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RGS4 inhibits platelet-activating factor receptor phosphorylation and cellular responses.

R M Richardson1, R J Marjoram, A J Barr

  • 1Departments of Medicine and Immunology, Duke University Medical Center, Durham, North Carolina 27710, USA. richa021@mc.duke.edu

Biochemistry
|April 12, 2001
PubMed
Summary
This summary is machine-generated.

Regulators of G-protein signaling 4 (RGS4) selectively inhibit platelet-activating factor receptor (PAFR) signaling, including receptor phosphorylation, but not responses mediated by formylated peptide or interleukin-8 receptors. This suggests RGS4 may sterically hinder PAFR activity.

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Area of Science:

  • Cellular signaling pathways
  • G protein-coupled receptor regulation
  • Molecular mechanisms of immune response

Background:

  • Regulators of G-protein signaling (RGS) proteins modulate G protein signaling cascades.
  • Chemoattractant receptors like PAFR, formylated peptide receptors (FR), and CXCR1 play critical roles in immune cell activation.
  • Understanding RGS protein interactions with specific receptors is crucial for deciphering cellular responses.

Purpose of the Study:

  • To investigate the specific role of RGS4 in chemoattractant receptor-mediated cellular responses.
  • To determine if RGS4 differentially affects signaling pathways activated by PAFR, FR, and CXCR1.
  • To elucidate the molecular mechanisms by which RGS4 might regulate these receptors.

Main Methods:

  • Stable coexpression of RGS4 and specific chemoattractant receptors (PAFR, FR, CXCR1) in a rat basophilic leukemia cell line (RBL-2H3).
  • Assessment of signaling events including phosphoinositide (PI) hydrolysis and Ca2+ mobilization.
  • Utilized RGS4 mutants (N-terminal deletion, point mutation) and a truncated PAFR mutant (mPAFR) to probe functional domains.
  • Analyzed receptor phosphorylation patterns.

Main Results:

  • RGS4 significantly inhibited PAFR-mediated phosphoinositide hydrolysis and Ca2+ mobilization, but not responses mediated by FR or CXCR1.
  • RGS4, but not its GAP-deficient mutant, blocked both homologous and heterologous phosphorylation of PAFR.
  • A truncated PAFR mutant lacking the cytoplasmic tail was resistant to RGS4 inhibition, suggesting a role for the tail in RGS4 interaction.
  • A GAP-deficient RGS4 mutant (N88S) partially blocked PAFR phosphorylation but not downstream signaling, indicating distinct roles for GAP activity and other functions.

Conclusions:

  • RGS4 selectively inhibits signaling downstream of PAFR, which primarily couples to Gq, but not FR or CXCR1, which couple to Gi.
  • RGS4's inhibitory effect on PAFR appears to involve steric interference with the receptor's cytoplasmic tail, in addition to its GTPase activating protein activity.
  • These findings highlight a specific regulatory role for RGS4 in PAFR-mediated cellular responses and receptor phosphorylation.