Multiple requirements for SHPTP2 in epidermal growth factor-mediated cell cycle progression

Area of Science:

• Molecular Biology
• Cell Signaling
• Biochemistry

Background:

• SHPTP2 is a protein tyrosine phosphatase implicated in various cellular processes.
• Growth factor signaling pathways involve complex cascades of protein-protein interactions and post-translational modifications.

Purpose of the Study:

• To investigate the specific role of SHPTP2 in growth factor signaling pathways, particularly in response to epidermal growth factor (EGF) and platelet-derived growth factor (PDGF).
• To determine whether SHPTP2's catalytic activity or its phosphorylation status is essential for its function in signal transduction.

Main Methods:

• Transient overexpression of wild-type and mutant SHPTP2 in 293 cells.
• Microinjection of anti-SHPTP2 antibodies and glutathione S-transferase (GST) fusion proteins into NIH 3T3 cells.
• Assays for mitogen-activated protein (MAP) kinase activation, Elk-1 transactivation, and S-phase entry.

Main Results:

• Catalytically inactive SHPTP2 (PTP2CS) inhibited EGF-induced MAP kinase activation and Elk-1 transactivation, while inactive SHPTP1 did not.
• A mutant SHPTP2 lacking C-terminal phosphorylation sites (PTP2YF) was ineffective, and rescued PTP2CS inhibition, indicating phosphatase activity is required.
• SHPTP2 inhibition did not affect Ras- or PDGF-induced signaling, suggesting pathway specificity.
• Anti-SHPTP2 antibodies and GST-SH2 fusion protein inhibited EGF-induced S-phase entry for up to 8 hours, affecting late cell cycle events.

Conclusions:

• SHPTP2's protein-tyrosine phosphatase activity, not its tyrosyl phosphorylation, is essential for immediate-early responses to EGF.
• SHPTP2 plays a critical role in both early and late cellular responses to EGF, but not to PDGF or serum.
• The signaling pathways regulated by SHPTP2 for immediate-early and late events are distinct.