Tight junction proteins: From barrier to tumorigenesis

• Traditional roles of tight junction proteins as regulators of barrier integrity are introduced.
• Novel research areas of tight junction protein such as cell proliferation, transformation, and metastasis are highlighted.
• Genetic alterations of two key tight junction factors are noted in large-scale cancer genomic studies.

The tight junction is a multi-protein complex and is the apical most junctional complex in certain epithelial and endothelial cells. A great deal of attention has been devoted to the understanding of these proteins in contributing to the barrier function – that is, regulating the paracellular flux or permeability between adjacent cells. However, tight junction proteins are now recognized as having functions beyond the barrier. The focus of this review is to discuss the barrier function of the tight junction and to summarize the literature with a focus on the role of tight junction proteins in proliferation, transformation, and metastasis.