Representative signaling pathways

Question 1

Describe process from ligand binding to transcription of the TGFß signaling pathway

Answer 1

1. RIII receptor binds and concentrates TGFß, brings to RII
2. RII Ser/Thr kinase dimer bound by TGFß
3. RI Ser/Thr kinase dimer phosphorylated by RII
4. RI phosphorylates Smad transcription factor
5. Phosphorylated Smads and co-smads move to nucleus
6. Smads and co-smads activate transcription

Question 2

Label the steps of the Cytokine JAK/STAT signaling pathway from Ligand binding to Transcription

Answer 2

1. Ligand binds cytokine receptor, dimerizing it
2. Activated receptor recruits 2x JAK-Kinase
3. Tyrosine residues on receptor phosphorylated
4. 2x STAT protein dimerized after phosphorylation by JAK-kinase
5. STAT transcription factor translocated to nucleus
6. Activation of transcription

Question 3

TNFα signaling pathways from ligand binding to transcription

Answer 3

1. TNFα ligand binds receptor
2. Receptors trimerize
3. SODD dissociates due to conformational change, and TRADD binds death domain
4. IKK is recruited to phosphorylate IκBα
5. IκBα releases from NFκB transcription factor
6. NFκB translocates to nucleus
7. Activation of transcription

Question 4

GPCR pathway from ligand binding to transcription activation using AC as example

Answer 4

1. Ligand binds
2. 7TM receptor conformation change activates Gα GTPase
3. Gα activates effector protein (adenylate cyclase (AC) in this case)
4. AC cyclizes ATP into cAMP
5. cAMP binds to PKA regulatory subunit, activating it
6. PKA catalytic subunit translocates to nucleus
7. PKA phosphorylates CREB transription factor, leading to its activation
8. Transcriptional activation

Question 5

Wingless (Wnt) signaling pathway from ligand binding to transcription

Answer 5

1. Wnt ligand binds to both frizzled and LRP5/6
2. GSK3ß-cyto-complex is inactivated
3. ß-catenin is allowed to build up in cytosol because no longer targeted for destruction by GSK3ß complex
4. ß-catenin translocates to the nucleus
5. ß-catenin acts as a co-activator of TCF-LEF transcription factor
6. Transcription activation

Question 6

Notch signaling pathway from ligand binding to transcription

Answer 6

1. Ligand on extracellular surface of ligand expressing cell binds Notch receptor on surface of Notch expressing cell
2. γ-secretase cleaves Notch protein inside Notch expressing cell membrane
3. Notch intracellular domain (NICD) translocates into nucleus
4. NICD activates transcription factor CSL
5. Transcription activated

Question 7

RTK MAPK pathway from ligand binding to transcription

Answer 7

1. Growth/Survival factor ligand binds receptor, dimerizing it
2. Tyrosine kinase domains phosphorylate each other
3. SH2 domain containing adaptor protein Grb2 is activated
4. Grb2 acts as a GEF for Ras GTPase
5. Ras phosphorylates and activates MAP-kinase
6. MAPK translocates to nucleus
7. MAPK activates transcription factors
8. Transcription activation