Reduced expression of claudin-2 is associated with high histological grade and metastasis of feline mammary carcinomas

Metastasis in the wild: investigating metastasis in non-laboratory animals

Humans are not the only species to spontaneously develop metastatic cancer as cases of metastasis have been reported in a wide range of animals, including dinosaurs. Mouse models have been an invaluable tool in experimental and clinical metastasis research, with the use of genetically-engineered mouse models that spontaneously develop metastasis or ectopic/orthotopic transplantation of tumour cells to wildtype or immunodeficient mice being responsible for many key advances in our understanding of metastasis. However, are there other species that can also be relevant models? Similarities to humans in terms of environmental exposures, life-span, genetics, histopathology and available therapeutics are all factors that can be considered when looking at species other than the laboratory mouse. This review will explore the occurrence of metastasis in multiple species from a variety of domestic, captive and free-living veterinary cases to assist in identifying potential alternative experimental and clinical research models relevant to humans.

TiHo-0906: a new feline mammary cancer cell line with molecular, morphological, and immunocytological characteristics of epithelial to mesenchymal transition

Feline mammary carcinomas (FMCs) with anaplastic and malignant spindle cells histologically resemble the human metaplastic breast carcinoma (hMBC), spindle-cell subtype. hMBCs display epithelial-to-mesenchymal transition (EMT) characteristics. Herein we report the establishment and characterization of a cell line (TiHoCMglAdcar0906; TiHo-0906) exhibiting EMT-like properties derived from an FMC with anaplastic and malignant spindle cells. Copy-number variations (CNVs) by next-generation sequencing and immunohistochemical characteristics of the cell line and the tumour were compared. The absolute qPCR expression of EMT-related markers HMGA2 and CD44 was determined. The growth, migration, and sensitivity to doxorubicin were assessed. TiHo-0906 CNVs affect several genomic regions harbouring known EMT-, breast cancer-, and hMBCs-associated genes as AKT1, GATA3, CCND2, CDK4, ZEB1, KRAS, HMGA2, ESRP1, MTDH, YWHAZ, and MYC. Most of them were located in amplified regions of feline chromosomes (FCAs) B4 and F2. TiHo-0906 cells displayed an epithelial/mesenchymal phenotype, and high HMGA2 and CD44 expression. Growth and migration remained comparable during subculturing. Low-passaged cells were two-fold more resistant to doxorubicin than high-passaged cells (IC50: 99.97 nM, and 41.22 nM, respectively). The TiHo-0906 cell line was derived from a poorly differentiated cellular subpopulation of the tumour consistently displaying EMT traits. The cell line presents excellent opportunities for studying EMT on FMCs.

Elevation of sensitivity to anticancer agents of human lung adenocarcinoma A549 cells by knockdown of claudin-2 expression in monolayer and spheroid culture models

Claudins, tight junctional proteins, regulate the paracellular permeability of ions and small molecules. Claudin-2 is highly expressed in human lung adenocarcinoma cells and is involved in the up-regulation of cell proliferation. However, the effect of claudin-2 on cellular sensitivity to anticancer agents has not been clarified. The cytotoxicity of anticancer agents such as cisplatin, gefitinib and doxorubicin (DXR) was increased by claudin-2 knockdown in A549 cells. Claudin-2 knockdown also significantly decreased the expression level of multidrug resistance-associated protein/ABCC2. The expression levels of other drug efflux transporters were unchanged. The intracellular accumulation of 5-chloromethylfluorescein diacetate (CMFDA) and DXR, substrates of ABCC2, was increased by claudin-2 knockdown, whereas the efflux was decreased. MK-571, an inhibitor of ABCC2, enhanced the cytotoxicity of anticancer agents. Claudin-2 knockdown decreased the levels of p-c-Jun and nuclear Sp1. SP600125, an inhibitor of c-Jun, and mithramycin, an inhibitor of Sp1, decreased the level of ABCC2. The promoter activity of ABCC2 was decreased by claudin-2 knockdown, SP600125 and mithramycin treatments, suggesting that claudin-2 is involved in the up-regulation of ABCC2 expression at the transcriptional level. Claudin-2 knockdown increased the paracellular permeability of DXR in a 2D monolayer culture model. In addition, the accumulation of DXR into spheroids was enhanced by claudin-2 knockdown, resulting in a reduction in cell viability. We suggest that claudin-2 may be a novel therapeutic target in lung adenocarcinoma, because claudin-2 knockdown increased the accumulation of anticancer agents in cancer cells and spheroids.

The epithelial barrier and beyond: Claudins as amplifiers of physiological organ functions

Epithelial cell layers are interconnected by a meshwork of tight junction (TJ) protein strands, which are localized within apicolateral membranes. The proteins that form TJs are regarded to provide a static barrier, determining epithelial properties. However, recent findings in the field of barriology suggest that TJs contribute to more physiological aspects than indicated by the sum of the qualities of the single TJ proteins. Generally, TJs exhibit four major functions: (i) a "gate function," defining transepithelial permeability (i.e., barrier) properties, (ii) a "fence function" determining epithelial cell polarity, (iii) a "signaling function," affecting regulatory pathways, and (iv) a "stabilizing function," maintaining the integrity of the epithelium. This review presents a critical view on how the efficacy of physiological processes in epithelia and thus organ function might be improved by changes in the expression of claudins, the latter representing the largest and most variable family of TJ proteins. Major focus is set on (i) the coordinated regulation of transport and barrier in the intestine, (ii) the role of TJs in defining the route for antigen uptake and presentation in intestinal Peyer's patches, and (iii) the TJ function in mammary glands in response to milk accumulation, which represent impressive examples to highlight the amplification of epithelial functions by TJ proteins. © 2017 IUBMB Life, 69(5):290-296, 2017.

Down-regulation of Claudin-2 Expression and Proliferation by Epigenetic Inhibitors in Human Lung Adenocarcinoma A549 Cells

Claudin-2 is highly expressed in lung adenocarcinoma tissues and increases proliferation in adenocarcinoma cells. The chemicals that reduce claudin-2 expression may have anti-cancer effects, but such therapeutic medicines have not been developed. We found that azacitidine (AZA), a DNA methylation inhibitor, and trichostatin A (TSA) and sodium butyrate (NaB), histone deacetylase (HDAC) inhibitors, decrease claudin-2 levels. The effect of AZA was mediated by the inhibition of phosphorylated Akt and NF-κB. LY-294002, an inhibitor of phosphatidylinositol 3-kinase (PI3K), and BAY 11-7082, an NF-κB inhibitor, decreased claudin-2 levels. The reporter activity of claudin-2 was decreased by AZA and LY-294002, which was blocked by the mutation in a putative NF-κB-binding site. NF-κB bound to the promoter region of claudin-2, which was inhibited by AZA and LY-294002. AZA is suggested to decrease the claudin-2 mRNA level mediated by the inhibition of a PI3K/Akt/NF-κB pathway. TSA and NaB did not change phosphorylated Akt and NF-κB levels. Furthermore, these inhibitors did not change the reporter activity of claudin-2 but decreased the stability of claudin-2 mRNA mediated by the elevation of miR-497 microRNA. The binding of histone H3 to the promoter region of miR-497 was inhibited by TSA and NaB, whereas that of claudin-2 was not. These results suggest that HDAC inhibitors decrease claudin-2 levels mediated by the elevation of miR-497 expression. Cell proliferation was additively decreased by AZA, TSA, and NaB, which was partially rescued by ectopic expression of claudin-2. We suggest that epigenetic inhibitors suppress the abnormal proliferation of lung adenocarcinoma cells highly expressing claudin-2.

Cat Mammary Tumors: Genetic Models for the Human Counterpart

The records are not clear, but Man has been sheltering the cat inside his home for over 12,000 years. The close proximity of this companion animal, however, goes beyond sharing the same roof; it extends to the great similarity found at the cellular and molecular levels. Researchers have found a striking resemblance between subtypes of feline mammary tumors and their human counterparts that goes from the genes to the pathways involved in cancer initiation and progression. Spontaneous cat mammary pre-invasive intraepithelial lesions (hyperplasias and neoplasias) and malignant lesions seem to share a wide repertoire of molecular features with their human counterparts. In the present review, we tried to compile all the genetics aspects published (i.e., chromosomal alterations, critical cancer genes and their expression) regarding cat mammary tumors, which support the cat as a valuable alternative in vitro cell and animal model (i.e., cat mammary cell lines and the spontaneous tumors, respectively), but also to present a critical point of view of some of the issues that really need to be investigated in future research.

Clinicopathological significance of immunoexpression of claudin-1 and claudin-7 in feline mammary carcinomas

Claudins (CLDNs) are tight junction proteins that have a role in regulating cell adhesion and polarity, paracellular permeability, proliferation and differentiation. Several immunohistochemical studies have shown reduced expression of CLDN-1 and CLDN-7 in human and canine mammary carcinomas, suggesting that these proteins may participate in mammary carcinogenesis, invasion and metastasis. The present study characterizes expression of CLDN-1 and CLDN-7 in feline mammary carcinomas (n = 52) and their metastases (n = 29). There was an inverse association between CLDN-7 expression and histological grade of tumour. Reduced expression of CLDN-7 was significantly associated with decreased tubule formation, high proliferative activity and metastasis. No significant associations were found between CLDN-1 expression and any of these features. Evaluation of expression of CLDN-7, but not CLDN-1, may therefore provide prognostic information, assisting in the diagnosis of a subgroup of aggressive feline mammary carcinomas that share some features with the recently described 'claudin-low' subgroup of human breast cancer.