Lecture 8 - Molecular events in T cell activation

Question 1

Cell signalling: what is it and what components are involved in it?

Answer 1

Turning an extracellular signal
into a cellular response

Ligand, receptor, intracellular signals, target (often nucelus)

Question 2

Protein phosphorylation

Answer 2

Protein becomes (de)phosphorylated and becomes either activated or inactivated

• Kinase - serine/threonine kinases or tyrosines
• Phosphatases

Question 3

Scaffold proteins

Answer 3

Large proteins that get phosphorylated and phosphorylate other proteins

Question 4

Are only proteins phosphorylated?

Answer 4

No, membrane lipids can too

Question 5

Signal amplification: what is it and what examples are there?

Answer 5

Growing a signal larger

• Kinase cascades - MAP cascade
• Release of secondary messengers (calcium)

Question 6

Intracellular signals: how do they modulate gene expression?

Answer 6

Regulation of transcription factors:
* Assembly of TF subunits
* Phosphorylation status of TFs
* Location of TF subunits

Question 7

CD4+ T-cell activation: what does it require

Answer 7

• Signal 1 - antigen recognition by CD4+ T-cell receptor (presented by MHCII)
• Signal 2 - co-stimulatory molecule interaction (e.g. CD28-CD80/86)

These interactions may be strengthened by adhesion receptors (e.g. LFA1-ICAM1 interaction)

Signal 3 - cytokine signal to promote differentiation of T cells

Question 8

TcR complex: what is it and what is it composed of?

Answer 8

• α and β chains of the TcR recognise antigen
  but don’t have any signalling ability
• TcR needs to form a larger complex to
  signal = with CD3
  CD3 complex is composed of:

Heterodimer of ε and δ chains
Heterodimer of ε and γ chains
Homodimer of ζ chains

All CD3 chains contain ITAM motifs in
cytoplasmic domains which are required
for signalling

Question 9

ITAMs: what are they, where are they found, what do they do, and what are they phosphorylated by?

Answer 9

Immunoreceptor tyrosine-based activation motifs (ITAMs)

Many different immunoreceptors - B-cell receptor complex, NK cell receptors, Fc receptors

Creates binding sites for additional signalling proteins (scaffold proteins)

Lck = Src-family kinase

Question 10

Recruitment and activation of ZAP-70

Answer 10

• The kinase ZAP-70 is recruited to phosphorylated ITAMs via SH2 domains
• recruited ZAP-70 is activated via phosphorylation by Lck
• activated ZAP-70 can phosphorylate several
  different proteins
  to trigger signalling
• signalling proposed to be enhanced by TcR complex clustering

Activated ZAP-70 can phosphorylate the scaffold proteins LAT (linker of activated t cells) and SLP-76

Question 11

SMACs

Answer 11

leccy/tb

Answer 12

PIP3

For example: The adapter protein Gads brings LAT and SLP-76 together

The Gads:LAT:SLP-76 complex recruits phospholipase C-γ (PLC- γ) using PIP3

The kinase Itk activates PLC- γ via phosphorylation once attahed to PIP3

Question 13

PLC-gamme

Answer 13

Cleaves PIp2 to IP3 and DAG

IP3 triggers Ca2+ mediated signalling events (opneing ER calcium stores)

DAG recruits signalling proteins
to the plasma membrane

Question 14

B7

Answer 14

CD80 or CD86

Answer 15

B7 + CD28

PI3K can bind phosphorylates PIP2 to PIP3

Answer 16

PIP3 can reinforce signals from TCR

• recruit and activate PLC-γ

recruit the kinases PDK and Akt

Question 17

Note: important to realise that pathways mentioned here are not the only signals triggered by the TcR

Answer 17

read tb/ ER

Question 18

TcR signalling downstream pathways

Answer 18

• Calcineurin pathway
• NF-kB pathway
• AP-1 pathway
• MAPK pathway

Question 19

Calcineuirn pathway

Answer 19

Phosphorylated NFAT - inactive

Calmodulin binds to calcium - undergoes a conformational change, allowing calcineurin to bind

Calcineurin dephosphorylates NFAT, allowing it to translocate to the nucelus and affect gene expression

Question 20

NF-kB pathway

Answer 20

leccy/tb