Abstract C08: Stability of hypoxia induced expression of colon cancer metastasis-associated genes
Authors: Flinders Colin , Liu Sonya , Mumenthaler Shannon 
Published: October 2016

Introduction: Metastasis is responsible for over 90% of cancer related mortality; however, somatic 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 is a component of the TME that arises due to improper vascular architecture, which leads to reduced oxygen delivery to tissues 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 or 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 metastasis, 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 cells migrate away from regions of low oxygen toward oxygen rich environments (e.g. 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 back to normoxic conditions. Gene expression changes were assessed during hypoxia adaptation and for 3 additional weeks following re-oxygenation.

Results: The continued expression of hypoxia induced genes following re-oxygenation varied greatly among those tested. Gene transcription associated with epithelial-to-mesenchymal transition (EMT) such as VIM and ZEB1 were induced by 3 weeks of hypoxic conditioning and remained elevated following their return to normoxic culturing conditions. However, in contrast, hypoxia induced genes involved in the Warburg effect such as PDK1 were induced during hypoxia, yet quickly returned to at or below basal levels following re-oxygenation.

Conclusion: Continued expression of hypoxia induced genes following re-oxygenation varies from gene to gene and from pathway to pathway. There appears to be some consistency in expression of genes following re-oxygenation that are involved in migration and invasion such as ZEB1. These results suggest that certain pathways such as EMT may be vital for the maintenance of the hypoxia induced metastatic phenotype as these cells transit from regions of low oxygen to regions of higher or normal oxygen levels.

Citation Format: Colin Flinders, Sonya Liu, Shannon Mumenthaler. Stability of hypoxia induced expression of colon cancer metastasis-associated genes. [abstract]. In: Proceedings of the AACR Special Conference: Function of Tumor Microenvironment in Cancer Progression; 2016 Jan 7–10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2016;76(15 Suppl):Abstract nr C08.