BackgroundThe BRM and BRG1 tumor suppressor genes are mutually exclusive ATPase subunits of the SWI/SNF chromatin remodeling complex. The human adrenal carcinoma SW13 cell line can switch between a subtype which expresses these subunits, SW13+, and one that expresses neither subunit, SW13-. Loss of BRM expression occurs post-transcriptionally and can be restored via histone deacetylase (HDAC) inhibition. However, most previously used HDAC inhibitors are toxic and broad-spectrum, providing little insight into the mechanism of the switch between subtypes. In this work, we explore the mechanisms of HDAC inhibition in promoting subtype switching and further characterize the oncogenic potential of the two epigenetically distinct SW13 subtypes.MethodsSW13 subtype morphology, chemotaxis, growth rates, and gene expression were assessed by standard immunofluorescence, transwell, growth, and qPCR assays. Metastatic potential was measured by anchorage-independent growth and MMP activity. The efficacy of HDAC inhibitors in inducing subtype switching was determined by immunofluorescence and qPCR. Histone modifications were assessed by western blot.ResultsTreatment of SW13- cells with HDAC1 inhibitors most effectively promotes re-expression of BRM and VIM, characteristic of the SW13+ phenotype. During treatment, hyperacetylation of histone residues and hypertrimethylation of H3K4 is pronounced. Furthermore, histone modification enzymes, including HDACs and KDM5C, are differentially expressed during treatment but several features of this differential expression pattern differs from that seen in the SW13- and SW13+ subtypes. As the SW13- subtype is more proliferative while the SW13+ subtype is more metastatic, treatment with HDACi increases the metastatic potential of SW13 cells while restoring expression of the BRM tumor suppressor.ConclusionsWhen compared to the SW13- subtype, SW13+ cells have restored BRM expression, increased metastatic capacity, and significantly different expression of a variety of chromatin remodeling factors including those involved with histone acetylation and methylation. These data are consistent with a multistep mechanism of SW13- to SW13+ conversion and subtype stabilization: histone hypermodification results in the altered expression of chromatin remodeling factors and chromatin epigenetic enzymes and the re-expression of BRM which results in restoration of SWI/SNF complex function and leads to changes in chromatin structure and gene expression that stabilize the SW13+ phenotype.Electronic supplementary materialThe online version of this article (doi:10.1186/s12885-016-2353-7) contains supplementary material, which is available to authorized users.

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HDAC (histone deacetylase) enzymes are highly expressed in cancer cells and HDAC inhibitors have shown promise in clinical trials for certain patients in multiple types of cancer. In this context, the ability of the SW13 human adrenal adenocarcinoma line to switch between two well-established subtypes in response to HDAC inhibition is of interest. However, the previously characterized inhibitor (trichostatin A) is a toxic, broad-spectrum inhibitor affecting both class I and class II HDACs which have roles in the nucleus and cytosol, respectively. Multiple HDAC inhibitors are screened for their ability induce switching between the SW13 subtypes to identify which HDAC enzyme is necessary for controlling SW13 subtype switching. Results suggest that inhibition of class I HDAC1 increases the rate of conversion between SW13- to SW13+ cells. The effect of HDAC1 inhibition may be enhanced by HDAC3 inhibition as MS-275, an inhibitor specific for HDAC1 but with some specificity for HDAC3, is most effective, particularly when compared to the efficacy of depudecin, an HDAC1 specific inhibitor. After conversion to SW13+, there is increased acetylation on histone H3 but not histone H4 when compared to levels in SW13-, suggesting that the role of acetylation on the H3 tail plays an essential role in the subtype switch. SW13- cells do not express Brg1 or Brm, the mutually exclusive ATPase subunits of the SWI/SNF complex, and do not have an active SWI/SNF complex. Altered activity of this complex and the increased histone H3 acetylation may contribute to the extensive changes in gene expression observed between SW13+ and SW13- subtypes. Citation Format: Jessica M. Lam, Juliane Daggett, Kathryn J. Leyva, Elizabeth E. Hull. Inhibition of HDAC1 leads to subtype switching in the SW13 adrenal adenocarcinoma line. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5141. doi:10.1158/1538-7445.AM2014-5141