Binding of HMG‐I(Y) elicits structural changes in a silencer of the human β‐globin gene

Proteins involved in repression of the human β‐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 β‐globin expression upon repression, this approach could be useful in additional hemoglobinopathies. We previously showed that repression of the β‐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 ogligonucleotide 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 β‐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 β‐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 β‐globin gene. Am. J. Hematol. 60:27–35, 1999. © 1999 Wiley‐Liss, Inc.