Last Class:

A. intracellular vesicle traffic1. ER to golgi

2. endocytosis, exocytosis B. Signaling Transduction

1. Ligand Receptor Interactions, 2. Intracellular signaling molecules, 3. molecule switches:

phosphorylation and GTP binding, 4. Signaling integration, 5. complex formation, 6. Signaling

amplification, 7. Signaling desensitization

• Cell Communication

• Different Receptor Types• Ion channel-linked receptors• *GPCR signaling• *Enzyme linked receptors

• G Protein Coupled Receptors (GPCR)

A G-Protein-Coupled ReceptorOr G Protein-linked Receptor7 transmembrane domains

The disassembly of G-Protein upon stimulation

Spontaneous deactivation is very fast, in minutes.

However, with the help of RGS (regulator of G

protein signaling, a GAP for unit), signals can be

shut off even faster

The Activation cycle of G-

Protein

• GPCR Signaling: cAMP

The visualization of cAMP in nerve cellsGPCR->Gs->adenylyl cyclase->cAMP

Gi

cAMP cycle: GPCR->Gs->adenylyl cyclase->cAMP

Cyclic AMP phosphodiesterase breaks down cAMP to 5’-AMP

The function of cAMPTargeting PKA (cyclic-AMP-dependent protein

kinase A)

The Whole Signaling Network related to cAMP

Terminology: CRE(cyclic AMP response element); CREB: CRE binding protein; CBP: CREB binding

protein

• GPCR Signaling: Calcium

Three Types of Inositol phospholipidsPI, PI(4)P, PI(4,5)P2

Phospholipase C-

(PLC-) Produces DAG

(diacylglycerol) and IP3 (inositol 1,4,5-

trisphosphate (IP3))

Gq->PLC-

Gq signaling pathways and Calcium

Fertilization of an egg by a sperm triggering an increase in cytosolic Calcium

3 major types of calcium channels:

1. Voltage dependent Ca channels on plasma membrane

2. IP3-gated Ca release channels on ER membrane

3. Ryanodine receptor on ER membrane

Calcium uptake and deprivation1. Na/Ca exchanger on plasma membrane, 2. Ca pump on ER

membrane, 3. Ca binding molecules, 4. Ca pump on Mitochondia

Calcium Frequency encoding signaling

strength

Local Ca blips, sparks, puffs, reflecting local opening of individual

channels in ER, strong local signal induces global activity, the

elevated Calcium trigger calcium deprivation

system

Targeting molecules for Calcium

Calcium binding protein Calmodulin

Ca2+/calmodulin dependent protein kinase (CaM-kinase)Memory function: 1. calmodulin dissociate after 10 sec of low calcium level; 2. remain active after calmodulin dissociation

Ca2+/calmodulin dependent protein kinase (CaM-kinase)Frequency decoder of Calcium oscillation

High frequence, CaM-kinase does not return to basal level before the second wave of activation starts

Desensitization of GPCR

1. Inhibitory structural alteration of receptor; 2. receptor internalization; 3. receptor degration

GRK (G protein-linked receptor kinase)

Arrestin takes to clathrin-coated pits and degradation

• GPCR Signaling Summary• 1. G-protein types• 2. cAMP and Calcium signaling

pathways• 3. desensitization

Enzyme-Linked Cell Surface Receptors

•*Receptor Tyrosine Kinase•*Tyrosine kinase associated receptors•*Receptor-like tyrosine phosphatase•*Receptor serine/threonine kinase•Receptor guanylyl cyclase•Histidine like associated receptor

• Receptor Tyrosine Kinases (RTKs)

Seven subfamilies of receptor tyrosine kinases

Three ways in which signaling proteins can cross-link receptor chains

1. dimer, 2. monomer but brought together by proteoglycan, 3. cluster on membrane

The importance of receptor oligomerization

The docking of signaling molecules at RTK

The binding of SH2-containing intracellular signaling proteins to an activated PDGF receptor

The structural view of SH2 domain

• RTK Signaling: Ras Pathway

The regulation of Ras activity, a famous downstream molecule of RTK responsible for

cancer development

The activation of Ras by RTK signaling

The MAP-kinase regulated by Ras

• RTK Signaling: PI3K Pathway

The inositol phospholipids generated by PI3K

The recruitment of signaling molecules with

PH domains to the plasma membrane during B cell

activation

One PI3K pathway

PH domain: pleckstrin homology domain

Another PI3K pathway to regulate cell survival

Another PI3K pathway to regulate cell migration

PI3K->PIP3->GEF->Rac->Wave->Arp2/3->Actin polymerization

Movie: chemotaxis, PI3K and cell migration

Intracellular Signaling Pathways activated by RTKs and GPCRs

1. Tyrosine kinase associated receptors

Integrins: cell-extracellular matrix adhesionBinding to Src and FAK

1. Receptorlike tyrosine phosphatasesIntracellular protein and receptor

1. Receptor Serine/threonine kinase2. Transforming growth factor (TGF-b) and

Smad signaling pathway

1. Protein kinase Summary

• Enzyme-linked Receptor Signaling Summary

• 1. receptor types• 2. RTK and its signaling: Ras and PI3K• 3. Tyrosine kinase associated receptors

and Receptor-like tyrosine phosphatase• 4. Receptor serine/threonine kinase, TGF-

and Smad

•Other Signaling Pathways•Proteolysis mediated

1. Notch and Delta interactionLateral inhibition

1. The inhibitory pathway of NotchProteolysis-mediated

1. The inhibitory pathway of Notch

Proteolysis-mediated

1. Wnt Signaling pathwayLRP: LDL-receptor-related protein; GSK-3: glycogen synthase

kinase-3APC: adenomatous polyposis coli;

1. NF-KB pathway

• Summary

• 1. GPCR signaling: PKA and Calcium• 2. Enzyme-linked Receptor signaling: RTK-

>Ras and PI3K• 3. Proteolysis-mediated signaling pathways