7. Extracellular Interaction

<!-- Terms -->

Terms in chapter
================
	* Glycocalyx (GC) - Layer of sugar mols coming from PM
	* Basement Membrane (BM) - After GC, think protein molecules 50-200nm
	* Connective Tissue (CT) - eg. cartilage
	* Chondrocyte cells - excrete ECM
	* Haptotaxis - cells guided by ECM
	* MMPs vs. TIMPs

<!-- Basics -->

ECM
===
	* Components
	* How ECM molecules connect w/ inside
	* Cell-cell connect
	* Signals to respond to ECM

Basics of ECM
=============
	* Glycocalyx (GC) - Layer of sugar mols coming from PM
	* Basement Membrane (BM) - After GC, think protein molecules 50-200nm
	* Connective Tissue (CT) - eg. cartilage
	* Chondrocyte cells - excrete ECM
	* ECM proteins 
		* long, flexible, fibrous (NOT globular)
		* need to be hydrated, sugar part absorbs water

Cell-ECM interaction
====================
	* Cell migration during embryogenesis
		* 3D organization of tissues
	* Cell growth
	* Cell differentation
	* Cancer

ECM is composed of
==================
	* Collagen & Elastin:		Strength and flex
	* Laminin & Fibronectin:	Adhesion
	* Proteoglycans:			Matrix constitution

<table>
  <tr>
	<td>
Collagen
--------
	* Func: Fibrous, high tensile strength
	* Struct: Each strand is 3 helicies intertwined, comprised of many PRO and GLY
	* One of most abundant proteins
	* DIFFERENT TYPES
		* SEE: TABLE OF COLLAGEN TYPES
		* SEE: TABLE OF COLLAGEN DISORDERS
			* Eg. Scurvy - Vitamin C required as co-factor to produce collagen

	</td>
	<td>

Elastin
-------
	* Func: Elastic, resumption of tissue shape after deformation
	* Struct: Highly crosslinked

	</td>
  </tr>
  <tr>
	<td>

Fibronectin
-----------
	* Func: Link between ECM & PM
	* Important in Development and Cell Migration
		* Haptotaxis - cells guided by ECM
	* Struct: 2 domains 
		* ECM-binding domain
		* RGD-binding domain, eg. Integrin-binding
	* Eg, neural crest cell migration

	</td>
	<td>

Laminin
-------
	* Dimers or trimers w/ helicies
	* WHAT DOES IT DO????

	</td>
  </tr>
  <tr>
	<td>

Proteoglycans
-------------
	* Func: Amorphous gel-like ECM, reduces friction / impact
	* Struct: Highly hydrophobic GAGs
		* Free GAGs found in joints, however usually components of Proteoglyans
		* ...
		* STUDY STRUCTURE

	</td>
	<td>
	</td>
  </tr>
</table>


??????
======
	* microdomains - lipid rafts
	* phosphoglycerides
	


Matrix Metalloproteinases (MMPs)
================================
	* Contain Zn
	* Break down and remodel matrix
	* Inhibitors: TIMPs

<!-- Integrins -->

Integrins
=========
	* alpha-subunit, beta-subunit
	* two conformations:
		* bent: inactive
		* straight: active
	* Binding depends on Alpha/Beta combo
		* RGD domains, Fibronectin, ICAM, VCAM, etc...

Signalling
==========
	* Inside-out: 
		* Via growth factor modulation
		* Change affinity for ligand
		* Change avidity - clustering & grouping of integrins
	* Outside-in:
		* Affects cytoplasmic domain
		* Recruits proteins, signal transduction, gene expression
		* Influences Differentation, Motility, Growth, Survival

Platelet adhesion
=================
	* Inside out: Von-Willibrand Factor
	* Outside in: Fibrinogen
	* ...
	* Anti-thrombiotic drugs - RGD antagonist


<!--- Membrane lipids -->

Membrane Asymmetry
==================
	* Cargo domain facing lumen will face extracellularly
		* Glycosylated part ALWAYS extracellular only

Synthesis of Membrane Lipids
============================
	* Occurs in SER
	* Modification types:
		* Head Group - flippases, lateral diffusion
		* Budding vesicles can choose their phospholipids
		* Phospholipid transferases

<!-- Cell-ECM Adhesion Complexes -->

Cell-ECM adhesion
=================
	* Focal Adhesions	- via Fibronectin (RGD-mediated), Fibroblasts and Muscle
	* Hemidesmosomes 	- via Laminin (non-RGD), Epithelial 

Focal Adhesions
===============
	* Binds ACTIN intracellularly
	* Binds FIBRONECTIN (RGD) extracellularly
	* Complexes where cells attach to substratum
		* Integrin clusters - bind ECM
		* Src & FAK - involved in growth, diff, and motility
	* Can create traction forces on substratum

Hemidesmosome
=============
	* Binds KERATIN and INTERMEDIATE FILAMENT intracellularly
	* Binds LAMININ (non-RGD) extracellularly
	* Contains BP180

<!-- Cell-Cell Adhesion molecules -->

Cell-Cell Adhesion molecules
============================

<table>
  <tr>
	<td>

Selectins (Selectin-Lectin)
---------------------------
	* **Ca+2 dependant**
	* Selectin binds oligosaccharide on adjacent cell
	* Ends in Lectin-like domain (Carbohydrate)
	* L-selectin (leukocyte), E-selectin (epithelial), P-selectin (platelets)

	</td>
	<td>

Cadherins (Cadherin-Cadherin)
-----------------------------
	* **Ca+2 DEPENDANT**
	* Important in empryogenesis and cancer
	* N cad, P cad, E cad

	</td>
  </tr>
  <tr>
	<td>

IgSF (IgSF-IgSF)
----------------
	* IgSF domains on both cells interact
	* NCAM, VCAM, L1, etc.

	</td>
	<td>

Integrins (Integrin-IgSF)
-------------------------
	* Integrin on one cell interacts with IgSF on another cell
	* Eg. Integrin on leukocyte w/ VCAM on vascular endothelium

	</td>
  </tr>
</table>

<!-- Cell Junctions -->

Cell-Cell Junctions
===================
	* Gap & Tight Junctions:			Allow and prevent molecule exchange
	* Adherens Junction & Desmosome:	Hold cells together

<table>
  <tr>
	<td>

Adherens Junction
-----------------
	* Utilize **Cadherins**
	* Bind **Actin**
	* Signal adapters: **a/b Catenin**

	</td>
	<td>
	
Desmosomes
----------
	* Utilize **Desmogliens**, **Desmocollins**
	* Bind **Intermediate Filament**
	* Signal adapters: **Plankoglobin**, **Desmoplankin**

	</td>
  </tr>
  <tr>
	<td>

Tight Junctions
---------------
	* Paracellular pathway - differential control of molecule movement
	* Maintains polarity of epithelial cell
	* Seen on epithelial cells at apical surface, Blood-brain barrier
	* **Claudin**, **Occludin** - Do what? 
	* ZO-1 intracellular adapter

	</td>
	<td>

Gap Junctions
-------------
	* Pipelines connecting cells
	* Small molecules, ~1000 Daltons
	* Connexon -- hexamer of connexin subunits
	* Regulation: Low Ca+2, Phosphorylation, changes in membr potential
		* High Ca+2 shuts down
	* Responsible for coordinated heart

	</td>
  </tr>
</table>

Cadheren Switching
==================
	* Cadherens differentially up/downreg'd during development
	* E-cadheren (epithelial) polarized, tight binding to one another
	* N-cadheren (neural) nonpolar, loose binding, more motile
	* E binds E, N binds N. E cannot bind N.
		* E-to-N cadheren switching as migration occurs	
		* Switch seen often in tumorgenesis
	* TGF receptors upreg'd
	* Increased Rac & cdc42

Inflammation process
====================
	* Cytokines & chemokines recruit
	1. Activation of endothelial
	2. Trapping
	3. Activation of neutrophil
	4. Adhesion
	5. Invasion

Tight Junction pathogen target
==============================
	* **CAG protein** on bacteria alters polarity and adhesiveness
	* Binds/recruits **ZO-1**
	* also need **VAC**

Gap Junctions
=============
	* Nerve cells - ions able to be transported via gap junctions
	* IPv3 can travel between gap junctions, as can cAMP
	* IPv3 triggers Ca+2 release from SER

Follicle Stimulating Hormone (FSH)
==================================
	* Pituitary hormone
	* Signal cascade utilizing cAMP
	* ...

<!-- Test Question:-->
Degradation of cell adhesion
============================
	* The effects of the following on L1 (an IGSF) & selectin
	* Trypsin (protease) - degrades both
	* RGD -- no effect (binds integrins)
	* Neuroaminidase (clips oligosac) -- inhibits selectins
	* Collagenase -- no effect (collagen is extracellular)
	* EGTA/EDTA (Ca+2 inhib) -- inhibits selectins