CFB 28: Signal Transduction 2

Gq couples hormones to ___ to generate _ second messengers.

PLC; 2

What is the cascade that activates calcium channels and protein kinase C?

E → GPCR → Gaq → PLC → IP3 + DAG

What second messengers are proudced by PLC?

IP3 and DAG

What does IP3 do?

Triggers release of Ca2+ from ER

What does DAG do?

Activates protein kinase C

What is the target of PLCβ?

Gq

Which two kinases become activated?

Protein Kinase C

Ca2+/calmodulin activated kinase (CaM kinase)

What activates Protein Kinase C?

DAG and Ca++

Is PKA self-inhibited?

No, has regulatory subunits

Calcium functions through __________.

Calmodulin

What does calmodulin do upon binding calcium?

Binds to other proteins and either inhibits or activates them (ie CaM-dependent kinase)

What activates calmodulin-dependent kinase?

Calmodulin

Phosphoinositide signaling pathways

Serotonin release by blood platelets -- epinephrine (alpha adrenergic)

Histamine secretion in mast cells -- IgG

Extracellular hormone binding leads to activation of...

Intracellular protein kinase

What does intracellular protein kinase do?

Phosphorylates targets on tyrosine

What is the unique feature of Tyrosine Receptor Kinases?

They are themselves kinases

Major substrate of TKR

Receptor itself

Mechanism of tyrosine kinase receptor function

Ligand-ligand receptor dimerization

Cross phosphorylation

Generation of docking sites for signaling molecules

Tyrosine kinase receptors can generate docking sites for multiple signaling molecules containing which domains?

SH2

Phosphorylated tyrosines on ___________ part of receptor generate docking sites for proteins with SH2 domains.

Cytoplasmic

What are SH2 domains?

Protein domains that bind phosphorylated tyrosines; allows RTK to dock on receptor

What do SH2 domains bind to?

A specific stretch of amino acids in a protein that contains a phosphorylated tyrosine

Individual SH2 domains bind only to ______________ ________ surrounded by specific amino acids.

Phosphorylated tyrosine

Example of a protein with an SH2 domain

Grb2

What is Grb2?

Adaptor protein

What activates the Ras GTPase?

Tyrosine Kinase Receptors

What is Grb2 always bound to?

Sos

What is Sos?

Guanine nucleotide exchange factor (GEF)

TKRs recruit Grb2/Sos to Ras where?

Plasma membrane

TKR pathway

TKR → Grb2 → Sos → Ras-GTP → Raf

What is Ras-GAP?

Ras GTPase Activating Protein

Converts Ras-GTP to Ras-GDP

Defective Ras genes (called ________) and thus their encoded proteins are found in many human tumors.

Oncogenes

Can Ras genes be constitutively activated?

Yes

What is the biochemical defect when Ras genes are mutated?

Single amino acid differences prevents the protein from hydrolyzing GTP to GDP

Ras mutations are analogous to what disease and what other signaling molecule already discussed?

Cholera and Gsα

T/F: Ras protein switches between on and off conformations.

True

In tumor cells, Ras is locked in the __ state.

On

What is NF1?

Negative regulator of Ras signaling

Tumor suppressor gene; promotes hydrolysis

Cells of which tissue can promote tumor profression?

Connective surrounding tissue

Some TKRs can activate ___.

PLC

PLCγ gets __________ phosphorylated by receptor which activates what?

Tyrosine; its catalytic activity

Activation of PKCγ involves both its targets to the plasma membrane. Why is this important?

Enhancement of catalytic activity

How are GPCRs and TKRs similar?

Involvement of GTPase

Activation of a cytoplasmic kinase

How are GPCRs and TKRs different?

No second messenger for TKR -- TKR functions to target molecules to the cell surface where they can function

Serine/threonine kinase receptors are important in development of...

Teeth

What are BMPRs?

Hetero-dimers of type I and type II proteins with intracellular kinase domains

What is BMP?

Bone morphogen protein

Steps of BMP signaling pathway

1. Ligand binding causes complex formation between two subunits of BMPR

2. Type II phosphorylates Type I receptor which then phosphorylates R-Smad

3. Smad complex then enters the nucleus and regulates gene expression

What do Smads do?

Go to nucleus to turn on genes quickly

Biological processes that use BMP signaling

Mineralization/ectopic bone formation

Embryonic development of skeletal and non-skeletal tissues

BMP signaling increases the expression of ____________ ______ proteins and transcription factors that are crucial for bone formation.

Extracellular matrix

BMP signaling increases the expression of which transcription factors that are crucial for early tooth development?

MSX1 and MSX2

BMP works by regulating the expression of transcription factors in both _____derm and ____derm to promote tooth development at many stages.

Ectoderm and mesoderm

Which of the following hormones is not derived from an amino acid?

Prostaglandin E2

3 multiple choice options

In general, which type of hormone works fastest?

Peptide hormones

What inhibits signaling by prostaglandins?

Aspirin

What enhances signaling by epinephrine?

Cholera toxin and caffeine

What receptor type signals most directly to the nucleus?

Serine threonine kinase receptors

2 multiple choice options

There is a new cholera epidemic in Botswana. Imagine they found that a new strain of vibrio cholera was responsible and after investigation it was found that the cholera toxin produced by this bacteria did not do what the previously described cholera toxin did at the biochemical level, even though it did produce identical effects on people. Which could be the molecular mechanism made by this new strain of cholera?

It ADP ribosylates the β subunit of the Gsα such that it never binds the α subunit

3 multiple choice options