Valproic Acid Upregulates The Expression of The Neurotrophin Receptor TrkC in Human Neuroblastoma Cells

Abstract

Preclinical and clinical studies have shown that the Trk receptors of neurotrophic factors play an important role in regulating the biological properties and the clinical evolution of neuroblastoma, the most frequent extracranial solid tumor in childhood. We have recently reported that treatment of retinoic acid (RA)‐differentiated human neuroblastoma cells with valproic acid (VPA) and other histone deacetylase (HDAC) inhibitors downregulates the expression and signaling of the BDNF receptor TrkB, a marker of unfavorable and aggressive neuroblastoma. In the present study we report that VPA, at therapeutically relevant concentrations, upregulates the expression of the neurotrophin 3 receptor TrkC in undifferentiated and RA‐differentiated SH‐SY5Y neuroblastoma cells. The exposure to VPA markedly increased the TrkC mRNA and the levels of the full length and truncated forms of TrkC protein. This change was associated with enhanced expression of TrkC at the plasma membrane, as indicated by cell surface biotinylation experiments and immunofluorescence assays in non permeabilized cells. The upregulation of TrkC was time‐dependent, being evident after 24 h of drug addition, and was accompanied by the emergence of apoptotic cell death. VPA increased the levels of the transcription factor RUNX3, a positive regulator of the NTRK3 gene encoding TrkC, and inhibition of this response by siRNA treatment attenuated the upregulation of TrkC. Moreover, pharmacological blockade of either ERK1/2 or JNK, but not p38MAPK, signaling pathways reduced VPA‐induced TrkC expression. VPA was found to induce TrkC also in MYCN‐amplified BE(2)C, NB‐1 and Kelly neuroblastoma cells and its effect was mimicked by other HDAC inhibitors, such as romidepsin and entinostat. These data indicate that VPA upregulates TrkC by activating a transcriptional programme involving epigenetic changes and MAPK signaling. As the expression of TrkC has been associated with a favorable outcome in neuroblastoma, the upregulation of this neurotrophin receptor may constitute an important component of the antineuroblastoma activity of VPA.Support or Funding InformationSardegna Ricerche‐Progetto IBERNAT‐NBL P.O.R. Sardegna 2014–2020, CUP F21B17000730005.