Activation and regulation of platelet-activating factor receptor: role of G(i) and G(q) in receptor-mediated chemotactic, cytotoxic, and cross-regulatory signals.

Abstract

Platelet-activating factor (1-O-alkyl-2-acetyl-sn-glycerolphosphocholine; PAF) induces leukocyte accumulation and activation at sites of inflammation via the activation of a specific cell surface receptor (PAFR). PAFR couples to both pertussis toxin-sensitive and pertussis toxin-insensitive G proteins to activate leukocytes. To define the role(s) of G(i) and G(q) in PAF-induced leukocyte responses, two G-protein-linked receptors were generated by fusing G alpha(i3) (PAFR-G alpha(i3)) or G alpha(q) (PAFR-G alpha(q)) at the C terminus of PAFR. Rat basophilic leukemia cell line (RBL-2H3) stably expressing wild-type PAFR, PAFR-G alpha(i3), or PAFR-G alpha(q) was generated and characterized. All receptor variants bound PAF with similar affinities to mediate G-protein activation, intracellular Ca2+ mobilization, phosphoinositide (PI) hydrolysis, and secretion of beta-hexosaminidase. PAFR-G alpha(i3) and PAFR-G alpha(q) mediated greater GTPase activity in isolated membranes than PAFR but lower PI hydrolysis and secretion in whole cells. PAFR and PAFR-G alpha(i3), but not PAFR-G alpha(q), mediated chemotaxis to PAF. All three receptors underwent phosphorylation and desensitization upon exposure to PAF but only PAFR translocated beta arrestin to the cell membrane and internalized. In RBL-2H3 cells coexpressing the PAFRs along with CXCR1, IL-8 (CXCL8) cross-desensitized Ca2+ mobilization to PAF by all the receptors but only PAFR-G alpha(i3) activation cross-inhibited the response of CXCR1 to CXCL8. Altogether, the data indicate that G(i) exclusively mediates chemotactic and cross-regulatory signals of the PAFR, but both G(i) and G(q) activate PI hydrolysis and exocytosis by this receptor. Because chemotaxis and cross-desensitization are exclusively mediated by G(i), the data suggest that differential activation of both G(i) and G(q) by PAFR likely mediate specific as well as redundant signaling pathways.

• Authors: Stephan L Brown, Venkatakrishna R Jala, Sandeep K Raghuwanshi, Mohd W Nasser, Bodduluri Haribabu, Ricardo M Richardson
• Journal: Journal of immunology (Baltimore, Md. : 1950) (J Immunol) Vol. 177 Issue 5 Pg. 3242-9 (Sep 01 2006) ISSN: 0022-1767 [Print] United States
• PMID: 16920964 (Publication Type: Journal Article, Research Support, N.I.H., Extramural)

Chemical References

• Platelet Activating Factor
• Platelet Membrane Glycoproteins
• Receptors, G-Protein-Coupled
• Receptors, Interleukin-8A
• platelet activating factor receptor
• Pertussis Toxin
• Mitogen-Activated Protein Kinase 1
• Mitogen-Activated Protein Kinase 3
• GTP-Binding Protein alpha Subunits, Gi-Go
• GTP-Binding Protein alpha Subunits, Gq-G11
• Calcium

Topics

• Animals
• Calcium (metabolism)
• Cell Line, Tumor
• Chemotaxis
• Enzyme Activation
• GTP-Binding Protein alpha Subunits, Gi-Go (metabolism)
• GTP-Binding Protein alpha Subunits, Gq-G11 (metabolism)
• Mitogen-Activated Protein Kinase 1 (metabolism)
• Mitogen-Activated Protein Kinase 3 (metabolism)
• Pertussis Toxin (pharmacology)
• Phosphorylation (drug effects)
• Platelet Activating Factor (pharmacology)
• Platelet Membrane Glycoproteins (metabolism)
• Protein Binding
• Rats
• Receptors, G-Protein-Coupled (metabolism)
• Receptors, Interleukin-8A (metabolism)
• Signal Transduction (drug effects)