Problem: 

Occludin is a self-associating transmembrane tight junction protein affected in oxidative stress. However, its function is unknown.

Methods: 

HEK-293 and MDCK-II cell were transfected with YFP/CFP-occludin and the oligomerization of occludin was investigated by gel electrophoresis, fluorescence resonance energy transfer, transcellular fluorescence scanning, freeze-fracture electron microscopy, and paracellular permeability measurement.

Results: 

The cytosolic C-terminal tail contains a coiled coil-domain forming dimers contributing to the self-association. Studying the hypothesis that the self-association is redox-sensitive we found the dimerization, the cis-interaction along the cell membrane, and the trans-interaction between the plasma membrane of two adhering cells, depending on hypoxia, the sulfhydryl concentration of the environment in low-millimolar range. All the effects mentioned were prevented by a mutant in the coiled coil-domain (hOccludin-C409A).

Conclusion: 

The data demonstrates, for the first time, that disulfide bridge formation of the domain is involved in the oligomerization and cell communication of occludin. It is concluded that the redox-dependent oligomerization may play a regulatory role in the tight junction assembly as well as in the paracellular tightening under physiological and pathological conditions.