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Molecular Mechanisms for Reciprocal Regulation of the PDGF Receptor and G Protein‐coupled Receptor Kinase‐5
Author(s) -
Cai Xinjiang,
Wu JiaoHui,
Freedman Neil J.
Publication year - 2008
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.22.1_supplement.1044.8
Subject(s) - phosphorylation , platelet derived growth factor receptor , kinase , biology , receptor , receptor tyrosine kinase , microbiology and biotechnology , immunoprecipitation , biochemistry , chemistry , growth factor , gene
Seryl (Ser) phosphorylation of the platelet‐derived growth factor receptor‐β (PDGFRβ) by G protein‐coupled receptor kinase‐5 (GRK5) diminishes the PDGFRβ signaling in vascular smooth muscle cell (SMCs). This work tests the hypothesis that the PDGFRβ tyrosine (Tyr)‐phosphorylates and activates GRK5 Using immunoprecipitated PDGFRβs, purified bovine GRK5 and [ã‐32P]ATP, we found that the PDGFRβ Tyr‐phosphorylated GRK5 with a stoichiometry of 0.8±0.1, a value 4‐fold higher than that obtained with a Y857F PDGFRβ mutant, which autophosphorylates normally but fails to phosphorylate exogenous substrates. GRK5 was activated only by the PDGF‐stimulated WT, but not the Y857F PDGFRβ. We found 26±2% more substrate peptide phosphorylation with PDGFRβs IP’d from grk5−/− than WT SMCs (p<0.05). In vitro peptide phosphorylation assays showed that PDGFRβ‐mediated Tyr phosphorylation of GRK5 increased GRK5 activity by 1.6±0.2‐fold, by increasing GRK5 V max (3.4±0.6‐fold, p<0.05) without altering GRK5's K M for substrate. Conversely, GRK5‐mediated Ser phosphorylation of the PDGFRâ decreased PDGFRβ activity by 40±10%. In conclusion, the PDGFRβ and GRK5 are functionally coupled in a novel feedback regulatory mechanism.