Assuntos
Linfócitos B/patologia , Linfócitos B/fisiologia , Linhagem da Célula/genética , Rearranjo Gênico , Genes de Imunoglobulinas , Neoplasias Hematológicas/genética , Receptores de Antígenos de Linfócitos T/genética , Linfócitos T/patologia , Linfócitos T/fisiologia , Animais , Genoma , Neoplasias Hematológicas/patologia , Humanos , Ativação LinfocitáriaRESUMO
Chromosome translocations involving antigen receptor loci are a genetic hallmark of non-Hodgkin's lymphomas in humans. Most commonly, these translocations result in juxtaposition of the immunoglobulin heavy-chain (IgH) locus with one of several cellular proto-oncogenes, leading to deregulated oncogene expression. The V(D)J recombinase, which mediates physiologic rearrangements of antigen receptor genes, may play a mechanistic role in some lymphoma translocations, although evidence is indirect. A high incidence of B-lineage lymphomas has been observed in mice with severe combined immunodeficiency (SCID) and p53-null mutations. We show that these tumors are characteristic of the pro-B-cell stage of development and that they harbor recurrent translocations involving chromosomes 12 and 15. Fluorescence in situ hybridization (FISH) shows retention of IgH sequences on the derivative chromosome 12, implying that breakpoints involve the IgH locus. Pro-B-cell lymphomas were suppressed in SCID p53(-/-) mice by a Rag-2-null mutation, demonstrating that DNA breaks generated during V(D)J recombination are required for oncogenic transformation, and suggesting that t(12;15) arise during attempted IgH rearrangement in pro-B cells. These studies indicate that the oncogenic potential inherent in antigen receptor diversification is controlled in vivo by efficient rejoining of DNA ends generated during V(D)J recombination and an intact cellular response to DNA damage.
Assuntos
DNA Nucleotidiltransferases/genética , Linfoma de Células B/enzimologia , Linfoma de Células B/genética , Translocação Genética , Animais , Linfócitos B/imunologia , Rearranjo Gênico de Cadeia Pesada de Linfócito B , Cadeias Pesadas de Imunoglobulinas/genética , Imunofenotipagem , Linfoma de Células B/imunologia , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Endogâmicos ICR , Camundongos Knockout , Camundongos SCID , Receptores de Antígenos de Linfócitos B/genética , Células-Tronco/imunologia , Translocação Genética/imunologia , Proteína Supressora de Tumor p53/deficiência , Proteína Supressora de Tumor p53/genética , VDJ RecombinasesRESUMO
Erythropoietin triggers the differentiation of erythrocyte progenitors by binding to receptors on their plasma membrane. We report here that pretreatment of erythropoietin-responsive murine erythroleukemia cells with chemical inducers resulted in a striking increase in erythropoietin-specific hemoglobinization. This amplification of the erythropoietin biologic response was accompanied by the induction of a new population of high-density receptors (approximately 20,000 per cell) exhibiting marked positive cooperativity. Erythropoietin binding to new receptors displayed a convex upward Scatchard plot and a Hill coefficient (nH) of 6.75. Measurement of erythropoietin receptor mRNA demonstrated an initial decrease in receptor transcript followed by an approximately 2- to 3-fold increase after 24-48 hr. This increase in receptor message does not appear to account for the magnitude of the receptor up-regulation by dimethyl sulfoxide. We propose that this positive cooperativity reflects the interaction (clustering) of receptors, presumably through the formation of homooligomers or heterooligomers, and that this receptor interaction may amplify the erythropoietin signal transduction pathway.
Assuntos
Dimetil Sulfóxido/farmacologia , Eritropoetina/metabolismo , Receptores de Superfície Celular/biossíntese , Animais , Northern Blotting , Linhagem Celular , Cinética , Leucemia Eritroblástica Aguda , Leucemia Experimental , Camundongos , Modelos Biológicos , RNA Neoplásico/genética , RNA Neoplásico/isolamento & purificação , Receptores de Superfície Celular/efeitos dos fármacos , Receptores de Superfície Celular/genética , Receptores da Eritropoetina , Proteínas Recombinantes/metabolismoRESUMO
We have shown previously that purified human erythropoietin rapidly alters the phosphorylation of an integral erythroid membrane protein, pp43 (Choi, H.-S., Wojchowski, D. M., and Sytkowski, A. J. (1987) J. Biol. Chem. 262, 2933-2936). We have now purified pp43 to apparent homogeneity and have prepared antibodies to it. After sodium dodecyl sulfate-polyacrylamide gel electrophoresis and electrophoretic transfer of membrane proteins to nitrocellulose, the antibodies identified pp43 and a series of higher molecular weight antigenically related proteins, up to 50 kDa, in erythropoietin-responsive Rauscher murine erythroleukemia cells and in normal murine erythroid cells. Examination of purified subcellular fractions confirmed the localization of pp43 and the related proteins to the plasma membrane. Phosphorylation with [gamma-32P]ATP demonstrated that, in contrast to pp43, these higher molecular weight proteins were not phosphorylated. Marked differences in both the abundance of pp43 and related proteins and the degree of erythropoietin-sensitive pp43 phosphorylation were found between the plasma membranes of Rauscher cells and those of "non-responsive" Friend murine erythroleukemia cells. In addition only trace amounts of a 50-kDa antigenically related protein and no phosphorylated pp43 were detected in the plasma membranes of two erythropoietin-insensitive human erythroid cells lines, K562 and HEL. The results suggest that the abundance and degree of phosphorylation of pp43 and the antigenically related proteins is strongly correlated with the erythropoietin responsiveness of the particular erythroid cell types.