cell communication single cell multicellular organism
TRANSCRIPT
Cell Communication
Single cell
Multicellular organism
Budding yeast cellsresponding to matingfactor
One haploid cell
Another haploid cell
Sexual mating (requires many downstream signalpathways to beactivated)
GENERAL PRINCIPLES OF CELL COMMUNICATION
Extracellular signal molecules bind to specific receptors
Extracellular signal molecules can act over either short or long distance
Autocrine signaling can coordinate decision by groups of identical cells
“Community effect” in early developmentIn tumor biology---cancer cells stimulate their own proliferation
Gap junctions allow signaling information to be shared by neighboring cells
Ca2+, cAMP etc. but not for proteins or nucleic acids
Intracellular electrodes, small water-soluble dyes
Connexin 43 deficiency --- abnormal heart development
Each cell is programmed to respond to specific combinations of extracellular signal molecules
Different cells can respond differently to the same extracellular signal molecules
The concentration of a molecule can be adjusted quickly only if the lifetime of the molecule is short
Nitric oxide gas signals by binding directly to an enzyme inside the target cell
Nitroglycerine --- anginaViagra --- PDE inhibitorCO
Nuclear receptors are ligand-activated gene regulatory proteins
Ligand-binding domain
The three largest classes of cell-surface receptor proteins are ion-channel-linked, G-proteins-linked, and enzyme-linked receptors
Most activated cell-surface receptors relay signals via small molecules and a network of intracellular signaling proteins
Some intracellular signaling proteins act as molecular switches
2% of human genes Monomeric GTPaseTrimeric GTPase
Signal integration by protein phosphorylation
Intracellular signaling complexes enhance the speed, efficiency, and specificity of the response
Complex forms transiently
Interactions between intracellular signaling proteins are mediated by modular binding domains
PDZ Domain Domain binding and function: PDZ domains bind to the C-terminal 4–5 residues of their t
arget proteins, frequently transmembrane receptors or ion channels. These interactions can be of high affinity (nM Kd). The consensus binding sequence contains a hydrophobic residue, commonly Val or Ile, at the very C-terminus. Residues at the –2 and –3 positions are important in determining specificity. PDZ domains can also heterodimerize with PDZ domains of different proteins, potentially regulating intracellular signaling. In addition to engaging in protein-protein interactions, several PDZ domains including those of syntenin, CASK, Tiam1 and FAP are capable of binding to the phosphoinositide PIP2. PIP2-PDZ domain binding is thought to control the association of PDZ domain-containing proteins with the plasma membrane.Structure Reference: Doyle, D.A. et al. (1996) Cell 85(7), 1067–1076.
The third PDZ domain from PSD-95.
www.cellsignal.com
Binding Examples:
PDZ domain proteins
Binding partners domain binding sites
Post-synaptic Density Protein 95 (PSD-95)
NMDA receptor B via PDZ1 and PDZ2 of PSD-95
– IESDV-COOH
Post-synaptic Density Protein 95 (PSD-95)
Kvl1.4 Shaker-type K+ channel via PDZ1 and PDZ2 of PSD-95
– VETDV-COOH
Post-synaptic Density Protein 95 (PSD-95)
Neural Nitric Oxide Synthase (nNOS) via PDZ2
PDZ/PDZ interaction
Enriched in cholesterol and glycolipids
Lipid raft
c-Src tyrosine kinase
Cells can respond abruptly to a gradually increasing concentration of an extracellular signal
Chicken oviduct cells Stimulated by estradiol
effector/target : 1~16
maximal activation
One type of signaling mechanism expected to show a steep thresholdlike response
A cell can remember the effect of some signals
Signals trigger muscle cell determinationAutophosphorylation of Ca2+/CaM-kinase II
Cells can adjust their sensitivity to a signal
SIGNALING THROUGH G-PROTEIN-LINKEDCELL-SURFACE RECEPTORS
1. The largest family of cell-surface receptors2. 5% of the C. elegans genes3. Signal molecules: hormones, neurotransmitters and local medicators4. Rhodopsin-light receptor5. Genome sequencing --- vast numbers of new family members6. Major targets for drug discovery
Trimeric G proteins disassemble to relay signals from G-protein-linked receptors
Transducin-G protein in visual transduction
The disassembly of a activated G-protein into two signaling components
The switching off of the G-protein subunit by the hydrolysis of its bound GTP
RGS proteins --- regulators of G protein signaling, act as subunit-specific GTPase activating proteins (GAPs)
~25 RGS proteins in the human genome
Some G-proteins signal by regulating the production of cyclic AMP
Nerve cell culture, preloaded with a fluorescent protein that changes its fluorescence when it binds to cAMP.
>10-6 M~5 X 10-8 M
(Science 260:222-226, 1993)
cAMP-dependent protein kinase (PKA) mediate most of the effects of cyclic AMP
Role of cAMP, PKA in glycogenmetabolism
How gene transcription is activated by a rise in cAMP concentration
(CRE, cAMP response element)
Role of protein phosphatases?
Some G-proteins activate the inositol phospholipid signaling pathway by activating phospholipase C-
(<1% of total phospholipids)
The two branches of the inositol phospholipid pathway
Ca2+ functions as a ubiquitous intracellular messenger
Ca2+ signaling in fertilization of starfish, detected by Ca2+-sensitive fluorescence dye
The main ways eucaryotic cells maintain a very low concentration of free Ca2+ in their cytosol
The frequency of Ca2+ oscillations influences a cell’s response
In a liver cell
Ca2+/calmodulin-dependent protein kinases (CaM-kinases) mediate many of the actions of Ca2+ in animal cells
The structure of Ca2+/calmodulin
A peptide derived from CaM-Kinase II
The activation of CaM-kinases II
~2% of total mass in some brain regions, especially in synapses
It can function as a molecular memory device ---(1) Learning defect (where things are in space) in mutant mice that lack the brain-specific subunit of CaM-kinase II(2) Same defect also observed in mutant mice that have their CaM-kinase II mutated at the autophosphorylation site
CaM-kinases II as a frequency decoder of Ca2+ oscillations
CaM-kinase II is immobilized on a solid surface +a brain protein phosphatase +repetitive pulse of Ca2+/calmodulin at different frequencyKinase activity assay
What a nice experiment it is!
Smell and vision depend on G-protein-linked receptors that regulate cyclic-nucleotide-gated ion channels
Cyclic GMPA rod photoreceptor cell
The response of a rod photoreceptor cell to light
Extracellular signals are greatly amplified by the use of small intracellular mediators and enzymatic cascades
Amplification in the light-induced
catalytic cascade in vertebrate rods
G-protein-linked receptors desensitization depends on receptor phosphorylation
SIGNALING THROUGH ENZYME-LINKEDCELL-SURFACE RECEPTORS
Six classes:
1. Receptor tyrosine kinases2. Tyrosine kinase-associated receptors3. Receptorlike tyrosine phosphatases4. Receptor serine/threonine kinases5. Receptor guanylyl cyclases6. Histidine-kinase-associated receptors
Activated tyrosine kinases phosphorylate themselves
angiogenesiscell/axon migration
Three ways in which signaling proteins can cross-link receptor chains
Monomeric vs. dimeric ligand
Inhibition of signaling through normal receptor tyrosine kinases by an excess of mutant receptors
As a tool for determining normal function of receptor
Phosphorylated tyrosine serves as docking sites for proteins with SH2 domains
The binding of SH2-containing intracellular signaling proteins to an activated PDGF receptor
determine the binding specificity
Ras is activated by a guanine nucleotide exchange factor
GEF: guanine nucleotide exchange factorGAP: GTPase-activating protein
In cells [GTP] > [GDP] ~10 fold
The activation of Ras by an activated receptor tyrosine kinase
The MAP-kinase serine/threonine phosphorylation pathway activated by Ras
The organization of MAP-kinase pathway by scaffold proteins in budding yeast
PI 3-kinase produces inositol phospholipid docking sites in the plasma membrane
Cell division vs. cell growthPI 3 kinase is one of the major cell growth signaling transduces
The recruitment of signaling proteins with PH domains to the plasma membrane during B cell activation
SH2domain
Mutation of BTKleads to severely deficiency in Abproduction
The PI 3-kinase/protein kinase B signaling pathway can stimulate cells to survive and grow
Brief summarization
Signal proteins of the TGF- superfamily act through receptor serine/threonine kinases and Smads
Kinase catalytic domain ~250 amino acids
SIGNALING PATHWAY THAT DEPEND ON REGULATED PROTEOLYSIS
1. Notch2. Wnt3. Hedgehog4. NF-kB
The receptor protein Notch is activated by cleavage
In Drosophila, mutation in Delta leads to produce a huge excess of neurons at the expense of epidermal cells
The processing and activation of Notch by proteolytic cleavage
Inhibit neural differentiation
Wnt proteins bind to Frizzled receptors and inhibit the degradation of -catenin
(c-Myc protein)(APC, adenomatous polyposis coli,a tumor suppressor )
Multiple stressful and proinflammatory stimuli act through an NF-B-dependent signaling pathway
inflammationdevelopmentcancer