| Tight junctions, or zona occludens, form a continuous barrier to fluids across the epithelium and endothelium. They function in regulation of paracellular permeability and in the maintenance of cell polarity, blocking the movement of transmembrane proteins between the apical and the basolateral cell surfaces (reviewed in 1). Tight junctions are composed of claudin and occludin transmembrane proteins, which join the junctions to the cytoskeleton. Occludin is thought to be important in the assembly and maintenance of tight junctions. Differential phosphorylation of occludin at various residues may regulate its interaction with other tight junction proteins such as ZO-1 (3). VEGF-induced phosphorylation of occludin regulates tight junction stability and vascular permeability (4). Expression of occludin as well as claudin1 is required for infection of liver cells by hepatitis C virus (HCV). |
