A negative regulatory element in the bcl-2 5'-untranslated region inhibits expression from an upstream promoter.
bcl-2 mRNA is present at high levels in pre-B-cell lines but is down-regulated in most mature B-cell lines. To investigate the mechanisms responsible for its developmental control, we studied the regulation of bcl-2 expression in human B-lineage cell lines. Using nuclear run-on assays, we found that bcl-2 transcription decreases in parallel with levels of steady-state mRNA during B-cell development. To define cis-acting elements that regulate bcl-2 transcription, we analyzed the expression of transiently transfected promoter-reporter constructs. We identified a novel negative regulatory element (NRE) in the bcl-2 5'-untranslated region that decreased expression from the bcl-2 P1 promoter or heterologous promoters in a position-dependent fashion. The NRE functions in either orientation but contains distinct orientation-dependent subfragments. Additional analyses demonstrated that multiple, functionally redundant sequence elements mediate NRE activity. Though the bcl-2 NRE is active in pre-B- and mature B-cell lines, chromatin structure of the endogenous NRE differs in these cells, suggesting that its activity or effect may vary during B-cell development. Our results indicate that negative control of transcription initiated at the P1 promoter is an important determinant of the differential expression of bcl-2.
Young
R L
RL
Department of Medicine, Howard Hughes Medical Institute, Washington University School of Medicine, St. Louis, Missouri 63110.
Korsmeyer
S J
SJ
D001402:B-Lymphocytes; D001483:Base Sequence; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D003587:Cytomegalovirus / Q000235:genetics; D005786:Gene Expression Regulation; D006801:Humans; D008969:Molecular Sequence Data; D016296:Mutagenesis; D016366:Open Reading Frames; D010957:Plasmids; D011401:Promoter Regions, Genetic; D014176:Protein Biosynthesis; D011518:Proto-Oncogene Proteins / Q000235:genetics* / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2; D011519:Proto-Oncogenes; D012045:Regulatory Sequences, Nucleic Acid; D015183:Restriction Mapping; D017384:Sequence Deletion; D013698:Templates, Genetic; D014158:Transcription, Genetic; D014162:Transfection
D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2