Imaging Sites of Receptor Dephosphorylation by PTP1B on the Surface of the Endoplasmic Reticulum

TLDR

Receptor tyrosine kinases transmit signals from the cell surface, but how the ER‑localized phosphatase PTP1B terminates these signals remains unclear. The authors used fluorescence resonance energy transfer to track interactions between EGFR, PDGFR, and PTP1B. PTP1B dephosphorylates internalized RTKs at discrete ER‑surface sites, revealing that activation and inactivation are spatially and temporally segregated within cells.

Abstract

When bound by extracellular ligands, receptor tyrosine kinases (RTKs) on the cell surface transmit critical signals to the cell interior. Although signal termination is less well understood, protein tyrosine phosphatase–1B (PTP1B) is implicated in the dephosphorylation and inactivation of several RTKs. However, PTP1B resides on the cytoplasmic surface of the endoplasmic reticulum (ER), so how and when it accesses RTKs has been unclear. Using fluorescence resonance energy transfer (FRET) methods, we monitored interactions between the epidermal- and platelet-derived growth factor receptors and PTP1B. PTP1B-catalyzed dephosphorylation required endocytosis of the receptors and occurred at specific sites on the surface of the ER. Most of the RTKs activated at the cell surface showed interaction with PTP1B after internalization, establishing that RTK activation and inactivation are spatially and temporally partitioned within cells.