RESUMEN
The SLAM family of human genes currently consists of seven related members of the immunoglobulin superfamily, membrane-associated proteins, including CD150 (SLAM), CD244 (2B4), CD84, CD229 ( Ly-9), BLAME, CD48, and 19A. These genes are expressed to varying degrees in subsets of immune cells (T, B, natural killer, and myeloid cells) and may function as ligands or receptors. This set of genes, related to CD2 and CD58 on Chromosome (Chr) 1p98, are found clustered close together in the human genome on Chr 1q22. Four of these family members (CD150, CD244, CD84, CD229) contain conserved tyrosine motifs in their cytoplasmic tails that enable them to bind intracellular signaling molecules SAP and EAT-2. SAP is mutated in human X-linked lymphoproliferative disease (XLP), and studies in XLP patients have shown that improper signaling via molecules that bind SAP contributes to the disease. We have identified two new members of the SLAM family (SF), which we term SF2000 and SF2001, which are expressed in immune cells and map in the SLAM gene cluster. SF2001 does not contain SAP-binding motifs in its short cytoplasmic tail. SF2000, which is co-expressed with SAP in T cells, binds both SAP and EAT-2. The data suggest that signaling through SF2000, together with CD150, CD244, CD84, and CD229, is controlled by SAP and therefore contributes to the pathogenesis of XLP.
Asunto(s)
Antígenos CD2/química , Glicoproteínas/química , Inmunoglobulinas/química , Péptidos y Proteínas de Señalización Intracelular , Secuencia de Aminoácidos , Animales , Antígenos CD , Antígenos CD2/genética , Proteínas Portadoras/química , Proteínas Portadoras/metabolismo , Mapeo Cromosómico , Clonación Molecular , Etiquetas de Secuencia Expresada , Perfilación de la Expresión Génica , Glicoproteínas/genética , Humanos , Inmunoglobulinas/genética , Linfocitos/metabolismo , Datos de Secuencia Molecular , Familia de Multigenes/genética , Fosforilación , Fosfotirosina/metabolismo , Filogenia , Unión Proteica , Proteínas Proto-Oncogénicas/metabolismo , Proteínas Proto-Oncogénicas c-fyn , ARN Mensajero/metabolismo , Receptores de Superficie Celular , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Homología de Secuencia de Aminoácido , Proteína Asociada a la Molécula de Señalización de la Activación Linfocitaria , Familia de Moléculas Señalizadoras de la Activación Linfocitaria , Miembro 1 de la Familia de Moléculas Señalizadoras de la Activación Linfocitaria , Técnicas del Sistema de Dos HíbridosRESUMEN
Notch signaling plays a critical role in cell fate determination in many developmental systems, including the hematopoietic system. We and others have recently cloned a novel Notch ligand called Delta4. In this study, we show the effect of retrovirus-mediated ectopic expression of Delta4 in hematopoietic cells. Lethally irradiated mice transplanted with bone marrow cells expressing Delta4 initially suffered from leukopenia and thrombocytopenia. Although all lineages were affected, the deficit in B cells and platelets was the most durable and profound. A rapid expansion of CD4(+)CD8(+) cells occurred shortly after transplantation. CD4(+)CD8(+) cells progressively invaded all tissues analyzed except the thymus, which surprisingly was atrophic. CD4(+)CD8(+) cells were mainly non-Delta4-transduced cells, strongly suggesting that the disease was not cell autonomous. Around 15 weeks after transplantation, mice died from this severe lymphoproliferative disorder, which was not transplantable in late-stage disease into secondary recipients. Mice transduced with a soluble form of Delta4 behaved like control mice. Characterization of early hematopoietic development revealed that Delta4 expression impaired formation of day-12 spleen colony-forming units (CFU-Ss) and, to a greater extent, pre-CFU-Ss. No effect was observed on myeloid colony-forming cells (CFU-Cs), indicating that Delta4 specifically acted on the earliest hematopoietic stem cell compartment. These results show that constitutive expression of Delta4 in hematopoietic cells impairs the development of B cells, platelets, and early stem cells and induces a lethal lymphoproliferative disease.