Cadmium induces Wnt signaling to upregulate proliferation and survival genes in sub-confluent kidney proximal tubule cells.

BACKGROUND: The class 1 carcinogen cadmium (Cd2+) disrupts the E-cadherin/beta-catenin complex of epithelial adherens junctions (AJs) and causes renal cancer. Deregulation of E-cadherin adhesion and changes in Wnt/beta-catenin signaling are known to contribute to carcinogenesis. RESULTS: We investigated Wnt signaling after Cd2+-induced E-cadherin disruption in sub-confluent cultured kidney proximal tubule cells (PTC). Cd2+ (25 microM, 3-9 h) caused nuclear translocation of beta-catenin and triggered a Wnt response measured by TOPflash reporter assays. Cd2+ reduced the interaction of beta-catenin with AJ components (E-cadherin, alpha-catenin) and increased binding to the transcription factor TCF4 of the Wnt pathway, which was upregulated and translocated to the nucleus. While Wnt target genes (c-Myc, cyclin D1 and ABCB1) were up-regulated by Cd2+, electromobility shift assays showed increased TCF4 binding to cyclin D1 and ABCB1 promoter sequences with Cd2+. Overexpression of wild-type and mutant TCF4 confirmed Cd2+-induced Wnt signaling. Wnt signaling elicited by Cd2+ was not observed in confluent non-proliferating cells, which showed increased E-cadherin expression. Overexpression of E-cadherin reduced Wnt signaling, PTC proliferation and Cd2+ toxicity. Cd2+ also induced reactive oxygen species dependent expression of the pro-apoptotic ER stress marker and Wnt suppressor CHOP/GADD153 which, however, did not abolish Wnt response and cell viability. CONCLUSIONS: Cd2+ induces Wnt signaling in PTC. Hence, Cd2+ may facilitate carcinogenesis of PTC by promoting Wnt pathway-mediated proliferation and survival of pre-neoplastic cells.

DNA methylation analysis in the intestinal epithelium-effect of cell separation on gene expression and methylation profile.

BACKGROUND: Epigenetic signatures are highly cell type specific. Separation of distinct cell populations is therefore desirable for all epigenetic studies. However, to date little information is available on whether separation protocols might influence epigenetic and/or gene expression signatures and hence might be less beneficial. We investigated the influence of two frequently used protocols to isolate intestinal epithelium cells (IECs) from 6 healthy individuals. MATERIALS AND METHODS: Epithelial cells were isolated from small bowel (i.e. terminal ileum) biopsies using EDTA/DTT and enzymatic release followed by magnetic bead sorting via EPCAM labeled microbeads. Effects on gene/mRNA expression were analyzed using a real time PCR based expression array. DNA methylation was assessed by pyrosequencing of bisulfite converted DNA and methylated DNA immunoprecipitation (MeDIP). RESULTS: While cell purity was >95% using both cell separation approaches, gene expression analysis revealed significantly higher mRNA levels of several inflammatory genes in EDTA/DTT when compared to enzymatically released cells. In contrast, DNA methylation of selected genes was less variable and only revealed subtle differences. Comparison of DNA methylation of the epithelial cell marker EPCAM in unseparated whole biopsy samples with separated epithelium (i.e. EPCAM positive and negative fraction) demonstrated significant differences in DNA methylation between all three tissue fractions indicating cell type specific methylation patterns can be masked in unseparated tissue samples. CONCLUSIONS: Taken together, our data highlight the importance of considering the potential effect of cell separation on gene expression as well as DNA methylation signatures. The decision to separate tissue samples will therefore depend on study design and specific separation protocols.