3.2 Cell Adhesions

Cell Adhesion

Is the binding of a cell​ to another cell, a surface, or to the extracellular matrix.

Selectins, integrins, lg superfamily CAMs (NCAM) and cadherins

Cell Adhesion uses molecules such as​?

Link the cytoplasm of cells and involved in signal transduction

Correct cellular adhesion is essential in maintaining multicellular structure. It can?

Cell Junctions​

• collections of adhesion molecules that join cells together within tissues.​

• important in maintaining the structure of a tissue as well as its integrity.

Adhesive Junctions (desmosomes, hemidesmosomes, adherens junctions)

Link adjoining cells to each other and to the ECM. They are similar in structure and function, but contain distinct intracellular attachment proteins and transmembrane linker proteins.​

Tight or occluding junctions (zonulae occludentes)

Function: Prevent the leakage of substances between cells, creating a barrier (e.g., in epithelial cells)

Components: Claudins and occludins

Adherens junctions (zonulae adherentes)

Function: Provide mechanical strength by linking the cytoskeletons of adjacent cells.

Components: Cadherins linked to actin filaments.

Desmosomes or anchoring junctions (maculae adherentes)​

Function: Provide strong adhesion between cells, particularly in tissues subject to mechanical stress (e.g., skin).

Components: Cadherins linked to intermediate filaments.

Hemidesmosomes

Function: focus on cell-to-extracellular matrix adhesion

Structure: contain integrins that bind to components of the extracellular matrix (like laminin), distinguishing them from other junctions that connect neighboring cells

Gap Junctions

Function: Allow direct communication between adjacent cells through channels that permit the passage of ions and small molecules.

Components: Connexins that form connexons.

Cadherins

Homophilic Binding: Mediate strong and specific homophilic adhesion, allowing cells of the same type to adhere tightly to one another, which is essential for maintaining tissue architecture.

Tissue Morphogenesis: Influencing the shape and structure of developing organs and tissues

Cancer Suppression: Prevent tumor cell invasion and metastasis by maintaining cell adhesion and integrity

Immunoglobulin Superfamily CAMs(NCAM) or lg superfamily

Cell-Cell Recognition: Nervous system, they help neurons identify and connect with one another

Neuronal Adhesion: Ensures proper connectivity between neurons and contributing to neural network formation

Developmental Processes: tissue organization and immune responses

Integrins

Cell-Matrix Adhesion: anchoring cells to the extracellular matrix (ECM), providing structural support and stability to tissues

Bidirectional Signaling: between cells and the ECM, influencing cell behavior, survival, differentiation, and migration

Tissue Integrity and Repair: wound healing by promoting cell migration and proliferation at injury sites

Selectins

Initial Adhesion: mediate the initial adhesion between circulating leukocytes and the endothelial cells lining blood vessels, which is crucial during immune responses

Rolling Mechanism: rolling of leukocytes on the endothelium, allowing immune cells to slow down and adhere more firmly to the endothelium before migrating to tissues

Inflammatory Response: recruitment of immune cells to sites of inflammation, Selectins are essential for a proper immune response and tissue repair.

Extravasation

Mechanism: Normal leukocyte movement; exploited by monocytes

Implication: Contributes to fatty streak formation

Cancer Progression

Mechanism: Loss of E-cadherin; changes in adhesion molecule expression

Implication: Facilitates metastasis and tumor aggressiveness

Leukocyte Adhesion Deficiency (LAD)

Mechanism: Deficiency of ß2 integrin subunits

Implication: Leads to severe infections and death at an early age

Chronic Inflammation

Mechanism: Increased expression of adhesion molecules

Implication: Associated with asthma and rheumatoid arthritis

Viral Infections

Mechanism: Viruses use adhesion molecules as receptors

Implication: Initiates infections such as rhinovirus in humansI

Plasmodesma

microscopic channel which goes between the cell walls of plant cells enabling transport and communication between them

Plasmodesmata

Connects two neighboring cells