RESUMEN
Tetraspanins are commonly believed to act only as "molecular facilitators," with no direct role in signal transduction. We herein demonstrate that upon ligation, CD37, a tetraspanin molecule expressed on mature normal and transformed B cells, becomes tyrosine phosphorylated, associates with proximal signaling molecules, and initiates a cascade of events leading to apoptosis. Moreover, we have identified two tyrosine residues with opposing regulatory functions: one lies in the N-terminal domain of CD37 in a predicted "ITIM-like" motif and mediates SHP1-dependent death, whereas the second lies in a predicted "ITAM motif" in the C-terminal domain of CD37 and counteracts death signals by mediating phosphatidylinositol 3-kinase-dependent survival.
Asunto(s)
Antígenos de Neoplasias/metabolismo , Apoptosis , Linfocitos B/metabolismo , Leucemia Linfocítica Crónica de Células B/metabolismo , Transducción de Señal , Tetraspaninas/metabolismo , Secuencias de Aminoácidos , Secuencia de Aminoácidos , Antígenos de Neoplasias/química , Antígenos de Neoplasias/genética , Apoptosis/efectos de los fármacos , Proteínas Reguladoras de la Apoptosis/genética , Proteínas Reguladoras de la Apoptosis/metabolismo , Linfocitos B/efectos de los fármacos , Linfocitos B/patología , Proteína 11 Similar a Bcl2 , Línea Celular Tumoral , Supervivencia Celular , Cromatografía Liquida , Proteína Forkhead Box O3 , Factores de Transcripción Forkhead/metabolismo , Células HEK293 , Humanos , Inmunoglobulina G/farmacología , Leucemia Linfocítica Crónica de Células B/genética , Leucemia Linfocítica Crónica de Células B/patología , Microdominios de Membrana/metabolismo , Potencial de la Membrana Mitocondrial , Proteínas de la Membrana/genética , Proteínas de la Membrana/metabolismo , Datos de Secuencia Molecular , Nanotecnología , Fosfatidilinositol 3-Quinasa/metabolismo , Fosforilación , Transporte de Proteínas , Proteómica/métodos , Proteínas Proto-Oncogénicas/genética , Proteínas Proto-Oncogénicas/metabolismo , Interferencia de ARN , Proteínas Recombinantes de Fusión/farmacología , Transducción de Señal/efectos de los fármacos , Espectrometría de Masas en Tándem , Tetraspaninas/química , Tetraspaninas/genética , Factores de Tiempo , Transfección , TirosinaRESUMEN
No major susceptibility genes for sporadically occurring congenital vertebral malformations (CVM) in humans have been identified to date. Body patterning genes whose mutants cause axial skeletal anomalies in mice are candidates for human CVM susceptibility. T (also known as Brachyury) and TBX6 are critical genes needed to establish mesodermal identity. We hypothesized that mutations in T and/or TBX6 contribute to the pathogenesis of human CVMs. The complete T and TBX6 coding regions, splice junctions, and proximal 500 bp of the promoters were sequenced in 50 phenotyped patients with CVM. Three unrelated patients with sacral agenesis, Klippel-Feil syndrome, and multiple cervical and thoracic vertebral malformations were heterozygous for a c.1013C>T substitution, resulting in a predicted Ala338Val missense alteration in exon 8. A clinically unaffected parent of each patient also harbored the substitution, but the variant did not occur in an ethnically diverse, 443-person reference population. The c.1013C>T variant is significantly associated with CVM (p < 0.001). Alanine 338 shows moderate conservation across species, and valine at this position has not been reported in any species. A fourth patient harbored a c.908-8C>T variant in intron 7. This previously unreported variant was tested in 347 normal control subjects, and 11 heterozygotes and 2 T/T individuals were found. No TBX6 variants were identified. We infer that the c.1013C>T substitution is pathogenic and represents the first report of an association between a missense mutation in the T gene and the occurrence of sporadic CVMs in humans. It is uncertain whether the splice junction variant increases CVM risk. TBX6 mutations do not seem to be associated with CVM. We hypothesize that epistatic interactions between T and other developmental genes and the environment modulate the phenotypic consequences of T variants.