The role of protein tyrosine phosphatase δ in axon guidance

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The relation between Semaphorin-3A (Sema3A) signaling and LAR class protein tyrosine phosphatases, LAR, PTPδ and PTPσ, was investigated. I found that the ectodomains of PTPδ and PTPσ but not LAR bind to Neuropilin-1 (NRP1). Using alkaline phosphatase (AP) fusion proteins, I have determined the binding constant of the ectodomains PTPδ/σ. AP-PTPδ and AP-PTPσ bind NRP1 with Kd values of 1.1nM and 1.9nM, respectively. AP-Sema3A binds to NRP1 with a Kd of 0.19nM at the same condition. The first immunoglobulin domain of PTPδ/σ binds to the CUB domain of NRP1, which is the binding site for Sema3A. The ecdodomains of PIPδ/σ suppress Sema3A-induced growth cone collapse of dorsal root ganglion neurons. Ectopically expressed a cytoplasmic deletion mutant of PTPδ in the neurons suppresses the response. Surprisingly, overexpression of a phosphatase inactive mutant of PTPδ, but not of wild-type PIPδ, interferes Sema3A-response in the neurons. COS-7 cells co-expressing NRP1 and PIPδ reduce the adhered area upon Sema3A stimulation. This response is completely abolished with the phosphatase inactive mutant of PTPδ. Neither LAR nor PTPσ mediate. the response. Furthermore, NRP1 is co-immunoprecipitated with PTPδ from mouse embryonic brain. These results suggest that the extracellular domains of PTPδ/σ insulate NRP1 from Sema3A binding while full-length PTPδ mediates Sema3A signaling via its phosphatase domains.