Identification of a putative Syp substrate, the PDGF beta receptor

Area of Science:

• Biochemistry
• Cell Signaling
• Molecular Biology

Background:

• Platelet-derived growth factor receptor (PDGFR) signaling is crucial for cell growth and differentiation.
• Protein-tyrosine phosphatases (PTPs) play vital roles in regulating signal transduction pathways by dephosphorylating tyrosine kinases.
• Syp (also known as PTPN12) is a PTP implicated in various cellular processes, but its specific substrates and regulatory mechanisms are not fully understood.

Purpose of the Study:

• To investigate whether Syp dephosphorylates the beta-PDGFR, a known binding partner.
• To determine the substrate selectivity of Syp towards different tyrosine phosphorylation sites on the beta-PDGFR.
• To elucidate the role of Syp in regulating beta-PDGFR-mediated signaling in vivo.

Main Methods:

• In vitro dephosphorylation assays using recombinant Syp (rSyp) and recombinant PTP1B (rPTP1B) with phosphorylated beta-PDGFR.
• Two-dimensional phosphopeptide mapping to analyze site-specific dephosphorylation.
• In vivo studies using beta-PDGFR mutants with altered Syp binding affinity.
• Analysis of the association of downstream signaling molecules (GAP, PI3K) with the beta-PDGFR.

Main Results:

• rSyp dephosphorylated the beta-PDGFR in vitro, but with significant site selectivity, favoring Tyr(P)-771 and Tyr(P)-751.
• rPTP1B dephosphorylated the beta-PDGFR without site preference.
• A beta-PDGFR mutant (F1009) with reduced Syp association showed slower in vivo dephosphorylation.
• Syp's SH2 domains contribute to, but are not solely responsible for, its substrate selectivity.
• Selective dephosphorylation of specific sites on beta-PDGFR by Syp influenced the recruitment of GAP and PI3K.

Conclusions:

• Syp is a substrate-selective PTP that dephosphorylates the beta-PDGFR.
• Both the catalytic and SH2 domains of Syp contribute to its substrate specificity.
• Syp regulates PDGF-dependent signaling by selectively modulating beta-PDGFR phosphorylation, thereby controlling the assembly of downstream signaling complexes.