9: External Control (of devision and behavior)

Question 1

What kind of external influences can the cell detect?

Answer 1

1. Chemical
   
   • hormones, Growth factors, ions, nutrinents, dissolved gases etc.
2. Physical
   
   • mechanical, temperature, stretch,

Question 2

What are the main external influcences to the cell are often important in cancerous cell behaviour?

Answer 2

• •Growth factors
• •Cell-cell adhesion
• Cell-ECM adhesion

Question 3

Next to Growth factors, what is the other importnat part needed for cell proliferation?

Answer 3

Binding to the extracellular matrix

• Achorage dependance!

Question 4

Explain the concept of Anchorage dependance

Answer 4

Cells need bindin to ECM (+ a degree of spreading of cells) for

• survival
• Protein synthesis and DNA replication
• proliferation

Question 5

Explain the role of ECM in cell phenotype

Answer 5

The composition of the ECM has a crucial role in determenin the cells organisation and phenotype

Question 6

How do cells “sense” the composition of the ECM?

Answer 6

Via binding of integrins

• Special ECM receptors that can bind to many different ECM molecules
• Link to cytoplasm
  
  • Contunitnity between cytoplasm and external environment

Question 7

Explain the structure of Integrins

Answer 7

Are compsed of

• alpha and ß subunit
• have a head binding to ECM molecules
• and a tail/Leg which has the membrane and cytoplasmic domains

Question 8

How do integrins sense different ECM compositions?

Answer 8

There are different combiations of the alpha and beta subunits

• Each recognises different short AA sequences of ECM molecules
• They can be specific to one ECM molecule or are found in more than one molecule

Question 9

Explain the intracelluar organisation of integrins

Answer 9

Bind to Actin (exeptino in epithelial cells–> can also bind to intermediate filaments) Intracellularly via actin binding proteins

• induce signal transduction intracellularly

Question 10

Explain the structure of focal adhesions

Answer 10

Integrins cluster togetheer to then form focal adhesions (sometimes can also form hemidesmosomes)

• involved in signal transduction
  *

Question 11

What is “outiside-in” signaling?

Answer 11

• ECM receptors (e.g. integrins) can act to transduce signals
• e.g. ECM binding to an integrin complex can stimulate the complex to produce a signal inside the cell,
• This changes the cells phenotype

Question 12

Explain ther role of Intrgrins during “outide in” -signal regulation

Answer 12

Integrins can undergo confirmational change and therefore change ability to

1. bind ligands
2. change the signaling pathway

Question 13

How can integrins sense the mechanical properties of the surrounding?

Answer 13

Via the amoun of force that is generated at a focal adhesion depends on

• both the force generated by the cytoskeleton (F cell)
• and stiffness of the ECM

Question 14

What is “inside-out” integrin signalling?

Answer 14

An intracellular signal (e.g. as response to a homone binding etc.) can

• change the integrin affinity for the ECM
  
  • used e.g. in inflammation, blood clotting

Question 15

Explain the mechanism of anchorage dependance

Answer 15

1. growth factor receptors and integrin signalling complexes can each activate identical signalling pathways (e.g. MAPK)
2. Alone: this activation is weak and/or transient
   
   1. •Both needed for strong proliferative signal!

Question 16

Explain the concept of density dependance of cell devision

Answer 16

In cell monolayers–> cells compete for GF and therefore proliferate less (not just inhibted by contact inhibition)

Question 17

Explain the two different types of cell-cell contacts that can occur

Answer 17

1. Short term
   
   • normally non-epithelial cells
   • transient intercations, don’t form stable junctions
2. Long term
   
   • normally epitheilial cells
   • stable cell-cell junctions

Question 18

Explain the concept of contact inhibition of locomotion

Answer 18

Mostly

• collision of non-epithelial cells repells the cells
  
  • paralisation of motiliy at contact side
  • promoting formation of otile front at other side and moving to opposide direction

Question 19

Explain the concept of Contact-induced spreading of epithelial cells

Answer 19

When epitelial cells meet:

• form stable junctions/cell-cell adhesions
• leading to cell spreading to form stable mono-layers

Question 20

Explain the intracellular mechanism how cell-cell adhesions influence proliferation

Answer 20

Cell-cell junctions are calcium dependant: low Ca2+= low juncitons= high proliferation

• Without cell-cell junction
  
  • high MAPK activity
  • low p27KIP1 (CKI)
  • promote proliferation
• With cell junctions
  
  • MAPK inhibited
  • inhibit proliferation

Question 21

What is the mediator molecule that might be responeible for the link of cell-cell adhesions and proliferation

Answer 21

Thought to be mediated by ß-cadenin (link between calcium dependant junction and further intracellular signaling)

Question 22

Explaint the role and regulation of ß-catenin in cell proliferation

Answer 22

ß-catenin is bound to cell-cell junction molecules

• When there is no junction–> ß-catenenin is free in cytoplasms
  
  1. Binds to LEF-1 and promotes gene transcription and cell proliferation
  2. Gets inactivated by APC complex

Question 23

Explain the formation and Mechanism of Adenomatous polyposis coli (APC)

Answer 23

It is a form of inhierited disease forming uncontrolled colorectal polyps

• Due to a disfunciton of the APC gene that cannot degrade ß-catenin
• No degradation of ß-catenin –> uncontrolled proliferation

Question 24

Other than ß-catenin mediatied, how can cell-cell jucntions als alter cell proliferation?

Answer 24

1. Cadherin clusterin after cell-cell junciton can activate small GTPases (e.g. Rac activation, Rho inhibitiob)–> proliferation
2. GF receptors involved in Cell-Cell junctions reduced their ability to respond to extracellular stimmuli

Question 25

What happens to contact inhibtion in tumor cells?

What does that lead to?

Answer 25

Tumor cell often loose contact-inhibition leading to

1. Uncontrolled proliferation
2. Multilayering
3. Epithelial break down of cell-cell contacts

–> Solid tumor formation and invasion of tissues

Question 26

What are the different steps in metastisis formation?

Answer 26

1. Cells must break away from the primary tumour
2. travel to a blood or lymph vessel
3. enter the vessel
4. lodge at a distant site
5. leave the vessel,ultimately
6. establish a secondary tumour

Question 27

What do primary carcinomal cells alter/have to metastisise?

Answer 27

1. Reduction of cell-cell adhesions (e.g. cadherin levels reduced)
2. Primary cells must be motile
3. degradation of ECM must take place; matrix metaloproteinase (MMP) levels increased in order to migrate through basal lamina and interstitial ECM
   
   1. the degree of carcinoma cell-cell adhesion is an indicator of how differentiated the primary tumour is, and indicates its invasiveness and the prognosis

Question 28

What is Blebbing?

Answer 28

Happens when Cells are detached from ECM

• membrane swells into several spherical bubbels

Can end

• apoptotic
• Non-apoptotic = cell locomotion, cell division and stresses