Scenario 4

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Scenario 4 Local invasion Cell-cell
adhesion E-cadherin
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Scenario 4 Local invasion Cell-cell adhesion
E-cadherin

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Scatter factor aka Hepatocyte Growth Factor (HGF)
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• Tumours, but also normal developmental
• Epithelial-mesenchymal transition
• Triggered in cell culture by Scatter factor/HGF

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Similar structures in other types of tissue
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Components of the Epithelial Junctional Complex

• Permeation- associated
• Tight Junctions
• Gap Junctions

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Tight junctions seal the intercellular space
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Tight Junctions also maintain distinct
populations of proteins In the Apical and
Baso-lateral domains
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Gap Junctions
Allow diffusional exchange between cells without
leakage to extracellular space Limited to size
cf nucleotides and thus NOT Macromolecules, eg.
Protein, Nucleic Acid Very extensive GJs
synchronise contraction of muscle cells of heart.
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Cartoon of connexons making intercellular channels
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TM
Ligand ?self
Cytoskeleton and signalling
Cell adhesion molecules make mechanical links
but also convey information across PM in both
directions
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Components of Epithelial Junctional Complex

• Permeation- associated
• Tight Junctions
• Gap Junctions

• Cell-cell adhesion-associated
• Intermediate junctions (actin)
• Desmosomes (cytokeratin)

• Cell-ECM adhesion-associated
• Focal adhesions (actin)
• Hemi-desmosomes (cytokeratin)

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Cadherin Ca adherin Refers to absolute
dependence on Ca2 Unique external Cadherin
domains Family includes E(epithelial)-cadherin
which is determining molecule of epithelial
sheets. Attach to F-actin filaments via
catenins
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ASSAYS ARE EVERYTHING!
Problem how to get from complex cell
behaviour to identity of the molecules involved
Especially when the behaviour involves intact
cells, so you cant measure it during protein
purification

• See two different examples - in identification of
  
• E-cadherin
• integrins

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Assay for cell-cell adhesion e.g. chick embryo
liver cells Sprinkle fluorescent cells from
suspension onto confluent lawn
Incubate, then rinse off non-adherent cells Test
cell-surface fractions as antigens to
raise Inhibitory antibody
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Epithelial and neural cadherins distinguish each
other
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Crystal structure of an ectodomain
Calcium ions are bound between domains
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Cadherin domain structure N-terminal domain
crystallised in both parallel and anti-parallel
orientations Latter may reveal the cell-cell
interaction at molecular level
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E-cadherin summary
Calcium-dependent function Expression drives
formation of cell sheets (responsible for
intermediate junctions) Associates with actin
cytoskeleton via catenins Down regulation in
tumour progression
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Regulation of E-cadherin by GSK3b (September 2004)
GS kinase 3 b
Snail (transcription factor
E-cadherin mRNA
nucleus
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Regulation of E-cadherin by GSK3b (September 2004)
Mechanism of EMT (summary of proposal) Epithelial
state transcription factor snail phosphorylated
by glycogen synthase kinase (GSK3b). gt exclusion
from nucleus and ubiquitin-pathway destruction in
cytoplasm ? Various signalling pathways inhibit
GSK3b. gt stabilises snail gt inhibits E-cadherin
transcription gt Mesenchymal state (whole
sequence reversible)