Valproic acid upregulates the expression of the p75NTR/sortilin receptor complex to induce neuronal apoptosis

Abstract

The antiepileptic and mood stabilizer agent valproic acid (VPA) has been shown to exert anti-tumour effects and to cause neuronal damage in the developing brain through mechanisms not completely understood. In the present study we show that prolonged exposure of SH-SY5Y and LAN-1 human neuroblastoma cells to clinically relevant concentrations of VPA caused a marked induction of the protein and transcript levels of the common neurotrophin receptor p75NTR and its co-receptor sortilin, two promoters of apoptotic cell death in response to proneurotrophins. VPA induction of p75NTR and sortilin was associated with an increase in plasma membrane expression of the receptor proteins and was mimicked by cell treatment with several histone deacetylase (HDAC) inhibitors. VPA and HDAC1 knockdown decreased the level of EZH2, a core component of the polycomb repressive complex 2, and upregulated the transcription factor CASZ1, a positive regulator of p75NTR. CASZ1 knockdown attenuated VPA-induced p75NTR overexpression. Cell treatment with VPA favoured proNGF-induced p75NTR/sortilin interaction and the exposure to proNGF enhanced JNK activation and apoptotic cell death elicited by VPA. Depletion of p75NTR or addition of the sortilin agonist neurotensin to block proNGF/sortilin interaction reduced the apoptotic response to VPA and proNGF. Exposure of mouse cerebellar granule cells to VPA upregulated p75NTR and sortilin and induced apoptosis which was enhanced by proNGF. These results indicate that VPA upregulates p75NTR apoptotic cell signalling through an epigenetic mechanism involving HDAC inhibition and suggest that this effect may contribute to the anti-neuroblastoma and neurotoxic effects of VPA.

Histone Deacetylases and Histone Deacetylase Inhibitors in Neuroblastoma

“…One suggested mechanism for the direct activation of apoptosis was the inverse regulation of pro-apoptotic and anti-apoptotic proteins, as combination treatments incorporating HDACi are known to increase the expression of caspases and Bid, and promote the inactivation of the anti-apoptotic proteins XIAP, Bcl-x, RIP, and survivin ( Muhlethaler-Mottet et al, 2006 ). Similarly, the ability of VPA to promote pro-apoptotic neutrophin receptor signaling by upregulating p75NTR and sortilin expression has been identified as an additional mechanism that leads to increased apoptosis of neuroblastoma cells ( Dedoni et al, 2020 ). Pro-nerve growth factor (proNGF) induced activation of p75NTR plays a key role in regulating the survival of neurons and process formation during early development, neuronal death in the developing and aging brain, as well as several neurodegenerative diseases ( Dechant and Barde, 2002 ; Schor, 2005 ).…”

“…Pro-nerve growth factor (proNGF) induced activation of p75NTR plays a key role in regulating the survival of neurons and process formation during early development, neuronal death in the developing and aging brain, as well as several neurodegenerative diseases ( Dechant and Barde, 2002 ; Schor, 2005 ). Prolonged exposure of SH-SY5Y cells to VPA further predisposed the cells to proNGF-induced cell death, triggering apoptosis through JNK-mediated caspase and PARP cleavage ( Dedoni et al, 2020 ). Additionally, studies evaluating the radiosensitization effect of HDACi also observed impairment of DNA repair mechanisms by downregulation of the DNA repair enzyme Ku-86 upon combination with vorinostat ( Mueller et al, 2011 ).…”

Upregulation of p75NTR by Histone Deacetylase Inhibitors Sensitizes Human Neuroblastoma Cells to Targeted Immunotoxin-Induced Apoptosis

“…Entinostat was also found to induce a greater enhancement of CASZ1 levels in SH-SY5Y, and LAN-1 cells. These findings suggest that the superior efficacy of entinostat in inducing p75NTR was the result of a greater action on the epigenetic machinery that controls the expression of the neurotrophin receptor in neuroblastoma cells [ 17 , 18 , 19 ]. The induction of p75NTR by entinostat occurred within a concentration range (0.1–1.0 µM) which correlated with the reported micromolar potency of the drug in inhibiting HDAC activity [ 31 ] and with the plasma concentrations that were required to produce anti-cancer effects in clinical trials [ 26 ].…”

“…Thus, the exposure to HDAC inhibitors caused the downregulation of TrkB expression and signaling [ 15 ], which promote neuroblastoma cell survival and aggressiveness [ 9 , 10 ], and the upregulation of the truncated isoform of TrkC that is associated with neurotrophin 3-induced apoptosis [ 16 ]. Moreover, the treatment of neuroblastoma cells with HDAC inhibitors upregulated the expression of the common neurotrophin receptor p75NTR and the co-receptor sortilin, thus allowing the execution of proNGF-induced cell death [ 17 ]. The induction of p75NTR expression by HDAC inhibitors has been shown to occur through an epigenetic mechanism involving depletion of the methyltransferase EZH2, a core component of the polycomb repressor complex 2, and the consequent derepression of the transcription factor CASZ1, a positive regulator of the NGFR gene, encoding for p75NTR [ 17 , 18 , 19 ].…”

“…Moreover, the treatment of neuroblastoma cells with HDAC inhibitors upregulated the expression of the common neurotrophin receptor p75NTR and the co-receptor sortilin, thus allowing the execution of proNGF-induced cell death [ 17 ]. The induction of p75NTR expression by HDAC inhibitors has been shown to occur through an epigenetic mechanism involving depletion of the methyltransferase EZH2, a core component of the polycomb repressor complex 2, and the consequent derepression of the transcription factor CASZ1, a positive regulator of the NGFR gene, encoding for p75NTR [ 17 , 18 , 19 ]. In addition, it has been reported that HDAC1 inhibition impairs the activity of a SP1/MIZ1/MYCN repression complex, which negatively control the NGFR promoter [ 20 ].…”