Transforming growth factor-beta induces epithelial to mesenchymal transition by down-regulation of claudin-1 expression and the fence function in adult rat hepatocytes.
OBJECTIVE
Transforming growth factor-beta (TGF-beta) initiates and maintains epithelial-mesenchymal transition (EMT), which causes disassembly of tight junctions and loss of epithelial cell polarity. In mature hepatocytes during EMT induced by TGF-beta, changes in the expression of tight junction proteins and the fence function indicated that epithelial cell polarity remains unclear.


METHODS
In the present study, using primary cultures of adult rat hepatocytes at day 10 after plating, in which epithelial cell polarity is well maintained by tight junctions, we examined the effects of 0.01-20 ng/ml TGF-beta on the expression of the integral tight junction proteins, claudin-1, -2 and occludin, as well as the fence function.


RESULTS
In adult rat hepatocytes, TGF-beta induced EMT, which was indicated as upregulation of Smad-interacting protein-1 (SIP1) and Snail and down-regulation of E-cadherin. Down-regulation of claudin-1 and upregulation of occludin were observed beginning from a low dose of TGF-beta, whereas upregulation of claudin-2 was observed at a high dose of TGF-beta. Furthermore, treatment with TGF-beta caused disruption of the fence function, which was closely associated with the expression of claudin-1 via p38 mitogen-activated protein kinase (MAPK), phosphoinositide-3 kinase and protein kinase C but not MAPK signalling pathways.


CONCLUSIONS
These results suggest that in mature hepatocytes in vitro, TGF-beta induces EMT by down-regulation of claudin-1 and the fence function via distinct signalling pathways.
Kojima
Takashi
T
Department of Pathology, Sapporo Medical University School of Medicine, Sapporo, Japan. ktakashi@sapmed.ac.jp
Takano
Ken-ichi
K
Yamamoto
Toshinobu
T
Murata
Masaki
M
Son
Seiichi
S
Imamura
Masafumi
M
Yamaguchi
Hiroshi
H
Osanai
Makoto
M
Chiba
Hideki
H
Himi
Tetsuo
T
Sawada
Norimasa
N
D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D062445:Claudin-1; D004195:Disease Models, Animal; D015536:Down-Regulation; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects; D005786:Gene Expression Regulation; D022781:Hepatocytes / Q000166:cytology / Q000187:drug effects*; D007150:Immunohistochemistry; D008297:Male; D008565:Membrane Proteins / Q000187:drug effects / Q000378:metabolism*; D008648:Mesoderm / Q000187:drug effects / Q000502:physiology*; D011336:Probability; D012313:RNA / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012680:Sensitivity and Specificity; D015398:Signal Transduction; D019108:Tight Junctions / Q000187:drug effects* / Q000502:physiology; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
D062445:Claudin-1; C568114:Cldn1 protein, rat; D008565:Membrane Proteins; D016212:Transforming Growth Factor beta; D012313:RNA