The anti-p75 antibody, MC192, and brain-derived neurotrophic factor inhibit nerve growth factor-dependent neurite growth from adult sensory neurons

We have investigated nerve growth factor-dependent neurite growth from adul t sensory neurons using the compartmented culture system. The requirement o f both TrkA and the p75 neurotrophin receptors in neurite growth was examin ed using several experimental interventions. Inhibition of TrkA activation using K252a resulted in a total block of distal neurite extension into nerv e growth factor-containing compartments. Brain-derived neurotrophic factor and the anti-p75 monoclonal antibody MC192 have been shown to interfere wit h the binding of nerve growth factor to p75. Brain-derived neurotrophic fac tor, which binds p75 but not TrkA, competes with nerve growth factor for p7 5, while the anti-p75 antibody MC192 has been shown to decrease the interac tion of nerve growth factor with TrkA. The addition of brain-derived neurot ophic factor to nerve growth factor-containing distal compartments inhibite d, but did not totally block, distal neurite extension. MC192, on the other hand, totally inhibited nerve growth factor-dependent neurite growth. To t est whether MC192 and brain-derived neurotrophic factor might be influencin g Trk activation, TrkA phosphorylation was examined biochemically. Both com pounds were found to attenuate nerve growth factor induced Trk phosphorylat ion, although neither inhibited the activation completely. The possibility that MC192 or brain-derived neurotrophic factor might activate p75 signalin g directly (and potentially antagonize TrkA signaling) was also investigate d. This was assessed by quantitating the activation and nuclear translocati on of the transcription factor NFkB using immunocytochemistry. Only treatme nt with the anti-p75 antibody MC192 resulted in prolonged and significant i ncrease in the number of neurons displaying nuclear staining for NFkB. Our results demonstrate that both TrkA and p75 play a role in neurite growt h response to nerve growth factor, and further suggest that any alteration in optimal TrkA-p75 interactions, or direct activation of p75 at the expens e of TrkA, results in an inhibition of nerve growth factor-dependent neurit e growth in adult sensory neurons. (C) 1999 IBRO. Published by Elsevier Sci ence Ltd.