Hypoxia stimulates an increase of Neuropeptide Y Y1 and Y5 receptor expression in human breast cancer cells

Abstract

A hypoxic microenvironment is a common physiological attribute in solid tumors. Low O2 in tumors promotes a malignant phenotype, associated with increased proliferative, angiogenic and metastatic potential. Accumulating evidence suggests that neuroendocrine factors and their corresponding receptors may contribute to the initiation, development and progression of various cancers. Neuropeptide Y (NPY) and its receptors have been implicated as such a factor in the progression of breast cancer. Previous studies have reported the expression of the Y1R and Y5R receptor subtypes in human breast cancer cells and tumors. We have demonstrated that in breast cancer cells, NPY stimulation of Y5R increased proliferation and migration, and induced the release of vascular endothelial growth factor. In the current study, we examined the effects of O2 concentration on NPY receptor expression in MCF‐7 and MDA‐MB‐231 cells. Using quantitative PCR (qPCR) and Western blot, we compared Y1R and Y5R mRNA and protein expression in cells exposed to 1% (hypoxia) and 21% (normoxia) O2. Y1R and Y5R mRNA was quantified after 1h, 3h, 6h, 12h and 24h of hypoxia. Relative to normoxic cells, we observed a significant increase in Y1R and Y5R mRNA after 3h's of hypoxia in both cell lines. Protein expression of Y1R and Y5R was examined after a 24h hypoxic exposure. Y1R increased 2‐fold (MDA‐MB231) compared to normoixa. Y5R expression increased 79% (MCF‐7) and 55% (MDA‐MB231) relative to normoxic cells. Previous work from our group has demonstrated that hypoxic cancer cells require eukaryotic initiation factor 4E2 (eIF4E2) to direct the cap‐dependent translation of select mRNAs, therefore we tested whether the hypoxia‐induced increases in Y1R and Y5R expression were dependent on eIF4E2. Using MDA‐MB 231 cells depleted of eIF4E2, we found that hypoxic treatment had no effect on Y1R and Y5R expression compared to normoxic cells. These data provide insight into the O2‐mediated regulation of NPY receptors in breast cancer. Taken together with our previous functional NPY receptor studies, our findings provide further evidence of pathological implications of the NPY system in breast cancer. Ongoing studies will further elucidate the transcriptional and translational regulation of NPY receptors in response to hypoxia.Support or Funding InformationSupported by Ontario Ministry of Research and Innovation and Cancer Research Society