Glucocorticoid Down-regulation of Fascin Protein Expression Is Required for the Steroid-induced Formation of Tight Junctions and Cell-Cell Interactions in Rat Mammary Epithelial Tumor Cells*
- From the ‡Department of Molecular and Cell Biology and the Cancer Research Laboratory, University of California, Berkeley, California 94720-3200 and the §Department of Biochemistry and Molecular Biology, University of Texas M.D. Anderson Cancer Center, Houston, Texas 77030-4095
Abstract
Glucocorticoid hormones, which are physiological regulators of mammary epithelium development, induce the formation of tight junctions in rat Con8 mammary epithelial tumor cells. We have discovered that, as part of this process, the synthetic glucocorticoid dexamethasone strongly and reversibly down-regulated the expression of fascin, an actin-bundling protein that also interacts with the adherens junction component β-catenin. Ectopic constitutive expression of full-length mouse fascin containing a Myc epitope tag (Myc-fascin) in Con8 cells inhibited the dexamethasone stimulation of transepithelial electrical resistance, disrupted the induced localization of the tight junction protein occludin and the adherens junction protein β-catenin to the cell periphery, and prevented the rearrangement of the actin cytoskeleton. Ectopic expression of either the carboxyl-terminal 213 amino acids of fascin, which includes the actin and β-catenin-binding sites, or the amino-terminal 313 amino acids of fascin failed to disrupt the glucocorticoid induction of tight junction formation. Mammary tumor cells expressing the full-length Myc-fascin remained generally glucocorticoid responsive and displayed no changes in the levels or protein-protein interactions of junctional proteins or the amount of cytoskeletal associated actin filaments. However, a cell aggregation assay demonstrated that the expression of Myc-fascin abrogated the dexamethasone induction of cell-cell adhesion. Our results implicate the down-regulation of fascin as a key intermediate step that directly links glucocorticoid receptor signaling to the coordinate control of junctional complex formation and cell-cell interactions in mammary tumor epithelial cells.
Footnotes
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↵* This work was supported by National Institutes of Health 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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↵¶ 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{at}uclink4.berkeley.edu.
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↵2 P. McCrea, unpublished observation.
- Abbreviations:
- TER
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transepithelial electrical resistance
- PAGE
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polyacrylamide gel electrophoresis
- SGK
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serum and glucocorticoid inducible protein kinase
- TLCK
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N α-p-tosyl-l-lysine chloromethyl ketone
- PIPES
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1,4-piperazinediethanesulfonic acid
- CMV
-
cytomegalovirus
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- Received May 29, 1998.
- Revision received November 16, 1998.
- The American Society for Biochemistry and Molecular Biology, Inc.
