Cell Bio 12

Question 1

Receptor Tyrosine Kinase Structure

Answer 1

Extracellular domain
Transmembrane domain
Cytoplasmic domain

Question 2

Extracellular Domain

Answer 2

Bind Ligands

Ligands include growth factor and Insulin

Question 3

Transmembrane

Answer 3

Single alpha helix

Question 4

Cytoplasmic Domain

Answer 4

Instrinsic tyrosine kinase activity which is stimulates by ligand binding due to receptor dimerization

Question 5

Adapter Proteins

Answer 5

Required, recruited by tyrosine kinases.

Contain unique domains that recognize specific sequences.

Common adapter domains: SH2

acts as adaptors linking one protein to another

Question 6

Ras

Answer 6

Acts as a GTPase switch protein to signal further downstream kinases

Monomeric protein, lipid anchored protein.

Downstream effector of RTK signaling

Similar to G-alpha but smaller, lower GTPase actibity not linked directly to cell surface receptors

Ras activity is regulated by GEFs and GAPs.

Question 7

Cell surface receptors and signal transduction pathways

Answer 7

Cytoplasmic domain with kinase activity, can directly phosphorylate proteins they can phosphorylate TFs or intermediate proteins that lead to a phophorylation cascade. One kinase phosphorylates another which phosphorylates another.

More steps involved in signaling and activity

Question 8

Activation of RTKs

Answer 8

Dimerization allows for trans-autophosphorylation of cytoplasmic domains

phosphotyrosines serve as docking sites for downstream signal-transduction proteins containing SH2 domains (adaptor proteins)

Question 9

Rous Sarcoma Virus Gene

Answer 9

Encodes a tyrosine kinase (src)

Highly conserved and found in humans

Normal version is cellular src (c-src)

Viral Version is viral src (v-src): constituively active

v-src lacks the carboxyl terminus, inhibitory phosphorylation of the receptor cannot occur

The kinase is constantly active and transmitting mitogenic signals in the absence of growth factor, the kinase was perpetual turned on all the time, and the kinase is unregulated and not controlled by csk. On all the time.

Question 10

FGF-induced Ras Activation: Step 1

Answer 10

Fibroblast growth factor binds to the FGF receptor

Autophosphorylation sets up docking scaffold for adapter proteins containing SH2 and SH3 domain

GRB (growth factor receptor bound protein) binds to the phosphorylated kinase

Question 11

FGF-induced Ras Activation: Step 2

Answer 11

SH3 proteins of GRB2 binds to proline residues in Sos, while SH2 binds to phosphotyrosine residues on the RTK

connects the complex to Ras

Question 12

FGF-induced Ras activation: step 3

Answer 12

Sos is a GEF, GDP dissociates from Ras, GTP binds and active ras dissociates from sos and will activate Raf, Raf activates MEK and MEK activates MAPK

Question 13

Raf activation

Answer 13

Ras can move along and will encounter cytosolic Raf a kinase, Raf is inactivated by an inhibotry protein called protein 14-3-3

When ras binds to raf it promotes dephosphorylation of one of the phosphate groups on raf promoting the partial dissociation of 14-3-3 allowing raf to be active, Raf can phosphorylate downstream kinase

Question 14

RTK/RAS/MAP kinase pathway components are frequently mutated in cancer

Answer 14

Constitutive activation of RAS can arise from a recessive loss-of-function mutation in a GTPase activating protein (NF1)

Loss of GAP leads to sustained RAS activation of down stream signal transducing proteins

Question 15

Her2 Receptor mutation

Answer 15

Causes dimerization and activation of receptor in absence of ligand

A mutation within the transmembrane causing the her2 receptor to dimerize all the time turning the receptor on.

Question 16

Epidermal growth factor receptor mutation

Answer 16

Deletion that causes loss of extracellular ligand binding domain in EGF receptor leads to constitutive activation of cytoplasmic kinase domain (ErbB oncoprotein)

Question 17

Human epidermal growth factor receptors (HERs)

Answer 17

EGF family

HER1 to HER4

HER2 does not directly bind a ligand

HER2 forms heterodimers with other HER RTKs and EGF is bound it leads to activation of the RTK dimeric complex

Question 18

HER2 Amplification

Answer 18

Amplification of HER2 gene a duplication that expresses more copies of Her2

Cell is stimulated by very small amounts of Epidermal gF triggerinf the cells to divide very quivkly

antibody based treatment

Question 19

Herceptin Mode of Action (4)

Answer 19

Cleavage of the extracellular domain of HER2 leaves a membrane-bound phosphorylated p95, which can activate signal-transduction pathway in absence of ligand, possibly inhibited by HER2

Herceptin may reduce HER2 signaling by physically inhibiting either homodimerization or heterodimerization

Herceptin may recruit immune cells to promote antibody-dependent cytotoxicity

Herceptin may promote increased endocytosis of HER2

Question 20

Ras Mutation

Answer 20

20-30% Human cancers: Ras binds GTP but no hydrolysis, mutation of glycine-12 which prevents binding GAPs (RasD protein).