Abstract 206: High mobility group A1(HMGA1) proteins localize at the mitochondria and inhibit the p53-mediated intrinsic-apoptotic pathway

Abstract

Abstract The high mobility group A (HMGA) non-histone chromosomal proteins play key roles in chromatin architecture and orchestrate the assembly of nucleoprotein complexes involved in gene transcription, replication, and chromatin structure. HMGA overexpression and gene rearrangements are frequent events in human cancer, but the molecular basis of HMGA oncogenic activity has not been completely elucidated. Recently, we have defined a new physical and functional interaction between HMGA1 and p53. This interaction modulates the transcription of p53 target genes such as Mdm2, p21waf1, Bax, Bcl-2, and inhibits p53-mediated apoptosis. Here we report that HMGA1 does not act only at transcriptional level but it has also a direct, anti-apoptogenic role at the mitochondria. In fact, we found that in mouse embryonic fibroblast (MEF) and several tumour cell lines overexpressing HMGA1, this protein is present at cytoplasmic level other than in the nucleus. Moreover, we demonstrate that HMGA1 stably localizes at the mitochondria, in which it binds Bcl-2, displacing it from the binding to p53, thus counteracting the release of cytochrome C. In agreement with this observation, the HMGA1-overexpressing cells show a significant reduction of cytochrome C release, after lethal dose of Ultraviolet (UV) light, whereas HMGA1-depleted cells are more susceptibile to UV treatment. These data define a new localization of HMGA1 at the mitochondria level that allows HMGA1 to inhibit by a new mechanism the p53-mediated intrinsic-apoptotic pathway. This mechanism may also have a role in the resistance of malignant cells to chemo- and radio-therapy, in particularly for the tumor cells harboring wild-type form of p53. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 206. doi:10.1158/1538-7445.AM2011-206