Ch. 6: Cytoplasmic Signaling Circuitry

Question 1

signal transduction

Answer 1

• generally the transmission of a molecular signal outside of a cell to the inside of a cell.
  -A way for cells to communicate with
  each other.
• One cell can produce a ligand which causes a neighboring cell to have a
  response.

Question 2

How do you get from the input layer to the final output layer?

Answer 2

Ex- growth factor binding to activation of cell division
- Signal processing (intracellular signaling, signal relay, middle-men, cascade)?

Question 3

What happens after receptor trans-phosphorylation?

Answer 3

Specific proteins are able to bind to specific phosphorylated parts
on the intracellular side of the RTK.

Question 4

What does the phosphorylated intracellular domain do?

Answer 4

serves as a docking site for specific proteins

Question 5

Structure of GRB2

Answer 5

• SH2 domain
• SH3 domain

Question 6

What does SH2 domain do?

Answer 6

binds to specific phosphorylated tyrosine amino acids

Question 7

What does SH3 domain do?

Answer 7

Binds to proline-rich parts of proteins

Question 8

What is Sos? What does it do?

Answer 8

• a guanine nucleotide exchange factor
• activates RAS proteins by replacing GDP with GTP

Question 9

What happens when RAS is activated?

Answer 9

binding of GTP causes RAs to change shape and release the effector loop. Once released, the effector loop can bind downstream signaling proteins.

Question 10

What are the three pathways of active RAS?

Answer 10

3 pathways
- MAPK (proliferation)
- PI3K (inhibition of apoptosis)
- RaI-GEFs (motility)

Question 11

MAPK pathway

Answer 11

RAS activates MAPKKK
- Ras binds to MAPKKK, activating it and MAPKKK is a kinase that phosphorylated MAPKK

MAPKK -> MAPK
- phosphorylation of MAPKK activates the kinase domain so MAPKK can then phosphorylate MAPK

Phosphorylation of MAPK causes activation of its kinase domain so it can then phosphorylate further downstream molecules

Question 12

Importance of scaffold protein

Answer 12

• Ensures all members of
  pathway are physically
  located near one another
• KSR scaffold organizes this
  highly efficient signal
  transduction

Question 13

what is downstream of ERK?

Answer 13

• activated ERK can then enter
  the nucleus and phosphorylate
  transcription factors (ex: ETS).
• Activated TFs can then cause the transcription of genes that promote cell division (ex: HB-
  EGF, cyclin D1, FOS, P21Waf1)
• Activated ERK also activates
  widespread protein synthesis by activating a translation initiation factor (eIF4E)

Question 14

What is RAF?

Answer 14

• a common
  oncogene
• vRAF murine and ckn retrovirus
• 50% human melanomas
• B-RAF, single aa substitution, moves an inhibitory part of the protein out of the way, causes RAF
  to be constitutively active

Question 15

What would happen if RAF was constitutively active?

Answer 15

it would cause constant proliferation, leading to tumorigenesis

Question 16

PI3K pathway

Answer 16

• PI3K itself is recruited to the membrane when receptor is activated/phosphorylated
• At the membrane, activated
  RAS is also able to bind PI3K
  and enhance its function (Causes PI3K to become close to its PI substrates present at the plasma membrane)
• Activation of PI3K enhances formation of PIP3
• Proteins that carry a PH
  domain can bind to PIP3
• Recruitment of AKT to the membrane, causes
  activation of AKT
• At the membrane AKT is
  phosphorylated by other
  proteins (PDK1 and
  mTORC2) and activated
• AKT can then
  phosphorylate a variety
  of substrates

Question 17

Inositol biology: Can be phosphorylated by? can be cleaved by?

Answer 17

• PI (inositol) can be phosphorylated by PI kinases to form PIP2
• PIP2 can be phosphorylated by PI3K to form PIP3
• can be cleaved by PLC to form DAG and IP3

Question 18

AKT

Answer 18

Serine/Threonine kinase

Question 19

Downstream effects of activated AKT

Answer 19

inhibition of cell death (apoptosis)
* At the membrane AKT is
phosphorylated by other
proteins (PDK1 and
mTORC2) and activated
* AKT can then phosphorylate a variety of
substrates

Question 20

How is AKT regulated?

Answer 20

Normally highly regulated
- PTEN causes PIP3 to turn
back into PIP2, this
causes the inactivation of
AKT
* Protein phosphatases de-
phosphorylate AKT as
well

Question 21

How is AKT deregulated in cancer cells?

Answer 21

1. Loss of PTEN
2. Hyperactivity of PI3K

Question 22

What do activated Rho proteins promote?

Answer 22

invasive qualities
- Re-organization of actin
cytoskeleton
- filopodia
- lamellipodia

Question 23

Filopodia

Answer 23

Small finger like extensions from the plasma membrane, cell uses to explore environment and adhere to the extracellular matrix

Question 24

Lamellipodia

Answer 24

Broad ruffles at the leading
edge of motile cells

Question 25

What is the second most common mutated oncogene pathway in all human cancers?

Answer 25

PI3K pathway

Question 26

RAL GEFs pathway

Answer 26

RAS activates RAL proteins via RAL GEFs
- Active Ras can bind to Ral-GEFs and recruit them to the membrane.
- Ras binding to Ral-GEFs also changes Ral-GEF shape and activates the guanine
nucleotide exchange function.
- RAL proteins promote cell motility/invasion

Question 27

What is the #1 most commonly mutated oncogene in human cancers?

Answer 27

RAS

Question 28

One of the mechanisms to stop intracellular signaling molecules so proliferation only occurs when necessary?

Answer 28

CBL
1) CBL ubiquitinates receptor and tags it for degradation by the proteasome. (Book)
2) CBL ubiquitinates receptor which induces endocytosis and subsequent sorting to a
lysosome for ultimate
destruction. (Literature)

Question 29

CBL destruction via activated SRC oncogene causes…

Answer 29

an increase in RTK at the cell surface