Lecture 9 & 10 (tyrosine kinases)

Question 1

Two forms of tyrosine kinases

Answer 1

• Receptor tyrosine kinases
• Non-RTKs

Question 2

A common mechanism to regulate protein function

Answer 2

Phosphorylation

Question 3

Is phosphorylation reversible?

Answer 3

Yes

Question 4

__ kinases function in the early steps of signal transduction, whereas __ kinases function at later steps.

Answer 4

Tyrosine kinases
Serine/threonine kinases

Question 5

Receptors for known tyrosine kinases

Answer 5

• EGF receptor (ErbB)
• CSF-1 receptor (fms)
• PDGF receptor
• Insulin receptor
• IGF-1 receptor
• FGF receptor

Question 6

First tyrosine kinase discovered

Answer 6

Src gene

Question 7

General features of kinases

Answer 7

• All have similar catalytic domains
• 250-300 amino acids
• Differences in this domain distinguish tyrosine kinases from serine/threonine kinases

Question 8

Related structural features of RTKs

Answer 8

Ligand binding domain in N-terminal extracellular region (25 aa hydrophobic region spanning the membrane)

Question 9

v-ErbB (oncogene)

Answer 9

• truncated version of ErbB (EGFR)
• lacks N-terminal extracellular domain → receptor constitutively activated
• amplification occurs in many tumours e.g. glioblastomas, squamous cell carcinomas

Question 10

Fms oncogene

Answer 10

• derived from CSF-1
• not deleted but has an activating point mutation in the extracellular domain
• deletions of the extreme -COOH end also positively regulates transforming activity

Question 11

Other oncogenes that encode RTKs

Answer 11

Ros, Sea, Rrk, Met, Ret Kit

Question 12

N-terminal deletions have been found in…

Answer 12

ErbB2, Kit, Ros, Met, Ret and Trk oncogenes

Question 13

Example of a tyrosine kinase inhibitor

Answer 13

Lapatinib

Question 14

How does Herceptin (Trastuzumab) work?

Answer 14

mAb binds the ligand-binding domain of HER2 & stops the growth factor from binding

Question 15

Benefit of administering Herceptin in combination with a tyrosine kinase inhibitor

Answer 15

Herceptin inhibits ligand-binding domain of HER2, TKI inhibits catalytic domain of HER2

Question 16

Another very important non-RTK oncoprotein

Answer 16

Abl

Question 17

Src sub-family

Answer 17

Comprised of 9 genes that encode non-RTKs: Src, Yes, Fgr, Lck, Fes, Fyn, Lym, Yrk, Hck

Question 18

What do the src sub-family genes have in common?

Answer 18

• All encode ~60 kDa phosphoproteins with extensive homology
• Share SH1 catalytic domain

Question 19

Modification of src is necessary for…

Answer 19

membrane association and transforming activity

Question 20

Src autophosphorylates Tyr416, which leads to…

Answer 20

increased kinase activity and increased transforming potential

Question 21

Src does not phosphorylate itself on __

Answer 21

Tyr527 (negative regulation)

Question 22

Why is v-src truncated?

Answer 22

Tyrosine residue 527 is deleted, which inhibits src from negatively regulating the protein

Question 23

Kinase involved in negative regulation of src

Answer 23

Csk: C-terminal src kinase

Question 24

Amino acid regulatory regions of src

Answer 24

• SH2: phosphotyrosine-binding domains
• SH3: binds proline-rich domains

Question 25

What domain is deleted in many cases during transition from c-onc to v-onc, or spliced out of mRNA for the oncoprotein?

Answer 25

SH3 domain

Question 26

Examples of non-RTK oncoproteins that lack the SH3 domain

Answer 26

• v-ABL
• BCR/c-ABL (Philadelphia chromosome)

Question 27

Src also interacts with __

Answer 27

p53

Question 28

Src functions downstream of __ and upstream of __

Answer 28

PDGF
c-myc

Question 29

__ can activate src kinase

Answer 29

Phosphatases

Question 30

Src SH2 interacts with pTyr on activated __ or __ receptor

Answer 30

PDGF or CSF-1

Question 31

Fyn protein binds __

Answer 31

T cell antigen receptor

Question 32

Lck protein binds…

Answer 32

CD4+ and CD8+ T cells

Question 33

Src knockout mice develop…

Answer 33

osteopetrosis due to osteoclasts inability to resorb bone