8/30/10 Cell Signaling

Front 1

Distinguish between membrane permeable and membrane impermeable signals in terms of : (1) their biochemical properties; and (2) the localization of their cognate receptor

Back 1

Impermeable: hydrophillic, larger (i.e. prostaglandins)

Permeable: hydrophobic, small (i.e. steroids)

Front 2

Discuss the mechanism by which the steroid/thyroid family of signaling molecules regulate transcription of target genes

Back 2

Cortisol diffuses through PM into cytosol, binds nuclear receptor protein, activated receptor/ligand complex moves into nucleus, complex binds to regulatory region of target gene, transcription

Most receptors dimerize in response to binding

Front 3

Define the term “second messenger” in the context of signal transduction and signal amplification

Back 3

As the name implies, a second messenger is an intracellular signal synthesized in response to the initial signal (i.e. NO binds GC -> cGMP)

Front 4

Discuss the mechanism by which nitric oxide regulates vasodilation and how compounds such as nitroglycerine and sildenafil are used clinically to influence regulation through this pathway

Back 4

Neurotransmitter to Endothelial cell-> activated NO synthase, converts arginine to NO, rapid diffusion of NO, go into smooth muscle cell (diffusion?), bind to GC, causes GTP->cGMP, rapid relaxation of smooth muscle, vasodilation

Nitroglycerin->NO synthase activation->NO->increased blood flow to heart

Viagra inhibits PDE3 so cyclic GMP not broken down

Front 5

Define the following signal transduction concepts: (1) relay; (2) amplify; (3) integrate; and (4) distribute

Back 5

Slide 15

Relay: Receptor bind to intracellular protein

Amplify: start with a single signal molecule, result in large cellular response

Integrate: integrate signals from other signaling pathways

Distribute: all integrated signals result in a wide array of cellular responses

Front 6

Define the general structure of a G-protein coupled receptor (GPCR) and how activation of a GPCR modulates the activity of the alpha, beta, and gamma subunits of their associated G-proteins

Back 6

seven-pass transmembrane receptor

alpha and gamma subunit have lipid attachment to keep them on PM

GDP-bound = inactive form of G protein (alpha, beta, gamma together)

GDP exchanged off for a GTP activates the G protein. activated G protein has activated beta-gamma subunit released and activated alpha subunit (alpha contains GTP).

G Proteins has an inherent GTPase activity which eventually dephosphorylates GTP back to GDP, but some other proteins help stimulate this ATPase activity.

Front 7

Define the mechanism by which signaling through GPCRs can either activate or inhibit signaling through the Protein Kinase A (PKA) pathway

Back 7

Alpha subunit activates AC (so alpha subunit is called Gs for Gstimulatory subunit).

ATP->cAMP

cAMP binds to regulatory subunits of PKA, activates PKA

active PKA travels into nucleus, phosphorylates transcription factors (activators or inhibitors) -> transcription

usually, high PKA favors growth

Front 8

Outline the downstream effects of phospholipase C (PLC) activation in terms of inositol phospholipid signaling

Back 8

activated Gq protein activates phospholipase C, cleaves PIP2 into DAG and IP3. IP3 binds to IP3-gated Ca channel on ER. ER release Ca into cytosol. Ca binding in addition to DAG binding to Protein Kinase C activates PKC.

Front 9

Discuss the role of calcium as a second messenger in signal transduction cascades

Back 9

will come back to this one

Front 10

Explain the mechanism by which the nicotinic acetylcholine receptor becomes activated.

Back 10

At presynapse, voltage gated Ca channels opens, allowing Ca to enter. Synaptic vescles in response to Ca and release acetylcholine into cleft. Ligand gated ion channels bind acetyocholine, resulting in flux of cations, membrane depolarizaiton, and muscle contraction

Front 11

Describe how a receptor tyrosine kinase (RTK) becomes activated.

Back 11

Receptor Tyrosine Kinases
- single transmembrane domain
- forms dimers on ligand binding
- cross-phosphorylation on tyrosine residues (Y)
-signal in the form of dimer causes dimerization of receptor

after this, forms the activated RTK

This forms a number of docking sites for any protein that contains an SH domain. Activated by RTK, then released into cytosol.

Front 12

Describe how a receptor tyrosine kinase (RTK) activates Ras.

Back 12

Activation of Ras by RTKs

-Ras proteins are monomeric GTPases
- Ras is membrane-associated (e.g., palmitoylation)
- 3 human genes (HRAS, NRAS, KRAS)
- mutated Ras is found in many tumors

A Guanine nucleotide exchange factor (GEF) increases rate of GDP for GTP exchange.(ratio of GTP/GDP in cytosol is > 10)

A GTPase-activating protein (GAP) increases rate of hydrolysis GTP -> GDP + Pi

Forms basic molecular switch

Front 13

Define the MAP kinase signaling module.

Back 13

MAP Kinases

-downstream of Ras
-serine-threonine kinase cascade (????)
- final signaling target are transcription factors (activators, repressors, chromatin remodeling proteins)

Scaffolding adds additional flexibility in signaling responses (potential drug targets)

Front 14

Describe how activation of PI3-kinase by receptor tyrosine kinases (RTKs) leads to downstream activating events at the plasma membrane.

Back 14

Activated RTK leads to activation of PI3-Kinase, which catalyzes inositol phospholipid to PIP3. PIP3 is a docking station at PM. AKT binds to PIP3 and can be activated (phosphorylated) by Protein Kinase-1 or Protein Kinase-2

Front 15

Describe how activation of the AKT kinase can promote cell survival and growth.

Back 15

Activated AKT then dissociates from PIP3 and phosphorylates protein Bad (normally sequesters apoptosis inhibitory protein), releases the sequestered apoptosis inhibition protein, leads to no apoptosis

mTOR integrates signals from growth factors to phosphoroylate Akt. Rapamycin inhibits mTOR

Front 16

Distinguish between phosphatidylinositol 3,4,5-triphosphate (PIP3; generated by PI3 kinase) and inositol 1,4,5-triphosphate (IP3; generated by PLC).

Back 16

IP3 leads to ER release of Ca2+, which in combination with DAG, leads to PKC activation

PIP3 leads to docking station for activation of AKT

PTEN = tumor suppressor gene
phosphatase activity dephosphorylates PIP3 back to PIP2. Can cause tumors if mutated.
Loss of heterozygosity mutation in 1 allele then followed by sporadic loss of second allele.

Front 17

Outline the general steps involved with JAK-STAT signaling.

Back 17

Janus Kinases (JAKs) are recruited to activated receptor and
cross-phosphorylate each other and the receptor

STATS bind and are in turn phosphorylated

activated STATs dimerize, translocate to the nucleus and
function directly as transcription factors.

direct/rapid transcription signal

Front 18

Outline the general steps involved in TGF-b signaling.

Back 18

Come back to this one