Breakout 3

Question 1

how do cytokine receptors signal?

Answer 1

Stimulation of the appropriate cytokine receptor induces the production of “master regulators” of Th differentiation

Question 2

how cytokine signaling induces master regulators

Answer 2

• Cytokine receptors tend to be dimers that signal through the JAK/STAT pathway
• JAK Kinases initiates signal transduction cascade
• STAT proteins are phosphorylated by JAK Kinases and then dimerize
  Once dimerized, STAT proteins translocate into the nucleus where they act as transcription factors at canonical STAT binding sites

Question 3

how master regulators promote Th cell phenotype

Answer 3

Positively regulate genes that polariez cytokine production toward the appropriate phenotype

Question 4

how cytokine phenotype of Th cells is maintained

Answer 4

epigenetic modificaion of chromosomal DNA

Question 4

Th1 differentiation:
cytokine receptor and STAT

Answer 4

1st: IFN-gamma and STAT1
2nd: IL-12 and STAT4
Mater regulator: T-bet

Question 5

how IFN-gamma and IL-12 work together

Answer 5

IFN-gamma stimulates IFN-gammaR (STAT1)
IFN-gamma feeds back on the same T cell to further influence Th1 differentiation
IL-12R is upregulated and binds IL-12

Question 6

master regulator for Th1 differentiation

Answer 6

• T-bet induction is critical for the development of Th1 cells
• Significantly increases the levels of IFN-gamma transcription
• Is required for commitment to Th1 development by shutting down IL-4 gene expression and altering IFN-gamma promoter

Question 7

pathway for Th1 induction

Answer 7

• T cell receptor activated by Ag and activates NFAT
• NK cell and APC secrete IFN-gamma that stimulates the IFN-gammaR (STAT1)
• Increase STAT1 phosphorylation induces low levels of T-bet

Question 8

STAT involved in Th2 differentiation

Answer 8

STAT6

Question 9

master regulator required for Th2 differentiation

Answer 9

GATA-3
Permanently increases Th2 cytokine production
Blocks Th1 differentiation
Shutting down IFN-gamma gene expression and altering IL-4 promoter

Question 10

cytokine receptor and STAT for Th2 differentiation

Answer 10

1st: IL-4R and STAT6
Master regulator: GATA-3

Question 11

How are these changes in cytokine expression maintained in successive generations?

Answer 11

• Permanent modification of CK promoters
• T-bet and GATA-3 bind to chromatin modifying enzymes

Question 12

Permanent modification of CK promoters

Answer 12

Master regulators are transcription factors that associate with proteins that modify chromatin structure
Genes for cytokines are altered in a state that makes them “permanently open or closed”

Question 13

T-bet and GATA-3 bind to chromatin modifying enzymes to:

Answer 13

Open up the cytokine promoter by:
- Decreasing methylation of DNA cytosines of the promoter
- Increasing acetylation of histones