Abstract 4521: Long term hypoxia induces stable overexpression of JUNB and the TGFβ pathway in colon cancer
Authors: Flinders Colin , Alwash Norah , Mumenthaler Shannon 
Published: July 2017

Introduction: Metastasis is responsible for over 90% of cancer related mortality, however mutations unique to the metastatic phenotype have yet to be identified. This raises the possibility that the metastatic phenotype is the result of a transcriptional profile adopted by cells of the primary tumor enabling them to spread to distal regions of the body. The tumor microenvironment (TME) is capable of influencing gene expression and cellular behavior. Hypoxia, low oxygen tension, is a component of the TME that arises due to improper tissue architecture and correlates with poor survival outcome. Stabilization of the transcription factor HIF-1α during hypoxia induces the expression of genes involved in metastasis through direct activation and through the alteration of the epigenome. However, upon re-oxygenation HIF-1α is degraded and can no longer induce expression of hypoxic responsive genes. During the metastatic process, cells that have adopted hypoxia induced metastatic behavior such as increased motility and invasiveness must transit through regions of normoxia on their way to metastatic colonization.

Hypothesis: As hypoxic cell migrate away from regions of low oxygen towards oxygen rich environments, such venous blood, genes induced by hypoxia would be expected to return to basal levels of expression. Those genes whose expression does not return to levels associated with normoxia, but instead remain elevated following re-oxygenation, may be crucial for maintaining the hypoxia induced metastatic phenotype.

Experimental Design: To study the stability of hypoxia induced gene expression alterations following re-oxygenation, colon cancer cell lines were grown under hypoxic conditions (1% O2) for up to 3 weeks and then transitioned to normoxic conditions (21% O2). RNA sequencing was used to assess changes in gene expression during hypoxia adaptation and for 3 more weeks following re-oxygenation.

Results: While the majority of genes whose expression was induced by hypoxia returned to basal levels following re-oxygenation, a subset of genes clustered in the TGF-β pathway remained at elevated levels. In particular the expression of JunB, a component of the AP-1 transcription factor, was induced by hypoxia and continued to remain overexpressed after return to normoxic growth conditions. Conclusion: Long term culturing of colon cancer cells in hypoxic conditions induces changes in gene expression that remain stable following return to normoxic growth conditions. We hypothesis that genes whose expression follows this pattern may be involved in the hypoxia induced metastatic phenotype. RNA-seq profiling of cells grown in hypoxic conditions for three weeks and then returned to normoxic growth conditions for an additional three weeks identified genes involved in the TGF-β pathway and in particular JunB that were induced by hypoxia and remained stable following return to normoxia.

Citation Format: Colin Flinders, Norah Alwash, Shannon Mumenthaler. Long term hypoxia induces stable overexpression of JUNB and the TGFβ pathway in colon cancer [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 4521. doi:10.1158/1538-7445.AM2017-4521