The role of protein tyrosine phosphatase δ in axon guidance

研究了脑信号蛋白3A（Sema 3A）信号通路与LAR类蛋白酪氨酸磷酸酶（LAR、PTPδ和PTPσ）的关系。我发现PTPδ和PTPσ的胞外域与神经纤毛蛋白1（NRP 1）结合，但LAR不与之结合。利用碱性磷酸酶（AP）融合蛋白，测定了胞外结构域PTPδ/σ的结合常数。AP-PTPδ和AP-PTPσ与NRP 1结合，Kd值分别为1.1nM和1.9nM。在相同条件下，AP-Sema 3A与NRP 1结合的Kd为0.19nM。PTPδ/σ的第一个免疫球蛋白结构域与NRP 1的CUB结构域结合，该结构域是Sema 3A的结合位点。PIPδ/σ的胞外结构域抑制Sema 3A诱导的背根神经节神经元生长锥塌陷。在神经元中异位表达PTPδ的胞质缺失突变体抑制反应。令人惊讶的是，PTPδ磷酸酶失活突变体的过表达，而不是野生型PIPδ，干扰神经元中的Sema 3A反应。共表达NRP 1和PIPδ的COS-7细胞在Sema 3A刺激后减少粘附面积。这种反应被PTPδ的磷酸酶失活突变体完全消除。LAR和PTPσ均不介导。的反应。此外，NRP 1与来自小鼠胚脑的PTPδ免疫共沉淀。这些结果表明PTPδ/σ的胞外结构域使NRP 1与Sema 3A结合隔离，而全长PTPδ通过其磷酸酶结构域介导Sema 3A信号传导。

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.