RESUMO
BACKGROUND: Phosphorylation status of the transcription factor CCAAT/enhancer binding protein α (C/EBPα) has been demonstrated in a human hematopoietic cell model to regulate the formation of branched I antigen by affecting its binding affinity to the promoter region of the IGnTC gene during erythroid and granulocytic differentiation. STUDY DESIGN AND METHODS: The K-562 cell line was induced to differentiate into red blood cells (RBCs) or granulocytes by sodium butyrate or retinoic acid, respectively, to study the involvement of three MAP kinase pathways in I antigen synthesis. The regulatory effects of the extracellular signal-regulated kinase (ERK)2-Src homology region 2 domain-containing phosphatase 2 (SHP2) pathway on phosphorylation status and binding affinities of C/EBPα as well as the subsequent activation of IGnTC and synthesis of surface I formation were studied in wild-type K-562 cells and in mutant cells that overexpress ERK2 and SHP2. RESULTS: We found that SHP2-ERK2 signaling regulates the phosphorylation status of C/EBPα to alter its binding affinity onto the IGnTC promoter region, thereby activating the synthesis of cell surface I antigen formation during erythropoiesis. CONCLUSION: SHP2-ERK2 signaling acts upstream of C/EBPα as a regulator of cell surface I antigen synthesis. Such regulation is specific for RBC but not for granulocyte differentiation.
Assuntos
Proteína alfa Estimuladora de Ligação a CCAAT/metabolismo , Eritropoese , Sistema do Grupo Sanguíneo I/biossíntese , Proteína Quinase 1 Ativada por Mitógeno/metabolismo , N-Acetilglucosaminiltransferases/metabolismo , Proteína Tirosina Fosfatase não Receptora Tipo 11/metabolismo , Transdução de Sinais , Humanos , Células K562 , N-Acetilglucosaminiltransferases/genética , N-Acetilexosaminiltransferases , Fosforilação , Regiões Promotoras Genéticas , Ligação ProteicaAssuntos
Amino Açúcares/sangue , Eritrócitos Anormais/metabolismo , Eritropoese , Doenças Hematológicas/sangue , Sistema do Grupo Sanguíneo I/sangue , Polissacarídeos/sangue , Amino Açúcares/biossíntese , Amino Açúcares/química , Amino Açúcares/genética , Animais , Anticorpos/metabolismo , Sequência de Carboidratos , Eritrócitos Anormais/patologia , Regulação da Expressão Gênica no Desenvolvimento , Predisposição Genética para Doença , Humanos , Sistema do Grupo Sanguíneo I/biossíntese , Sistema do Grupo Sanguíneo I/química , Sistema do Grupo Sanguíneo I/genética , Dados de Sequência Molecular , Polimorfismo Genético , Polissacarídeos/biossíntese , Polissacarídeos/química , Polissacarídeos/genética , Transporte ProteicoRESUMO
Unlike most blood group antigen pairs, the I and i antigens are not antithetical (produced by allelic pairs) but, rather, they are reciprocal. The I antigen is formed by the action of an enzyme (a glycosyltransferase), which adds branches onto the i antigen. Thus, branched I antigen is formed at the expense of its precursor, the linear i antigen. The antigens are present on all blood cells and have a wide tissue distribution. Soluble I antigen is found in milk, saliva, and amniotic fluid, and a small amount is in plasma. The function of these antigens is unknown but the I antigen has a decreased expression and the i antigen has a concomitant increased expression in conditions that result in increased hematopoiesis. The gene encoding the branching transferase has been cloned and sequenced, and the mechanism underlying the i adult phenotype with and without association with cataracts has been elucidated.
Assuntos
Catarata/imunologia , Sistema do Grupo Sanguíneo I/genética , Sequência de Carboidratos , Catarata/congênito , Catarata/etiologia , Glicosiltransferases/genética , Glicosiltransferases/metabolismo , Glicosiltransferases/fisiologia , Humanos , Sistema do Grupo Sanguíneo I/biossíntese , Sistema do Grupo Sanguíneo I/metabolismo , Fenótipo , Distribuição TecidualRESUMO
The human blood group i and I antigens are determined by linear and branched poly-N-acetyllactosamine structures, respectively. In erythrocytes, the fetal i antigen is converted to the adult I antigen by I-branching beta-1,6-N-acetylglucosaminyltransferase (IGnT) during development. Dysfunction of the I-branching enzyme may result in the adult i phenotype in erythrocytes. However, the I gene responsible for blood group I antigen has not been fully confirmed. We report here a novel human I-branching enzyme, designated IGnT3. The genes for IGnT1 (reported in 1993), IGnT2 (also presented in this study), and IGnT3 consist of 3 exons and share the second and third exons. Bone marrow cells preferentially expressed IGnT3 transcript. During erythroid differentiation using CD34(+) cells, IGnT3 was markedly up-regulated with concomitant decrease in IGnT1/2. Moreover, reticulocytes expressed the IGnT3 transcript, but IGnT1/2 was below detectable levels. By molecular genetic analyses of an adult i pedigree, individuals with the adult i phenotype were revealed to have heterozygous alleles with mutations in exon 2 (1006G>A; Gly336Arg) and exon 3 (1049G>A; Gly350Glu), respectively, of the IGnT3 gene. Chinese hamster ovary (CHO) cells transfected with each mutated IGnT3 cDNA failed to express I antigen. These findings indicate that the expression of the blood group I antigen in erythrocytes is determined by a novel IGnT3, not by IGnT1 or IGnT2.
