P75(LNTR) - AN ENIGMATIC NEUROTROPHIN RECEPTOR

The neurotrophins (NGF, BDNF, NT-3, 4/5 et 6) control the proliferatio n, differentiation and survival of neurons. They bind to two types of receptors : a specific member of the Trk family of receptor tyrosine k inases and the p75(LNTR), Or low-affinity neurotrophin receptor, capab le of binding all the neurotrophins. The p75(LNTR) belongs to a family of transmembrane molecules which includes TNFR (tumor necrosis factor receptors) and the human antigene Fas. Accumulating evidence suggests that Trk is a functionally important neurotrophin receptor, whereas t he function of p75(LNTR) remains enigmatic. The first studies showed t hat p75(LNTR) controls the activity of Trk and participates in retrogr ade axonal transport. Some recent data obtained in systems without Trk allow to assign two specific functions to p75(LNTR): stimulation of S chwann cell migration involving the activation of NF kappa B and induc tion of apoptosis involving tile production of ceramide. While p75(LNT R) has long been overshadowed by Trk, it appears in fact to be an esse ntial mediator of neurotrophin action.