Abstract 2847: Loss of heterozygosity (LOH) within the hypoxia inducible factor 3A (HIF3A) locus in liver metastasis (LM) from primary colorectal cancer (CRC)

Abstract

Abstract Background and Aims: HIF3α is a hypoxia-regulated transcription factor that represses the effects of HIF1α and HIF2α under hypoxia at transcriptional and posttranslational levels. We previously found that LOH at the HIF3A locus is frequent in LM (59%) and the expression of HIF3A protein is reduced in LM compared to primary CRC. At present, the smallest overlapping LOH (SOL-LOH) region has been mapped to the intron 8 of the HIF3A, spanning from 46,312,911 to 46,315,651 on chromosome 19 in LMs. This genomic region contains multiple FOXA1 binding sites embedded in the two DNase I hypersensitive sites (UCSC Genome Browser, https://genome.UCSC.edu). About 30% of the human population carries a deletion within our SOL-LOH region (1000 Genomes Consortium: esv3644527, Chr19: 46,314,109-46,315,478). In this study, we determined whether esv3644527 deletion affects on the expressions of HIF3A, HIF2A, HIF1A and their target genes under normoxic and hypoxic conditions. Methods: For LOH mapping, 75 resected LMs derived from primary CRC were analyzed for LOH using 8 polymorphic markers. We obtained three EBV-transformed B cell lines with heterozygous esv3644527 deletion and the one with the homozygous deletion from the Coriell Institute. The expression levels of 23 genes related to HIF pathways were determined by qRT-PCR. Results and Discussion: The expression levels of HIF3A mRNA were too low to compare among these B cell lines by qRT-PCR. However, the expression levels of HIF2A and its target gene, angiopoietin 2 (ANGPT2), are significantly elevated in B cells with a homozygous deletion compared to B cells with a heterozygous deletion under both normoxic and hypoxic conditions. These observations are compatible with the results obtained from a previous study where pulmonary endothelial cells from HIF3A-knockout mice expressed elevated levels of HIF2A and ANGPT2 (Kobayashi-S et al., Genes Cells, 2015, 20:224-241), suggesting that deletion of the FOXA1 sites present in this region may regulate the HIF3A expression. Conclusions: Our results show that about 60% of LMs exhibit LOH in the 2.7 Kb region surrounding intron 8 of the HIF3A locus. Deletion within this region may lead to upregulation of HIF2A and ANGPT2 by negatively regulating HIF3A expression. To prove our hypothesis, colon cancer cell lines with deleted FOXA1 sites will be assessed. Citation Format: Takahito Kitajima, Minoru Koi, Alexander Worix, John M. Carethers. Loss of heterozygosity (LOH) within the hypoxia inducible factor 3A (HIF3A) locus in liver metastasis (LM) from primary colorectal cancer (CRC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2847. doi:10.1158/1538-7445.AM2017-2847