Department of Molecular Biology and Biophysics, University of Connecticut Health Center, Farmington, CT, USA.
Department of Cell Biology, University of Connecticut Health Center, Farmington, CT, USA.
Oncogene. 2018 Jul;37(29):4013-4032. doi: 10.1038/s41388-018-0243-y. Epub 2018 Apr 26.
Hepcidin is a peptide hormone that negatively regulates iron efflux and plays an important role in controlling the growth of breast tumors. In patients with breast cancer, the combined expression of hepcidin and its membrane target, ferroportin, predict disease outcome. However, mechanisms that control hepcidin expression in breast cancer cells remain largely unknown. Here, we use three-dimensional breast cancer spheroids derived from cell lines and breast cancer patients to probe mechanisms of hepcidin regulation in breast cancer. We observe that the extent of hepcidin induction and pathways of its regulation are markedly changed in breast cancer cells grown in three dimensions. In monolayer culture, BMPs, particularly BMP6, regulate hepcidin transcription. When breast cancer cells are grown as spheroids, there is a >10-fold induction in hepcidin transcripts. Microarray analysis combined with knockdown experiments reveal that GDF-15 is the primary mediator of this change. The increase in hepcidin as breast cells develop a three-dimensional architecture increases intracellular iron, as indicated by an increase in the iron storage protein ferritin. Immunohistochemical staining of human breast tumors confirms that both GDF-15 and hepcidin are expressed in breast cancer specimens. Further, levels of GDF-15 are significantly correlated with levels of hepcidin at both the mRNA and protein level in patient samples, consistent with a role for GDF-15 in control of hepcidin in human breast tumors. Inclusion of tumor-associated fibroblasts in breast cancer spheroids further induces hepcidin. This induction is mediated by fibroblast-dependent secretion of IL-6. Breast cancer cells grown as spheroids are uniquely receptive to IL-6-dependent induction of hepcidin by tumor-associated fibroblasts, since IL-6 does not induce hepcidin in cells grown as monolayers. Collectively, our results suggest a new paradigm for tumor-mediated control of iron through the control of hepcidin by tumor architecture and the breast tumor microenvironment.
亚铁调素是一种负调控铁外流的肽类激素，在控制乳腺癌生长中发挥重要作用。在乳腺癌患者中，亚铁调素及其膜靶标铁蛋白的联合表达可预测疾病结局。然而，控制乳腺癌细胞中铁调素表达的机制在很大程度上仍然未知。在这里，我们使用源自细胞系和乳腺癌患者的三维乳腺癌球体来探讨乳腺癌中铁调素调控的机制。我们观察到，在三维培养的乳腺癌细胞中，铁调素诱导的程度及其调控途径发生了显著变化。在单层培养中，BMPs，特别是 BMP6，调节铁调素转录。当乳腺癌细胞生长为球体时，铁调素转录物的诱导增加了 10 倍以上。微阵列分析结合敲低实验表明，GDF-15 是这种变化的主要介导者。随着乳腺细胞形成三维结构，铁调素的增加导致细胞内铁增加，这表现为铁储存蛋白 ferritin 的增加。对人类乳腺癌肿瘤的免疫组织化学染色证实，GDF-15 和铁调素均在乳腺癌标本中表达。此外，在患者样本中，GDF-15 的水平与铁调素的 mRNA 和蛋白水平均呈显著相关，表明 GDF-15 在控制人类乳腺癌肿瘤中铁调素方面发挥作用。将肿瘤相关成纤维细胞纳入乳腺癌球体中进一步诱导铁调素。这种诱导是由成纤维细胞依赖性分泌 IL-6 介导的。与在单层培养中生长的细胞不同，生长为球体的乳腺癌细胞对肿瘤相关成纤维细胞依赖 IL-6 诱导铁调素的作用具有独特的易感性。总之，我们的结果提出了一个新的范例，即通过肿瘤结构和乳腺癌微环境控制铁调素来实现肿瘤对铁的调控。
