Visit our Expo - Redox and Inflammation signaling 2012

Session III : Protein kinase cascades as therapeutic targets Poster III, 8
Effects of pituitary adenylate cyclase-activating polypeptide (PACAP) on ERK1/2
(p44/p42 Mitogen-Activated Protein Kinases) cascade in pancreatic beta-cells
Christophe Broca, Safia Costes, Nathalie Linck, Joel Bockaert, Stephane Dalle and
Gyslaine Bertrand.
Equipe Avenir INSERM; IGF; INSERM U661; CNRS UMR5203; 141 rue de la
Cardonille, 34094 Montpellier cedex 5, France. E-mail : christophe.broca@igf.cnrs.fr
PACAP, neuropeptide belonging to the vasoactive intestinal peptide (VIP)/glucagon/secretin
family and interacting with both specific (PAC1) and VIP-shared (VPAC) receptors, plays an
important role in pancreatic beta-cell function. The ERK1/2 cascade, which modulates cell
proliferation and gene transcription but also cytoplasmic processes such as insulin granules
exocytosis, could thus mediate part of PACAP pancreatic effects. So, the aim of our study
was to investigate in pancreatic beta-cells (INS-1E and rat islets) the relationships between
PACAP and ERK1/2 activation (measured by western blotting of doubly phosphorylated
activated forms of these kinases) as well as the signaling cascade hereby activated.
First, in the absence of glucose, PACAP (100 nM) transiently (15 min) stimulated ERK1/2
phosphorylation whereas in the presence of a stimulating glucose concentration (8.3 mM),
PACAP induced a sustained and long lasting (( 3 h) stimulation of ERK1/2 phosphorylation
following a biphasic pattern. The activation of ERK1/2 cascade by PACAP was clearly
glucose-dependent (0-20 mM), and was totally abolished by the MEK (ERK1/2 kinases)
inhibitor PD98059 (20 µM). Moreover, PACAP-induced ERK1/2 phosphorylation was
clearly sensitive to the inhibition of the protein kinase A (PKA) by 10 µM H89 (-40%), the
inhibition of L-type calcium channel by 2 µM nifedipin (-65%), but also sensitive to the
inhibition of the phosphatidylinositol 3-kinase (PI3K) by 100 nM wortmannin or 10 µM
LY294002 (-40% and -50% respectively). Finally, compared to PACAP and forskolin, we
demonstrated that VIP exerts only minor effects on ERK1/2 cascade either in the absence or
the presence of glucose.
We thus concluded that PACAP exerts a sustained and prolonged effect on the pancreatic
beta-cell ERK1/2 cascade, mainly through the PAC1 receptor, and also through the
stimulation of both calcium-, PKA- and PI3K-cascade. The coupling of PAC1 receptors to
ERK1/2 could play an important role in the insulinotropic function as well as in the survival
of pancreatic beta-cells, and thus be relevant in diabetes physiopathology.
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