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Platelet activating factor activates MAPK and increases in intracellular calcium via independent pathways in B
R A Franklin1, A Tordai, B Mazer
1Department of Pediatrics, National Jewish Center for Immunology and Respiratory Medicine, Denver, Colorado 80206, USA.
Abstract:
Platelet activating factor (PAF)-stimulation of human B-lymphoblastoid cells results in the activation of microtubule associated protein 2-kinase (MAPK) and increases in intracellular calcium. Although increases in intracellular calcium induce MAPK activation in these cells, PAF can stimulate MAPK activation in the absence of detectable changes in intracellular calcium concentrations ([Ca2+]i). Treatment of the LA350 B-lymphoblastoid cell line with either pertussis toxin (PT) or cholera toxin (CT) blocked PAF-induced changes in [Ca2+]i. However, only PT blocked PAF-induced activation of MAPK as determined by shifts in the mobility of MAPK on immunoblots. In support of this finding, only PT but not CT blocked PAF-induced phosphorylation and activation of p90rsk, an event thought to be distal to MAPK activation. These results suggest that the PAF receptor is mediating MAPK activation through pathways separate from those mediating increases in intracellular calcium.
Insights
Platelet-activating factor (PAF) activates human B-cells, triggering both MAPK and calcium increases. However, PAF can activate MAPK independently of calcium, suggesting distinct signaling pathways.
Area of Science:
- Immunology
- Cell Signaling
- Molecular Biology
Background:
- Platelet-activating factor (PAF) is a potent lipid mediator involved in various cellular responses.
- Microtubule-associated protein 2-kinase (MAPK) activation is a key signaling event in B-lymphoblastoid cells.
- Intracellular calcium ([Ca2+]i) is known to play a role in MAPK activation.
Purpose of the Study:
- To investigate the relationship between PAF-induced MAPK activation and intracellular calcium changes in human B-lymphoblastoid cells.
- To elucidate the specific signaling pathways involved in PAF-mediated MAPK activation.
Main Methods:
- Stimulation of B-lymphoblastoid cells with PAF.
- Measurement of intracellular calcium concentrations ([Ca2+]i).
- Assessment of MAPK activation using immunoblotting and analysis of p90rsk phosphorylation.
- Treatment with pertussis toxin (PT) and cholera toxin (CT) to differentiate signaling pathways.
Main Results:
- PAF stimulation induced both MAPK activation and increased intracellular calcium.
- MAPK activation by PAF occurred even without detectable changes in [Ca2+]i.
- Pertussis toxin (PT) blocked PAF-induced MAPK activation and p90rsk phosphorylation, while cholera toxin (CT) did not.
- Both PT and CT blocked PAF-induced changes in [Ca2+]i.
Conclusions:
- The PAF receptor mediates MAPK activation through pathways distinct from those that increase intracellular calcium.
- Pertussis toxin-sensitive pathways are critical for PAF-induced MAPK activation in B-lymphoblastoid cells.