Nerve growth factor-induced protein kinase C stimulation contribute to TrkA-dependent inhibition of p75 neurotrophin receptor sphingoliplid signaling

Previous studies have established that reciprocal interactions between the low-affinity p75 nerve growth factor (NGF) receptor (p75^NTR) and the high-affinity TrkA NGF receptor can dictate the cellular response to NGF. As the most important interaction, TrkA signaling was found to inhibit p75 ^NTR-mediated sphingomyelinase (SMase) stimulation, ceramide production, and apoptosis. However, the mechanism by which TrkA counteracts p75^NTR- coupled sphingolipid signaling is still unclear. Considering the stimulatory effect of NGF on protein kinase C (PKC) activity, we investigated the role of PKC in TrkA/p75^NTR signaling interaction. In this study, we found that, in SK-N-BE cells, which selectively express p75 ^NTR, phorbol ester-induced PKC stimulation resulted in the abrogation of SMase stimulation and ceramide production induced by NGF. Moreover, in SK-N-BE neuroblastoma cells, which selectively express TrkA, NGF stimulated global PKC activity through two independent pathways involving phospholipase C-γ (PLC-γ) and phosphoinositide-3 kinase (PI3K). In SH-SY5Y, another neuroblastoma cell line, which coexpresses TrkA and p75^NTR, NGF induced PKC stimulation through a TrkA/PI3K signaling pathway, whereas there was no ceramide production. However, in these cells, the inhibition of TrkA, PI3K, and PKC resulted in the restoration of NGF-induced ceramide production. Thus, our study demonstrates for the first time that TrkA interferes with p75^NTR signaling through a PI3K/PKC-dependent mechanism.