A Fetal Globin Gene Mutation in ^Aϒ Nondeletion Hereditary Persistence of Fetal Hemoglobin Increases Promoter Strength in a Nonerythroid Cell

Abstract

Single base substitutions have been identified in the promoter regions of ^Aϒ-globin genes from individuals with certain types of nondeletion ^Aϒ hereditary persistence of fetal hemoglobin (HPFH). The presence of these mutations is closely associated with the ^Aϒ HPFH phenotype, but proof that they are the nondeletion HPFH determinants is lacking. To test directly whether these base substitutions can result in an increase in ^Aϒ-globin gene transcription, we studied cosmid clones containing the ^Gϒ- through beta-globin gene regions from individuals with Greek-type (G-to-A base substitution at -117) and Chinese-type (C-to-T base substitution at -196) ^Aϒ HPFH in a transient expression assay. When tested as part of a cosmid clone, the Greek HPFH ^Aϒ-globin gene consistently produced about 1.4 times as much RNA as the wild-type ^Aϒ-globin gene when standardized against RNA transcribed from the ^Gϒ genes in cis. The relative strengths of the normal and HPFH ^Aϒ-globin gene promoters were also compared in transient expression assays with plasmids containing the ^Aϒ-globin genes. Pseudo-wild-type ^Aϒ-globin genes containing a short, transcriptionally neutral deletion were used so that two ^Aϒ-globin genes that differed in their promoter sequences could be compared in the same transfection. The plasmid transient expression results indicated a 1.3- to 1.4-fold increase in steady-state RNA levels from the Greek-type ^Aϒ HPFH promoter compared with the wild-type ^Aϒ promoter, while no difference was documented between the Chinese-type ^Aϒ HPFH promoter and the wild-type ^Aϒ promoter.