Involvement of the Helix-Loop-Helix Protein Id-1 in the Glucocorticoid Regulation of Tight Junctions in Mammary Epithelial Cells*
- From the ‡Department of Molecular and Cell Biology and the Cancer Research Laboratory, University of California at Berkeley, Berkeley, California 94720-3200 and ¶Geraldine Brush Cancer Research Institute, California Pacific Medical Center, San Francisco, California 94115
Abstract
Mammary epithelial cell-cell junctions undergo morphological and structural differentiation during pregnancy and lactation, but little is known about the transcriptional regulators that are involved in this process. In Con8 mammary epithelial tumor cells, we have previously documented that the synthetic glucocorticoid, dexamethasone, induces the reorganization of the tight junction and adherens junction and stimulates the monolayer transepithelial electrical resistance (TER), a reliable in vitro measurement of tight junction sealing. Western blots demonstrated that dexamethasone treatment rapidly and strongly stimulated the level of the Id-1 protein, which is a serum-inducible helix-loop-helix transcriptional repressor. The steroid induction of Id-1 was robust by 4 h of treatment and maintained over a 24-h period. Isopropyl-1-thio-β-d-galactopyranoside-inducible expression of exogenous Id-1 in Con8 cells was shown to strongly facilitate the dexamethasone induction of TER in the absence of serum without altering the dexamethasone-dependent reorganization of ZO-1, β-catenin, or F-actin. Ectopic overexpression of Id-1 in the SCp2 nontumorigenic mammary epithelial cells, which does not undergo complete dexamethasone-dependent tight junction reorganization, enhanced the dexamethasone-induced ZO-1 tight junction localization and stimulated the monolayer TER. Moreover, antisense reduction of Id-1 protein in SCp2 cells prevented the apical junction reorganization and dexamethasone-stimulated TER. Our results implicate Id-1 as acting as a critical regulator of mammary epithelial cell-cell interactions at an early step in the glucocorticoid-dependent signaling pathway that controls tight junction integrity.
Footnotes
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↵* This work was supported by National Institutes of Health (NIH) Grant DK-42799 (to G. L. F.).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵§ Recipient of a predoctoral fellowship supported by NIH National Research Service Grant CA-09041. Portions of this work were submitted to fulfill the requirements for a doctorate of philosophy at the University of California at Berkeley.
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↵‖ To whom correspondence and reprint requests should be addressed: Dept. of Molecular and Cell Biology, 591 LSA, University of California at Berkeley, Berkeley, CA 94720-3200. Tel.: 510-642-8319; Fax: 510-643-6791; E-mail: glfire@uclink4.berkeley.edu.
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Published, JBC Papers in Press, June 30, 2000, DOI 10.1074/jbc.M910373199
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↵2 P. L. Woo and G. L. Firestone, unpublished result.
- Abbreviations:
- ZO-1
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zonula occludens-1
- TER
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transepithelial electrical resistance
- Dex
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dexamethasone
- ECM
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extracellular matrix
- EHS-ECM
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Englebreth Holm Swarm tumor extracellular matrix
- IPTG
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isopropyl-1-thio-β-d-galactopyranoside
- HA
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hemagglutinin
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- Received December 27, 1999.
- Revision received June 29, 2000.
- The American Society for Biochemistry and Molecular Biology, Inc.
