Poster Presentation 25th Lorne Cancer Conference 2013

Apoptotic sensitivity of tumour cells to HDACi is determined by sustained induction of the immediate-early genes Jun and Atf3. (#147)

Anderly C Chueh 1 , Lars Togel 1 , Ian Y Luk 1 , Janson Tse 1 , Matthew R Thompson 2 , Bryan R Williams 2 , John M Mariadason 1
  1. Ludwig Institute for Cancer Research, Heidelberg, VIC, Australia
  2. Monash Institute of Medical Research, Clayton, VICTORIA, Australia

Background/Aim: Histone deacetylase inhibitors (HDACi) are a novel class of cancer therapeutics approved for the treatment of cutaneous T-cell lymphoma (CTCL). We have previously established that sensitivity of colon cancer cells to HDACi is linked to induction of immediate-early (IE) gene expression. The aim of this study was to investigate whether HDACi also induce IE gene expression in other tumour types and to elucidate the mechanism by which induction of IE genes triggers apoptosis.

Methods: Apoptotic sensitivity to HDACi was determined in 50 cell lines derived from all major solid and haematological cancers, including CTCL. Apoptotic response was determined 72hr post drug treatment by measuring the sub-G1 cell population by PI staining and FACS analysis. Changes in IE gene expression were determined by Q-RT-PCR. Gene knockdown was achieved by transient transfection of siRNAs using Lipofectamine or Amaxa Nucleofector.

Results: HDACi treatment induced IE gene expression in cell lines derived from multiple tumour types and the magnitude of IE gene induction (Fos, Jun and Atf3) correlated positively with apoptosis induction across the cell line panel. HDACi-induced IE gene expression was evident 2hr post treatment and sustained over 24hr. Down-regulation of Jun and Atf3 attenuated HDACi-induced apoptosis in multiple cancer cell lines and Jun and Atf3 knockout MEFs were significantly less sensitive to HDACi compared to matched wild-type cells. Downstream transcriptional targets of Jun and Atf3 were identified by Q-RT-PCR using primers targeting a panel of well-characterized pro- and anti-apoptotic genes from both the intrinsic and extrinsic apoptotic pathways. Combining HDACi with the BCL2/BCL-xL inhibitor ABT-737, or the death receptor agonist TRAIL, resensitized resistant cell lines to HDACi-induced apoptosis.

Conclusions/Significance: Sustained induction of IE genes is a consistent transcriptional response induced by HDACi in multiple tumour types. Jun and Atf3 induction are functionally important in HDACi-mediated apoptosis, which acts via the transcriptional regulation of downstream apoptotic genes. This represents a novel transcriptional mechanism of apoptosis induction in response to a targeted therapy, which may facilitate biomarker discovery and the clinical use of these agents.