- Adherens junction
Adherens junctions (or zonula adherens) are protein complexes that occur at cell-cell junctions in epithelial tissues, usually more basal than
tight junctions .They can appear as bands encircling the cell (zonula adherens) or as spots of attachment to the extracellular matrix (adhesion plaques).
A similar cell junction in non-epithelial cells is the
fascia adherens . It is structurally the same, but appears in ribbon like patterns that do not completely encircle the cells. One example is incardiomyocytes .Proteins
They are composed of three major proteins:
*cadherins . The cadherins are a family of transmembrane proteins that form homodimers in a calcium-dependent manner with other cadherin molecules on adjacent cells.
*β-catenin andα-catenin . The catenins both form a complex with the intracellular portion of the cadherin molecule.Models
Adherens junctions were, for many years, thought to share the characteristic of
anchor cell s through their cytoplasmicactin filaments.The accepted model has been that adherens junctions serve as a
bridge connecting the actin cytoskeleton of neighboring cells through direct interaction. However, scientists have not been able to isolate the quaternary complex of cadherin-βcatenin-αcatenin-actinin vitro . Recent data (2005) from 2 labs atStanford University published in the journal "Cell" demonstrates that membrane associated actin is several fold less stable compared to components of the adherens junctional complex. [cite journal | author = Yamada S, Pokutta S, Drees F, Weis W, Nelson W | title = Deconstructing the cadherin-catenin-actin complex. | journal = Cell | volume = 123 | issue = 5 | pages = 889–901 | year = 2005 | pmid = 16325582 | doi = 10.1016/j.cell.2005.09.020] [cite journal | author = Drees F, Pokutta S, Yamada S, Nelson W, Weis W | title = Alpha-catenin is a molecular switch that binds E-cadherin-beta-catenin and regulates actin-filament assembly. | journal = Cell | volume = 123 | issue = 5 | pages = 903–15 | year = 2005 | pmid = 16325583 | doi = 10.1016/j.cell.2005.09.021]Additionally, the authors found that monomeric α-catenin preferentially binds to the cadherin junction complex through β-catenin. Dimeric α-catenin preferentially binds to actin and suppresses
Arp2/3 complex -mediated actin branching, thus acting as a molecular switch to regulate actin polymerization.Adherens junctions may serve as a regulatory module to maintain the actin
contractile ring with which it is associated in microscopic studies.References
External links
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