PTPσ binds and dephosphorylates neurotrophin receptors and can suppress NGF-dependent neurite outgrowth from sensory neurons

Neurotrophin receptors of the Trk family play a vital role in the survival of developing neurons and the process of axonogenesis. The Trk family are receptor protein tyrosine kinases (RTKs) and their signalling in response to neurotrophins is critically dependent upon their ability to transphosphorylate and act as signalling centres for multiple adaptor proteins and distinct, downstream pathways. Such phosphotyrosine signalling also depends upon the appropriate counter-regulation by phosphatases. A large family of receptor-like protein tyrosine phosphatases (RPTPs) are also expressed in developing neurons and in this study we have examined the ability of the phosphatase PTPσ to interact with and regulate Trk proteins in transfected HEK 293T cells. PTPσ can bind differentially to Trk proteins, binding stably in complexes with TrkA and TrkC, but not TrkB. The transmembrane domains of PTPσ and TrkA appear to be sufficient for the direct or indirect interaction between these two receptors. Furthermore, PTPσ is shown to dephosphorylate all three Trk receptors and suppress their phosphorylation in the presence of neurotrophins. In addition, overexpression of PTPσ in primary sensory neurons in culture inhibits neurite outgrowth without affecting the short-term survival of these neurons. PTPσ can thus show differential complex formation with different Trk family members and in neurons can selectively target the neurite-forming signalling pathway driven by TrkA.