Myelin-associated glycoprotein (MAG), an inhibitor of axon regeneration, binds with high affinity to the Nogo-66 receptor (NgR). Here we report that the p75 neurotrophin receptor (p75NTR) is a coreceptor of NgR for MAG signaling. In cultured human embryonic kidney (HEK) cells expressing NgR, p75NTR was required for MAG-induced intracellular Ca2+ elevation. Co-immunoprecipitation showed an association of NgR with p75NTR that can be disrupted by an antibody against p75NTR (NGFR5), and extensive coexpression was observed in the developing rat nervous system. Furthermore, NGFR5 abolished MAG-induced repulsive turning of Xenopus axonal growth cones and Ca2+ elevation, both in neurons and in NgR/p75NTR-expressing HEK cells. Thus we conclude that p75NTR is a co-receptor of NgR for MAG signaling and a potential therapeutic target for promoting nerve regeneration.
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