cell cell interaction

7/28/2019 Cell Cell Interaction

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CELL-CELLINTERACTION

Evy Sulistyoningrum


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Introduction

Cells of multicellular organism communicate each other

Coordinate integrated function

Communication between cells:

Releasing signal molecules Cells receptor proteinspecific

Cell signaling:

Autocrine signaling

Direct contacts

Paracrine signaling

Endocrine signaling

Synaptic signaling


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Means of cell signaling


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Speficity of cells receptor

protein


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Cells receptor protein

Intracellular receptor

Cytoplasm or nuclear

receptor

Lipid soluble signalsEx: steroid hormone,

vitamin D, etc

Mechanism of action:

Gene regulators

Enzymes


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Cells receptor protein

Cell surface receptor

Water soluble signals

Converts extracellular to intracellular signals

3 class of cell surface receptors:Chemically gated ion channels

Enzyme-linked receptors

G-protein linked receptorMost abundant

7 trans-membrane protein linked with GTP-

binding protein


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Cells surface receptor


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G-protein linked receptor


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Second messengers

Second messengers : intracellular mediators

Substances that relay receptors to target protein

Most widely used:

Cyclic adenosine monophosphate (cAMP)

Produced by adenylil cyclase

Calcium

Stored in RECalmodulin helps activated target protein


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How 2nd messengers work?


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Signal amplification

Low signals must be amplified to acquiredadequate response

Tyrosine kinases


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Direct contacts

Direct contact between cells surfaces

Cell junctions: long-lasting

interactions/permanent contacts between cells

Types of direct contacts:

Tight junctions

Anchoring junctions

Communicating junctions


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Direct contacts


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Tight junctions

Occluding junctions: Zonula Occludens

Connects plasma membrane of adjacent cells in

a sheet

Locate at the very apical end of junctionalcomplexes between cells

Functions:

Form a selective permeability barrieracrossepithelial sheet

Seals off body cavities such as intestine, stomach

lumen, bile duct, blood-brain barrier, etc.


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Tight junction

Structure of tight junction as a honeycomb-likenetwork of ridges & grooves

Linkage of rows of protein particles (3-4 nm )

Major proteins: occludin, claudin-1, JAM(junction adhesion molecule)

Prevents the diffusion of macromoleculesacross epithelial sheet

Prevents diffusion of membrane proteins andglycolipids between the apical and thebasolateral regions of the plasma membrane


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17/43Lodish et al., 2004


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Alberts et al., 2002


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The role of tight junctions in allowing epithelia

to serve as barriers to solute diffusion


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Anchoring junctions

Specialized region on the cell surface

Contains cell-adhesion molecules oradhesionreceptors that interact with other cells or the

extracellular matrix and with cytoskeletal fibersCommon in tissues exposed by mechanical stress, ex:

muscle, skin

Major types:

Adherens junctions (zonula adherens)Desmosomes (macula adherens)

Hemidesmosomes


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Adherens Junctions

Also known aszonula adherens

A type of specialized adhesive junction,

partially common in epithelia

Plasma membranes of adjacent cells are

connected by cadherins orother cell adhesion

molecules (e.g., integrins)


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Lodish et al., 2004


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Desmosome

macula adherens

Disc-shaped adhesive junction (~1 mm diameter)

Located basal to adherens junction

Contains desmogleins & desmocollins

(desmosomal cadherins)

Found in variety of tissues (need mechanical

strength: e.g., cardiac muscle & epithelia of skinand uterine cervix)


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Desmosomes


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Desmosome

Inner surface of plasma membrane: dense cytoplasmic

plaques

As site of anchorage for looping intermediate filaments

that extend into the cytoplasmcontains desmoplakins & plakoglobin (adaptor proteins

that link desmosomal cadherins to intermediate filaments

)

3-D network of intermediate filaments provides structural

continuityand tensile strength to the entire sheet of cells

Pemphigus vulgaris : has antibody against one of his/her

own desmo leins loss of e idermal cell-cell adhesion


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Pemphigus vulgaris


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Hemidesmosome

Half desmosome

Specialized adhesive structure at the basal

surface of epithelial cells

Function: attach the cells to their underlying

basement membrane (basal lamina)

Contains a dense plaque on the innermembrane, with keratin-containing

intermediate filaments coursing out into the

cytoplasm


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Lodish et al., 2004


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Karp, G., 2005

a b


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Communicating junctions

Passageways between cells that allow transferof chemical or electrical signals

Types:

Plasmodesmata: plantsGap junctions: animal


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Gap Junctions

Sites between animal cells that are specialized for

intercellular communication

Span the adjacent plasma membranes with very fine

molecular pipelines that allow the passage of smallmolecules (1000 daltons)

Electrical & metabolic couplings

RegulationpH: Low pH closes

Calcium: High calcium closes

Extracellular signals: Dopamine closes


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Gap junction

Gap junctions are constructed from transmembrane

protein called connexin

Six identical protein subunits assemble to form a

structure called connexonTwo connexons from adjacent plasma membranes

align to form a continuous aqueous channelof gap

junction

Gap junctions in different tissues can have different

permeability due to difference in connexin (there are

at least 11 distinct connexins)


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Gap

Junctions

Comprised of

connexons

Connexons

made

of connexins


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A summary of various cell junctions found in vertebrate

epithelial cells



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Paracrine signaling

Signal molecules released by cells diffuse

through the extracellular fluid to other cells

Molecules are taken up by neighboring cells or

quickly removed Influence is restricted to cells in the immediate

vicinity of the releasing cell

short-lived, local effects Early development, coordinating the activities

of clusters of neighboring cells


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Paracrine signaling


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Endocrine signaling

Released signal molecule enterthe organismscirculatory system travel widely throughout

the body.

Longer lived signal molecules May affect cells very distant from the releasing

Cell

Signal molecules: hormones Endocrine system


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Endocrine signaling


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Synaptic signaling

Cells of the nervous system provide rapid

communication with distant cells.

Signal molecules travel through long, fiberlike

extensions of nerve cells from their tips veryclose to the target cells

Signal molecules (neurotransmitters)

The narrow gap between the two cells :

chemical synapse

Neurotransmitters cross the synapse and persist

only briefly


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Synaptic signaling


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Thank you..

cell cell interaction

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