Abstract 3599: Expression and function of HFE in mammary gland iron homeostasis and its relevance to breast cancer

Emerging evidences on the role of iron-regulatory proteins in tumor growth provide new insights into the role of iron in cancer. Iron, though essential for normal cellular function, is toxic if present in excess. Hemochromatosis is an autosomal recessive disease of iron overload linked to mutations in HFE gene [Histocompatability leukocyte antigen class I-like protein involved in iron (FE) homeostasis]. HFE interacts with transferrin receptors, TfR1 and TfR2, and inhibits cellular iron uptake. The prevalence of the disease is very high with homozygosity incidence of ∼1 in 300 and heterozygosity incidence of ∼1 in 10. The disease manifests with liver cirrhosis/cancer, cardiomyopathy, diabetes, and arthritis. Several studies have shown increased prevalence of HFE mutations in breast cancer patients across all races. There is also evidence of increased levels of iron in breast cancer tissue. Although excessive iron and oxidative stress have been postulated to play a role in breast cancer, the expression/function of HFE in mammary gland iron homeostasis and how mutations in HFE affect breast cancer progression have not been studied directly. Here we demonstrate the expression of HFE mRNA in mouse mammary gland and primary mammary epithelial cells. The mRNA was absent in HFE-/- mice. Immunohistochemistry showed localization of HFE protein in luminal and myoepithelial cells. Similar staining was also seen in primary mammary epithelial cells from wild type mice but not from HFE-/- mice. We then examined the physiological role of HFE in mammary gland. Ferritin is a cytoplasmic protein involved in iron storage, and increase in intracellular iron levels results in increased level of ferritin. Recently, ferritin has also been shown to promote angiogenesis. Western blot and immunohistochemical analysis revealed that mammary tissue from HFE-/- mice had increased ferritin levels in an age-dependent manner. Thus, for the first time we show that HFE-/- mice have increased iron accumulation in the mammary gland. Immunostaining with antibody against 4-hydroxynonenal, one of the byproducts of lipid peroxidation, showed that HFE-/- mammary tissue have oxidative stress mediated by iron accumulation. MTT assay and thymidine incorporation showed that primary mammary epithelial cells from HFE-/- mice proliferate faster than the cells from HFE+/+ mice. Increase in histone deacetylase (HDAC) activity has been implicated in many cancers. We found that mammary tissue from HFE-/- mice has increased HDAC activity compared to wild type tissue. This shows that functional loss of HFE in mammary tissue can also promote cell cycle progression via epigenetic mechanisms. Based on these data, we hypothesize that tissue iron is an important modifier of breast cancer progression and that mutations in HFE (heterozygosity as well as homozygosity) may enhance the incidence and/or progression of breast cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3599. doi:1538-7445.AM2012-3599