Abstract 4085: The roles of HDACs in chromatin remodelling and response to chemotherapy in cancer

Abstract

Abstract Background: Chromatin is dynamic in higher-order structure in response to extracellular and environmental signals. We observed nuclear morphological changes in clinical cancer tissues after chemotherapy. Since chromatin structure dictates gene expression, and therefore function, further investigation of this phenomenon may help us to better understand therapeutic responses. We hypothesise that nuclear morphological changes in cancer in response to DNA-damage by chemotherapy are mediated by histone deacetylases (HDACs). Methods: Ovarian cancer cell lines PEO1/PEO4 (platinum sensitive/resistant) were selected as in vitro models, and primary ovarian cancer xenografts OV1002 and HOX424 as in vivo models. Expression levels of HDACs and heterochromatin protein 1 (HP1) were screened by reverse phase protein array (RPPA) and western blot after treatment with cisplatin. Immunofluorescence imaging was undertaken using confocal microscopy and nuclear texture was measured in Image J using GLCM texture analysis plugin. 38 ovarian cancer patient and 175 xenograft samples were assessed for HDAC and HP1 expression in response to chemotherapy by quantitative immunofluorescence. HDAC2 expression was modulated by interfering RNAs (siRNA). Results: We demonstrate nuclear morphological changes in clinical tumours, xenografts, and cell lines in response to platinum chemotherapy. HDACs and HP1 isoforms showed differential expression in a panel of 25 ovarian cancer cell lines associated with response to chemotherapy with increased expression in treated or resistant lines. Expression of HDACs increased in PEO1 cells treated with cisplatin in a time-dependent fashion. This was accompanied by quantifiable changes in nuclear texture (increased heterogeneity), and high expression of HP1s at early time point (4-24h). The proliferation of PEO1 cells was inhibited and HP1 protein expression decreased after HDAC2 knockdown. In clinical specimens, HDAC8 and HP1 gamma expression significantly increased after chemotherapy, and class I HDAC (1, 2, and 8) and HP1 expression were increased after carboplatin treatment in carboplatin-sensitive xenografts. Chromatin conformation, DNA damage response, and cell cycle progression showed sequential changes over time with carboplatin treatment. Conclusion: These results demonstrate alterations in chromatin structure after chemotherapy, and implicate the role of class I HDACs in higher order chromatin changes and the DNA damage response in ovarian cancer in vitro and in vivo. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4085. doi:1538-7445.AM2012-4085