The gammaPE complex contains both SATB1 and HOXB2 and has positive and negative roles in human gamma-globin gene regulation.
A large nuclear protein complex, termed gammaPE (for gamma-globin promoter and enhancer binding factor), binds to five sites located 5' and 3' of the human y-globin gene. Two proteins, SATB1 (special A-T-rich binding protein 1) and HOXB2, can bind to yPE binding sites. SATB1 binds to nuclear matrix-attachment sites, and HOXB2 is a homeodomain protein important in neural development that is also expressed during erythropoiesis. The present work showed that antisera directed against either SATB1 or HOXB2 reacted specifically with the entire gammaPE complex in electrophoretic mobility shift assays (EMSAs), suggesting that the two proteins can bind to the gammaPE binding site simultaneously. When SATB1 or HOXB2 was expressed in vitro, they could bind independently to gammaPE binding sites in EMSA. Interestingly, the proteins expressed in vitro competed effectively with each other for the gammaPE binding site, suggesting that this may occur under certain conditions in vivo. Transient cotransfections of a HOXB2 cDNA and a y-globin-luciferase reporter gene construct into cells expressing SATB1 suggested that SATB1 has a positive and HOXB2 a negative regulatory effect on transcription. Taking into account their potentially opposing effects and binding activities, SATB1 and HOXB2 may modulate the amount of gamma-globin mRNA expressed during development and differentiation.
Case
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Childrens Hospital Los Angeles, Research Immunology and Bone Marrow Transplantation, California 90027, USA.
Huber
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P
Lloyd
J A
JA
D000818:Animals; D001667:Binding, Competitive; D019556:COS Cells; D002457:Cell Extracts; D002522:Chlorocebus aethiops; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel / Q000379:methods; D004742:Enhancer Elements, Genetic / Q000235:genetics*; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D005914:Globins / Q000235:genetics*; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007106:Immune Sera; D020014:K562 Cells; D008156:Luciferases / Q000235:genetics; D036961:Matrix Attachment Region Binding Proteins; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011485:Protein Binding; D011817:Rabbits; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D012156:Reticulocytes / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
D002457:Cell Extracts; D004268:DNA-Binding Proteins; C086061:HOXB2 protein, human; D018398:Homeodomain Proteins; D007106:Immune Sera; D036961:Matrix Attachment Region Binding Proteins; D009687:Nuclear Proteins; D011993:Recombinant Fusion Proteins; C076189:SATB1 protein, human; D014157:Transcription Factors; D005914:Globins; D008156:Luciferases