Molecular mechanism of high hemoglobin F production in Southeast Asian-type hereditary persistence of fetal hemoglobin.
Hereditary persistence of fetal hemoglobin (HPFH) is associated with a high level of hemoglobin F (HbF) synthesis in adult heterozygotes. In this study, 2 of 6 unrelated HPFH Thai families were found to be Southeast Asian-type HPFH (SEA-HPFH) by analyses of the hematologic data and Southern blot hybridization with polymerase chain reaction-amplified DNA probes. DNA mapping with a probe for a delta-globin fragment showed a 27-kb deletion of DNA that included the beta-globin gene and the 3' deoxyribonuclease I hypersensitive site 1 (3'HS1) sequence downstream. Deletion of the insulator, 3'HS1, and the juxta-position of the HPFH-3 core enhancer downstream to the 3' breakpoint have been postulated to be the cause of high HbF production in these individuals. To test this hypothesis, we transfected K562 cells with 4 different bacterial artificial chromosome constructs containing the enhanced green fluorescent protein (EGFP) gene at the position of the Agamma-globin gene (pEBAC/148beta:EGFP). Flow cytometry was used to compare EGFP expression from the pEBAC/148beta:EGFP construct with the HPFH-3 core enhancer immediately 5' to the SEA-HPFH breakpoint (pEnH), from the pEBAC/148beta:EGFP construct with 8 kb of the breakpoint sequence and the HPFH-3 core enhancer (pSEA-HPFH), and from the construct with 3'HS1 followed by the pSEA-HPFH sequence (pSEA-HPFH_3pHS1). The results show that high HbF production in SEA-HPFH occurs from a deletion of the 3'HS1 sequence and the juxtaposition of the HPFH-3 enhancer downstream to the delta-globin gene.
Changsri
Khaimuk
K
Thalassemia Research Center, Institute of Science and Technology for Research and Development, Mahidol University, Salaya, Nakornpathom, Thailand.
Akkarapathumwong
Varaporn
V
Jamsai
Duangporn
D
Winichagoon
Pranee
P
Fucharoen
Suthat
S
D000293:Adolescent; D000328:Adult; D022202:Chromosomes, Artificial, Bacterial; D004252:DNA Mutational Analysis; D004742:Enhancer Elements, Genetic / Q000235:genetics*; D005260:Female; D005319:Fetal Hemoglobin / Q000096:biosynthesis / Q000235:genetics*; D017353:Gene Deletion; D005914:Globins / Q000235:genetics*; D006453:Hemoglobinopathies / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D020014:K562 Cells; D008297:Male; D008875:Middle Aged; D011247:Pregnancy; D013785:Thailand; D014162:Transfection
D005914:Globins; D005319:Fetal Hemoglobin