Nucleotide variation regulates the level of enhancement by hypersensitive site 2 of the beta-globin locus control region.
The beta-globin locus control region hypersensitive site 2 (HS2) enhancer possesses a unique property for stimulating high-level globin gene expression. Although the deletion of cis-acting motifs influences the level of enhancement conferred by HS2, there is controversy on whether polymorphism of the same elements contributes to variation of the fetal hemoglobin (HbF) level among patients with sickle cell anemia. We analyzed reporter gene activity of constructs containing variant HS2 enhancers derived from beta(S) chromosomes to directly test the effect of polymorphism on enhancer activity. Constructs containing four enhancer variants linked to an identical gamma-globin promoter showed markedly different levels of reporter gene activity. Juxtaposition of HS2 derived from the Asian and Senegal chromosomes, which are associated with similarly high levels of HbF, to cognate sequence extending to -1500 of the (G)gamma globin gene showed significantly different levels of reporter gene activity. Our findings indicate that nucleotide variation regulates the level of enhancement conferred by HS2; however, the reporter activities showed no correlation with the level of Hb F associated with the common beta(S) chromosomes.
Ofori-Acquah
S F
SF
Department of Haematological Medicine, Guy's King's and St. Thomas' School of Medicine, Denmark Hill Campus, Denmark Hill, London, United Kingdom. soforiac@usamail.usouthal.edu
Lalloz
M R
MR
Layton
D M
DM
D001665:Binding Sites / Q000235:genetics; D004742:Enhancer Elements, Genetic / Q000235:genetics; D005319:Fetal Hemoglobin / Q000378:metabolism; D005786:Gene Expression Regulation; D014644:Genetic Variation; D005914:Globins / Q000235:genetics*; D006801:Humans; D020014:K562 Cells; D019901:Locus Control Region; D020641:Polymorphism, Single Nucleotide / Q000235:genetics*; D011401:Promoter Regions, Genetic; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics*; D014162:Transfection
D005914:Globins; D005319:Fetal Hemoglobin