Binding of HMG-I(Y) elicits structural changes in a silencer of the human beta-globin gene.
Proteins involved in repression of the human beta-globin gene may be useful in the treatment of sickle cell anemia, in conjunction with therapy to reactivate fetal globin genes. If there is a reciprocal elevation of gamma-globin expression upon repression, this approach could be useful in additional hemoglobinopathies. We previously showed that repression of the beta-globin gene appears to be mediated through two DNA sequences, silencers I and II, and identified a protein termed BP1 which binds to both silencer sequences. In this study, we cloned two cDNAs encoding proteins which bind to an oligonucleotide in silencer I containing a BP1 binding site. These cDNAs correspond to HMG-I and HMG-Y, isoforms regarded as architectural proteins. We demonstrate that binding of HMG-I(Y) to this oligonucleotide causes bending/flexure of the DNA. HMG-I(Y) also binds to a second oligonucleotide containing a BP1 binding site located in a negative control region upstream of the delta-globin gene, suggesting a role for HMG-I(Y) in repression of adult globin genes. Expression studies revealed that HMG-I(Y) is ubiquitously expressed in human tissues that do not express beta-globin, being present in 48 of 50 tissues and six hematopoietic cell lines examined. Furthermore, HMG-I(Y) expression is down-regulated during differentiation of primary erythroid cells. We present a model in which HMG-I(Y) alters DNA conformation to allow binding of repressor proteins, and in which the relative amount of HMG-I(Y) helps to determine the repressive state of the beta-globin gene.
Chase
M B
MB
Department of Pediatrics, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA.
Haga
S B
SB
Hankins
W D
WD
Williams
D M
DM
Bi
Z
Z
Strovel
J W
JW
Obriecht
C
C
Berg
P E
PE
D015152:Blotting, Northern; D002454:Cell Differentiation / Q000502:physiology; D004268:DNA-Binding Proteins / Q000235:genetics; D004912:Erythrocytes / Q000166:cytology; D005914:Globins / Q000235:genetics* / Q000378:metabolism*; D025741:HMGA1a Protein; D006609:High Mobility Group Proteins / Q000235:genetics* / Q000378:metabolism*; D006801:Humans; D012333:RNA, Messenger / Q000378:metabolism; D014018:Tissue Distribution; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism*; D014158:Transcription, Genetic / Q000235:genetics
D004268:DNA-Binding Proteins; D006609:High Mobility Group Proteins; D012333:RNA, Messenger; D014157:Transcription Factors; D025741:HMGA1a Protein; D005914:Globins