Cell Communication-II (Fall 2010) Pin Ling ( 凌 斌 ), Ph.D. Department of Microbiology & Immunology, NCKU ext 5632; Reference: “Mechanisms of Cell Communication”, The Cell (5th edition), Chapter 15

Outline General principles of cell communication Signaling through G-protein-coupled cell surface receptors (GPCRs) and small intracellular mediators Signaling through enzyme-coupled cell- surface receptors Signaling pathways dependent on regulated proteolysis of latent gene regulatory proteins Signaling in plants

Six major classes of enzyme-coupled receptors 1.Receptor Tyrosine Kinases (RTKs) 2.Tyrosine kinase-associated receptors: No intrinsic enzyme activity. 3.Receptor Ser/Thr kinases 4.Histidine-kinase associated receptors : two-component signaling pathway 5.Receptor guanylyl cyclases 6.Receptor Tyr phosphatases

RTK Subfamilies (16): 60 human RTKs

Some growth factors or cytokines act via RTKs

Signaling via RTKs 1.Activated RTKs phosphorylate themselves. 2.Phosphorylated Tyr residues on RTKs => Docking sites 3. Proteins w/ SH2 domain (PTB domain) bind to phophorylated Tyr resides. 4.Ras, a family of monomeric GTPase, acts downstream of many RTKs. 5.Ras activates a MAPK signaling module via adaptors & GEFs.

Activation of RTKs via dimerization

Intracellular domains of activated RTKs provide “docking sites’

Figure 15-55a Molecular Biology of the Cell (© Garland Science 2008) Binding of SH2-containing proteins to activated PDGF receptor

SH2 domains recognize phospho-Tyr in the context of flanking sequences

Ras superfamily of monomeric GTPases

Sev RTK activates Ras in the fly

Ras activates the MAPK pathway

Activation of ERK/MAPK at various intracellular compartments-I

Scaffold proteins in formation of signaling complexes

Rho family GTPases couple surface receptors to the cytoskeleton

The downstream pathways activated by GPCRs & RTKs

PI3K (Phosphoinositide 3-kinase) Signaling 1.PI3K is involved in downstream pathways of many “Growth Factor Receptors”. 2. PI3K mainly phosphorylates inositol phospholipids => Docking sites on the plasma membrane. 3. PI3K activates the downstream AKt-mTOR pathway => Regulate cell survival & proliferation. 4. Deregulation of this pathway is often found in many cancer cells.

Generation of PI docking sites by PI3K

Cell survival via PI3K signaling

Cell growth via PI3K signaling

Tyrosine kinase-associated receptor signaling 1.Many cell surface receptors depend on Tyr phosphorylation but lack a Tyr kinase domain, e.g. Cytokine receptors, Integrins, …etc 2. These receptors act through Cytoplasmic Tyrosine Kinases, e.g. Src family kinases, FAK, ….etc. 3.Cytokine receptor activate the JAK-STAT pathway. 4.Tyr Phosphatases reverse Tyr phosphorylation on various Tyr-phosphorylated proteins. 5.Tyr phosphatases have transmembrane & cytoplasmic forms.

Cytokine signaling via the JAK- STAT pathways

Table 15-6 Molecular Biology of the Cell (© Garland Science 2008) Cytokine Receptor signaling via the JAK-STAT pathways-II

1.TGF  superfamily consists of various mediators to regulate cell proliferation, specification & differentiation, e.g. TGFb/activin family, BMP (bone morphogenetic protein) family. 2. All these mediators act via Ser/Thr kinase-coupled receptors. 3.Activated receptors trigger the Smad pathway. Transforming growth factor-  (TGF  ) Superfamily

TGF-beta signaling pathway

Ser/Thr and Tyr protein kinases are structurally related

1.In bacteria, chemotaxis response is mediated by Histidine kinase associated receptors. 2.These receptors activate a two-components signaling pathway, also seen in yeasts & plants. 3. Histidine kinase-associated chemotaxis receptors regulates flagella movements in a straight line or tumbling. Bacterial chemotaxis via Histidine kinase-associated receptors

Flagella movement during E. Coli swimming

Chemotaxis receptors control flagella movement CheW: Adaptor CheA: His kinase CheY: Effector/ Phosphatase

Outline General principles of cell communication Signaling through G-protein-coupled cell surface receptors (GPCRs) and small intracellular mediators Signaling through enzyme-coupled cell-surface receptors Signaling pathways dependent on regulated proteolysis of latent gene regulatory proteins =>Irreversible Signaling in plants

Signaling via Notch Receptor Protein 1.Notch signaling is involved in regulating cell fates & development. 2.Role of Notch in nerve cell production: Neighbor cell |= Precursor cell => Nerve cell 3.Signaling between adjacent cells via Notch & Delta (or other related ligands). 4.Notch is a single-pass transmembrane protein undergoing proteolytic process to function. 5. Deregulated Notch signaling is often found in cancer development.

“Lateral inhibition” of nerve cell development via Notch signaling

Proteolytic cleavage of Notch & its signaling

Wnt/  -Catenin signaling

Activation of NF-  B pathway by TNF 

Negative feedback control & NF-  B oscillations

Outline General principles of cell communication Signaling through G-protein-coupled cell surface receptors (GPCRs) and small intracellular mediators Signaling through enzyme-coupled cell-surface receptors Signaling pathways dependent on regulated proteolysis of latent gene regulatory proteins =>Irreversible Signaling in plants

Signaling in Plants 1.Multicellularity & Cell communication evolved independently in Plants & Animals. 2.Receptor Ser/Thr kinases are the largest family in plants. 3.Various plant hormones (growth factors) regulate plant development, e.g. ethylene, Auxin,….etc. 4.Signaling in plants mainly come from genetic studies on Arabidopsis.

Divergence of plant & animal lineage

Clavata1/Clavata2 (Clv1/Clv2) : Leucine- rich repeat receptor (LRR) kinases

Ethylene-mediated growth control: 1.Promote fruit ripening, leaf abscission, & senescence. 2.Germinating seedling: (1) Thicken its stem (2) Shield its tip of the shoot (3) Avoid obstacle

Ethylene Signaling Pathway Raf-like

Photochromes mediate a light response

“Discussion” to be continued