Interferon-β Inhibits Neurotrophin 3 Signalling and Pro-Survival Activity by Upregulating the Expression of Truncated TrkC-T1 Receptor

Although clinically useful for the treatment of various diseases, type I interferons (IFNs) have been implicated as causative factors of a number of neuroinflammatory disorders characterized by neuronal damage and altered CNS functions. As neurotrophin 3 (NT3) plays a critical role in neuroprotection, we examined the effects of IFN-beta on the signalling and functional activity of the NT3/TrkC system. We found that prolonged exposure of differentiated human SH-SY5Y neuroblastoma cells to IFN-beta impaired the ability of NT3 to induce transphosphorylation of the full-length TrkC receptor (TrkC-FL) and the phosphorylation of downstream signalling molecules, including PLC gamma 1, Akt, GSK-3 beta and ERK1/2. NT3 was effective in protecting the cells against apoptosis triggered by serum withdrawal or thapsigargin but not IFN-beta. Prolonged exposure to the cytokine had little effects on TrkC-FL levels but markedly enhanced the messenger RNA (mRNA) and protein levels of the truncated isoform TrkC-T1, a dominant-negative receptor that inhibits TrkC-FL activity. Cell depletion of TrkC-T1 by small interfering RNA (siRNA) treatment enhanced NT3 signalling through TrkC-FL and allowed the neurotrophin to counteract IFN-beta-induced apoptosis. Furthermore, the upregulation of TrkC-T1 by IFN-beta was associated with the inhibition of NT3-induced recruitment of the scaffold protein tamalin to TrkC-T1 and tamalin tyrosine phosphorylation. These data indicate that IFN-beta exerts a negative control on NT3 pro-survival signalling through a novel mechanism involving the upregulation of TrkC-T1.