Molecular interactions between neurotrophin receptors.

Neurotrophins signal via a dual-receptor system comprising receptor tyrosine kinases, the Trks, and a tumor necrosis factor (TNF) receptor like molecule, p75. Interest in these receptors was spurred on by the finding that they are employed by their neurotrophin ligands to activate opposing cellular mechanisms. Signalling via Trk receptors promotes the survival of embryonic neurons, whereas activation of p75 can trigger apoptosis. However, this antagonistic view is an oversimplification. It is more accurate to refer to this system as a signalling network in which ligands, receptors and their intracellular target proteins are linked by balanced biochemical interactions. This article reviews recent advances in our understanding of these molecular mechanisms which critically determine many cell-type-specific responses to neurotrophins. Emphasis is given to the formation of receptor complexes, the generation of receptor diversity by alternative splicing and the influence exerted by the local membrane environment on neurotrophin signalling.