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Bacterial lipopolysaccharide induces tyrosine phosphorylation and activation of mitogen-activated protein kinases in
S L Weinstein1, J S Sanghera, K Lemke
1Department of Physiology, University of California, San Francisco 94143-0552.
Abstract:
Bacterial lipopolysaccharide (LPS) is a potent activator of antibacterial responses by macrophages. Following LPS stimulation, the tyrosine phosphorylation of several proteins is rapidly increased in macrophages, and this event appears to mediate some responses to LPS. We now report that two of these tyrosine phosphoproteins of 41 and 44 kDa are isoforms of mitogen-activated protein (MAP) kinase. Each of these proteins was reactive with anti-MAP kinase antibodies and comigrated with MAP kinase activity in fractions eluted from a MonoQ anion-exchange column. Following LPS stimulation, column fractions containing the tyrosine phosphorylated forms of p41 and p44 exhibited increased MAP kinase activity. Inhibition of LPS-induced tyrosine phosphorylation of these proteins was accompanied by inhibition of MAP kinase activity. Additionally, induction of p41/p44 tyrosine phosphorylation and MAP kinase activity by LPS appeared to be independent of activation of protein kinase C, even though phorbol esters also induced these responses. These results demonstrate that LPS induces the tyrosine phosphorylation and activation of at least two MAP kinase isozymes. Since MAP kinases appear to modulate cellular processes in response to extracellular signals, these kinases may be important targets for LPS action in macrophages.
Insights
Bacterial lipopolysaccharide (LPS) rapidly activates macrophages by increasing tyrosine phosphorylation of mitogen-activated protein (MAP) kinase isoforms. This study identifies two MAP kinase isoforms (p41 and p44) as key targets of LPS signaling.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Bacterial lipopolysaccharide (LPS) potently activates macrophages, initiating antibacterial responses.
- Tyrosine phosphorylation of macrophage proteins increases rapidly after LPS stimulation, suggesting a role in mediating LPS effects.
Purpose of the Study:
- To identify the specific tyrosine phosphoproteins involved in macrophage responses to LPS.
- To investigate the role of mitogen-activated protein (MAP) kinases in LPS-induced signaling.
Main Methods:
- Utilized anti-MAP kinase antibodies to identify tyrosine phosphoproteins.
- Employed MonoQ anion-exchange chromatography to separate and analyze protein fractions.
- Assessed MAP kinase activity in response to LPS stimulation and inhibition.
Main Results:
- Identified two tyrosine phosphoproteins (41 and 44 kDa) as MAP kinase isoforms (p41 and p44).
- Demonstrated increased MAP kinase activity in LPS-stimulated macrophages, correlating with tyrosine phosphorylation.
- Showed that LPS-induced MAP kinase activation and phosphorylation are independent of protein kinase C.
Conclusions:
- LPS induces tyrosine phosphorylation and activation of at least two MAP kinase isozymes (p41 and p44) in macrophages.
- MAP kinases are likely crucial mediators of LPS action in macrophages, modulating cellular responses to extracellular signals.