Binding of Cbl to a phospholipase Cγ1-docking site on platelet-derived growth factor receptor β provides a dual mechanism of negative regulation

Ubiquitin conjugation to receptor tyrosine kinases is a critical biochemical step in attenuating their signaling through lysosomal degradation. Our previous studies have established Cbl as an E3 ubiquitin ligase for ubiquitinylation and degradation of platelet-derived growth factor receptor (PDGFR) alpha and PDGFR beta. However, the role of endogenous Cbl in PDGFR regulation and the molecular mechanisms of this regulation remain unclear. Here, we demonstrate that endogenous Cbl is essential for ligand-induced ubiquitinylation and degradation of PDGFR beta; this involves the Cbl TKB domain binding to PDGFR beta phosphotyrosine 1021, a known phospholipase C (PLC) gamma 1 SH2 domain-binding site. Lack of Cbl or ablation of the Cbl-binding site on PDGFR beta impedes receptor sorting to the lysosome. Cbl-deficient cells also show more PDGF-induced PLC gamma 1 association with PDGFR beta and enhanced PLC-mediated cell migration. Thus, Cbl-dependent negative regulation of PDGFR beta involves a dual mechanism that concurrently promotes ubiquitin-dependent lysosomal sorting of the receptor and competitively reduces the recruitment of a positive mediator of receptor signaling.