Claudin-3 acts as a sealing component of the tight junction for ions of either charge and uncharged solutes.
The paracellular barrier of epithelia and endothelia is established by several tight junction proteins including claudin-3. Although claudin-3 is present in many epithelia including skin, lung, kidney, and intestine and in endothelia, its function is unresolved as yet. We therefore characterized claudin-3 by stable transfection of MDCK II kidney tubule cells with human claudin-3 cDNA. Two clone systems were analyzed, exhibiting high or low claudin-2 expression, respectively. Expression of other claudins was unchanged. Ultrastructurally, tight junction strands were changed toward uninterrupted and rounded meshwork loops. Functionally, the paracellular resistance of claudin-3-transfected monolayers was strongly elevated, causing an increase in transepithelial resistance compared to vector controls. Permeabilities for mono- and divalent cations and for anions were decreased. In the high-claudin-2 system, claudin-3 reduced claudin-2-induced cation selectivity, while in the low-claudin-2 system no charge preference was observed, the latter thus reflecting the "intrinsic" action of claudin-3. Furthermore, the passage of the paracellular tracers fluorescein (332Da) and FD-4 (4kDa) was decreased, whereas the permeability to water was not affected. We demonstrate that claudin-3 alters the tight junction meshwork and seals the paracellular pathway against the passage of small ions of either charge and uncharged solutes. Thus, in a kidney model epithelium, claudin-3 acts as a general barrier-forming protein.
Milatz
Susanne
S
Institute of Clinical Physiology, Charité, Campus Benjamin Franklin, Berlin, Germany.
Krug
Susanne M
SM
Rosenthal
Rita
R
Günzel
Dorothee
D
Müller
Dominik
D
Schulzke
Jörg-Dieter
JD
Amasheh
Salah
S
Fromm
Michael
M
D000818:Animals; D002478:Cells, Cultured; D062465:Claudin-3; D062506:Claudin-4; D057167:Claudins; D004285:Dogs; D006801:Humans; D008565:Membrane Proteins / Q000502:physiology*; D010539:Permeability; D019108:Tight Junctions / Q000378:metabolism* / Q000648:ultrastructure; D014162:Transfection; D014867:Water / Q000737:chemistry
C491875:CLDN2 protein, human; C568122:CLDN3 protein, human; C568157:CLDN4 protein, human; D062465:Claudin-3; D062506:Claudin-4; D057167:Claudins; D008565:Membrane Proteins; D014867:Water