In Situ Proximity Ligation Assay (In Situ PLA) to Assess PTP-Protein Interactions

: Spatiotemporal aspects of protein-tyrosine phosphatase (PTP) activity and interaction partners for many PTPs are elusive. We describe here an elegant and relatively simple method, in situ proximity ligation assay (in situ PLA), which can be used to address these issues. The possibility to detect endogenous unmodified proteins in situ and to visualize individual interactions with spatial resolution is the major advantage of this technique. We provide protocols suitable to monitor association of the transmembrane PTPs PTPRJ/DEP-1/CD148 and PTPRB/VE-PTP with their substrates, the receptor tyrosine kinases FMS-like tyrosine kinase 3 (FLT3/CD135), and Tie2 and vascular endothelial growth factor receptor 2 (VEGFR2), respectively. Detailed description of method development and reagents as well as highlighting of critical factors will enable the reader to apply the method successfully to other PTP-protein interactions.