Lecture 19-21 - Tight Junctions

Intercellular Junctions

tight junctions

consists of transmembrane, cytoskeletal, cytoplasmic proteins

apically located

TJ functions

gate: barrier for paracellular passing

fence: between apical and basolateral plasma membrane

ZO-1

Zonula Occludens 1

Bruce Stevenson made antibodies

found at TJ but not inside (not transmembrane)

occludin

shoichiro tsukita

first transmembrane TJ protein

calcium independent

occludin KO mice

non lethal

= occludin is not the only transmembrane TJ protein

claudin

second transmembrane TJ protein Tsukita found

calcium independent

27 classes

claudin KO mice

functionally deficient

= somewhat crucial

claudin-5 KO

normal looking

die of dehydration within 1 day of birth

skin barrier disrupted = water evaporates

leaky tight junctions

claudin-11 KO

claudin-11 is in testes

male mice are sterile

small testes with no sperm

TJ pores

allow for selection of molecules to pass through

claudin-2 overexpression

leaky barrier

claudin-2 is TJ pore forming

claudin-15 crystals

pores are formed by claudin trans interactions

each TJ stand is formed by an antiparallel row of claudins

cation selective claudins

2, 10b, 15, 16, 21

anion selective claudins

10a and 17

claudin-7

chloride ion channel

CAR

found at cell-cell contacts

Ig like protein

co-localizes with ZO-1 at TJ

CAR KO mice

die before E11

cardiac CAR KO mice

die of heart defects

no interaction with Cx45

pancrease CAR KO mice

hypoglycaemic (low blood sugar) after 2 days

junctional adhesion molecules

JAMs

TJ docks into actin cytoskeleton through ZO-1, 2, 3

ZO-1 domains

PDZ-PDZ-PDZ-SH3-Guk--------Zu5

can self-bind

PDZ domain

binds to claudin

PDZ 3 binds to JAM

SH3 domain

binds to ZONAB (signal)

Guk domain

binds to occludin

Zu5 domain

only in ZO-1

ZO-3 KO

minimal effects

ZO-1 KO

embryologically lethal

ZO-2 KO

embryologically lethal

ZO-1, 2, 3 KO

no TJ formed at all

TJ disassembly

stable TJ turnover = 4 hour

endocytosed by cells

CL-18 KO

stomach inflammation + cancer

lung tumours

CL-7 KO

SI + colon inflammation

→ inflammatory bowel disorder

CL-5 knockdown

brain inflammation

→ depression + schizophrenia

central tube

channel formed between junction of 3+ cells

tricellulin

first identified central tube protein

looks like occludin

humans have 4 isoforms (TRIC a, a1, b, c)

tricellulin structure

4 transmembrane spanning proteins

2 extracellular loops

tricellulin knockdown

barrier comprimised

tricellular contact and bicellular TJ disorganized

tricellulin KO

not lethal

hearing loss (cochlear degeneration)

tricellulin mutation

deafness

hair cell degeneration

vertical/horizontal strands detached

less horizontal strands

MARVEL

4 transmembrane structural motif of occludin and tricellulin

found at TJs

MARVEL D1

occludin

MARVEL D2

tricellulin

TAMP

MARVEL D1-3

Tight junction Associated MARVEL Protein family

Angulin

Ig like protein

ANG 1-3

ANG-1 knockdown

barrier defects

decreased TER

rescue with ANG 2 and 3 overexpression

ANG-2 KO

deafness

molecular permeability

test for TJ molecule size permeabilty

transepithelial resistance

decreased TER = decreased resistance = leaky barrier

lipolysis-stimulated lipoprotein receptor LSR

Ig like protein

self assembles at multicellular junctions

LSR knockdown

decreased TER

occludin accumlilation

LSR KO

die before E15

blood brain barrier doesn’t seal

multicellular junction protein assembly order

LSR self assembles

recruits angulin

tricellulin last