28.5:
Anchoring Junctions
Cells connect with the ECM and other cells via different adhesion complexes, collectively called anchoring junctions.
In epithelial cells, focal adhesions and hemidesmosomes connect actin filaments, and intermediate filaments to a specialized form of ECM called the basal lamina.
Hemidesmosomes contain a dense plaque on the cytosolic side of the plasma membrane formed by the cytolinker protein plectin.
Keratin-containing intermediate filaments are connected to this plaque via alpha six beta four integrins and other proteins such as BP230, and BP180.
On the ECM face, the integrins bind laminin, a glycoprotein that is a major component of the basal lamina.
The resulting hemidesmosomes can transmit ECM signals helping the cell respond to mechanical forces and change shape, polarity, and direction of migration.
28.5:
Anchoring Junctions
Anchoring junctions are multiprotein complexes that help cells connect to other cells and the extracellular matrix. Anchoring junctions are present on the lateral and basal surfaces of cells, providing strong and flexible connections. Focal adhesions are often formed due to cell interactions with the ECM substrata, which initiate signal transduction via kinase cascades and other mechanisms. Together, they provide stability and tissue integrity. There are three types of anchoring junctions: desmosomes, hemidesmosomes, and adherens.
Desmosomes appear as dense, symmetrical, disc-shaped plaques on the cell membrane. Adhesion proteins called cadherins are involved in plaque formation. The distinctive appearance is due to structural proteins on the inner surface of the cell’s membrane.
Hemidesmosomes look like half a desmosome and link cells to the basal lamina. While similar in appearance to desmosomes, they include the adhesion proteins called integrins rather than cadherins. These connections are essential in holding cells together.
Adherens junctions use either cadherins or integrins depending on whether they link to other cells or the matrix. The junctions are characterized by the presence of the contractile protein actin located on the cytoplasmic surface of the cell membrane. The actin can connect isolated patches or form a belt-like structure inside the cell.
The three anchoring junctions influence the shape and folding of the epithelial tissue.
Adapted from section 4.2 Epithelial tissue- Anatomy and Physiology 2 e, Openstax
Suggested Reading
- Wei, Qi, and Hayden Huang. "Insights into the role of cell-cell junctions in physiology and disease." International review of cell and molecular biology 306 (2013): 187-221.
- Seetharaman, Shailaja, and Sandrine Etienne-Manneville. "Cytoskeletal crosstalk in cell migration." Trends in Cell Biology 30, no. 9 (2020): 720-735.
- https://www.mechanobio.info/what-is-mechanosignaling/what-are-cell-cell-adhesions/what-are-anchoring-junctions/