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Gene expression of Wnt-1, 2, 3, 4, 5a, 6 and 7a was analyzed by RT-PCR in eleven squamous cell carcinoma (SCC) cell lines and compared with that in two normal oral keratinocyte strains. There appeared to be an inverse relationship between Wnt-4 and Wnt-5a expressions, i.e., Wnt-4 was not expressed in HOC719-NE, HOC313 or TSU cells, while Wnt-5a was strongly expressed only in these cells. These cell lines showed decreased expression of E-cadherin and elevated expression of vimentin accompanied with strong expressions of Snail and δEF1, which have been reported to be transrepressors of E-cadherin and to trigger epithelial-mesenchymal transition (EMT), suggesting associations of Wnt-4 with epithelial phenotype and Wnt-5a with mesenchymal phenotype of SCC cells. To study whether the expressions of these Wnt genes are regulated by EMT, we transfected a Snailexpression vector into A431 and OM1 cells, which express Wnt-4 but not Wnt-5a. The stably Snail-overexpressing clones showed spindle morphology, increased expression of vimentin and decreased expression of E-cadherin accompanied with augmented expression of δEF1. In these clones, down-regulation of Wnt-4 and up-regulation of Wnt-5a were clearly observed. These results indicated that Wnt-4 and Wnt-5a are oppositely affected by EMT, and down-regulation of Wnt-4 and up-regulation of Wnt-5a are possible markers of the malignant phenotype of human SCC.