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Mol. Cell. Biol., Jul 1995, 3840-3847, Vol 15, No. 7
HM Chen and LM Boxer
The bcl-2 gene is differentially regulated during B-cell development, with
low-level expression in pre-B cells and higher-level expression in mature B
cells. These changes correlate with susceptibility to cell death by
apoptosis and suggest that the Bcl-2 protein may play a role in the control
of cell death during B-cell development. We have identified two negative
regulatory regions in the human bcl-2 5' flanking and 5' untranslated
regions in pre-B cells; these regions have no significant function in
mature B cells. Further investigation of these regions revealed two
pre-B-cell-specific enhancer elements (pi 1 sites) in the 5' negative
regulatory region and one in the 3' negative regulatory region. Mutational
analysis confirmed that these three sites functioned as negative regulators
of the bcl-2 promoter in the pre-B- cell line Nalm-6. Electrophoretic
mobility shift assays with each of the three sites demonstrated a complex
of identical mobility to that formed with the immunoglobulin heavy-chain
enhancer pi 1 site. UV cross- linking experiments revealed that a protein
with a molecular mass of 58 kDa bound to the three bcl-2 sites and to the
immunoglobulin enhancer site. This protein reacted with an antibody against
Ets family proteins. Constructs with the isolated pi 1 sites linked to the
simian virus 40 promoter were used in transient transfection experiments in
the pre-B-cell line. The bcl-2 sites decreased expression of the simian
virus 40 promoter, while the immunoglobulin enhancer site increased its
expression. The pi 1 sites in the bcl-2 gene may play a role in the
developmental regulation of bcl-2 expression during B-cell differentiation.
Copyright © 1995, American Society for Microbiology
Pi 1 binding sites are negative regulators of bcl-2 expression in pre-B cells
Center for Molecular Biology in Medicine, Palo Alto VAMC, California, USA.
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