Occludin Is Involved in Adhesion, Apoptosis, Differentiation and Ca2+-Homeostasis of Human Keratinocytes: Implications for Tumorigenesis

Abstract

Tight junction (TJ) proteins are involved in a number of cellular functions, including paracellular barrier formation, cell polarization, differentiation, and proliferation. Altered expression of TJ proteins was reported in various epithelial tumors. Here, we used tissue samples of human cutaneous squamous cell carcinoma (SCC), its precursor tumors, as well as sun-exposed and non-sun-exposed skin as a model system to investigate TJ protein alteration at various stages of tumorigenesis. We identified that a broader localization of zonula occludens protein (ZO)-1 and claudin-4 (Cldn-4) as well as downregulation of Cldn-1 in deeper epidermal layers is a frequent event in all the tumor entities as well as in sun-exposed skin, suggesting that these changes result from chronic UV irradiation. In contrast, SCC could be distinguished from the precursor tumors and sun-exposed skin by a frequent complete loss of occludin (Ocln). To elucidate the impact of down-regulation of Ocln, we performed Ocln siRNA experiments in human keratinocytes and uncovered that Ocln downregulation results in decreased epithelial cell-cell adhesion and reduced susceptibility to apoptosis induction by UVB or TNF-related apoptosis-inducing ligand (TRAIL), cellular characteristics for tumorigenesis. Furthermore, an influence on epidermal differentiation was observed, while there was no change of E-cadherin and vimentin, markers for epithelial-mesenchymal transition. Ocln knock-down altered Ca2+-homeostasis which may contribute to alterations of cell-cell adhesion and differentiation. As downregulation of Ocln is also seen in SCC derived from other tissues, as well as in other carcinomas, we suggest this as a common principle in tumor pathogenesis, which may be used as a target for therapeutic intervention.

Equine Epidermis: A Source of Epithelial-Like Stem/Progenitor Cells with In Vitro and In Vivo Regenerative Capacities

“…It is likely that the noted discrepancies in cellular localization associated with the different antibodies arise from the differences in epitope specificity. In several studies [32,64], other markers for adult keratinocytes were used, such as CK5 and E-Cadherin; however, we were unable to evaluate the expression of these markers in or on our equine EpSCs or their differentiated progeny, due to a lack of crossreactivity of several commercially available antibodies tested (data not shown). In this regard, it has been reported that only about 4% of human antibodies reacts with the equivalent equine epitopes [65].…”

The barrier function of organotypic non-melanoma skin cancer models

“…Subsequent to RCM imaging, the constructs were snap frozen, sectioned into 5 μm slices (Leica CM 1510S; Wetzlar, Germany), and analyzed by hematoxylin-eosin and immunofluorescence staining. Tight junction proteins were analyzed from paraffinembedded constructs as described [19]. Pictures were taken with a fluorescence microscope (BZ-8000, Keyence; Neu-Isenburg, Germany or Axiophot II, Zeiss; Göttingen, Germany), and analyzed with Openlab 2.0.9 or ImageJ software.…”

The levels of epithelial anchor proteins β-catenin and zona occludens-1 are altered by E7 of human papillomaviruses 5 and 8

“…Cells with strong b-catenin and ZO-1 expression were found in the skin of HPV8 transgenic mice and EV lesions, which supports a possible clinical relevance of our data. A broader expression pattern of ZO-1 in epidermal layers has previously been shown in skin SCC, which suggests that ZO-1 contributes to tumour progression, largely in a tight junction independent manner (Brandner et al, 2015;Hintsala et al, 2013;Kirschner & Brandner, 2012;Morita et al, 2004;Rachow et al, 2013). In melanoma cells, an increase of ZO-1 mRNA and protein levels was observed compared to normal melanocytes.…”