Adherens junction

In cell biology, adherens junctions (or zonula adherens, intermediate junction, or "belt desmosome"^[1]) are protein complexes that occur at cell–cell junctions and cell–matrix junctions in epithelial and endothelial tissues,^[2] usually more basal than tight junctions.

Adherens junction
Details
Identifiers
Latin	junctio adhaesionis
MeSH	D022005
TH	H1.00.01.1.02002
FMA	67400
Anatomical terminology [edit on Wikidata]

Principal interactions of structural proteins at cadherin-based adherens junction. Actin filaments are associated with adherens junctions in addition to several other actin-binding proteins such as vinculin. The head domain of vinculin associates to E-cadherin via α-, β - and γ -catenins. The tail domain of vinculin binds to membrane lipids and to actin filaments.

Adherens junctions (AJs) are crucial for cell adhesion in epithelial tissues, and play a significant role in cancer metastasis. While they initially help maintain tissue integrity and suppress tumor formation, their dysregulation can cause cancer cell invasion and spread. When adherens junctions are disrupted, cancer cells can detach from the primary tumor, gaining the ability to migrate and invade surrounding tissues. The breakdown of adherens junctions, particularly the loss of E-cadherin, is a key step in the epithelial-mesenchymal transition, a process where epithelial cells lose their cell-cell adhesion and polarity, transforming into a more mesenchymal (migratory) phenotype. ^[3][4] The suppression of E-cadherin expression is regarded as one of the main molecular events responsible for dysfunction in cell-cell adhesion, which can lead to local invasion and ultimately tumor development. Because E-cadherins play an important role in tumor suppression, they are also referred to as the "suppressors of invasion".^[5] Cancer cells can also remodel their adherens junctions, making them less stable but more dynamic, which can facilitate their movement and invasion. Specifically, the breakdown or remodeling of adherens junctions can lead to cancer cells detaching from the primary tumor, becoming more mobile, and metastasizing to other parts of the body.^[6][7]

An adherens junction is defined as a cell junction whose cytoplasmic face is linked to the actin cytoskeleton. They can appear as bands encircling the cell (zonula adherens) or as spots of attachment to the extracellular matrix (focal adhesion). Adherens junctions uniquely disassemble in uterine epithelial cells to allow the blastocyst to penetrate between epithelial cells.^[8]

A similar cell junction in non-epithelial, non-endothelial cells is the fascia adherens. It is structurally the same, but appears in ribbonlike patterns that do not completely encircle the cells. One example is in cardiomyocytes.^{[citation needed]}

Proteins

Adherens junctions are composed of the following proteins:^[9]

• cadherins. The cadherins are a family of transmembrane proteins that form homodimers in a calcium-dependent manner with other cadherin molecules on adjacent cells.
• p120 (sometimes called delta catenin) binds the juxtamembrane region of the cadherin.
• γ-catenin or gamma-catenin (plakoglobin) binds the catenin-binding region of the cadherin.
• α-catenin or alpha-catenin binds the cadherin indirectly via β-catenin or plakoglobin and links the actin cytoskeleton with cadherin. Significant protein dynamics are thought to be involved.^[10]

Models

Adherens junctions were, for many years, thought to share the characteristic of anchor cells through their cytoplasmic actin filaments.^{[citation needed]}

Adherens junctions may serve as a regulatory module to maintain the actin contractile ring with which it is associated in microscopic studies.^{[citation needed]}

See also

• Tight junction