Claudin-6 is a
protein component of tight junctions and its expression has been found to be undetectable or at low levels in some human and rat
breast cancer cells. Here we investigated the effect of
claudin-6 upregulation on the malignant phenotype of human MCF-7
breast cancer cells. MCF-7 sublines with stable
claudin-6 expression were established by transfection with a pcDNA3.1-claudin-6 expressing vector. The expression of
claudin-6 on
mRNA and
protein levels was confirmed by reverse transcription-PCR, western blot and immunofluorescent assays. Then the effects of
claudin-6 on cell proliferation and cell cycle were examined by 5-diphenyl terazolium-
bromide assay and flow cytometry, respectively. Colony-forming assays were used to examine two-dimensional and three-dimensional colony forming ability. Invasive and migratory traits of
claudin-6 expressing cells were determined by
matrigel-based Boyden chamber invasion assay and monolayer wound-healing assay. The structure and function of tight junctions in both parental and
claudin-6 expression MCF-7 cells were evaluated by measuring transepithelial electrical resistance. Immunofluorescent assays showed that transfected cells expressed
claudin-6 on their membranes. Cells with high level expression of
claudin-6 grew slowly and had a higher rate of death than control cells. Anchorage-independent growth, invasive and migratory traits were also substantially decreased in cells with
claudin-6 expression; whereas the transepithelial electrical resistance was increased in the
claudin-6 transfected cells. In conclusion, these results suggest that
claudin-6 may function as a
cancer suppressor; its downregulation may contribute to the malignant progression of certain types of breast
cancers.