codon in exon 1B. Expression analyses confirmed that PAX-5 transcription was upregulated due to efficient initiation at the Smicro promoter in the malignant B lymphocytes of patient MZL-1. For comparison we have analyzed PAX-5 expression in another B-cell lymphoma, KIS-1, indicating that transcription from the distal PAX-5 promoter was increased in this tumor in agreement with the previously characterized translocation of the immunoglobulin Emicro; enhancer adjacent to PAX-5 exon 1A. In both lymphomas, the J-chain gene, which is thought to be under negative control by BSAP, was not expressed, whereas transcription of the putative target gene p53 was unaffected by PAX-5 overexpression. Together these data indicate that the t(9;14)(p13;q32) translocation contributes to lymphoma formation as a regulatory mutation that leads to increased PAX-5 expression in late B-cell differentiation due to promoter replacement or enhancer insertion.
Assuntos
Cromossomos Humanos Par 14/genética , Cromossomos Humanos Par 9/genética , Proteínas de Ligação a DNA/genética , Regulação Neoplásica da Expressão Gênica , Genes Homeobox , Genes de Imunoglobulinas , Genes de Troca , Cadeias Pesadas de Imunoglobulinas/genética , Linfoma de Células B/genética , Proteínas Nucleares/genética , Regiões Promotoras Genéticas , Fatores de Transcrição , Translocação Genética , Idoso , Idoso de 80 Anos ou mais , Sequência de Aminoácidos , Sequência de Bases , Cromossomos Humanos Par 14/ultraestrutura , Cromossomos Humanos Par 9/ultraestrutura , Proteínas de Ligação a DNA/biossíntese , Elementos Facilitadores Genéticos , Feminino , Genes p53 , Humanos , Cariotipagem , Linfoma de Células B/patologia , Dados de Sequência Molecular , Proteínas Nucleares/biossíntese , Fator de Transcrição PAX5RESUMO
It has previously been shown that interaction of eukaryotic initiation factor 5A (eIF-5A) with the Rev trans-activator protein of HIV-1 mediates the transport of unspliced or incompletely spliced viral mRNAs across the nuclear envelope. Consequently, mutants of eIF-5A block Rev function and thereby replication of HIV-1 in trans, indicating that eIF-5A is a crucial protein that connects the viral Rev regulator with cellular RNA transport systems. Here we show that the ribosomal protein L5, which is the central protein component of the 5S rRNA export system, is a cellular interaction partner of eIF-5A. Functional studies demonstrate that overexpression of L5 protein significantly enhances Rev activity. Furthermore, Rev nuclear export activity is inhibited in human somatic cells by antibodies that recognize eIF-5A or L5. Our data suggest that the Rev export pathway shares components of a cellular transport system involved in the intracellular trafficking of polymerase III (5S rRNA) transcripts.
Assuntos
Produtos do Gene rev/metabolismo , HIV-1/genética , Fatores de Iniciação de Peptídeos/metabolismo , RNA Viral/metabolismo , Proteínas de Ligação a RNA , Proteínas Ribossômicas/metabolismo , Sequência de Aminoácidos , Transporte Biológico , Núcleo Celular/metabolismo , Regulação Viral da Expressão Gênica , Células HeLa , Humanos , Dados de Sequência Molecular , Ligação Proteica , Proteínas Recombinantes/metabolismo , Proteínas Ribossômicas/química , Saccharomyces cerevisiae , Alinhamento de Sequência , Produtos do Gene rev do Vírus da Imunodeficiência Humana , Fator de Iniciação de Tradução Eucariótico 5ARESUMO
Eukaryotic initiation factor 5A(eIF-5A) is a cellular cofactor require d for the function of the human immunodeficiency virus type-1 (HIV-1) Rev trans-activator protein. The majority of a set of eIF-5A mutants did not support growth of yeast cells having an inactivated genomic copy of eIF-5A, indicating that the introduced mutation eliminated eIF-5A activity. Two nonfunctional mutants, eIF-5AM13 and eIF-5AM14, retained their binding capacity for the HIV-1 Rev response element:Rev complex. Both mutants were constitutively expressed in human T cells. When these T cells were infected with replication-competent HIV-1, virus replication was inhibited. The eIF-5AM13 and eIF5AM14 proteins blocked Rev trans-activation and Rev-mediated nuclear export.
