Abstract 447: Hypoxia upregulates Nodal expression via the HIF-1 pathway in poorly metastatic breast cancer cells

Abstract

Abstract Low tumour oxygen levels (hypoxia) are associated with a poor clinical prognosis for breast cancer patients. The acquisition of a plastic, stem cell-like phenotype is similarly associated with resistance to therapy and increased metastatic potential. Recent studies have demonstrated that metastatic breast cancer cells express the embryonic stem cell factor Nodal, and that the expression of this protein is correlated with breast cancer progression. Our research establishes that hypoxia induces Nodal expression in poorly metastatic breast cancer cells. The effects of hypoxia on Nodal expression in poorly metastatic MCF-7 and T47D breast cancer cells, which do not endogenously express Nodal, were examined by exposing cells to decreasing concentrations of oxygen (20%-0.5%) for varying amounts of time (0 h - 48 h). Additionally, reoxygenation experiments were performed by exposing cells to 0.5% oxygen for 24 h and restoring them to 20% oxygen for 0 h - 6 days. Time course and dose response experiments determined that T47D cells exposed to 0.5% oxygen for 48 hours saw a maximal (1.5 fold) induction of Nodal mRNA expression and marked increase in protein levels. This expression persisted for up to 6 days with reoxygenation at 20% oxygen. The molecular mechanism underlying the hypoxic induction of Nodal expression was examined by investigating the role of the HIF-1 pathway. HIF-1α expression was knocked down with siRNA and cells exposed to 0.5% oxygen, and conversely, HIF-1α was over-expressed and cells exposed to 20% oxygen. The HIF-1α-specific siRNA returned Nodal expression to control levels in hypoxia and over-expression of HIF-1α elicited an upregulation of Nodal expression in normoxic conditions. This work reveals a mechanism by which a normally stem cell-associated factor can be upregulated by hypoxia in poorly metastatic breast cancer cells. Furthermore, it provides additional insight into the oxygen-mediated regulation of cancer cell plasticity and metastatic potential. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 447.