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The differential time-course of extracellular-regulated kinase activity correlates with the macrophage response
A F Valledor1, M Comalada, J Xaus
1Departament de Fisiologia (Biologia del Macròfag), Facultat de Biologia, and Fundació August Pi i Sunyer, Campus Bellvitge, Universitat de Barcelona, Av. Diagonal 645, 08028 Barcelona, Spain.
Abstract:
Bone marrow-derived macrophages proliferate in response to specific growth factors, including macrophage colony-stimulating factor (M-CSF). When stimulated with activating factors, such as lipopolysaccharide (LPS), macrophages stop proliferating and produce proinflammatory cytokines. Although triggering opposed responses, both M-CSF and LPS induce the activation of extracellular-regulated kinases (ERKs) 1 and 2. However, the time-course of ERK activation is different; maximal activation by M-CSF and LPS occurred after 5 and 15 min of stimulation, respectively. Granulocyte/macrophage colony-stimulating factor, interleukin 3, and TPA, all of which induced macrophage proliferation, also induced ERK activity, which was maximal at 5 min poststimulation. The use of PD98059, which specifically blocks ERK 1 and 2 activation, demonstrated that ERK activity was necessary for macrophage proliferation in response to these factors. The treatment with phosphatidylcholine-specific phospholipase C (PC-PLC) inhibited macrophage proliferation, induced the expression of cytokines, and triggered a pattern of ERK activation equivalent to that induced by LPS. Moreover, PD98059 inhibited the expression of cytokines induced by LPS or PC-PLC, thus suggesting that ERK activity is also required for macrophage activation by these two agents. Activation of the JNK pathway did not discriminate between proliferative and activating stimuli. In conclusion, our results allow to correlate the differences in the time-course of ERK activity with the macrophagic response toward proliferation or activation.
Insights
Macrophage colony-stimulating factor (M-CSF) and lipopolysaccharide (LPS) trigger distinct macrophage responses. Differences in extracellular-regulated kinases (ERK) activation timing correlate with whether macrophages proliferate or activate.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- Macrophages are key immune cells with distinct responses to stimuli.
- Macrophage colony-stimulating factor (M-CSF) promotes proliferation, while lipopolysaccharide (LPS) induces activation and cytokine production.
- Extracellular-regulated kinases (ERKs) 1 and 2 are involved in both proliferation and activation pathways.
Purpose of the Study:
- To investigate the role of extracellular-regulated kinases (ERK) activation timing in macrophage proliferation versus activation.
- To determine if ERK activation is essential for M-CSF-induced proliferation and LPS-induced activation.
- To explore the involvement of ERK in phosphatidylcholine-specific phospholipase C (PC-PLC)-induced responses.
Main Methods:
- Stimulation of bone marrow-derived macrophages with M-CSF, LPS, granulocyte/macrophage colony-stimulating factor, interleukin 3, TPA, and PC-PLC.
- Measurement of ERK 1 and 2 activation over time using specific inhibitors like PD98059.
- Analysis of macrophage proliferation and pro-inflammatory cytokine expression.
Main Results:
- M-CSF and proliferative stimuli induced rapid ERK activation (maximal at 5 min), while LPS induced delayed activation (maximal at 15 min).
- ERK activation was necessary for M-CSF-induced proliferation, as shown by PD98059 inhibition.
- PC-PLC treatment mimicked LPS effects, inhibiting proliferation and inducing cytokine expression, with ERK activation also being essential.
- JNK pathway activation did not differentiate between proliferative and activating stimuli.
Conclusions:
- The temporal pattern of ERK 1 and 2 activation is a critical determinant of macrophage response, distinguishing proliferation from activation.
- ERK signaling is indispensable for both M-CSF-driven macrophage proliferation and LPS/PC-PLC-mediated activation.
- These findings provide insights into the signaling mechanisms governing macrophage functional plasticity.