Week 8 Cell-Cell Junctions & ECM

Two types of Adhesive Junctions

• Adherenes

• Desmosomes

main difference between adherens and desmosomes

• adherens linker proteins attach to cytoskeleton and microtubules

• desmosomes attach to intermediate filaments

Desmosomes

spot welds

• strong “button like” connection to another cell

anchoring junctions

aka as adhesive junction

• link cells together to allow for a function as a unit

transient junctions

• less strong but promote cell to cell adhesions

• typically for carbs

Types of Transient cell junctions

• integrin

• selectin

• CAM

transient cell junctions are important for

• immune response

• tissue repair

• cell migration

tight junctions

• prevents movement across a cell layer

  • acts as a barrier

what does transient junctions allow through

• small ions and small molecules

if damaged tight junction, what happens?

• bacteria, proteins, and viruses can enter

  • digestive enzymes can leak and degrade

paracellular transport

• movement between cells rather than through cells

gap junctions

• small tunnels

• 3nm diameter

What is gap juntions for?

• rapid communication

what can go through a gap junction?

• small ions

• small molecules

• single sugars/nucleotides

Plasmodesmata

• similar to gap but larger in plant cells

• 20-200nm

desmotubule

• extension of ER from plant cell to plant cell

annulus

• responsible for opening and closing of gap junction/plasmodesmata

homophilic i.e

cadherin to cadherin

heterophilic interaction

• CAM and selectin

main components of ECM

• proteins

• proteoglycans

• glycoproteins

fibroblast

secretes ECM components

• collagen

• elastin

• hyaluronic acid

glycosamiglycans (GAGs)

repeating disaccharides with amine functional units

proteoglycans

big long core protein with sugars attached to it

fibronectin

• adhesive glycoprotein

• interacts with integrins to attach to ECM

relationship to fibronectin and cancer

• cancer cells don’t make fibronectin

  • so don’t have ECM interaction

Matrix Metalloproteinases

enzymes that degrades proteins (fibronectin)

relationship between MMPs and cancer

• cancer cells produce MMPs and break free from ECM and spread

laminins

glycoprotein connect epithelial layer to connective tissues

integrins

heterodimer

integrate cytoskeleton with ECM

heterodimer

molecule formed by two different polypeptide chains or subunits.

focal adhesion

transient connection to ECM

• relies on integrins

Focal Adhesion Kinases (FAK)

phosphorylates other molecules based on signaling

FAK relation to cancer

FAK stop listening to receptors

• can continue to promote growth

hemidesmosomes

• cell junctions to ECM

• connect to IF

costamere

attach muscle fiber to PM

what happens when dystrophin does not function properly?

Muscle weakness