KCl cotransporter-3 down-regulates E-cadherin/beta-catenin complex to promote epithelial-mesenchymal transition

• Published in: Cancer research (Chicago, Ill.) Ill.), 2007-11, Vol.67 (22), p.11064-11073
• Main Authors: Hsu, Yueh-Mei, Chen, Yih-Fung, Chou, Cheng-Yang, Tang, Ming-Jer, Chen, Ji Hshiung, Wilkins, Robert J, Ellory, J Clive, Shen, Meng-Ru
• Format: Article
• Language: English
• Subjects: beta Catenin - metabolism; Cadherins - metabolism; Cell Line, Tumor; Cell Movement; Epithelium - metabolism; Gene Expression Regulation, Neoplastic; Humans; Mesoderm - metabolism; Models, Biological; Neoplasm Invasiveness; Promoter Regions, Genetic; Proteasome Endopeptidase Complex - metabolism; Protein Isoforms; Reverse Transcriptase Polymerase Chain Reaction; Symporters - metabolism
• ISSN: 0008-5472; 1538-7445
• DOI: 10.1158/0008-5472.CAN-07-2443

The potassium chloride cotransporter (KCC) is a major determinant of osmotic homeostasis and plays an emerging role in tumor biology. Here, we investigate if KCC is involved in the regulation of epithelial-mesenchymal transition (EMT), a critical cellular event of malignancy. E-cadherin and beta-catenin colocalize in the cell-cell junctions, which becomes more obvious in a time-dependent manner by blockade of KCC activity in cervical cancer SiHa and CaSki cells. Real-time reverse transcription-PCR on the samples collected from the laser microdissection indicates that KCC3 is the most abundant KCC isoform in cervical carcinoma. The characteristics of EMT appear in KCC3-overexpressed, but not in KCC1- or KCC4-overexpressed cervical cancer cells, including the elongated cell shape, increased scattering, down-regulated epithelial markers (E-cadherin and beta-catenin), and up-regulated mesenchymal marker (vimentin). Some cellular functions are enhanced by KCC3 overexpression, such as increased invasiveness and proliferation, and weakened cell-cell association. KCC3 overexpression decreases mRNA level of E-cadherin. The promoter activity assays of various regulatory sequences confirm that KCC3 expression is a potent negative regulator for human E-cadherin gene expression. The proteosome inhibitor restores the decreased protein abundance of beta-catenin by KCC3 overexpression. In the surgical specimens of cervical carcinoma, the decreased E-cadherin amount was accompanied by the increased KCC3 abundance. Vimentin begins to appear at the invasive front and becomes significantly expressed in the tumor nest. In conclusion, KCC3 down-regulates E-cadherin/beta-catenin complex formation by inhibiting transcription of E-cadherin gene and accelerating proteosome-dependent degradation of beta-catenin protein. The disruption of E-cadherin/beta-catenin complex formation promotes EMT, thereby stimulating tumor progression.