Cell Adhesion Molecules (CAMs) PDF

Cell Adhesion molecules Content Basics of cell communication Cell-adhesion molecules (CAMs) Cadherins Integrins Selectins Immunoglobulin (Ig) Superfamily Experimental Case Study Cell communication In cell biology refers to the process by which cells send and receive s...

Cell Adhesion molecules Content Basics of cell communication Cell-adhesion molecules (CAMs) Cadherins Integrins Selectins Immunoglobulin (Ig) Superfamily Experimental Case Study Cell communication In cell biology refers to the process by which cells send and receive signals to coordinate their activities. It enables cells to interact with their environment and with each other, allowing them to respond appropriately to external stimuli. Cell-adhesion molecules (CAMs) CAMs CAMs are transmembrane or membrane-linked glycoproteins. Mediate connections between cells. Attachment of cells to their substrate (such as the stroma or basement membrane). CAMs help cells stick to each other and to their surroundings. They act as “molecular glue” and are essential for maintaining tissue integrity and function. Structure CAMs typically have three conserved domains Intracellular domain: Interacts with the cytoskeleton. Transmembrane domain: Anchors the protein in the cell membrane. Extracellular domain: Involved in binding to other cells or the extracellular matrix (ECM). Interact through homophilic binding (with the same CAMs) or heterophilic binding (with different CAMs on other cells). Biological Functions Cell–cell adhesion: Directly binding neighboring cells. Cell–matrix adhesion: Attaching cells to the ECM. Growth, contact inhibition, and apoptosis: Regulating cell behavior. Types of cell-adhesion molecules Cadherins Transmembrane proteins that play a role in cell-cell adhesion. Bind to cadherins on adjacent cells, providing mechanical strength and cells stick together. Integrins Heterodimeric proteins that connect the extracellular matrix (ECM) to the cell’s cytoskeleton. They allow cells to adhere to the ECM and participate in signaling pathways. Selectins Involved in the initiation of inflammatory processes. They mediate interactions between immune cells and endothelial cells during inflammation. Immunoglobulin (Ig) Superfamily Immunoglobulin-like structure and function as receptors for signal transmission. They are involved in cell recognition and communication. Major families of cell-adhesion molecules (CAMs) and adhesion receptors ICAM and VCAM mediate heterotrophic binding  Homophilic Binding (Cadherins, lg-superfamily) Heterophilic Binding (Integrins, Selectins) Involves the same CAMs on interacting cells Involves different CAMs on interacting cells Typically involves similar or identical molecules Typically involves distinct molecules that can binding to each other recognize and bind to each other Contributes to cell sorting by promoting adhesion Facilitates interactions between different cell types among similar cell types or within the extracellular matrix Seen in processes like tissue formation and Important for processes such as immune maintenance responses and development Cadherins Definition: Cell adhesion molecules that allow cells to stick together. Function: Maintaining cell-cell contact and regulating cytoskeletal complexes. Structure: Cadherins are type-1 transmembrane proteins with extracellular cadherin repeats (Ca2+ binding domains), a transmembrane domain, and an intracellular cytoplasmic tail. Dependence on Ca2+: Their name comes from their reliance on calcium ions (Ca2+) for proper function. Adhesion Mechanism: Extracellular cadherin domains mediate cell-cell adhesion, while the intracellular tail interacts with adaptors and signaling proteins (collectively known as the cadherin adhesome). Cadherin structure  Experiment If the extracellular Ca2+ concentration is decreased artificially in an experiment, Ca2+ binding decreases. As a result, increased flexibility in the hinge regions results in a floppier molecule that is no longer oriented correctly to interact with a cadherin on another cell—and adhesion fails. Cadherin structure The extracellular region contains five copies of the extracellular cadherin domain separated by flexible hinge regions. At a typical extracellular Ca2+ concentration (>1 mM), Ca2+ ions (red dots) bind in the neighborhood of each hinge, preventing it from flexing. To generate cell– cell adhesion, the cadherin domain at the N-terminal tip of one cadherin molecule binds the cadherin domain at the N-terminal tip of a cadherin molecule on another cell. The structure was determined by x-ray diffraction of the crystallized C-cadherin extracellular region. Types of Cadherins Classical Cadherins Form homodimers within the same cell (cis interaction). Involved in tissue layer formation and structure. Examples: E-cadherin (found in various epithelial cells), N-cadherin (expressed in nerve, muscle, and lens cells), and P-cadherin (present in placenta and epidermis). Desmosomal Cadherins (non classical) Heterodimeric. Focus on resisting cell damage. Examples: Desmogleins and desmocollins, which maintain desmosome function. Interact with proteins like plakoglobin, plakophilins, and desmoplakins. Atypical Cadherins Retain extracellular repeats and binding activities but differ significantly in structure. Transmit developmental signals rather than adhesion. Example: CELSR13. Cis and trans interaction Trans (Intercellular) and Cis (On the Same Cell) Interactions Classical cadherins participate in both trans (intercellular) and cis (on the same cell) interactions. Trans interactions Occur between cadherins on adjacent cells. The binding of the extracellular cadherin domains (EC1-EC5) stabilizes these interactions. Cis interactions involve binding between cadherins on the same cell. The EC1 domain of one cadherin binds to the EC2 domain of an adjacent cadherin on the same cell. The EC1 domain of one cadherin also binds to the EC1 domain of a cadherin on the adjacent cell. These multiple low-affinity interactions sum up to create a very tight intercellular adhesion. Calcium-Dependent Binding The extracellular domains of classical cadherins contain five repeats (EC1-EC5). Binding of three Ca2+ ions at each site between the cadherin repeats stabilizes the elongated and curved structure of the extracellular domain. This curved structure is essential for proper molecular complementarity, which in turn stabilizes both cis and trans binding between cadherin molecules. Structure of Cadherin Vedemy Capsule Cadherin Type Characteristics Subtypes Examples Structure Domains Classical Mediate strong cell-cell Extracellular cadherin E-cadherin (CDH1) Epithelial tissues Cadherins adhesion (EC) repeat domains Found in adherens N-cadherin (CDH2) Neural tissues Rigidified by Ca²⁺ ions junctions Regulate tissue Linker regions P-cadherin (CDH3) Placental tissues morphogenesis between EC domains Essential for adult tissue VE-cadherin (CDH5) Endothelial cells architecture Desmosomal Mediate strong cell-cell Desmocollins (DSC1, Desmosomes EC repeat domains Cadherins adhesion DSC2, DSC3) Desmogleins (DSG1, Found in desmosomes Epidermal tissues Rigidified by Ca²⁺ ions DSG2, DSG3) Essential for tissue Linker regions Desmoplakin (DSP) Cardiac tissues integrity between EC domains Interact with intermediate Plakoglobin (JUP) Muscle tissues filaments Vedemy Capsule Cadherin Type Characteristics Subtypes Examples Structure Domains Proto-Flamingo Involved in tissue Protocadherin-03 Multiple EC repeat Neural tissues Cadherins morphogenesis (PCDH3) domains Regulate cell motility Protocadherin-B1 Brain development Variable EC domains and gene expression (PCDH1) Protocadherin-1 Synaptic Signaling scaffolds (PCDH1) connections Altered in diseases Protocadherin-8 with compromised Embryonic tissues (PCDH8) function Involved in tissue Up to 34 EC repeat Fat-Like Cadherins Fat (FAT1, FAT2) Epithelial tissues organization domains Function as signaling Dachsous (DCHS1, Large extracellular Planar cell polarity scaffolds DCHS2) domains Altered pathways in Flamingo (CELSR1, Neural tissues EGF domains diseases CELSR2) Fat-like related Tissue-specific Cadherin-binding cadherins functions domains Integrins Consist of two subunits α and β noncovalently associated to form a heterodimer. Transmembrane Proteins: Both α and β subunits span the cell membrane. Domains Extracellular Domains: These large N-terminal domains interact with specific amino acid motifs in extracellular matrix (ECM) proteins or other cell surface proteins. Intracellular C-Terminal Tails: These short tails extend into the cytoplasm and participate in signal transduction. Binding Sites The RGD sequence (Arg-Gly-Asp) is a well-studied binding site for integrins. It is found in fibronectin and other ECM proteins. Some integrins also recognize the Leu-Asp-Val (LDV) sequence in fibronectin. Integrins can bind to additional sequences in laminins and collagens. Function of Integrins Cell-ECM Adhesion Signal Transduction Regulate processes like the cell cycle, cytoskeletal organization, and receptor trafficking. Dynamic Responses: Integrins enable rapid and flexible cellular responses to external events, such as platelets initiating interactions with coagulation factors. Structure of Integrins The subunit structure of an active integrin molecule, linking extracellular matrix to the actin cytoskeleton. The N-terminal heads of the integrin chains attach directly to an extracellular protein such as fibronectin; the C- terminal intracellular tail of the integrin β subunit binds to adaptor proteins that interact with filamentous actin. Adaptor is a giant protein called talin, which contains a string of multiple domains for binding actin and other proteins, such as vinculin, that help to regulate the linkage to actin filaments. One end of talin binds to a specific site on the integrin β-subunit cytoplasmic tail; other regulatory proteins, such as kindlin, bind at another site on the tail. Types of Integrins Types of Integrins Selectins Function: Selectins are cell-surface proteins (lectins) that mediate transient cell–cell adhesion interactions in the bloodstream. Role: In vertebrates, their primary role is to govern the traffic of white blood cells (leukocytes) into lymphoid organs and inflamed tissues. Adhesive Behavior: White blood cells move between the bloodstream and tissues, requiring specialized adhesion behavior. Binding to Endothelial Cells: Selectins control the binding of white blood cells to endothelial cells lining blood vessels. Types: L-selectin: Found on white blood cells. P-selectin: Present on blood platelets and locally activated endothelial cells during inflammation. E-selectin: Expressed by endothelial cells later in the inflammatory response. Recognition: In lymphoid organs (e.g., lymph nodes, spleen), endothelial cells express oligosaccharides recognized by L-selectin on lymphocytes, causing lymphocytes to linger and become trapped. Inflammation: During inflammation, endothelial cells switch on selectin expression, recognizing oligosaccharides on white blood cells and platelets, guiding them to the site of emergency. The structure of selectins Types of Selectins Selectin Type Characteristics Subtypes Examples Structure Domains Induced by Expressed primarily on E-selectin E-selectin (CD62E) inflammatory N-terminal lectin domain endothelial cells cytokines Epidermal growth factor (EGF)-like domain Variable consensus repeat units Transmembrane domain Intracellular cytoplasmic tail Expressed on Found in most L-selectin L-selectin (CD62L) Similar structure to E-selectin leukocytes leukocytes Targeted to tips of microfolds on leukocytes Stored in α- Expressed on platelets P-selectin P-selectin (CD62P) granules of Similar structure to E-selectin and endothelial cells platelets Translocated to cell surface upon activation Targeted to secretory granules Binds to PSGL-1 (P-selectin glycoprotein ligand-1)  How selectins and integrins mediate the cell–cell adhesions required for a white blood cell to migrate out of the bloodstream into a tissue. Selectins on endothelial cells bind weakly to oligosaccharides on the white blood cell, so that it becomes loosely attached and rolls along the vessel wall. The white blood cell then activates a cell surface integrin called LFA1, which binds to a protein called ICAM1 (belonging to the Ig superfamily) on the membrane of the endothelial cell. The white blood cell adheres to the vessel wall and then crawls out of the vessel. Selectin Collaborate with Integrins Integrins: Integrins are another major class of receptors within the extracellular matrix (ECM). Roles Integrins mediate cell–ECM interactions with components like collagen, fibrinogen, fibronectin, and vitronectin. They provide essential links between the extracellular environment and intracellular signaling pathways. Integrins influence cell behaviors such as apoptosis, differentiation, survival, and transcription. Heterophilic Binding: Both selectins and integrins participate in heterophilic cell–cell adhesions, binding to different types of molecules. Specificity Selectins bind to specific oligosaccharides on glycoproteins and glycolipids. Integrins bind to specific Ig-family proteins. Immunoglobulin superfamily Roles in cell recognition, adhesion, and signal transduction. Extracellular immunoglobulin-like domains and are involved in various cell-cell interactions. ICAMs, VCAMs, NCAMs, and Nectins. ICAMs (Intercellular Cell Adhesion Molecules) They play a critical role in immune response and inflammation. ICAMs are recognized by white blood cell integrins. These proteins mediate heterophilic binding to integrins on endothelial cells. Examples include ICAM-1, ICAM-2, and ICAM-3. VCAMs (Vascular Cell Adhesion Molecules) They are expressed on endothelial cells. VCAMs facilitate adhesion of immune cells (such as leukocytes) during inflammation. VCAM-1 (CD106) is a well-known member of this family.  NCAM (Neural Cell Adhesion Molecule) Expressed by various cell types, including nerve cells. It plays a role in neural development, cell migration, and synaptic plasticity. NCAM can exist in different forms due to alternative splicing of its RNA transcript. Some NCAM forms carry polysialic acid chains (long chains of sialic acid). The negative charge of polysialic acid can interfere with cell adhesion, inhibiting it rather than promoting it. Nectins They contain three Ig-like domains and can interact either homophilically or heterophilically Link to the actin cytoskeleton via their short intracellular tail and also bind to cadherins. During embryonic development, nectins help establish cell-cell interactions. Immunoglobulin superfamily NCAM is expressed on neurons and many other cell types, and it mediates homophilic binding. ICAM is expressed on endothelial cells and some other cell types and binds heterophilically to an integrin on white blood cells. Nectin is expressed in many cell types and is often found at adherens junctions, where it interacts with cadherins to help establish and strengthen specific cell–cell interactions during tissue formation. Mega Vedemy Capsule Feature Cadherins Integrins Selectin Immunoglobulin Superfamily Function Mediate cell-to-cell Mediate cell-to- Mediate leukocyte rolling Mediate cell-cell adhesion extracellular matrix and adhesion during interactions in the adhesion inflammation immune system Type Transmembrane Transmembrane Transmembrane Transmembrane proteins proteins receptors proteins Dependence Require Calcium ions Not dependent on Ca²⁺ Not dependent on Ca²⁺ Not dependent on Ca²⁺ (Ca²⁺) for function Synthesis Synthesized as Formed by noncovalent Synthesized as Synthesized as polypeptides binding of α and β polypeptides polypeptides subunits Amino Acid Length About 720-750 amino Varies based on subunit Varies based on subunit Varies based on subunit acids composition composition composition Cell-to-extracellular Cell Adhesion Type Cell-to-cell adhesion Cell-to-cell adhesion Cell-to-cell adhesion matrix adhesion Mega Vedemy Capsule C-terminal Lectin domain, EGF-like Variable domains, Ig-like Distinct Parts Transmembrane α subunit and β subun it domains, Short domains, Extracellular domain cytoplasmic tail Transmembrane region Stability of Strong and stable Flexible responses to Short-lived interactions Variable interactions Interactions interactions events at the cell surface Tissue Integrity Helps maintain tissue Involved in wound Involved in immune Involved in immune integrity healing, immune response, neural response, inflammation, response, and development, and and cancer metastasis metastasis cell migration Junctions Adherens junctions and Not associated with Not associated with Not associated with desmosomes specific junctions specific junctions specific junctions ICAM-1, VCAM-1, Examples Classical cadherins (E- Collagen-binding L-selectin, P-selectin, E- NCAM, L1-CAM, cadherin, N-cadherin), integrins, Laminin- selectin, GlyCAM-1, JAMs Desmoglein and binding integrins, CD34 desmocollin, RGD-binding integrins, Protocadherins, Leukocyte-specific Unconventional cadherins integrins Experimental Case: Investigating the Effects of N-Cadherin and N-CAM Mutations Objective: To determine the effects of mutations in N-cadherin and N-CAM on embryonic development and nervous system formation in mice. Methodology Generation of Genetically Modified Mice Set A: Mice with a mutation in the gene encoding N-cadherin. Set B: Mice with a mutation in the gene encoding N-CAM. Observations and Recordings Monitor developmental progress and survival rates of embryos and postnatal mice from both sets. Conduct histological examinations of nervous tissue from surviving mice. Experimental Case: Investigating the Effects of N-Cadherin and N-CAM Mutations Set A: Mice with a mutation in Set B: Mice with a mutation in the gene encoding N-cadherin the gene encoding N-CAM Expected Results Expected Results Set B (N-CAM Mutations) Set A (N-Cadherin Mutations) Prediction: Mice from Set B will survive embryonic Prediction: Mice from Set A are likely to die during development but may exhibit mild abnormalities within early stages of embryonic development. their nervous systems. Rationale: N-cadherins are essential for Rationale: N-CAM, belonging to the Ig-SF, is involved in Ca2±dependent cell-cell adhesion processes critical fine-tuning adhesive interactions rather than for tissue formation. A mutation disrupting this establishing initial adhesion. Mutations here might not function would compromise proper tissue be lethal but could affect neural tissue where these development. molecules play significant roles. Vedemy Capsule Cell Adhesion Therapeutic Definition Mutations Mechanism of Action Molecule Family Implications Calcium-dependent Loss-of-function: Homophilic interactions adhesion proteins Reduced adhesion due via extracellular domains. Potential impact on Cadherins maintaining tissue to altered function. Connect to actin cancer metastasis and integrity and cell-cell Gain-of-function: cytoskeleton via tissue regeneration. adhesion. Abnormal adhesion. catenins. Bind to extracellular Heterodimeric Functional mutations: matrix proteins (e.g., Applications in cancer transmembrane Integrins Alter integrin affinity. fibronectin, collagen). therapy and tissue receptors mediating cell- Expression changes. Transmit bidirectional repair. matrix interactions. signals. Loss-of-function: Mediate transient Impaired leukocyte interactions between Adhesion molecules in Modulating selectin rolling/adhesion. leukocytes and Selectins leukocyte recruitment activity for Gain-of-function: endothelial cells. during inflammation. inflammatory diseases. Excessive Recognize carbohydrate inflammation. ligands. Mediate homophilic and Immunoglobulin-like Implications in Structural mutations: heterophilic interactions. domain-containing neurodevelopmental IgCAMs Affect binding affinity. Roles in neural molecules participating disorders and immune- Expression changes. development, immune in cell-cell interactions. related diseases. responses, etc. CSIR NET practice problem Q. Which of the following is not a cell adhesion molecule? (Dec 2008) (a) Cadherin (b) Selectin (c) Integrin (d) Immunoglobulin Answer; d CSIR NET practice problem Q. The essential mineral required for cell adhesion molecule, cadherin is? (June 2009) (a) Calcium (b) Magnesium (c) Iron (d) Sodium Answer; a CSIR NET practice problem Q. Which of the following molecules is involved in Ca2+-dependent cell-cell adhesion? (June 2011) (a) Calmodulin (b) Cadherin (c) N-CAM (d) Calpain Answer; b CSIR NET practice problem Q. Which of the following is an intracellular anchor protein? (Dec 2012) (a) Vitronectin (b) Vinculin (c) Integrin (d) Elastin Answer; b CSIR NET practice problem Q. Vascular endothelial (VE)-cadherin is an important cell adhesion molecule for endothelial cells. Endothelial cells that are unable to express VE- cadherin still can adhere to one another via N- cadherin (neural cadherin), but these cells do not survive. Which of the following is the most appropriate reason for this? (Dec 2013) a. N-cadherin uses VE-cadherin as co-receptor for adhesion. b. VE-cadherin acts as co-receptor for VEGF (vascular endothelial growth factor) mediated signal transduction in endothelial cells. c. VE-cadherin is important for desmosome formation and interaction of intermediate filaments. d. Loss of VE-cadherin impairs Ca2+ homeostasis of vascular endothelial cells leading to their death. Answer; b  CSIR NET practice problem Q. Which one of the following statements about cell-cell interactions is NOT true? (Dec 2014) A. Cadherins are transmembrane linker proteins which carry out Ca2+-mediated adhesion between adjacent cells. B. Integrins are transmembrane adhesion proteins that mediate hemophilic adhesion through actin and intermediate filaments. C. Selectins are cell surface lectins that mediate a variety of transient, cell-cell adhesion interactions in the bloodstream. D. ICAMs (intracellular cell adhesion molecules) and VCAMs (vascular cell adhesion molecules) are members of immunoglobulin (Ig) superfamily. (a) Only A (b) Only B (c) Both C and D (d) Both A and D Answer; b CSIR NET practice problem Q. Cadherins mediate Ca2+-dependent cell-cell adhesion and play an important role in embryonic development by changing the adhesive properties of cell. Aggregation of nerve cells to form an epithelium is correlated with the appearance of N- cadherins on cell surface and vice versa. N-CAM (neural cell adhesion molecules) belongs to Ig-SF (immunoglobulin superfamily) and involved in fine tuning of adhesive interaction. In order to see the effect of mutations of N-cadherin and N-CAM, two sets of mice were generated. Set A - mice with' /nutation in N-cadherin and set B - mice with mutation in N- CAM. Which of the following results is most likely to occur? (June 2016) (a) Mice of both set A and set B will die in early development. (b) Mice of set A will die in early development but mice of set B will develop normally and show mild abnormalities in the development of nervous system. (c) Mice of Set A will show mild abnormalities in the development of nervous system whereas mice of set B will die early in development. (d) Mice of both set A and set B develop normally as other cell adhesion molecules will compensate for the mutations. Answer; b  CSIR NET practice problem Q. In animals, four separate families of cell–cell adhesion proteins are listed in Column A and their functional characteristics are given in Column B: (Dec 2016) Column A Column B (A) Integrin (i) Lectins that mediates a variety of transient, cell- cell adhesion interactions in the blood stream (B) Cadherin (ii) Contains extracellular Ig-like domain and are mainly involved in the fine tuning of cell-cell adhesive interaction during development and regeneration. (C) Ig-superfamily (iii) Mediates Ca2+- dependent strong homophilic cell - cell adhesion. (D) Selectin (iv) Transmembrane cell adhesion proteins that acts as a extracellular matrix receptor a. A – (i), B – (ii), C – (iii), D – (iv) b. A – (ii), B – (iii), C – (iv), D – (i) c. A – (iii), B – (iv), C – (i), D – (ii) d. A – (iv), B – (iii), C – (ii), D – (i) Answer; d CSIR NET practice problem Q. Several types of molecules including transmembrane glycoproteins can function as matrix receptors and co- receptors. However, the principal receptors on animal cells for binding most extracellular matrix proteins are the integrins. Which of the following statements is NOT true for integrins? (Dec 2017) a. Integrins are transmembrane linker proteins that link to the cytoskeleton. b. An integrin molecule is composed of two non-covalently associated glycoprotein subunits. Both subunits span the cell membrane, with short intracellular C-terminal tails and large N-terminal extracellular domains. c. The extracellular portion of the integrin dimer binds to specific carbohydrate residues in extracellular matrix proteins or to ligands on the surface of other cells. d. The intracellular portion binds to a complex of proteins that form a linkage to the cytoskeleton. Answer; c CSIR NET practice problem Q. There are many super families of adhesion proteins, which play a central role in cell-cell adhesion in animals. Ig superfamily proteins are one such adhesion proteins. Which one of the following statements about Ig superfamily proteins is INCORRECT? (Sep 2022) a. The white blood cell proteins recognized by endothelial cell integrins are called ICAM (intercellular cell adhesion molecule) or VCAM (vascular cell adhesion molecules) b. These are called Ig superfamily because they contain one or more extracellular Ig-like domains that are characteristic of antibody molecules. c. ICAM and VCAM mediate heterotrophic binding to integrin, whereas NCAM (neural cell adhesion molecule) mediates homotrophic binding. d. They contain large quantities of sialic acid which inhibit adhesion by charge-based repulsion contributing to fine tuning of cell-cell adhesion. Answer; d  If you can’t fly, then run If you can’t run, then walk If you can’t walk, then crawl But by all means, keep moving