GFP claudins (cldns) make dynamic strand patches between fibroblasts regulated by ZO-1 binding. Independent of ZO-1, cldn strands break and reanneal; new cldns are preferentially incorporated into break sites. Intermittent tethering of cldns to actin is speculated to allow the paracellular seal to accommodate physiological changes in cell shape.

Background: Biotin ligase tagging with ZO-1 was applied to identify a more complete tight junction proteome. Results: Identical but also different proteins and functional networks were identified near the N and C ends of ZO-1. Conclusion:The ends of ZO-1 are embedded in different functional subcompartments of the tight junction. Significance: Biotin tagging with ZO-1 expands the tight junction proteome and defines subcompartments of the junction.

Known proteins associated with the cell-adhesion protein Ecadherin include catenins and proteins involved in signaling, trafficking and actin organization. However, the list of identified adherens junction proteins is likely to be incomplete, limiting investigation into this essential cell structure. To expand the inventory of potentially relevant proteins, we expressed Ecadherin fused to biotin ligase in MDCK epithelial cells, and identified by mass spectrometry neighboring proteins that were biotinylated. The most abundant of the 303 proteins identified were catenins and nearly 40 others that had been previously reported to influence cadherin function. Many others could be rationalized as novel candidates for regulating the adherens junction, cytoskeleton, trafficking or signaling. We further characterized lipoma preferred partner (LPP), which is present at both cell contacts and focal adhesions. Knockdown of LPP demonstrated its requirement for Ecadherin-dependent adhesion and suggested that it plays a role in coordination of the cell-cell and cell-substrate cytoskeletal interactions. The analysis of LPP function demonstrates proof of principle that the proteomic analysis of E-cadherin proximal proteins expands the inventory of components and tools for understanding the function of E-cadherin.