Submitted May 10, 2002
Accepted October 26, 2002
Bcl-x promoter function in erythroid progenitor cells
Cuixia Tian, Paul A Gregoli, and Maurice C Bondurant*
Research Service, Veterans Affairs Medical Center, Nashville, TN, USA
Department of Medicine, Vanderbilt University, Nashville, TN, USA
* Corresponding author; email: maurice.c.bondurant{at}vanderbilt.edu.
The protein Bcl-xL is essential for survival of erythroid progenitor cells, and it increases substantially during late erythrocyte differentiation due to an increase of mRNA. We mapped the transcription start sites of bcl-x mRNA in mouse and human erythroblasts, and we analyzed the function of the mouse bcl-x promoter by transient and stable transfection assays in a mouse erythroid cell line using plasmids containing the bcl-x promoter fused to a luciferase reporter gene. In mouse erythroblasts, a cluster of start sites at positions -664, -655 and -644 relative to the ATG initiation codon account for almost all transcripts. Human erythroblasts exhibit a start site at -654 that is homologous to the triplet in the mouse. A short sequence element in the mouse bcl-x promoter that includes nucleotides -1804 through -1734 was identified as very important for transcription. This element also showed strong enhancer-like activity in concert with the SV40 promoter in an enhancer test vector. Analyses of mutations indicated that two short sequences within the element, about 15 bp apart, are necessary for full enhancer activity. Gel shift experiments with oligonucleotides representing these sequences revealed specific binding of nuclear proteins from erythroblasts. Some of these proteins are regulated during the late erythroid differentiation.
