Over-expression of PAR-3 suppresses contact-mediated inhibition of cell migration in MDCK cells.
BACKGROUND
PAR-3 is one of the PAR proteins, previously named ASIP, which are indispensable for the establishment of cell polarity in the embryo as well as differentiated epithelial cells. In mammalian epithelial cells, it forms a ternary complex with aPKC and PAR-6, and is localized to the tight junction that has been suggested as being important for creating cell polarity.


RESULTS
To gain insights into the mode of PAR-3 function in mammalian epithelial cells, we examined the effect of PAR-3 over-expression in MDCK cells. Although exogenous PAR-3-expression does not affect the epithelial polarity of confluent cells, it drastically transforms the morphology of cells at low density into a fibroblastic form with developed membrane protrusions. Time-lapse observations have revealed that PAR-3 over-expressing cells show intense motility, even after they have assembled into loose colonies, suggesting that the contact-mediated inhibition of cell migration (CIM) is suppressed. The expressions of E-cadherin and vimentin do not change with PAR-3 over-expression, suggesting that exogenous PAR-3 only disturbs the endogenous equilibrium of cellular states between a fundamental fibroblastic structure and an epithelial one. The co-expression of a dominant negative mutant of Rac1 and the addition of nocodazole strongly antagonize the effect of PAR-3 over-expression, suggesting the involvement of Rac1 activation and microtubule polymerizations.


CONCLUSIONS
: The data presented here suggest an intriguing link between the contact-mediated inhibition of cell migration and the regulation of cell polarity. The putative PAR-3 activities demonstrated here may function endogenously in the epithelial cell polarization process by being sequestered from the cytosol to the cell-cell junctional regions with aPKC and PAR-6 upon cell-cell adhesion.
Mishima
Aki
A
Department of Molecular Biology, Yokohama City University School of Medicine, 3-9 Fuku-ura, Kanazawa-ku, Yokohama 236-0004, Japan.
Suzuki
Atsushi
A
Enaka
Makiko
M
Hirose
Tomonori
T
Mizuno
Keiko
K
Ohnishi
Tetsuo
T
Mohri
Hiroshi
H
Ishigatsubo
Yoshiaki
Y
Ohno
Shigeo
S
D000199:Actins / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D029742:Caenorhabditis elegans Proteins / Q000235:genetics / Q000502:physiology*; D002450:Cell Communication; D002452:Cell Count; D002460:Cell Line; D002464:Cell Migration Inhibition; D002465:Cell Movement / Q000502:physiology*; D018715:Microscopy, Video; D008870:Microtubules / Q000502:physiology; D009154:Mutation; D017346:Protein Serine-Threonine Kinases; D014162:Transfection; D020764:cdc42 GTP-Binding Protein / Q000235:genetics / Q000502:physiology; D020830:rac1 GTP-Binding Protein / Q000235:genetics / Q000502:physiology
D000199:Actins; D029742:Caenorhabditis elegans Proteins; C097238:PAR-3 protein, C elegans; D017346:Protein Serine-Threonine Kinases; D020764:cdc42 GTP-Binding Protein; D020830:rac1 GTP-Binding Protein