A T-to-G transversion at nucleotide -567 upstream of HBG2 in a GATA-1 binding motif is associated with elevated hemoglobin F.
Increased fetal hemoglobin (Hb F; alpha(2)gamma(2)) production in adults can ameliorate the clinical severity of sickle cell disease and beta-thalassemia major. Thus, understanding the regulation of gamma-globin gene expression and its silencing in adults has potential therapeutic implications. We studied a father and son in an Iranian-American family who had elevated Hb F levels and found a novel T-to-G transversion at nucleotide (nt) -567 of the HBG2 promoter. This mutation alters a GATA-1 binding motif to a GAGA sequence located within a previously identified silencing element. DNA-protein binding assays showed that the GATA motif of interest is capable of binding GATA-1 transcription factor in vitro and in vivo. Truncation analyses of the HBG2 promoter linked to a luciferase reporter gene revealed a negative regulatory activity present between nt -675 and -526. In addition, the T-to-G mutation at the GATA motif increased the promoter activity by two- to threefold in transiently transfected erythroid cell lines. The binding motif is uniquely conserved in simian primates with a fetal pattern of gamma-globin gene expression. These results suggest that the GATA motif under study has a functional role in silencing gamma-globin gene expression in adults. The T-to-G mutation in this motif disrupts GATA-1 binding and the associated repressor complex, abolishing its silencing effect and resulting in the up-regulation of gamma-globin gene expression in adults.
Chen
Zhiyi
Z
Center of Excellence in Sickle Cell Disease, Division of Hematology/Oncology, Department of Medicine, Boston University School of Medicine, Boston, Massachusetts 02118, USA.
Luo
Hong-Yuan
HY
Basran
Raveen K
RK
Hsu
Tien-Huei
TH
Mang
Daniel W H
DW
Nuntakarn
Lalana
L
Rosenfield
Cathy G
CG
Patrinos
George P
GP
Hardison
Ross C
RC
Steinberg
Martin H
MH
Chui
David H K
DH
D000293:Adolescent; D000818:Animals; D001483:Base Sequence; D045744:Cell Line, Tumor; D002648:Child; D005260:Female; D005319:Fetal Hemoglobin / Q000378:metabolism*; D050982:GATA1 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D015894:Genome, Human / Q000235:genetics; D005914:Globins / Q000235:genetics*; D006147:Guanine; D006801:Humans; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics*; D009711:Nucleotides / Q000235:genetics*; D010802:Phylogeny; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D016415:Sequence Alignment; D037941:Silencer Elements, Transcriptional / Q000235:genetics; D013941:Thymine; D014158:Transcription, Genetic
D050982:GATA1 Transcription Factor; C494688:GATA1 protein, human; D009711:Nucleotides; D006147:Guanine; D005914:Globins; D005319:Fetal Hemoglobin; D013941:Thymine