Inhibitors of histone deacetylase (HDAC) restore the p53 pathway in neuroblastoma cells

Abstract

Background and purpose: Inhibitors of histone deacetylase (HDAC) are emerging as a promising class of anti-cancer drugs, but a generic deregulation of transcription in neoplastic cells cannot fully explain their therapeutic effects. In this study we evaluated alternative molecular mechanisms by which HDAC inhibitors could affect neuroblastoma viability. Experimental approach: Effects of HDAC inhibitors on survival of the I-type SK-N-BE and the N-type NB SH-SY5Y neuroblastoma cell lines were assessed by the MTT assay. Molecular pathways leading to this were examined by western blot, confocal microscopy and cytofluorometry. The mRNA levels of apoptotic mediators were assessed semi-quantitatively by RT-PCR. Tumour-suppressor p53 trans activity was assessed in EMSA experiments. HDAC inhibitors were also studied in cells subjected to plasmid-based p53 interference (p53i). Key results: HDAC inhibitors induced cell death via the mitochondrial pathway of apoptosis with recruitment of Bcl-2 family members. Bcl-2 overexpression rendered neuroblastoma cells resistant to HDAC inhibitor treatment. Low concentrations of HDAC inhibitors (0.9 mM) caused a G 2 cell-cycle arrest and a marked upregulation of the p21/Waf1/Cip1 protein. HDAC inhibitors also activate the p53 protein via hyper-acetylation and nuclear re-localization, without affecting its protein expression. Accordingly, HDAC inhibitor-induced cell-killing and p21/Waf1/Cip1 upregulation is impaired in p53i-cells. Conclusions and implications:In neuroblastoma cells, HDAC inhibitors may overcome the resistance to classical chemotherapeutic drugs by restoring the p53 tumour-repressor function via its hyper-acetylation and nuclear migration, events usually impaired in such tumours. In neuroblastoma cells, HDAC inhibitors are not able to induce p21/Waf1/Cip1 in the absence of a functional p53.

Epigenetics and ncRNAs in Brain Function and Disease: Mechanisms and Prospects for Therapy

“…Similarly both DNA methyltransferase inhibitors and HDAC inhibitors can cause apoptosis through p53 activation. In the case of epigenetic therapies for neurodegenerative disorders, which require long-term treatment, this p53 activation could lead to increased loss of neurons and thereby exacerbate pathology [106]. Consequently, off-target effects induced by epigenetically active small molecule pharmaceuticals must be considered carefully.…”

“…RITS also includes the histone deacetylase, HDAC1, the histone methyltransferases SUV39H1 and EZH2 [108], and the DNA methyltransferase DNMT3A. AGO1 facilitates the interaction between the small RNA effector and the promoter-associated RNA target [106]. Subsequently, recruitment of RITS induces heterochromatin formation and promoter DNA methylation at the target promoter.…”

EGR1 reactivation by histone deacetylase inhibitors promotes synovial sarcoma cell death through the PTEN tumor suppressor

“…Interestingly, we noticed a clear increase in C-terminal modifications of p53 after addition of romidepsin (data not shown). In fact, six lysine residues have been identified at the Cterminus of human p53, all of which can be acetylated by many HDAC inhibitors (Zhao et al, 2006;Roy and Tenniswood, 2007;Condorelli et al, 2008). Growing evidence suggests that acetylated p53 physically associates with EGR1, which in turn enhances the stability and transcriptional activation capacity of p53 (Liu et al, 2001;Habold et al, 2008).…”

Recurrent Neuroblastoma

“…HDAC inhibition leads to histone acetylation, opening of chromatin structure, and reactivation of previously silenced genes (Johnstone, 2002). In NB, HDAC inhibitors have been shown to induce apoptosis and impair VEGF production (MuhlethalerMottet et al, 2008), restore the p53 pathway (Condorelli et al, 2008), synergize with retinoic acid to inhibit growth (Coffey et al, 2001), and enhance RT (S. Mueller et al, 2011). In a phase I trial of vorinostat, one CR was observed in a NB patient receiving vorinostat in combination with 13-cis-retinoic acid (Fouladi et al, 2010).…”