Altered expression of adhesion molecules and epithelial–mesenchymal transition in silica-induced rat lung carcinogenesis

Abstract

Loss of the epithelial phenotype and disruption of adhesion molecules is a hallmark in the epithelialmesenchymal transition (EMT) reported in several types of cancer. Most of the studies about the relevance of adhesion and junction molecules in lung cancer have been performed using established tumors or in vitro models. The sequential molecular events leading to EMT during lung cancer progression are still not well understood. We have used a rat model for multistep lung carcinogenesis to study the status of adherens and tight junction proteins and mesenchymal markers during EMT. After silica-induced chronic inflammation, rats sequentially develop epithelial hyperplasia, preneoplastic lesions, and tumors such as adenocarcinomas and squamous cell carcinomas. In comparison with normal and hyperplastic bronchiolar epithelium and with hyperplastic alveolar type II cells, the expression levels of E-cadherin, a-catenin and b-catenin were significantly reduced in adenomatoid preneoplastic lesions and in late tumors. The loss of E-cadherin in tumors was associated with its promoter hypermethylation. a-and b-catenin dysregulation lead to cytoplasmic accumulation in some carcinomas. No nuclear b-catenin localization was found at any stage of any preneoplastic or neoplastic lesion. Zonula occludens protein-1 was markedly decreased in 66% of adenocarcinomas and in 100% squamous cell carcinomas. The mesenchymal-associated proteins N-cadherin and vimentin were analyzed as markers for EMT. N-cadherin was de novo expressed in 32% of adenocarcinomas and 33% of squamous cell carcinomas. Vimentin-positive tumor cells were found in 35% of adenocarcinomas and 88% of squamous cell carcinomas. Mesenchymal markers were absent in precursor lesions, both hyperplastic and adenomatoid. The present results show that silica-induced rat lung carcinogenesis is a good model to study EMT in vivo, and also provide in vivo evidence suggesting that the changes in cell-cell adhesion molecules are an early event in lung carcinogenesis, while EMT occurs at a later stage.

Proteomic analysis of stage I primary lung adenocarcinoma aimed at individualisation of postoperative therapy

“…Aberrant expression of vimentin in tumours and transformed cell lines has been correlated with increased motility, invasive behaviour and poor prognosis (Gilles et al, 1996;Hendrix et al, 1997). Recently, it was reported that the presence of vimentin-positive tumour cells mainly in fibrotic areas is consistent with other studies that have shown a correlation between tumour fibrosis and epithelial -mesenchymal transition (Blanco et al, 2004).…”

Junctional Adhesion Molecule 1 Regulates Epithelial Cell Morphology through Effects on β1 Integrins and Rap1 Activity

“…The lack of change in ␤4 integrins suggests that the observed effect on ␤1 integrins is not a generalized effect on all epithelial integrins. In addition, the lack of change in E-cadherin and ZO-1 argues against this being a global change in cell phenotype as seen with epithelialmesenchymal transition (46). These results suggest that JAM1 expression specifically affects ␤1 integrin protein levels, and this is consistent with the observed differences in cell-matrix adhesion and spreading presented in Fig.…”

“…In addition, E-cadherin is considered to be a marker of epithelial differentiation, so the lack of changes in E-cadherin levels (Fig. 5) suggests that the morphologic changes associated with JAM1 knockdown are not due to a gross change in the epithelial phenotype such as epithelialmesenchymal transition (46). In addition, cells treated with JAM1 siRNA were tested for expression of vimentin, a known mesenchymal marker, but no vimentin expression was detected (data not shown).…”

Global DNA methylation and PTEN hypermethylation alterations in lung tissues from human silicosis

“…For example, DNA methylation in the promoter region of (ADP-ribose) polymerases-1 (PARP-1) might be responsible for silica-induced DNA double strand breaks in vitro (19,20). In addition, silica-induced tumors tissues exhibited widespread genomic hypomethylation in rat model (21). Furthermore, silicosis patients with lung cancer had higher risk of aberrant promoter methylation in at least one of the five tumor suppressor genes than those without lung cancer (31) …”

“…But the reports about the relationship between silica and aberrant DNA methylation have been limited and focus on certain gene, rats model and blood from silicosis patient (19)(20)(21). PTEN was downstream of PI3K using siRNA in silicainduced human embryo lung fibroblasts (HELFs) (unpublished data).…”