13: Extracellular Matrix and Cell Adhesion
- Page ID
- 16176
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Interactions between a cell and its environment or with other cells are governed by cell-surface proteins. This chapter examines a subset of those interactions: direct cell contact with either other cells or extracellular matrix (ECM). Extracellular matrix is a general term for the extremely large proteins and polysaccharides that are secreted by some cells in a multicellular organism, and which acts as connective material to hold cells in a defined space. Cell density can vary greatly between different tissues of an animal, from tightly-packed muscle cells with many direct cell-to-cell contacts to liver tissue, in which some of the cells are only loosely organized, suspended in a web of extracellular matrix.
- 13.1: Introduction to Extracellular Matrix and Cell Adhesion
- This page discusses cell-surface proteins that mediate interactions between cells and their environment, focusing on direct contact with other cells and the extracellular matrix (ECM). It describes the ECM's composition, which supports tissue organization, and notes that tissue function is influenced by varying cell densities and ECM types.
- 13.2: Collagen
- This page discusses collagen, a key extracellular matrix protein that constitutes a significant part of the body's dry mass. It exists in both fibrillar and non-fibrillar forms, essential for structural support in tissues like tendons and ligaments. Collagen's unique amino acid composition contributes to its strength, and mutations in its genes can cause diseases such as epidermolysis bullosa and osteogenesis imperfecta.
- 13.3: Proteoglycans
- This page discusses proteoglycans, which consist of a core protein and glycosaminoglycans (GAGs). Despite being less voluminous than collagen, their extensive glycosylation allows them to attract water and ions. Important GAGs include chondroitin sulfate, heparan sulfate, and hyaluronic acid. Heparin acts as an anti-clotting agent by activating antithrombin III.
- 13.4: Fibronectins
- This page discusses the roles of fibronectin and laminin in the extracellular matrix (ECM), highlighting fibronectin's structure of two polypeptide subunits with functional domains. It emphasizes its importance in cell migration, development, and wound healing, pointing out the significance of the RGD sequence for cell binding. Disruption of this sequence affects adhesion, and fibronectin's ability to self-associate into fibrils contributes to ECM stability.
- 13.5: Laminins
- This page discusses laminin, a glycoprotein family in the extracellular matrix essential for cell adhesion and development. Comprised of three subunits in a cruciform structure, laminin has various isoforms and is key in neural development and germ cell migration through interactions with integrins. Mutations in certain laminin types can lead to congenital muscular dystrophy, highlighting its importance in forming fibrils and networks in the basal lamina.
- 13.6: Integrins
- This page discusses integrins, a diverse family of receptors that bind to extracellular matrix proteins like collagen and fibronectin. They are essential for cell adhesion, migration, and signaling via focal adhesions, which can be transient or stable based on cell type. Integrins consist of α and β subunits and can exist in active or inactive states, with inside-out signaling enabling quick ligand binding.
- 13.7: Hemidesmosomes
- This page discusses hemidesmosomes, crucial structures anchoring epithelial cells to the basement membrane for stability. It highlights the role of the α6β4 integrin and the electron-dense plaque with plectins and BP230. BP180, a transmembrane glycoprotein, also connects to the basement membrane. The page notes the involvement of BP230 and BP180 in bullous pemphigoid, an autoimmune disorder that causes skin blistering due to wrongful immune responses against these proteins.
- 13.8: Dystrophin Glycoprotein Complex
- This page discusses the dystrophin glycoprotein complex (DGC) essential for linking skeletal muscle cells to the extracellular matrix (ECM), providing mechanical support. Key components include dystroglycan, which binds to laminin, and the sarcoglycan complex, which may enhance membrane integrity. Although mutations in DGC components cause muscular dystrophies, the role of sarcospan remains unclear, and its absence has not been directly associated with these disorders.
- 13.9: Desmosomes
- This page explains how cells use proteins, especially integrins and cadherins, to form adhesive interactions. It details the structure and function of desmosomes and hemidesmosomes in linking epithelial cells and the ECM. Desmosomes contain dense plaques with plakoglobins and desmoplakins connected to keratin filaments.
- 13.10: Cadherins
- This page discusses the cadherin superfamily, which includes various proteins essential for cell adhesion in different tissues. It highlights the structure and function of cadherins, including their interactions with catenins and actin filaments. Key types like E-cadherin, N-cadherin, and P-cadherin play vital roles in embryonic development and cancer metastasis.
- 13.11: Tight Junctions
- This page discusses tight junctions in epithelial layers, highlighting their role in sealing cell membranes, especially in the digestive tract to prevent leakage and assist in nutrient transport. It details the composition, including claudins and occludins, and emphasizes the significance of multiple arrays of tight junctions in enhancing sealing.
- 13.12: Ig Superfamily CAMs
- This page discusses Junction adhesion molecules (JAMs), integral components of tight junctions within the immunoglobulin superfamily. JAMs facilitate cell adhesion via immunoglobulin loop domains and vary in structure, encompassing variable and constant loops. They are essential for cellular adhesion, impacting immune responses and neural development by guiding axon routing.
- 13.13: Selectins
- This page covers selectins, a group of cell adhesion molecules that bind to specific oligosaccharides on glycoproteins. The main types are L-selectin, E-selectin, and P-selectin, each important for immune responses and inflammation. They enable calcium-dependent adhesion, essential for neutrophil migration during injuries. Key ligands such as PSGL-1 are involved, making selectin-mediated adhesion crucial for understanding immune cell movement and inflammatory reactions.
- 13.14: Gap Junctions
- This page discusses gap junctions, which are formed by connexons made of connexin proteins and connect adjacent cells’ cytoplasm. They enable the passage of small molecules and ions, playing essential roles in cardiac muscle synchronization and neural communication, especially in the retina. The page also notes that phosphorylation can regulate gap junction conductance, showcasing their functional versatility in cellular communication.
Thumbnail: Illustration depicting extracellular matrix (basement membrane and interstitial matrix) in relation to epithelium, endothelium and connective tissue. (Public Domain; Twooars via Wikipedia).