THE LOW-AFFINITY NGF RECEPTOR, P75, CAN COLLABORATE WITH EACH OF THE TRKS TO POTENTIATE FUNCTIONAL-RESPONSES TO THE NEUROTROPHINS

NGF and the other neurotrophins all bind to the low affinity NGF receptor (LNGFR). Although early studies suggested that the LNGFR was absolutely required for the formation of a functional neurotrophin receptor, current evidence indicates that the Trk family of receptor tyrosine kinases, in the absence of the LNGFR, can directly bind to and mediate responses to the neurotrophins. Here we describe a functional approach, in fibroblasts, designed to assay for the ability of the LNGFR to potentiate Trk-mediated responses to the neurotrophins. We report that although collaboration between the LNGFR and the Trks could be detected in this system, a truncated form of the LNGFR displayed a much more dramatic ability to interact functionally with each of the Trks, potentiating masked autocrine loops as well as responses to limiting amounts of exogenously provided neurotrophins.