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.
Chakraborty
Prabir K
PK
ZBAF, Department of Physiology & Pathophysiology, University of Witten/Herdecke, Stockumer Strasse 12, D-58453 Witten, Germany. Prabir.Chakraborty@uni-wh.de
Lee
Wing-Kee
WK
Molitor
Malte
M
Wolff
Natascha A
NA
Thévenod
Frank
F
D000818:Animals; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D015820:Cadherins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D002104:Cadmium / Q000633:toxicity*; D002273:Carcinogens / Q000633:toxicity*; D049109:Cell Proliferation / Q000187:drug effects; D002471:Cell Transformation, Neoplastic / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D024202:Electrophoretic Mobility Shift Assay; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D007687:Kidney Tubules, Proximal / Q000187:drug effects* / Q000378:metabolism; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects* / Q000502:physiology; D000073940:Transcription Factor 4; D014157:Transcription Factors / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D014162:Transfection; D015854:Up-Regulation; D051153:Wnt Proteins / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D051176:beta Catenin / Q000187:drug effects / Q000235:genetics / Q000378:metabolism
D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D015820:Cadherins; D002273:Carcinogens; C532096:TCF4 protein, human; D000073940:Transcription Factor 4; D014157:Transcription Factors; D051153:Wnt Proteins; D051176:beta Catenin; D002104:Cadmium
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