cell adhesion

Cell adhesion

The process by which cells attach to each other or to the extracellular matrix (ECM) to maintain tissue structure and communication.

Cell adhesion molecules (CAMs)

Transmembrane proteins that mediate cell–cell and cell–matrix interactions.

Main CAM families

Cadherins, Selectins, Ig-superfamily CAMs, and Integrins.

Cadherins

Ca²⁺-dependent proteins responsible for strong cell–cell adhesion in tissues like epithelium and muscle.

E-cadherin

Found in epithelial tissues; loss of E-cadherin is linked to cancer metastasis.

P-cadherin

Present in placenta and epidermis.

N-cadherin

Found in neural tissue; plays a role in brain and nerve cell connections.

Protocadherins

Non-classical cadherins found mainly in the brain, important for neural diversity.

Desmosomal cadherins

Include desmoglein and desmocollin; provide mechanical strength to tissues like skin and heart.

T-cadherin

Attached to the membrane via lipids; found in muscles and nerves.

Cadherin function

Maintains adherens junctions and desmosomes, regulates development, cell polarity, and tissue morphogenesis.

Selectins

Ca²⁺-dependent transmembrane proteins that bind specific carbohydrates to mediate transient cell–cell adhesion in the bloodstream.

L-selectin

Found on leukocytes; helps them roll along vessel walls.

P-selectin

Found on platelets and activated endothelial cells.

E-selectin

Found on activated endothelial cells; promotes leukocyte adhesion during inflammation.

Leukocyte extravasation

The process by which leukocytes roll, adhere, and migrate out of blood vessels into tissues.

Ig-superfamily CAMs (Ig-CAMs)

Ca²⁺-independent adhesion molecules containing immunoglobulin-like domains; involved in immune and neural cell adhesion.

ICAM-1 and VCAM-1

Found on endothelial cells; mediate leukocyte binding during inflammation.

NCAM

Found on nerve cells; promotes adhesion during neural development and regeneration.

L1-CAM

Mutations cause L1 syndrome (neurological disorder with mental retardation and hydrocephalus).

Integrins

Transmembrane heterodimers (α and β subunits) that mediate cell–ECM adhesion and signal transduction.

Integrin ligands

Fibronectin, collagen, laminin, and vitronectin.

Integrin functions

Mediate adhesion, transmit signals, convert mechanical forces to biochemical signals, and help immune cells migrate.

Occluding junctions

Tight junctions that seal neighboring cells to prevent leakage of molecules.

Anchoring junctions

Junctions that mechanically attach cells to one another or to the ECM.

Communicating junctions

Junctions that allow the passage of ions and small molecules between cells (e.g., gap junctions).

Tight junctions

Form a barrier at the apical side of epithelial cells; composed of claudins and occludins.

Adherens junctions

Cadherin-based junctions linked to actin filaments; form adhesion belts below tight junctions.

Desmosomes

Button-like junctions connecting intermediate filaments between cells; provide mechanical strength.

Focal adhesions

Integrin-based junctions connecting actin filaments to the extracellular matrix.

Hemidesmosomes

Integrin-based junctions that anchor epithelial cells to the basal lamina via intermediate filaments.

Gap junctions

Channels formed by connexons (6 connexins) that allow ions and small molecules to pass between cells.

Connexins

Channel-forming proteins that create connexons in gap junctions.

Gap junction function

Enable direct electrical and metabolic communication between adjacent cells.

Regulation of gap junctions

Can open or close in response to changes in pH, Ca²⁺ levels, or extracellular signals.

Importance of cell adhesion

Essential for embryonic development, immune responses, wound healing, and tissue repair.

Disease link: Cancer

Loss of E-cadherin or abnormal integrin signaling leads to metastasis.

Disease link: Autoimmune disorders

Overexpression of ICAM/VCAM causes chronic inflammation.

Disease link: Neurological disorders

L1-CAM mutations cause developmental brain defects.

Mechanotransduction

The process by which integrins convert mechanical forces from the ECM into biochemical signals.