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Protein kinase C-alpha modulates lipopolysaccharide-induced functions in a murine macrophage cell line
A St-Denis1, F Chano, P Tremblay
1Institut Armand-Frappier, Université du Québec, Laval, Québec H7V 1B7, Canada.
Abstract:
Lipopolysaccharide (LPS), a potent modulator of macrophage functional activity, binds to CD14 and triggers the activation of several protein kinases, leading to the secretion of variety of immunomodulatory molecules such as nitric oxide and proinflammatory cytokines. In this study, we have examined the role of the alpha isoenzyme of protein kinase C (PKC) in the regulation of LPS-initiated signal transduction in macrophages. To this end, we have stably overexpressed a dominant-negative (DN) version of PKC-alpha (DN PKC-alpha) in the murine macrophage cell line RAW 264. 7. Clones overexpressing DN PKC-alpha were indistinguishable from the parental line with respect to morphology and growth characteristics. At the functional level, DN PKC-alpha overexpression strongly inhibited LPS-induced interleukin-1alpha mRNA accumulation, and to a lesser extent inducible nitric oxide synthase and tumor necrosis factor-alpha expression. DN-PKC-alpha overexpression did not cause a general unresponsiveness to LPS, as secretion of the matrix metalloproteinase-9 was up-regulated in our DN PKC-alpha-overexpressing clones. Moreover, LPS-induced phosphorylation and degradation of IkappaBalpha, NF-kappaB activation, as well as p38 mitogen-activated protein kinase and Jun N-terminal kinase phosphorylation, were not affected by DN PKC-alpha overexpression. Collectively, these data provide evidence that PKC-alpha regulates selective LPS-induced macrophage functions involved in host defense and inflammation.
Insights
Protein kinase C-alpha (PKC-alpha) selectively regulates macrophage responses to lipopolysaccharide (LPS). Inhibiting PKC-alpha in macrophages affects key inflammatory molecule production, impacting host defense mechanisms.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Lipopolysaccharide (LPS) activates macrophages via CD14, initiating signaling cascades.
- Macrophage activation leads to the release of nitric oxide and proinflammatory cytokines.
- Protein kinases play crucial roles in mediating LPS-induced macrophage responses.
Purpose of the Study:
- To investigate the specific role of protein kinase C-alpha (PKC-alpha) in LPS-mediated signal transduction in macrophages.
- To determine how PKC-alpha influences the expression of key inflammatory mediators upon LPS stimulation.
Main Methods:
- Stable overexpression of a dominant-negative PKC-alpha (DN PKC-alpha) in murine RAW 264.7 macrophage cell line.
- Assessment of LPS-induced gene expression (interleukin-1alpha, inducible nitric oxide synthase, tumor necrosis factor-alpha) via mRNA accumulation.
- Analysis of protein secretion (matrix metalloproteinase-9) and signaling pathway activation (IkappaBalpha degradation, NF-kappaB, p38 MAPK, JNK phosphorylation).
Main Results:
- DN PKC-alpha overexpression significantly inhibited LPS-induced interleukin-1alpha mRNA accumulation.
- Inducible nitric oxide synthase and tumor necrosis factor-alpha expression were moderately reduced by DN PKC-alpha.
- DN PKC-alpha did not impair LPS-induced matrix metalloproteinase-9 secretion or affect IkappaBalpha degradation, NF-kappaB activation, or p38/JNK phosphorylation, indicating selective regulation.
- Macrophage morphology and growth were unaffected by DN PKC-alpha overexpression.
Conclusions:
- PKC-alpha is a key regulator of specific LPS-induced macrophage functions.
- PKC-alpha selectively modulates the production of certain immunomodulatory molecules involved in host defense and inflammation.
- These findings highlight PKC-alpha as a potential therapeutic target for inflammatory conditions.