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© The Rockefeller University Press, 0021-9525/1997//1047 $5.00
The Journal of Cell Biology, Volume 139, Number 4, , 1997 1047-1059

Article

Regulation of Cell–Cell Adhesion by Rac and Rho Small G Proteins in MDCK Cells



Kenji Takaishi*, Takuya Sasaki*, Hirokazu Kotani*, Hideo Nishioka{ddagger}, and Yoshimi Takai*,{ddagger}

* Department of Molecular Biology and Biochemistry, Osaka University Medical School, Suita 565, Japan; and {ddagger} Takai Biotimer Project, ERATO, Japan Science and Technology Corporation, JCR Pharmaceuticals Co., Ltd., Nishi-ku, Kobe 651-22, Japan

The Rho small G protein family, consisting of the Rho, Rac, and Cdc42 subfamilies, regulates various cell functions, such as cell shape change, cell motility, and cytokinesis, through reorganization of the actin cytoskeleton. We show here that the Rac and Rho subfamilies furthermore regulate cell–cell adhesion. We prepared MDCK cell lines stably expressing each of dominant active mutants of RhoA (sMDCK-RhoDA), Rac1 (sMDCK-RacDA), and Cdc42 (sMDCK-Cdc42DA) and dominant negative mutants of Rac1 (sMDCK-RacDN) and Cdc42 (sMDCK-Cdc42DN) and analyzed cell adhesion in these cell lines. The actin filaments at the cell–cell adhesion sites markedly increased in sMDCK-RacDA cells, whereas they apparently decreased in sMDCK-RacDN cells, compared with those in wild-type MDCK cells. Both E-cadherin and β-catenin, adherens junctional proteins, at the cell–cell adhesion sites also increased in sMDCK-RacDA cells, whereas both of them decreased in sMDCK-RacDN cells. The detergent solubility assay indicated that the amount of detergent-insoluble E-cadherin increased in sMDCK-RacDA cells, whereas it slightly decreased in sMDCK-RacDN cells, compared with that in wild-type MDCK cells. In sMDCK-RhoDA, -Cdc42DA, and -Cdc42DN cells, neither of these proteins at the cell–cell adhesion sites was apparently affected. ZO-1, a tight junctional protein, was not apparently affected in any of the transformant cell lines. Electron microscopic analysis revealed that sMDCK-RacDA cells tightly made contact with each other throughout the lateral membranes, whereas wild-type MDCK and sMDCK-RacDN cells tightly and linearly made contact at the apical area of the lateral membranes. These results suggest that the Rac subfamily regulates the formation of the cadherin-based cell– cell adhesion. Microinjection of C3 into wild-type MDCK cells inhibited the formation of both the cadherin-based cell–cell adhesion and the tight junction, but microinjection of C3 into sMDCK-RacDA cells showed little effect on the localization of the actin filaments and E-cadherin at the cell–cell adhesion sites. These results suggest that the Rho subfamily is necessary for the formation of both the cadherin-based cell– cell adhesion and the tight junction, but not essential for the Rac subfamily-regulated, cadherin-based cell– cell adhesion.

Abbreviations used in this paper: ERM, Ezrin, Radixin, Moesin; GEP, GDP/GTP exchange protein; PKC, protein kinase C; TPA, 12-O-tetradecanoylphorbol-13-acetate.

This investigation was supported by Grants-in-Aid for Scientific Research and for Cancer Research from the Ministry of Education, Science, Sports, and Culture, Japan (1995–1997), by Grants-in-Aid for Abnormalities in Hormone Receptor Mechanisms and for Aging and Health from the Ministry of Health and Welfare, Japan (1995–1997), and by grants from the Human Frontier Science Program (1995–1997) and the Uehara Memorial Foundation (1995–1996).

Address all correspondence to Y. Takai, Department of Molecular Biology and Biochemistry, Osaka University Medical School, Suita 565, Japan. Tel.: (81) 6 879 3401. Fax: (81) 6 879 3419. E-mail: ytakai{at}molbio.med.osaka-u.ac.jp

Hirokazu Kotani's present address is First Department of Internal Medicine, Mie Univeristy School of Medicine, 2-174 Edobashi, Tsu, Mie 514, Japan.


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