11 T Cell receptor activation II

Question 1

how is signaling important for medicine?

Answer 1

The vast majority of pharmaceuticals target the signaling proteins. (The majority of new drugs are targeted to signaling proteins)

Question 2

which part of the T cell receptor interacts with the MHC complex?

Answer 2

The variable regions (alpha and Beta) of the TCR

Question 3

what is the complimentary determining region (CDR) of TCR?

Answer 3

The part that interacts with the antigen and MHC

Question 4

CDR1 and CDR2 are encoded by which region of the TCR? what about CDR3?

Answer 4

CDR1 and CDR2 are encoded by the V regions

CDR3 is encoded by the junction of V, D, and J.

Question 5

The alpha and beta chains of the TCR make up 3 complementary regions that control the activation/interaction of the TCR. What are these 3 motifs (regions) called?

Answer 5

CDR1 (binds both MHC and antigen)
CDR2 (binds mainly MHC)
CDR3 ((binds mainly antigen)

Question 6

T/F Each TCR has variable contacts with the antigen/MHC complex?

Answer 6

True. These variations in binding are important for allowing flexibility in the binding of the pool of TCR’s to multiple peptides.

Question 7

what do the MHC classes with bound antigen bind to on the T cell?

Answer 7

1) TCR and CD8 or CD4

The binding occurs simultaneously

Question 8

what is considered to be a co-receptor? what is the function of a co-receptor?

Answer 8

1) Co-receptors are CD4 and CD8’s

2) The function of a co-receptor is to enhance the sensitivity of the T cell to and antigen/MHC complex

Question 9

T/F CD8 is a monomer?

Answer 9

False. CD8 is a hetero-dimer, and CD4 is a monomer.

Question 10

do CD4 and CD8 interact at the peptide binding cleft of MHC complexes?

Answer 10

No, they interact with invariant regions which are distant to the cleft.

Question 11

If you do not have CD4 or CD8 cells, will the T cells become activated with the TCR and MHC complexes?

Answer 11

Yes, but they are greatly reduced! you need the co-receptors to be present for an efficient activation. They increase the responsiveness by 10-100x.

Question 12

what makes up the T cell receptor complex?

Answer 12

The normal T cell receptor with alpha and beta units, and two lateral CD3 units which act to transmit intracellular signals.

Question 13

what makes up the parts of the CD3 complex?

Answer 13

CD3 gamma, delta, epsilon, and zeta

Possibilities are:
CD3 epsilon/delta (heterodimer)
CD3 epsilon/gamma (heterodimer)
CD3 zeta/zeta (homodimer)

Question 14

What is an ITAM?

Answer 14

Immuno tyrosine activation motif.

Each CD3 combination has at lease one ITAM motif used for signaling.

Question 15

What causes the ITAM (of TCR subunit) to send a signal?

Answer 15

phosphorylation.
Binding the TCR to the antigen/MHC complex recruits the CD4 or CD8. These co-receptors activate tyrosine kinase (Lck) which phosphorylates the ITAMS. Phosphorylated ITAMS recruit ZAP 70. ZAP 70 activates LAT.

Question 16

what does ZAP 70 do?

Answer 16

Phosphorylates and activates LAT which results in most of the down stream signaling within the T cell.

Question 17

What does phospholipase gamma do? what does it make?

Answer 17

1) cleaves 4,5 phosphytidyl inositol phosphate.
2) It makes:
DAG
Inositol 1,4,5 phosphate [IP3]

Question 18

what happens after ZAP 70 phosphorylates LAT?

Answer 18

SLP 76 binds LAT and recruits the tyrosine kinase ITK. At the same time, PLC gamma1 binds LAT and becomes phosphorylated by ITK. This sends the signal.

Question 19

How is PIP3 formed?

Answer 19

PI is phosphorylated at the 3rd position on the head group by PI3K. This forms PIP3. This is reversible.

Question 20

Besides favoring the formation of PIP3, what else does PI3K do? (phospho inositol 3 kinase)

Answer 20

It activates Akt (a serine/threonine kinase)

Question 21

What does Akt do?

Answer 21

regulates:
cell survival
apoptosis 
protein translation
Transcription Factor activation 
Metabolism

Question 22

kinase cascades are essential for activation of transcription factors. The Ras pathway is well understood, how does it work?

Answer 22

1) activation of LAT, activates Ras
2) Ras induces Raf
3) Raf activates MEK and Erk
4) Activated Erk drives gene transcription.

Question 23

What does the influx of Ca+ do inside the T cell?

How does it work?

Answer 23

1) activates the transcription factor NFAT.
2) Influx of calcium binds up calmodulin, and the calcium bound calmodulin binds calcineurin. This complex (calmodulin/calcineurin) dephosphorylates NFAT allowing it to drive gene transcription.

Question 24

why would you want to target calcineurin with a drug?

Answer 24

You could do so if you wanted to design an immunosuppressant.

Question 25

what happens when you activate IKK?

Answer 25

The IKK degrades Ikb or P100 which are inhibiting NF-kb and RelB respectively. Degrading P100 forms P52 which together with RelB can activate transcription. NF-kb also drives gene transcription.

Question 26

T/F transcription factors control the transcription of multiple genes?

Answer 26

True. Each gene promoter is regulated by the function of multiple transcription factors.

Question 27

T/F Activation of TCR causes actin polymerization and changes in cell morphology? How long would this take?

Answer 27

True, it normally occurs within minutes.

Question 28

why are changes in t cell morphology (actin) needed?

Answer 28

1) For maximal adhesion and TCR/MHC contact.

2) Formation of lamellipodia and phyllopodia.

Question 29

recruitment of proteins to what, drives actin cytoskeletal rearrangements?

Answer 29

LAT

Question 30

What activates Arp2/3 to induce actin branching?

Answer 30

Wasp
Rac
CDC42

Question 31

mutations in Wasp and Rac2 cause what?

Answer 31

T cell defects

Question 32

what recruits Wasp to LAT?

Answer 32

Nck

Question 33

What is the full order of activation with a TCR and a CD4?

Answer 33

LCK ( on CD4)
ITAMS (on TCR)
ZAP 70
LAT + (SLP 70 & ITK)
PLC gamma (phosphorylated)
PIP --->DAG and IP3 (Ca+ release)

Question 34

What makes PIP? What makes IP3?

Answer 34

PIP made from IP3 and PI3K ( activates atk)

IP3 made from PIP and PTEN

Question 35

Cascade order?

Answer 35

Ras 
Raf 
mek
Erk
Transcription factors