RESUMO
Lasting B cell persistence depends on survival signals that are transduced by cell surface receptors. In this study, we describe a novel biological mechanism essential for survival and homeostasis of normal peripheral mature B cells and chronic lymphocytic leukemia cells, regulated by the heparin-binding cytokine, midkine (MK), and its proteoglycan receptor, the receptor-type tyrosine phosphatase ζ (RPTPζ). We demonstrate that MK initiates a signaling cascade leading to B cell survival by binding to RPTPζ. In mice lacking PTPRZ, the proportion and number of the mature B cell population are reduced. Our results emphasize a unique and critical function for MK signaling in the previously described MIF/CD74-induced survival pathway. Stimulation of CD74 with MIF leads to c-Met activation, resulting in elevation of MK expression in both normal mouse splenic B and chronic lymphocytic leukemia cells. Our results indicate that MK and RPTPζ are important regulators of the B cell repertoire. These findings could pave the way toward understanding the mechanisms shaping B cell survival and suggest novel therapeutic strategies based on the blockade of the MK/RPTPζ-dependent survival pathway.
Assuntos
Antígenos de Diferenciação de Linfócitos B/imunologia , Linfócitos B/imunologia , Citocinas/imunologia , Antígenos de Histocompatibilidade Classe II/imunologia , Glicoproteínas de Membrana/imunologia , Proteínas Tirosina Fosfatases Classe 2 Semelhantes a Receptores/imunologia , Receptores de Fatores de Crescimento/imunologia , Transdução de Sinais/imunologia , Animais , Antígenos de Diferenciação de Linfócitos B/genética , Antígenos de Diferenciação de Linfócitos B/metabolismo , Linfócitos B/metabolismo , Linhagem Celular Tumoral , Sobrevivência Celular/genética , Sobrevivência Celular/imunologia , Citocinas/genética , Citocinas/metabolismo , Regulação da Expressão Gênica/genética , Regulação da Expressão Gênica/imunologia , Antígenos de Histocompatibilidade Classe II/genética , Antígenos de Histocompatibilidade Classe II/metabolismo , Glicoproteínas de Membrana/genética , Glicoproteínas de Membrana/metabolismo , Camundongos , Camundongos Knockout , Midkina , Proteínas Proto-Oncogênicas c-met/genética , Proteínas Proto-Oncogênicas c-met/imunologia , Proteínas Proto-Oncogênicas c-met/metabolismo , Proteínas Tirosina Fosfatases Classe 2 Semelhantes a Receptores/genética , Proteínas Tirosina Fosfatases Classe 2 Semelhantes a Receptores/metabolismo , Receptores de Fatores de Crescimento/genética , Receptores de Fatores de Crescimento/metabolismo , Transdução de Sinais/genética , Baço/imunologia , Baço/metabolismoRESUMO
The signals regulating the survival of mature splenic B cells have become a major focus in recent studies of B cell immunology. Durable B cell persistence in the periphery is dependent on survival signals that are transduced by cell surface receptors. In this study, we describe a novel biological mechanism involved in mature B cell homeostasis, the hepatocyte growth factor/scatter factor (HGF)/c-Met pathway. We demonstrate that c-Met activation by HGF leads to a survival cascade, whereas its blockade results in induction of mature B cell death. Our results emphasize a unique and critical function for c-Met signaling in the previously described macrophage migration inhibitory factor/CD74-induced survival pathway. Macrophage migration inhibitory factor recruits c-Met to the CD74/CD44 complex and thereby enables the induction of a signaling cascade within the cell. This signal results in HGF secretion, which stimulates the survival of the mature B cell population in an autocrine manner. Thus, the CD74-HGF/c-Met axis defines a novel physiologic survival pathway in mature B cells, resulting in the control of the humoral immune response.
Assuntos
Antígenos de Diferenciação de Linfócitos B/metabolismo , Linfócitos B/metabolismo , Fator de Crescimento de Hepatócito/metabolismo , Antígenos de Histocompatibilidade Classe II/metabolismo , Proteínas Proto-Oncogênicas c-met/metabolismo , Animais , Antígenos de Diferenciação de Linfócitos B/genética , Apoptose/efeitos dos fármacos , Linfócitos B/citologia , Western Blotting , Membrana Celular/metabolismo , Sobrevivência Celular/efeitos dos fármacos , Células Cultivadas , Citometria de Fluxo , Fator de Crescimento de Hepatócito/genética , Fator de Crescimento de Hepatócito/farmacologia , Antígenos de Histocompatibilidade Classe II/genética , Receptores de Hialuronatos/genética , Receptores de Hialuronatos/metabolismo , Fatores Inibidores da Migração de Macrófagos/farmacologia , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Ligação Proteica , Proteínas Proto-Oncogênicas c-met/genética , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Transdução de Sinais/efeitos dos fármacosRESUMO
Systemic lupus erythematosus (SLE) is an autoimmune disease that involves dysregulation of B and T cells. A tolerogenic peptide, designated hCDR1, ameliorates disease manifestations in SLE-afflicted mice. In the present study, the effect of treatment with hCDR1 on the CD74/macrophage migration inhibitory factor (MIF) pathway was studied. We report here that B lymphocytes from SLE-afflicted mice express relatively elevated levels of CD74, compared with B cells from healthy mice. CD74 is a receptor found in complex with CD44, and it binds the pro-inflammatory cytokine MIF. The latter components were also up-regulated in B cells from the diseased mice, and treatment with hCDR1 resulted in their down-regulation and in reduced B-cell survival. Furthermore, up-regulation of CD74 and CD44 expression was detected in brain hippocampi and kidneys, two target organs in SLE. Treatment with hCDR1 diminished the expression of those molecules to the levels determined for young healthy mice. These results suggest that the CD74/MIF pathway plays an important role in lupus pathology.
Assuntos
Antígenos de Diferenciação de Linfócitos B/imunologia , Autoantígenos/imunologia , Linfócitos B/imunologia , Antígenos de Histocompatibilidade Classe II/imunologia , Oxirredutases Intramoleculares/imunologia , Lúpus Eritematoso Sistêmico/imunologia , Fatores Inibidores da Migração de Macrófagos/imunologia , Proteínas do Tecido Nervoso/imunologia , Peptídeos/imunologia , Animais , Antígenos de Diferenciação de Linfócitos B/biossíntese , Antígenos de Diferenciação de Linfócitos B/genética , Apoptose/efeitos dos fármacos , Apoptose/imunologia , Autoantígenos/química , Linfócitos B/efeitos dos fármacos , Antígenos de Histocompatibilidade Classe II/biossíntese , Antígenos de Histocompatibilidade Classe II/genética , Humanos , Imunomodulação , Oxirredutases Intramoleculares/biossíntese , Oxirredutases Intramoleculares/genética , Lúpus Eritematoso Sistêmico/patologia , Fatores Inibidores da Migração de Macrófagos/biossíntese , Fatores Inibidores da Migração de Macrófagos/genética , Camundongos , Camundongos Endogâmicos NZB , Proteínas do Tecido Nervoso/química , Peptídeos/química , Peptídeos/farmacologiaRESUMO
In this study, we focus on the analysis of a previously identified cancer-related gene signature (CGS) that underlies the cross talk between the p53 tumor suppressor and Ras oncogene. CGS consists of a large number of known Ras downstream target genes that were synergistically upregulated by wild-type p53 loss and oncogenic H-Ras(G12V) expression. Here we show that CGS expression strongly correlates with malignancy. In an attempt to elucidate the molecular mechanisms underling the cooperation between p53 loss and oncogenic H-Ras(G12V), we identified distinguished pathways that may account for the regulation of the expression of the CGS. By knocking-down p53 or by expressing mutant p53, we revealed that p53 exerts its negative effect by at least two mechanisms mediated by its targets B-cell translocation gene 2 (BTG2) and activating transcription factor 3 (ATF3). Whereas BTG2 binds H-Ras(G12V) and represses its activity by reducing its GTP loading state, which in turn causes a reduction in CGS expression, ATF3 binds directly to the CGS promoters following p53 stabilization and represses their expression. This study further elucidates the molecular loop between p53 and Ras in the transformation process.