Cholesterol-mediated tight junction formation

Lipids have the ability to self-organize but the significance of this phenomenon in the assembly of membrane structures is unknown. We previously reported that cholesterol enrichment directs the formation of tight junctions (TJs), adhesion structures responsible for the epithelial barrier (Shigetomi et al., 2018). However, it is unclear how cholesterol accumulates and informs TJ formation. Cholesterol typically accumulates in the vicinity of apical cell junctions (Shigetomi et al., 2018). Surprisingly, cholesterol distribution is unaltered in an epithelial cell line that lacks TJs, generated by suppressing the expression of claudins, membrane proteins that determine the barrier properties of TJs. Assembly of claudin into hallmark ‘strands’ is canonically thought to require binding to Zonula occludens (ZO) proteins but a claudin mutant that cannot bind to ZO proteins still form strands. These results suggest a novel mechanism for TJ formation that is dependent on cholesterol and reveal an unexpected role of ZO proteins as organizers of the cholesterol domain.