J Biol Chem, Vol. 274, Issue 22, 15454-15465, May 28, 1999
Activation of the 9E3/cCAF Chemokine by Phorbol
Esters Occurs via Multiple Signal Transduction Pathways That Converge
to MEK1/ERK2 and Activate the Elk1 Transcription Factor
QiJing
Li,
Sucheta M.
Vaingankar,
Harry M.
Green, and
Manuela
Martins-Green
From the Department of Biology, University of California,
Riverside, California 92521
Using primary fibroblasts in culture, we have
investigated the signal transduction mechanisms by which phorbol
esters, a class of tumor promoters, activate the 9E3 gene
and its chemokine product the chicken chemotactic and angiogenic
factor. This gene is highly stimulated by phorbol 12,13-dibutyrate
(PDBu) via three pathways: (i) a small contribution through protein
kinase C (the commonly recognized pathway for these tumor promoters),
(ii) a contribution involving tyrosine kinases, and (iii) a larger
contribution via pathways that can be interrupted by dexamethasone. All
three of these pathways converge into the mitogen-activated protein
kinases, MEK1/ERK2. Using a luciferase reporter system, we show that
although both the AP-1 and PDRIIkB (a NF
B-like factor in chickens)
response elements are capable of activation in these normal cells,
regions of the 9E3 promoter containing them are
unresponsive to PDBu stimulation. In contrast, we show for the first
time that activation by PDBu occurs through a segment of the promoter
containing Elk1 response elements; deletion and mutation of these
elements abrogates 9E3/chicken chemotactic and angiogenic
factor expression. Electrophoretic mobility shift assays and functional
studies using PathDetect systems show that stimulation of the cells by
phorbol esters leads to activation of the Elk1 transcription factor,
which binds to its element in the 9E3 promoter.
Copyright © 1999 by The American Society for Biochemistry and Molecular Biology, Inc.