Abstract
BackgroundHistone deacetylation, a common hallmark in malignant tumors, strongly alters the transcription of genes involved in the control of proliferation, cell survival, differentiation and genetic stability. We have previously shown that HDAC1, HDAC2, and HDAC3 (HDAC1–3) genes encoding histone deacetylases 1–3 are upregulated in primary human hepatocellular carcinoma (HCC). The aim of this study was to characterize the functional effects of HDAC1–3 downregulation and to identify functionally important target genes of histone deacetylation in HCC.MethodsTherefore, HCC cell lines were treated with the histone deacetylase inhibitor (HDACi) trichostatin A and by siRNA-knockdown of HDAC1–3. Differentially expressed mRNAs were identified after siRNA-knockdown of HDAC1–3 using mRNA expression profiling. Findings were validated after siRNA-mediated silencing of HDAC1–3 using qRTPCR and Western blotting assays.ResultsmRNA profiling identified apoptotic protease-activating factor 1 (Apaf1) to be significantly upregulated after HDAC inhibition (HLE siRNA#1/siRNA#2 p < 0.05, HLF siRNA#1/siRNA#2 p < 0.05). As a component of the apoptosome, a caspase-activating complex, Apaf1 plays a central role in the mitochondrial caspase activation pathway of apoptosis. Using annexin V, a significant increase in apoptosis could also be shown in HLE (siRNA #1 p = 0.0034) and HLF after siRNA against HDAC1–3 (Fig. 3a, b). In parallel, caspase-9 activity was increased after siRNA-knockdown of HDAC1–3 leading to enhanced apoptosis after HDAC inhibition (Fig. 3c, d).ConclusionsThe present data show that siRNA-knockdown of HDAC1–3 plays a major role in mediating apoptotic response to HDAC inhibitors through regulation of Apaf1.
Highlights
Histone deacetylation, a common hallmark in malignant tumors, strongly alters the transcription of genes involved in the control of proliferation, cell survival, differentiation and genetic stability
Aiming to determine the influence of increased histone acetylation on mRNA expression in hepatocellular carcinoma (HCC), we investigated global mRNA expression by microarray analyses in HCC cell lines treated with specific small interfering RNA (siRNA) against HDAC1–3 for 48 h
Our studies demonstrate that HDAC1–3 play a major role in mediating apoptotic response to histone deacetylases (HDAC) inhibitors through direct regulation of apoptotic protease-activating factor 1 (Apaf1) in HCC
Summary
A common hallmark in malignant tumors, strongly alters the transcription of genes involved in the control of proliferation, cell survival, differentiation and genetic stability. We have previously shown that HDAC1, HDAC2, and HDAC3 (HDAC1–3) genes encoding histone deacetylases 1–3 are upregulated in primary human hepatocellular carcinoma (HCC). The aim of this study was to characterize the functional effects of HDAC1–3 downregulation and to identify functionally important target genes of histone deacetylation in HCC. Hepatocellular carcinoma (HCC) represents the fourth most common malignant tumor with more than 1 million persons affected per year worldwide [1, 2]. Epigenetic modifications are reversible and can be targeted by new drugs like DNA methyltransferase and HDAC inhibitor (HDACi), drugs that have shown efficacy in clinical phase I/II studies (http://www.clinicaltrials.gov) [10]. HDACi are found to have an anti-cancer function in many different tumors [11, 12]
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