Abstract 2061: Impaired acinar morphogenesis and cancer-like phenotype in hypoxic mammary epithelial cells
Authors: Marica Vaapil, Karolina Helczynska, Sven Påhlman, Annika Jogi
Journal: Cancer Research (2011)

Abstract Due to inadequate vascularization and tumor cell proliferation solid tumors are hypoxic compared to corresponding normal tissues. Tumor hypoxia has been associated with increased metastatic potential and worse patient outcome. The hypoxic response is mainly driven by the hypoxia inducible transcription factors; HIF -1α and HIF-2α. We have reported that hypoxia leads to a less differentiated phenotype in breast cancer and neuroblastoma, and in the clinic low tumor cell differentiation is related to poor prognosis in these diseases. We have shown that high levels of HIF-2α protein correlate to distant metastasis and poor survival in invasive breast cancer. The aim of the present study was to investigate the effect of hypoxia on mammary epithelial cell differentiation and epithelial organization. We employed the well-characterized model of acinar morphogenesis on extra cellular matrix substrate. In this model mammary epithelial cells MCF-10A that are cultured in three-dimensional culture on a laminin-rich matrix differentiate and form acini-like structures with evacuated lumen surrounded by polarized palisade cells. We found that hypoxia (1% oxygen) impaired the process of acinar morphogenesis and the hypoxic cells failed to obtain polarity and that markers of differentiation were affected at expression levels as well as cellular localization. The hypoxic cells remained proliferative whereas normoxic cells lost Ki-67 expression within a week. Addressing the mechanism behind the loss of differentiation in hypoxia, we found that hypoxia impaired the global histone deacetylation that has been shown by others to take place in the process of acini formation in mammary epithelial cells. Three days post-seeding, during the proliferation stage, both normoxic and hypoxic cells stained positive for acetylated histone 4. When the normoxic cells went through morphological changes and acinar formation the acetylation of histone 4 was reduced whereas it was maintained in the hypoxic cell-clusters at day10 post-seeding. Thus, the hypoxic conditions prevented global deacetylation, which is generally associated with high level of transcription and an undifferentiated proliferative cell stage, rendering the cells an open chromatin and hindering acinar formation. Transcription factors of the basic helix-loop-helix family are instrumental in mammary epithelial differentiation. The Inhibitor of Differentiation, ID, proteins are modulators of basic helix-loop-helix transcription factor activity and are reportedly hypoxia-induced. We therefore investigated their expression in the hypoxic cells and found increased expression of ID1, known to inhibit mammary epithelial differentiation and promote proliferation. These data indicate that hypoxia promotes loss of differentiation also at a non-malignant stage and render the cells a cancer-like phenotype. We are currently extending this study in primary cells. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2061. doi:10.1158/1538-7445.AM2011-2061