Abstract 428: HIC-1: A gene silenced in cancer stem cells of glioma

Abstract

Abstract Background : According to the cancer stem cell hypothesis, tumors contain and are driven by a minority cellular population which has retained or re-established key stem-cell properties. Studies have demonstrated frequent hypermethylation of the HIC-1 locus in human cancers and recent work has demonstrated hypermethylation of HIC-1 in ES cells. Targeted methylation of HIC-1 has been shown to transform mesenchymal stem cells into cancer stem/initiating cells. However, so far no study has established the epigenetic role/status of HIC-1 in cancer stem cells. Methods and Results: U87MG, a glioblastoma cell line, showed a consistent decrease of HIC-1 expression in gliomaspheres obtained in Stem cell media compared to same tumor cells grown in normal media. To examine for the role of HIC-1 in regulating stemness (Sox-2, Oct-4, Nanog), we established a U87 cell line with dominant negative p53 (dn-U87) expressing low HIC-1 levels. Increase in expression of stemness markers was observed in dn-U87 compared to wt-U87.Moreover,effect of hypoxia in increasing stemness was more pronounced in the dn-U87 cell line. Knockdown of HIC-1 in U87MG grown in normal or stem cell media exhibited an increase in expression of stemness markers (Sox2, Oct4, Nanog and Nestin) under both conditions compared to Mock and control, further confirming role of HIC-1 in modulating stemness expression . Also, gliomaspheres were obtained much earlier (i.e. on Day 4) in HIC-1 knockdown samples grown in stem cell media compared to both Mock and Control (Day7). To look for the difference in epigenetic signature of HIC-1 gene between gliomaspheres and tumor cells, we checked for changes in methylation and chromatin accessibility in the two cell populations. MNAse assay ascertained heterochromatization of the HIC-1 promoter in gliomaspheres compared to normal U87 cells, while bisulfite sequencing or High Resolution Melt PCR could not detect any change in methylation pattern of the HIC-1 promoter in the two cell populations studied. Interpretation and Conclusion: Down-regulation of HIC-1, by i) epigenetic changes or ii) knockdown by siRNA or iii) using mutant p53 cell line, may be responsible for contributing to stem cell-like properties to tumor cells. Since HIC-1 is a tumor suppressor gene silenced in many cancers as a result of promoter hypermethylation, it could by itself be a new target for epigenetic therapy. Moreover, increase in stemness on knockdown of HIC-1 could provide new insights into the behavior of cancer-initiating stem cells. Citation Format: Mohita Bhagat, Subrata Sinha, Parthaprasad Chattopadhyay. HIC-1: A gene silenced in cancer stem cells of glioma. [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 428. doi:10.1158/1538-7445.AM2014-428