Visit our Expo - Redox and Inflammation signaling 2012

Session XVII : Cell signaling in health and disease Poster XVII, 47
M-CSF-induced proliferation and LPS-dependent activation of macrophages requires
Raf-1 phosphorylation to induce MKP-1 (DUSP1) expression
Ester Sánchez-Tilló, Monica Comalada, Consol Farrera, Annabel F. Valledor, Jorge
Lloberas and Antonio Celada
Macrophage Biology Group, Institute of Biomedical Research, Barcelona Science Park,
University of Barcelona, Barcelona, Spain. E-mail: acelada@ub.edu
Macrophages are key regulators of immune responses. Bone marrow-derived macrophages
undergo proliferation in response to their specific growth factor, M-CSF. The addition of
activating agents, such as lipopolysaccharide (LPS), results in macrophage growth arrest and
engagement in a pro-inflammatory response, which produces nitric oxide (NO) and cytokines
including tumor necrosis alpha (TNF-"), IL-1 and IL-6. Although activation of ERK is
required for both macrophage proliferation and activation, the kinetics of these two processes
differs. In our cellular model, early peak of ERK activation (5 min) correlates with cellular
proliferation whereas a later peak (15 min) is associated with the activation program. M-CSF
and LPS also induce with different time-course the dual specificity MAP kinase phosphatase
MKP1 (DUSP1), which correlates with the dephosphorylation of ERK. Therefore, MKP1 is a
key regulator of the time-course of ERK activity. Using RNA interference and
pharmacological inhibitors, here we provide evidence that macrophagic MKP1 expression
induced by M-CSF and LPS is dependent on Raf-1 activation. In addition, Raf-1 interacts
with PKC', which is also involved in MKP-1 induction. Concordantly, the distinct timecourse
of Raf-1 and MEK-1/2 activation correlates with that of ERK-1/2 induced by M-CSF
or LPS. ERK activation in response to M-CSF is Raf-1-dependent, but an alternative pathway
induces ERK activation in response to LPS. Blockage of Raf-1 activity results in increased
expression of cyclin dependent kinase inhibitors p21Waf-1 and p27Kip-1 and macrophage
growth arrest even in the presence of M-CSF. In contrast, LPS stimulation has no effect on
the expression of pro-inflammatory cytokines and inducible nitric oxide synthase.
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