The Journal of Neuroscience, February 1, 2003, 23(3):807
Stimulation of the Calcitonin Gene-Related Peptide Enhancer by
Mitogen-Activated Protein Kinases and Repression by an
Antimigraine Drug in Trigeminal Ganglia Neurons
Paul L.
Durham and
Andrew F.
Russo
Department of Physiology and Biophysics, University of Iowa, Iowa
City, Iowa 52242
Calcitonin gene-related peptide (CGRP) is involved in the
underlying pathophysiology of all vascular headaches, including migraines. Elevated levels of CGRP during migraine are restored to
normal coincident with headache relief after treatment with the
antimigraine drug sumatriptan. We have used primary cultures of
trigeminal neurons under conditions simulating migraine pathology and
therapy to study the mechanisms controlling the CGRP promoter. Using
reporter genes in transient transfection assays, we demonstrate that an
18 bp enhancer containing a helix-loop-helix element is both
necessary and sufficient for full promoter activity. NGF treatment and
cotransfection with an upstream activator of the extracellular
signal-regulated MAP kinases (MAPKs) activated the enhancer. Treatment
with sumatriptan repressed NGF- and MAPK-stimulated CGRP promoter
activity. Repression was also observed using a synthetic MAPK-responsive reporter gene. Sumatriptan regulation of CGRP gene
expression did not couple to a Gi/Go
pathway, but rather caused a prolonged increase in intracellular
calcium. The importance of the prolonged calcium signal in repression
of MAPK activity was demonstrated by using the ionophore ionomycin to
mimic sumatriptan action. We propose that activation of MAPK pathways
may increase CGRP gene expression during migraine, and that sumatriptan
can diametrically oppose that activation via a prolonged elevation of
intracellular calcium.
Key words:
CGRP; trigeminal ganglia; MAPK; calcium; migraine; gene expression
Copyright © 2003 Society for Neuroscience 0270-6474/03/233807-09$05.00/0