CHARACTERIZATION OF NEUROTROPHIN RECEPTORS BY AFFINITY CROSS-LINKING

Neurotrophic factors regulate the developmental survival and different iation of specific neuronal populations. Brain-derived neurotrophic fa ctor (BDNF) and neurotrophin-3 (NT-3) are members of the nerve growth factor (NGF) protein family, also known as the neurotrophins. Insights into the different roles of neurotrophins can be gained by studying t he expression of their functional receptors. Here we report the develo pment of procedures for their radiolabeling and efficient crosslinking to specific cell-surface receptors. BDNF and NT-3 receptors in cell l ines and tissue preparations expressing receptors for the 2 neurotroph ins have been identified using this affinity crosslinking procedure. L ike NGF, BDNF and NT-3 crosslinked to the low affinity NGF receptor (p 75NGFR) on PC12 cells. BDNF and NT-3 also crosslinked to cells express ing p145trkB protein, producing an approximately 160 kD neurotrophin-r eceptor complex. Crosslinking of the 2 neurotrophins in vivo to specif ic trk family members in many areas of the central nervous system also produced a 160 kD receptor complex. However, in all brain regions a c omplex of approx. 100 kD could also be identified, all or most of whic h represents crosslinking to a truncated form of trkB. The broad distr ibution of BDNF and NT-3 receptors throughout the CNS suggests that ne urotrophins may have yet unrecognized functions on specific neuronal p opulations. BDNF and NT-3 receptors were also found in brain areas in which the neurotrophins themselves are also synthesized, suggesting th at beyond long-range trophic effects, these proteins may also act as a utocrine or short-range paracrine regulators.