Subtype-specific accumulation of intracellular zinc pools is associated with the malignant phenotype in breast cancer

Abstract

BackgroundZinc (Zn) hyper-accumulates in breast tumors and malignant cell lines compared to normal mammary epithelium. The mechanisms responsible for Zn accumulation and the consequence of Zn dysregulation are poorly understood.MethodsMicroarrays were performed to assess differences in the expression of Zn transporters and metallothioneins (MTs) in human breast tumors and breast cancer cell lines. Real-time PCR and immunoblotting were employed to profile Zn transporter expression in representative luminal (T47D), basal (MDA-MB-231), and non-malignant (MCF10A) cell lines. Zn distribution in human tumors was assessed by X-ray fluorescence imaging. Zn distribution and content in cell lines was measured using FluoZin-3 imaging, and quantification and atomic absorption spectroscopy. Functional consequences of ZnT2 over-expression in MDA-MB-231 cells including invasion, proliferation, and cell cycle were measured using Boyden chambers, MTT assays, and flow cytometry, respectively.ResultsGene expression profiling of human breast tumors and breast cancer cell lines identified subtype-specific dysregulation in the Zn transporting network. X-ray fluorescence imaging of breast tumor tissues revealed Zn hyper-accumulation at the margins of Luminal breast tumors while Zn was more evenly distributed within Basal tumors. While both T47D and MDA-MB-231 cells hyper-accumulated Zn relative to MCF10A cells, T47D cells accumulated 2.5-fold more Zn compared to MDA-MB-231 cells. FluoZin-3 imaging indicated that Zn was sequestered into numerous large vesicles in T47D cells, but was retained in the cytoplasm and found in fewer and larger, amorphous sub-cellular compartments in MDA-MB-231 cells. The differences in Zn localization mirrored the relative abundance of the Zn transporter ZnT2; T47D cells over-expressed ZnT2, whereas MDA-MB-231 cells did not express ZnT2 protein due to proteasomal degradation. To determine the functional relevance of the lack of ZnT2 in MDA-MB-231cells, cells were transfected to express ZnT2. ZnT2 over-expression led to Zn vesicularization, shifts in cell cycle, enhanced apoptosis, and reduced proliferation and invasion.ConclusionsThis comprehensive analysis of the Zn transporting network in malignant breast tumors and cell lines illustrates that distinct subtype-specific dysregulation of Zn management may underlie phenotypic characteristics of breast cancers such as grade, invasiveness, metastatic potential, and response to therapy.Electronic supplementary materialThe online version of this article (doi:10.1186/s12943-015-0486-y) contains supplementary material, which is available to authorized users.

Serum Levels of Selenium and Zinc in Patients with Breast Cancer: A Case-Control Study

“…Zinc (Zn) is a vital mineral for the operation of numerous cellular processes and growth and may play an important role in malignancy etiology and outcome (9). This mineral has an excessive accumulation in BCs and malignant cell lines compared with normal mammary epithelium (10). Also, it plays a role on the cellular level, the function of transcription factors, and cell proliferation; it defends against radicals and deoxyribonucleic acid (DNA) repair (11).…”

Spiropyran‐Based Nanocarrier: A New Zn2+‐Responsive Delivery System with Real‐Time Intracellular Sensing Capabilities

“…The proteasome is an important therapeutic target in the treatment of cancers, but most proteasome inhibitors produce dose‐limiting cytotoxicity to non‐malignant cells that preclude their widespread clinical use . With this in mind, a potent proteasome inhibitor, 5 (Figure A insert), was encapsulated inside the nanocarriers for release in breast cancer cells reported to possess high levels of Zn 2+ . This provides potential to reduce cytotoxicity to non‐malignant cells.…”

“…For example, elevated intracellular levels of Zn 2+ are associated with malignancy and invasiveness of breast tumors. Intracellular Zn 2+ is therefore an important biomarker for the diagnosis and subsequent treatment of invasive breast cancers . A real advance would come with a new nanocarrier that releases an encapsulated therapeutic agent specifically in response to Zn 2+ binding, with concomitant sensing of the analyte and tracking of the nanocarrier by fluorescence.…”

Zinc transporters and dysregulated channels in cancers

“…It seems paradoxical since breast cancer patients have low Zn levels in hair or serum and Zn deficiency is believed to contribute to the development of breast cancer. These studies suggest that the dysregulated Zn homeostasis is complicated, and relates not only to Zn concentrations but also to its distribution as well as its temporal pattern (107). The high Zn content in breast tumor tissues implies that cancer cells selectively increase Zn uptake or decrease Zn efflux via regulating one or more Zn transporters.…”

“…LNCaP and PC-3 cells. Abundant ZnT2 was observed in Luminal breast tumors but not in Basal tumors and adjacent non-malignant tissues (107). ZnT4 was found in cytoplasmic vesicles, Golgi apparatus, and the plasma membrane (109, 110).…”