Lecture 11: TGFb

Question 1

Cancer paradox of TGFB

Answer 1

Generally works in opposition to cell proliferation and tumor suppressor

but can also enhance motility and migration, participates in epithelial to mesenchymal transition which favour metastasis

Question 2

2 family groups of TGFb

Answer 2

1. TGF-B like group (TGFBs, activins, nodals and growth and differentiation factors GDFs)
2. Bone Morphogenetic Proteins (BMP) like group (BMPs, most GDFS and anti-mullerian hormone AMH)

Question 3

TGFB ligand structure

Answer 3

mature ligands determined by a structure called cysteine knot

result from formation of three intramolecular disulfide bonds between 6 highly conserved cysteine

the 7th cysteine mediates dimerization to form biologically active molecule

Question 4

TGFB receptors

Answer 4

single transmembrane domain

extracellular portion for ligand recognition and binding

Question 5

TGFB type 1 receptor

Answer 5

7 type 1 receptors

unique are called TGFBR1

Question 6

TGFB type II receptor

Answer 6

5 type II receptors

unique and called TGFBR2

Question 7

TGFB type III receptors

Answer 7

B-glycan and TGFBR3

acts as scaffold

Question 8

Chordin

Answer 8

decoy receptor in the extracellular space to inactivate TGFB

Question 9

3 steps in TGFB signalling

Answer 9

1. TGFB associates with B-glycan coreceptor (TGFBR3)
2. Complex recognize by TGFBR2 and undergoes dimerization and autophosphorylation
3. TGFBR2 recruit 2 molecules of TGFBR1 and phosphorylates it

Question 10

SMADs

Answer 10

TGFBR1 recruit and phosphorylate SMAD2 or 3 with the help from SARA

SMAD6 or 7 can inhibit the phosphorylation

phosphorylated SMAD2/3 associate with SMAD4 and translocate into nucleus

recruits coactivators and corepressors to trigger transcription

Question 11

SMURF and SKI

Answer 11

SMAD ubiquitinylation regulating factor targets SMAD2/3 to proteasome

SKI inhibits transcription in nucleus

Question 12

TGFB as tumor suppressor gene

Answer 12

loss of TGFBR3 gene expression - breast and lung cancer

mutations of TGFBR2 and SMAD4 - colon, pancreas and lung cancer

Question 13

TGFB on metastasis formation

Answer 13

1. inhibition of kinase activity of TGFBR1 inhibits formation of lung metastasis
2. potent induce of EMT through SMAD action on SNAI1 (SNAIL), SNAI2 (SLUG) and TWIST
3. angiogenesis

Question 14

3 Pharmacological targets in TGFB

Answer 14

1. ligand level - prevent TGFB synthesis
2. ligand-receptor level - prevent ligand - receptor interaction
3. intracellular level - TGFB receptor kinase inhibitor prevents signal transduction

Question 15

Targeting SMAD proteins

Answer 15

hard to target

Peptide aptamers can inhibit active domains of Smad2 and 3 to disrupt their interactions with Smad4

appear to be functional in vitro

reduce level of Smad2/3 in complex with Smad4 after TGFB stimulation