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


METHODS
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).


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
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.
DiSCAFF&DFB Center, Università del Piemonte Orientale, Novara, Italy. condorelli@pharm.unipmn.it
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F
Condorelli
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I
Gnemmi
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Vallario
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AA
Genazzani
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PL
Canonico
D000107:Acetylation; D021581:Active Transport, Cell Nucleus; D000970:Antineoplastic Agents / Q000494:pharmacology* / Q000627:therapeutic use; D017209:Apoptosis / Q000187:drug effects; D002087:Butyrates / Q000494:pharmacology; D002453:Cell Cycle / Q000187:drug effects; D002454:Cell Differentiation / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D019008:Drug Resistance, Neoplasm / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology* / Q000627:therapeutic use; D056572:Histone Deacetylase Inhibitors; D006655:Histone Deacetylases / Q000378:metabolism; D006801:Humans; D008239:Lysine / Q000378:metabolism; D009447:Neuroblastoma / Q000188:drug therapy* / Q000201:enzymology / Q000235:genetics / Q000473:pathology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D014162:Transfection; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*; D015854:Up-Regulation; D014635:Valproic Acid / Q000031:analogs & derivatives / Q000494:pharmacology
D000970:Antineoplastic Agents; D002087:Butyrates; C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004791:Enzyme Inhibitors; D056572:Histone Deacetylase Inhibitors; D019253:Proto-Oncogene Proteins c-bcl-2; D034741:RNA, Small Interfering; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; D014635:Valproic Acid; D006655:Histone Deacetylases; D008239:Lysine; C004651:dipropylacetamide