RESUMEN
The mesangial cell provides structural support to the kidney glomerulus. A polymerase chain reaction-based cDNA display approach identified a novel protein-tyrosine phosphatase, rPTP-GMC1, whose transcript expression is transiently and dramatically up-regulated during the period of mesangial cell migration and proliferation that follows mesangial cell injury in the anti-Thy 1 model of mesangial proliferative glomerulonephritis in the rat. In situ hybridization analysis confirmed that rPTP-GMC1 mRNA is up-regulated specifically by mesangial cells responding to the injury and is not detectable in other cells in the kidney or in many normal tissues. In cell culture, rPTP-GMC1 is expressed by mesangial cells but not by glomerular endothelial or epithelial cells (podocytes). The longest transcript (7.5 kilobases) encodes a receptor-like protein-tyrosine phosphatase consisting of a single catalytic domain, a transmembrane segment, and 18 fibronectin type III-like repeats in the extracellular segment. A splice variant predicts a truncated molecule missing the catalytic domain. rPTP-GMC1 maps to human chromosome 12q15 and to the distal end of mouse chromosome 10. The predicted structure of rPTP-GMC1 and its pattern of expression in vivo and in culture suggest that it plays a role in regulating the adhesion and migration of mesangial cells in response to injury.
Asunto(s)
Regulación Enzimológica de la Expresión Génica , Glomerulonefritis Membranoproliferativa/enzimología , Glomérulos Renales/enzimología , Glomérulos Renales/patología , Proteínas Tirosina Fosfatasas/genética , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Mapeo Cromosómico , Cromosomas Humanos Par 12 , Secuencia de Consenso , ADN Complementario , Modelos Animales de Enfermedad , Glomerulonefritis Membranoproliferativa/patología , Humanos , Glomérulos Renales/lesiones , Masculino , Ratones , Ratones Endogámicos C57BL , Datos de Secuencia Molecular , Muridae , Reacción en Cadena de la Polimerasa , Proteínas Tirosina Fosfatasas/biosíntesis , ARN Mensajero/genética , Ratas , Ratas Wistar , Proteínas Tirosina Fosfatasas Clase 3 Similares a Receptores , Alineación de Secuencia , Homología de Secuencia de Aminoácido , Homología de Secuencia de Ácido Nucleico , Transcripción GenéticaRESUMEN
B cell antigen receptors are multicomponent complexes consisting of the surface immunoglobulin and accessory molecules with associating protein-tyrosine kinases. A spleen tyrosine kinase, Syk, in porcine B cells and a 72-kDa protein-tyrosine kinase, PTK72, in murine B cells associate with the B cell antigen receptor. Herein, we report the isolation of a full-length cDNA encoding the human homologue of Syk. This cDNA predicted a polypeptide consisting of two NH2-terminal SH2 domains and a COOH-terminal tyrosine kinase domain. Syk is highly conserved between human and swine and is homologous to the T cell-associated protein-tyrosine kinase ZAP-70. Both Syk mRNA and protein were detected in cells derived from multiple hematopoietic lineages. Within the B cell compartment, Syk was expressed from pro-B cells to plasma cells. In vitro kinase assays conducted on the human Syk protein isolated from B cells revealed the presence of autophosphorylation activity on Syk tyrosine residues. Tyrosine phosphorylation of Syk associating with the B cell receptor complex in human was augmented rapidly after surface immunoglobulin cross-linking. The human SYK locus was mapped to chromosome 9 at band q22.