Heterogeneous Nuclear Ribonucleoprotein K Is Involved in the Estrogen-Signaling Pathway in Breast Cancer

Zinc transporter ZnT5 is associated with epithelial mesenchymal transition via SMAD1 in breast cancer

Zinc levels in breast cancer tissues have been reported to be higher than those in normal tissues. In addition, the expression levels of zinc transporters, including ZnT5 and ZnT6, are reportedly higher in breast cancer than in normal breast tissues. ZnT5 and ZnT6 also contribute to heterodimer formation and are involved in several biological functions. However, the functions of ZnT5 and ZnT6 heterodimers in breast cancer remain unknown. Therefore, we first investigated the immunolocalization of ZnT5 and ZnT6 in pathological breast cancer specimens and in MCF-7 and T-47D breast cancer cells. Next, we used small interfering RNA to assess cell viability and migration in ZnT5 knockdown MCF-7 and T-47D cells. Immunohistochemical analysis showed that the number of ZnT5-positive breast cancer cells was inversely correlated with the pathologic N factor status. ZnT5 knockdown had no effect on cell viability in the presence of 100 μM ZnCl2 in MCF-7 and T-47D cells. In a wound healing assay, 100 μM ZnCl2 treatment inhibited cell migration of MCF-7 and T-47D cells, whereas ZnT5 knockdown promoted cell migration, decreased E-cadherin expression and increased vimentin, slug and matrix metalloproteinase 9 expression. Antibody arrays showed that ZnT5 knockdown increased the expression of SMAD1, and that dorsomorphin treatment inhibited the promotion of migratory ability induced by ZnT5 knockdown. The results of this study revealed that both ZnT5 may be involved in less aggressive breast cancer subtypes, possibly through inhibition of cell migration.

Switchable tetraplex elements in the heterogeneous nuclear ribonucleoprotein K promoter: micro-environment dictated structural transitions of G/C rich elements

We have elucidated the hnRNP K promoter as a hotspot for tetraplex-based molecular switches receptive to micro-environmental stimuli. We have characterised the structural features of four tetraplex-forming loci and identified them as binding sites of transcription factors. These segments form either G-quadruplex or i-motif structures, the structural dynamicity of which has been studied in depth via several biophysical techniques. The tetraplexes display high dynamicity and are influenced by both pH and KCl concentrations in vitro. The loci complementary to these sequences form additional non-canonical secondary structures. In the cellular context, the most eminent observation of this study is the binding of hnRNP K to the i-motif forming sequences in its own promoter. We are the first to report a probable transcriptional autoregulatory function of hnRNP K in coordination with higher-order DNA structures. Herein, we also report the positive interaction of the endogenous tetraplexes with Sp1, a well-known transcriptional regulator. Treatment with tetraplex-specific small molecule ligands further uncovered G-quadruplexes' functioning as repressors and i-motifs as activators in this context. Together, our findings strongly indicate the critical regulatory role of the identified tetraplex elements in the hnRNP K promoter.Communicated by Ramaswamy H. Sarma.

Two-Dimensional Polyacrylamide Gel Electrophoresis Coupled with Nanoliquid Chromatography-Tandem Mass Spectrometry-Based Identification of Differentially Expressed Proteins and Tumorigenic Pathways in the MCF7 Breast Cancer Cell Line Transfected for Jumping Translocation Breakpoint Protein Overexpression

The identification of new genes/proteins involved in breast cancer (BC) occurrence is widely used to discover novel biomarkers and understand the molecular mechanisms of BC initiation and progression. The jumping translocation breakpoint (JTB) gene may act both as a tumor suppressor or oncogene in various types of tumors, including BC. Thus, the JTB protein could have the potential to be used as a biomarker in BC, but its neoplastic mechanisms still remain unknown or controversial. We previously analyzed the interacting partners of JTBhigh protein extracted from transfected MCF7 BC cell line using SDS-PAGE complemented with in-solution digestion, respectively. The previous results suggested the JTB contributed to the development of a more aggressive phenotype and behavior for the MCF7 BC cell line through synergistic upregulation of epithelial-mesenchymal transition (EMT), mitotic spindle, and fatty acid metabolism-related pathways. In this work, we aim to complement the previously reported JTB proteomics-based experiments by investigating differentially expressed proteins (DEPs) and tumorigenic pathways associated with JTB overexpression using two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). Statistically different gel spots were picked for protein digestion, followed by nanoliquid chromatography-tandem mass spectrometry (nLC-MS/MS) analysis. We identified six DEPs related to the JTBhigh condition vs. control that emphasize a pro-tumorigenic (PT) role. Twenty-one proteins, which are known to be usually overexpressed in cancer cells, emphasize an anti-tumorigenic (AT) role when low expression occurs. According to our previous results, proteins that have a PT role are mainly involved in the activation of the EMT process. Interestingly, JTB overexpression has been correlated here with a plethora of significant upregulated and downregulated proteins that sustain JTB tumor suppressive functions. Our present and previous results sustain the necessity of the complementary use of different proteomics-based methods (SDS-PAGE, 2D-PAGE, and in-solution digestion) followed by tandem mass spectrometry to avoid their limitations, with each method leading to the delineation of specific clusters of DEPs that may be merged for a better understanding of molecular pathways and neoplastic mechanisms related to the JTB's role in BC initiation and progression.

In Situ Proximity Ligation Assay to Visualize Protein-Protein Interactions in Tumor Specimens

Protein-protein interactions (PPI) are the basis of various biological phenomena, such as intracellular signal transduction, gene transcription, and metabolism. PPI are also considered to be involved in the pathogenesis and development of various diseases, including cancer. PPI phenomenon and their functions have been elucidated by gene transfection and molecular detection technologies. On the other hand, in histopathological analysis, although immunohistochemical analyses provide information pertaining to protein expression and their localization in pathophysiological tissues, it has been difficult to visualize the PPI of these proteins. An in situ proximity ligation assay (PLA) was developed as a microscopic visualization technique for PPI in formalin-fixed, paraffin-embedded (FFPE) tissues as well as in cultured cells and frozen tissues. PLA using histopathological specimens enables cohort studies of PPI, which can clarify the significance of PPI in pathology. We have previously shown the dimerization pattern of estrogen receptors and significance of HER2-binding proteins using breast cancer FFPE tissues. In this chapter, we describe a methodology for the visualization of PPI using PLA in pathological specimens.

The Visualization of Protein-Protein Interactions in Breast Cancer: Deployment Study in Pathological Examination

The therapeutic strategy is determined by protein expression using immunohistochemistry of estrogen receptor (ER), progesterone receptor, and human epidermal growth factor receptor 2 (HER2) in formalin-fixed paraffin-embedded (FFPE) breast cancer tissues. However, few proteins function independently, and many of them functions due to protein-protein interactions (PPIs) with other proteins. Therefore, it is important to focus on PPIs. This review summarizes the PPIs of ER and HER2 in breast cancer, especially those using a proximity ligation assay that can visualize PPIs in FFPE tissues. In particular, assessing the interaction of CEACAM6 with HER2 may serve as a surrogate marker for the efficacy of trastuzumab in patients with breast cancer. Therefore, in this review, the technique used to detect the interaction of CEACAM6 and HER2 in routinely processed pathological specimens will be applied to the clinical practice of drug selection. We showed the possibility as a novel pathological examination method using PPIs.