Cell-ECM Adhesion Flashcards
(38 cards)
cells in an anima live a crowded life
-we tend to study them as individual but in the animal they live in a crowded life surrounded by other cells and ECM
-if they’re epithelial cells, there’s a BM
-soluble and insoluble signals being exchanged
four major families of cell adhesion receptors
-cadherins
-IgCAMs
-integrins
-selectins- bind between immune cells and endothelium
integrins mediate cell-ECM adhesion
-some ECM protein bound by dimer of integrins- heterodimer with alpha and beta subunits
-cross a cell membrane and tail will accumulate adaptor proteins connected to a cytoskeleton
-epithelial tissue context- cells closely adhering to each other sitting on BM and major point of contact with ECM is with BM specifically
-immune cells and fibroblasts that sit in the mesenchyma stroma- relatively cell sparse with few cells per unit area volume
-cell-ECM adhesion is more than just tickling of receptors in a ligand, AJs needs to connect to cytoskeleton to achieve those strong changes in cell behavior
inactive (closed) and active (open) conformations of integrin dimers
closed- tucked away then domains swing open and much higher affinity for ligand in open state
integrin activity is regulated by both dimer conformation and receptor clustering
-is it open and touching its neighbor?
-important AAs that regulate cis or lateral interactions between integrin dimers in the membrane
integrins link the BM to the intermediate filament cytoskeleton at hemidesmosomes
-hemidesmosome is named b/c it looks like half of a desmosome in EM –> does not use the same adaptor proteins or adhesion receptors and doesn’t bind the same ligand on the other side
-ECM-integrins-adaptor proteins connecting to intermediate filaments or keratin cytoskeleton
integrins link the stromal ECM to actin cytoskeleton at focal adhesions
-immune cells/fibroblasts moving around- more dynamic adhesions
-thinking about ECM, integrins, adaptor proteins linking to actin cytoskeleton –> couples actin-myosin contractility directly to integrand ligation
when are anchoring junctions dynamic?
-cell migration, embryonic development, and tissue remodeling and repair
-if you want to change the structure of tissue, have to change the structure of the ECM –> junctions need to be dynamic
assembly and disassembly and focal adhesions during cell migration
-single cell on a substrate –> how does it move forward?
-important pocs organized as focal adhesions and basic rhthym of moving is you extend and make new adhesions then move cell body forward and release prior adhesion
-whole set of interactions to strengthen, mature, and disassemble focal adhesion
maturation and disassembly of focal adhesions is tightly coordinated during cell migration
-1st contact with integrin and ECM- start to recruit adaptor proteins and it matures –> start to recruit actin –> forms large, mature focal adhesion that produces significant forces –> starts to disassemble and fall apart
-cycles of assembly and disassembly that are constantly running underneath as a cell is migrating across a substrate
-in 3D environments, you might be pushing in different directions but still fundamentally need to reach out, grab, exert force, and release
what are the core components of the focal adhesion?
ECM, integrin, FAK, talin, vinculin, paxillin, and actin
regulation of cell adhesion receptors
-cell type specific expression- dozens of cadherins and integrins- change ones that re there and get different binding properties
-trafficking to or away from the cell surface- adhesion receptors in the membrane and endocytosis can remove them from the membrane individually or remove large clusters of them from the membrane to give almost immediate effect of reduction or increase in binding ability
-lateral interactions within membrane also matter- whether they’re mono dispersed in uniform fashion or clustered at discrete points organized into junctions
-state of activation- more important for integrins than adherins
ECM
-composed of macromolecules, proteins, and polysaccharides (sugars)
-synthesized and secreted by cells
-connective tissue (fibrillar) and BM (dense sheet)
-collagens in both groups
integrn binding to the ECM has signaling consequences inside the cell
-thought of as being simple places you attach- just mechanical contact
-cell notices whether integrins are ligated- if you have integrin bound to ECM, on the inside that accumulates proteins like FAK and Src
–> once you have FAK and Src, you can get to MAPK
–> once you’re at Src and MAPK, you can regulate any cell behavior- proliferation, migration, differentiation
-integrins themselves do not have enzymatic activities (no kinases or proteases)- they borrow enzymatic activity of intracellular kinases so ILK, FAK, and Src
–> binding of integrin FAK induces its auto phosphorylation and causes phosphorylation of a number of targets
FAK-mediated pathways target the cell cycle
-once you get right to FAK then you can control Src and JNK and MAPK and cyclin D1 and go to cell cycle progression
-Src can also get you to RAC –> actin cytoskeleton –> cell migration
what are the major classes of ECM?
-adhesive glycoproteins
-collagens
-proteoglycans
fibronectin
-when you look at the domain structure, you have heparin and fibrin binding, collagen binding, fibrin binding, cell binding, heparin binding –> great logic to build a sheet b/c every one of these individual domains binds to others and you get dense lateral interactions that make the ECM strong
-RGD loop is where cells bind and other domains are about positioning proteins in the right place relative to their protein neighbors and making RGD motif conditionally available depending on orientation
-fibronectin is single gene with alternatively spliced isoforms- present in ECM as fibrils and blood as soluble
laminins
-major compnent of BM- binds collagen IV, GAGs and integrins
-logic of binds type IV collagens, heparins, and integrins –> great way to organize that has lost of lateral interactions
-at least 15 ways to make laminin from combos of alpha, beta, and gamma laminin genes
collagens
-synthesized, secreted, and organized by cells
-major structural component of ECM and provides tensile strength to tissue
-regulates variety of cellular activities via integrins
-sheet forming (type IV) and fibrillar (type I)
collagen I: main fibrillar collagen
-most abundant protein in the body
-major structural component and provides tensile strength
biosynthesis of fibrillar collagen I
-fibers bundled into bigger bundles into bigger bundles
-make a polypeptide then synthesize pro-collagen alpha chains then hydroxylate them then you have to glycosylate them –> initiate folding of 3 pro-alpha chains –> pro collagen alpha helix that gets secreted –> cleave polypeptides and polypeptides form basic unit that assembles first into fibrils then fibers
proteoglycans
-in the ECM, they’re structural and mechanical support for tissues, allow diffusion of soluble factors and migration of cells, and they regulate activities of growth factors and secreted proteins
-co-receptors for integrins and growth factor receptors in the membrane
hierarchical structure of proteoglycans
-GAGs- major structural component of ECM and you have high density of negative charges that coordinate water-sugar with amino group
Ex. cartilage in knees resists compression when you run b/c of presence of GAGs
-have protein core decorated with GAGs and each of the red lines has a lot of negative charges that coordinates water then you put big strands with lots of these and all of them individually accumulating a lot of water then you have resistance to compressive strength
MMPs cleave ECM and other extracellular proteins
-pro domain and when it’s present the MMPs are inactive
-catalytic domain that actually does cutting
-once it’s active, these can do multiple things
-large gene family
-MMPs go out in front of migrating cells, degrade ECM, and make space for cell migration
-clear Exs. in development and cancer where MMP clears space through BM or stromal ECM
-they can also alter microenvironment to release signaling molecules
-change availability and activity of growth factors and other proteins
-ECM can act as memoory where you can secrete a lot into ECM and it will bind there and be unavailable to the cell until you release an enzyme to get it then all of the proteins become available —> provides way for cells to respond quickly
-accumulate in ECM for extended time then you release MMP you’re able to rapidly make them available to cell
-you can slo alter the balance of protease activities b/c they’re pro domains and they require cleavage to become active, one MMP can cleave the domain of another MMP and make it active
-endogenous inhibitors that allow cells to put away this activity –> make a lot of MMP activity and put it away by making more TIMPs
