TKRs

Question 1

Three categories of TKRs

Answer 1

1. scaffold protein
2. assembly of signaling proteins on activated receptor
3. assembly of signaling complex on phosphoinositide docking sites

Question 2

Extracellular domain of TKRs

Answer 2

• ligand binding

- vary across TKRs

Question 3

tyrosine kinase domain of TKRs

Answer 3

• kinase activity

- highly conserved

Question 4

intracellular domain of TKRs

Answer 4

• signal transduction

- highly conserved

Question 5

dominant negative mutations in TKRs

Answer 5

-prevent formation of active dimers because they need each other to auto-phosphorylate

Question 6

Achondroplasia

Answer 6

-caused by dominant negative mutation in gene encoding fibroblast GF receptor 3

Question 7

receptor dimerization

Answer 7

-the signal molecule of RTKs causes two halves of the dimer to come together so they can eventually auto-phosphorylate

Question 8

intrinsic tyrosine kinase activity

Answer 8

autophosphorylation of receptor

Question 9

SH2 domain proteins

Answer 9

intracellular signaling proteins that recognize the phosphorylations on the tyrosine kinase receptors

Question 10

types of SH2 domain proteins

Answer 10

adaptor proteins (Grb2) and enzymes (sarc, phospholipase C-gama, phosphatidyl inositol 3-kinase)

Question 11

Grb-2

Answer 11

an SH2 domain that acts as an adaptor between the activated RTK and SOS (a GEF protein needed for Ras activation)

Question 12

SOS

Answer 12

A GEF (guanine nucleotide exchange) protein; activates G-protein by exchanging GDP and GTP

Question 13

Ras (what is it? what does it activate? what is it important for?)

Answer 13

• A g-protein that activates a MAPK phosphorylation cascade, starting with activation of Raf (MAP kinase kinase kinase)
• central to cellular growth control–>initiates serine/threonine phosphorylation cascade, stimulates increased gene transcription
• mutations in Ras have a high incidence in cancer
• chemo has targeted Ras activity

Question 14

MAP kinase serine/threonine phosphorylation cascade

Answer 14

1. Was activates MAP kinase kinase kinase (Raf)
2. Raf activates MAPKK (mek)
3. Mek activates MAPK (Erk)
4. Erk phosphorylates different regulatory proteins that lead to changes in protein activity or gene expression

Question 15

Dysregulation of RAD-RAF-ERK

Answer 15

Can lead to ID syndromes

Question 16

PI-3 Kinase

Answer 16

• activated by RTK

- Phosphorylates PIP2 to get PIP3 to form docking sites on the membrane for signal transducing kinases

Question 17

PDK1

Answer 17

binds to PIP3 and activates Akt with the help of mTOR

Question 18

mTOR

Answer 18

with PDK1, activates Akt

Question 19

Akt

Answer 19

• gets activated by getting phosphorylated by PDK1 and mTOR

- stimulates protein synthesis and cell growth, inhibits cell death

Question 20

Insulin signaling

Answer 20

• receptor complex consists of RTK, SH domain proteins, scaffold proteins, phosphoinositide docking sites…
• acts through Ras pathway

Question 21

Tyrosine phosphatases

Answer 21

• oppose action of tyrosine kinases

- take tyrosine phosphate off

Question 22

down regulating RTK signaling

Answer 22

1. ligand binds
2. tyrosine kinase activity (required for targeting to lysosomes)
3. receptor internalization via clathrin coated pits
4. hormone degradation
5. receptor dephosphorylation
6. receptor recycling (eg insulin receptors) or receptor degradation (EGF receptors)

Question 23

tyrosine kinase-associated receptors (TK-ARs)

Answer 23

• transmembrane proteins, lack intrinsic catalytic activity
• activated receptors activate intracellular tyrosine kinases
• ligand binding results in receptor oligomerization (form heterodimers or heterotrimers), association with intracellular tyrosine kinases, activation of transcription

Question 24

Difference in what RTKs respond to and what TK-ARs respond to

Answer 24

RTKs: growth factors, insulin, ephrins

TK-ARs: cytokines, growth hormone

Question 25

JAK-STAT signaling pathway

Answer 25

• activated by TK-ARs
• JAKs phosphorylate each other and then phosphorylate receptors so that the SH2 binding domain on STAT can bind and get activated
• STAT is a TF that then goes to the nucleus

Question 26

STAT

Answer 26

transcription factor

Question 27

x-linked severe combined immune deficiency

Answer 27

missing subunit of TK-AR receptor (interleukin receptor)

Question 28

autosomal dominant combined immune deficiency

Answer 28

mutation in JAK 3 protein kinase

Question 29

autosomal recessive severe combined immune deficiency

Answer 29

T cell antigen receptor-associated protein kinase mutation

Question 30

Integrins

Answer 30

• Cell adhesion molecules that function as TK-ARs
• associated with FAK (a focal adhesion kinase)
• results in activation of Ras and sarc
• downstream activation of Rho, Raf, and CDC42 (small G-proteins) that results in cell shape changes due to remodeling of actin cytoskeleton

Question 31

Integrin interactions extracellularly

Answer 31

• form interactions with the cytoskeleton at focal adhesions with ECM and hemidesmosomes with connective tissue
• bind to intracellular bundles of cross linked actin filaments

Question 32

Receptor Serine/Threonine Kinases (Rs/tKs) activation mechanism

Answer 32

• binding of TGF-B family proteins (acitvins and bone morphogenic proteins) causes the Type II receptor to phosphorylate the Type I receptor
• type I receptor recruits and phosphorylates SMAD 2/3
• SMAD 2/3 oligomerizes with SMAD 4 and that goes to the nucleus to activate transcription

Question 33

TFs used by TK-ARs versus RstKs

Answer 33

TK-ARs use STATs

Rs/tKs use SMADs