1.17.8 Adherens Junction Definition

Adherens Junction Definition is a description of a specialized structure formed at the site of contact between two adjacent cells, in which cadherin adhesion molecules on each cell surface engage in stable, calcium-dependent binding, and in which this extracellular binding is coupled through a defined set of intracellular adaptor proteins to the actin cytoskeleton of each cell, together forming a mechanically reinforced adhesive junction that contributes substantially to the structural integrity of the contact between the two cells.

Conceptual Basis

A Specialized, Reinforced Adhesive Structure

An adherens junction is defined by its organization as a discrete, specialized structure at the cell surface, distinguished from a simple, unorganized scattering of individual cadherin molecules by the concentrated clustering of cadherins together with their associated intracellular adaptor proteins at a specific site of cell-cell contact.

Coupling Extracellular Binding to the Internal Cytoskeleton

A defining structural feature of the adherens junction is the physical linkage it establishes between the extracellular cadherin-cadherin binding interaction and the internal actin cytoskeleton of each of the two adjoining cells, a coupling that substantially reinforces the mechanical stability of the adhesive contact beyond what the cadherin binding interaction alone would provide.

Structural Components

Cadherin Molecules

The core adhesive component of the adherens junction is provided by cadherin molecules positioned on the surfaces of the two adjoining cells, which engage in homophilic, calcium-dependent binding to form the direct physical connection between the two cell surfaces at the site of the junction.

Intracellular Adaptor Proteins

A defined set of intracellular adaptor proteins associates with the cytoplasmic portion of the cadherin molecules within the adherens junction, serving as the physical bridge connecting the cadherin adhesion molecules to the underlying actin cytoskeleton of the cell.

Linkage to the Actin Cytoskeleton

The intracellular adaptor proteins of the adherens junction connect directly to filaments of the actin cytoskeleton, anchoring the junction to this internal structural network and enabling the junction to both withstand and transmit mechanical forces experienced at the site of cell-cell contact.

Functional Roles

Providing Mechanical Reinforcement to Cell-Cell Contact

By coupling cadherin-mediated adhesion to the actin cytoskeleton, the adherens junction provides substantially greater mechanical stability to the cell-cell contact than would be achieved by cadherin binding alone, contributing to the overall structural integrity and cohesion of the tissue formed by the adjoining cells.

Coordinating Cytoskeletal Organization Between Adjacent Cells

Because the adherens junction physically links the actin cytoskeletons of two adjoining cells through the intervening cadherin-mediated contact, it provides a mechanism through which the cytoskeletal organization and associated mechanical behavior of neighboring cells can be coordinated across the shared junction.

Relationship to Cell-Cell Adhesion and Cancer Cell Biology

A Structurally Reinforced Instance of Cell-Cell Adhesion

The adherens junction represents a structurally reinforced, organized manifestation of cell-cell adhesion, integrating cadherin-mediated binding with cytoskeletal coupling to form a more mechanically robust adhesive contact than an unorganized adhesion molecule interaction alone would provide.

Consequences of Adherens Junction Disruption in Cancer Cells

Because the adherens junction provides substantial mechanical reinforcement to cell-cell contact, disruption of its component parts, whether through reduced cadherin expression or impaired function of the associated adaptor proteins, is closely associated with the weakened cell-cell adhesion and increased capacity for detachment and movement characteristic of cancer cell adhesion.