Jit # 8 T Cell receptor Signaling for Activation

Question 1

Calcium’s role in T cell receptor signaling

Answer 1

Calcium is produced in the cell, binds to calmodulin (binding partner) ; calmodulin then activates calcineurin.

Question 2

Calcineurin

Answer 2

Enzyme activated by calmodulin, removes phosphates from serine 3ene residues, allows NF-AT to go from the cytoplasm to the nucleus

Question 3

NF-AT

Answer 3

Nuclear Factor of Activated T cells; activated by calcineurin; migrates from the cytoplasm to the nucleus; binds to promoter regions and upregulates the expression of IL-2 genes

Question 4

Process of IL-2 production

Answer 4

APC recognition; CD4 increases avidity of binding; LCK phosphroylates tyrosine residues (ITAMs on z proteins of cd3) creating docking sites for Zap70 enzyme; ITAMs phosphorylate Zap 70 enzyme; Zap 70 phosphorylates LAT creating a docking site for phospholipase C gamma -1 (PLCg) enzyme which is now activated. PLCg hydrolyzes phospholipids in plasma membrane (PIP2); PIP2 releases IP3; IP3 diffuses in the cell, migrates to the ER, binds to IP3 receptors, which releases ca2+; Ca2+ activates calmodulin/calcineurin complex, which releases NF-AT; which migrates from the cytoplasm to the nucleus which causes release of IL-2. Recognition of APC to T cell receptor up regulates IL-2 receptors.

Question 5

IL-2

Answer 5

binds to IL-2 receptor, signals for the growth, proliferation, and differentiation of T cells.

Question 6

LCK

Answer 6

CD4 associated phosphorylation protein; phosphorylates tyrosines in the ITAMs of CD3 and z chains

Question 7

LAT

Answer 7

Adaptor molecule that binds to Zap-70 and is phosphorylated; creates docking sites for PLCg1

Question 8

PLCg

Answer 8

cellular enzyme activated by LAT; activates exchange factors that activates DAG, PKC, which activates NF-kB; hydrolyzes PIP2 generating IP3;

Question 9

IP3

Answer 9

released upon hydrolyzation of PIP2 by PLCg; stimulates an increase in cytosolic calcium (Calmodulin/Calcineurin to NF-AT) and DAG, which activates the enzyme PKC (AP-1).

Question 10

STIM1

Answer 10

Calcium sensor; detects lower calcium amounts in the ER due to secretion of calcium caused by IP3; Opens CRAC channel, which causes the entry of extracellular calcium.

Question 11

What is an ITAM? What is it’s function in TCR signaling?

Answer 11

ITAM stands for Immunoreceptor tyrosine-based activation motif; it is located on the cytoplasmic tail of the CD3 (signaling) portion of the T cell receptor; each cytoplasmic domain (2) contains one ITAM; also the zeta chain has 2 long cytoplasmic regions tat each contains 3 ITAMs; is phosphorylated by LCK. The phosphorylation of ITAMs creates docking sites for Zap-70. Zap-70 is then phosphorylated and directs the phosphorylation of other enzymes and proteins that are important for the production of IL-2 later on.

Question 12

Which kinase phosphorylates TCR ITAMS?

Answer 12

LCK

Question 13

After PLC-gamma binds to LAT and is phosphorylated, what are the next 2 steps in the signaling cascade?

Answer 13

1. PLCg hydrolyzes phospholipids withing the plasma membane called PIP2 to generate IP3
2. IP3 modulates the level of calcium in the cell by binding to receptors on the ER.

Question 14

The dephosphorylated form of NFAT is it’s active form that allows translocation to the nucleus, binding to the IL-2 promoter and activation of transcription (true or false)

Answer 14

True

Question 15

Using the last figure in the supplemental pdf (from the textbook), name the 3 transcription factors that bind to the IL-2 promoter to induce transcription of IL-2.

Answer 15

Activated AP-1 ; Activated NF-AT; Activated NF-kB