Nerve growth factor signaling in caveolae-like domains at the plasma membrane

Nerve growth factor (NGF) binding to its receptors TrkA and p75(NTR) enhanc es the survival, differentiation, and maintenance of neurons. Recent studie s have suggested that NGF receptor activation may occur in caveolae or cave olae-like membranes (CLM). This is an intriguing possibility because caveol ae have been shown to contain many of the signaling intermediates in the Tr kA signaling cascade. To examine the membrane localization of TrkA and p75N TR, We isolated caveolae from 3T3-TrkA-p75 cells and CLM from PC12 cells. I mmunoblot analysis showed that TrkA and p75NTR were enriched about 13- and 25-fold, respectively, in caveolae and CLM. Binding and cross-linking studi es demonstrated that the NGF binding to both TrkA and p75NTR was considerab ly enriched in CLM and that about 90% of high affinity binding to TrkA was present in CLM. When PC12 cells were treated with NGF, virtually all activa ted (i.e. tyrosine phosphorylated) TrkA was found in the CLM. Remarkably, i n NGF-treated cells, it was only in CLM that activated TrkA was coimmunopre cipitated with phosphorylated Shc and PLC gamma. These results document a s ignaling role for TrkA in CLM and suggest that both TrkA and p75(NTR) Signa ling are initiated from these membranes.