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Characterization of platelet-derived growth factor-induced p38 mitogen-activated protein kinase activation in
H Yamaguchi1, M Igarashi, A Hirata
1Third Department of Internal Medicine, Yamagata University School of Medicine, Yamagata, Japan.
Background:
The mitogen-activated protein (MAP) kinase super-family plays a crucial role in cell growth and differentiation and even in programmed cell death in response to diverse extracellular stimuli. The platelet-derived growth factor (PDGF)-BB is well known to promote the proliferation of vascular smooth muscle cells (VSMC) via extracellular-regulated protein kinases (ERKs), leading to the development of cardiovascular diseases. However, it has not yet been clarified whether PDGFs that include other isoforms can activate the other parallel signal transduction pathways, c-jun NH2-terminal protein kinase (JNK) and p38 MAP kinase (p38), in VSMC. In this study, we investigated the effect of PDGFs on p38 activation in cultured rat VSMC.
Materials And Methods:
After stimulation by PDGFs with SB-203580 or PD-98059, the cells were solubilized, and the expressions of MAP kinases, MAP kinase kinases (MKKs), phosphorylated DNA-binding proteins, and cyclooxigenases (COXs) were examined by immunoblot analysis.
Results:
PDGFs activated p38 phosphorylation dose-dependently, and the phosphorylations were specifically inhibited by SB-203580 but not by PD-98059. PDGFs also activated the phosphorylation of MKK 3/MKK 6 but not that of either stress-activated protein kinase/ERK kinase or JNK. PDGFs affected the activation of a cyclic AMP response-element binding protein, which was inhibited by SB-203580. However, the activating transcription factor-2 was not activated by PDGFs. Interestingly, the stimulation of PDGFs for 72 h enhanced the level of COX-2, and these levels were decreased by SB-203580.
Conclusion:
These results have clarified that PDGFs activate the p38 cascade via an MKK 3/6 pathway, independently of the ERK cascade, and subsequently regulate the level of COX-2 in rat VSMC, providing that PDGFs influence the inflammatory process in the vascular wall.
Insights
Platelet-derived growth factors (PDGFs) activate the p38 MAP kinase pathway in vascular smooth muscle cells (VSMCs) via MKK 3/6, independent of the ERK pathway. This activation influences cyclooxygenase-2 (COX-2) levels, suggesting a role in vascular inflammation.
Area of Science:
- Cellular signaling pathways
- Molecular biology
- Cardiovascular research
Background:
- Mitogen-activated protein (MAP) kinase superfamily regulates cell functions.
- Platelet-derived growth factor (PDGF)-BB promotes vascular smooth muscle cell (VSMC) proliferation via extracellular-regulated protein kinases (ERKs), contributing to cardiovascular diseases.
- The role of other PDGF isoforms and MAP kinase pathways (JNK, p38) in VSMCs remains unclear.
Purpose of the Study:
- To investigate the effect of PDGFs on p38 MAP kinase activation in cultured rat VSMCs.
- To determine if PDGFs activate parallel signal transduction pathways beyond ERKs.
Main Methods:
- Cultured rat VSMCs were stimulated with PDGFs.
- Inhibitors SB-203580 (p38 inhibitor) and PD-98059 (ERK inhibitor) were used.
- Immunoblot analysis assessed the expression of MAP kinases, MKKs, phosphorylated proteins, and COXs.
Main Results:
- PDGFs dose-dependently activated p38 phosphorylation, specifically inhibited by SB-203580.
- PDGFs activated MKK 3/MKK 6 phosphorylation, but not JNK or ERK.
- PDGF stimulation enhanced COX-2 levels after 72 hours, which was reduced by SB-203580.
Conclusions:
- PDGFs activate the p38 cascade through MKK 3/6, independently of the ERK cascade, in rat VSMCs.
- PDGFs regulate COX-2 levels, indicating a role in vascular wall inflammatory processes.