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Mol. Cell. Biol., May 1997, 2605-2614, Vol 17, No. 5
SB Maggirwar, EW Harhaj and SC Sun
The CD28 costimulatory signal enhances antigen-mediated induction of
interleukin-2 (IL-2) gene transcription through activation of an enhancer
termed the CD28-responsive element (CD28RE). Although various nuclear
proteins have been shown to bind to CD28RE, their in vivo functions in the
regulation of this enhancer remain elusive. In this report, we show that
CD28RE binds distinct transcription factors in cells treated with different
mitogenic stimuli. Stimulation of the T- cell receptor (TCR) complex in the
absence of a CD28 costimulatory signal induces a member of the nuclear
factor of the activated T cells, NF-ATp; however, this treatment fails to
activate the CD28RE enhancer activity. Significant activation of CD28RE was
detected when the cells were treated with both the TCR stimulators and an
anti-CD28 monoclonal antibody (anti-CD28), which induces the NF-kappaB/Rel
enhancer binding proteins in addition to NF-ATp. The costimulatory activity
of anti-CD28 can be further enhanced by a phorbol ester. Kinetic analyses
demonstrate that activation of endogenous IL-2 gene transcription is
correlated with the binding of CD28RE by NF-ATp and different NF-
kappaB/Rel species. Transient-transfection studies reveal that expression
of either NF-ATp or the p50-RelA NF-kappaB heterodimer leads to the potent
transactivation of both the CD28RE enhancer and the intact IL-2 promoter in
mitogen-stimulated cells. Remarkably, coexpression of these two families of
enhancer-binding proteins in Jurkat T cells results in the transactivation
of the CD28RE enhancer even in the absence of any cellular stimuli.
Together, these results suggest that activation of IL-2 gene transcription
by the TCR- and CD28- mediated signals involves the interaction of CD28RE
with NF-ATp and various NF-kappaB/Rel transcription factors.
Copyright © 1997, American Society for Microbiology
Regulation of the interleukin-2 CD28-responsive element by NF-ATp and various NF-kappaB/Rel transcription factors
Department of Microbiology and Immunology, Pennsylvania State University College of Medicine, Hershey Medical Center, 17033, USA.
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