Cell Adhesion Flashcards
tight junction seals
gap between epithelial cells
adherent junction connects
actin filament bundle in one cell with that in the next cell
desmosomes connect
intermediate filaments in one cel to those in the next cell
gap junctions allow for the passage of
small water soluble molecules from cell to cell
actin linked cell matrix adhesion anchors
actin filaments in cell to extracellular matrix
hemidesmosome anchors
intermediate filaments in a cell to extracellular matrix
first principle of adhesion
cells define their capacity for adhesive interactions by selectively expressing plasma membrane receptors (cell adhesion molecules, aka: CAMs) with limited ligand-binding activity. Generally, expression of the proper mix of receptors is part of a genetic program for the differentiation of the cell. In some cases, extracellular stimuli control expression of adhesion receptors. For example, endothelial cells produce E-selectin only when stimulated by inflammatory hormones or endotoxin
second principle of adhesion
many adhesion proteins bind one main ligand, and many ligands bind a single type of receptor
if this one-to-one pairing were the rule, adhesion would be simple indeed. However, many exceptions exist, particularly in the
integrin family of receptors
these integrin receptors generally bind
more than one ligand, and some ligands, such as fibronectin, bind more than one integrin
Most cadherins prefer to bind
themselves
cadherins promote the adhesion of
like cells
homophilic interactions
association of like receptors on two cells
cadherin reactions require
ca
Selectins bind
anionic polysaccharides like those on mucins
Generally, such interactions bind together
two different types of cells
Most Ig-CAMs bind
other cell surface adhesion proteins
heterophilic interactions
association of unlike receptors on two cells
These heterophilic interactions may occur between
the same or different cell types
integrins stand apart because they bind
a variety of ligands
variety of ligands includes
matrix macromolecules, such as fibronectin and laminin; soluble proteins, such as fibrinogen in blood; and adhesion proteins on the surface of other cells, including Ig-CAMs and one cadherin
third principle of adhesion
Cells modulate adhesion by controlling the surface density, state of aggregation, and state of activation of their adhesion receptors
Surface density reflects not only the level of synthesis but also the
partitioning of adhesion molecules between the plasma membrane and intracellular storage compartments
endothelial cells express P-selectin constitutively but store it internally in membranes of cytoplasmic vesicles. When inflammatory cytokines activate endothelial cells, these vesicles
fuse with the plasma membrane, exposing P-selectin on the cell surface, where it binds white blood cells
cadherins control the
selective assortment of cells
cells can sort themselves out according to
the type and level of cadherins they express
cadherins
calcium-dependent adhesion molecules. Cadherins are critical for establishing and maintaining intercellular connections, and they appear to be crucial to the spatial segregation of cell types and to the organization of animal form (Takeichi 1987). Cadherins interact with other cadherins on adjacent cells, and they are anchored into the cell by a complex of proteins called catenins (Figure 3.31). The cadherin-catenin complex forms the classic adherens junctions that connect epithelial cells together. Moreover, since the catenins bind to the actin cytoskeleton of the cell, they integrate the epithelial cells together into a mechanical unit.
fourth principle of adhesion
The rates of ligand binding and dissociation are important determinants of cellular adhesion
Many cell surface adhesion proteins (including members of the Ig-CAM, cadherin, integrin, and selectin families) bind their ligands
weakly in comparison with other specific macromolecular interactions, such as the interaction of antigens and antibodies, hormones and receptors, or transcription factors and DNA
In some cases, this makes good biological sense. Rapidly reversible interactions allow white blood cells to
roll along the endothelium of blood vessels
