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Molecular and Cellular Biology, April 1999, p. 2495-2504, Vol. 19, No. 4
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Targeted Disruption of Smad3 Reveals an Essential Role in Transforming Growth Factor beta -Mediated Signal Transduction

Michael B. Datto,1 Joshua P. Frederick,1 Lihua Pan,2 Anita J. Borton,1 Yuan Zhuang,2 and Xiao-Fan Wang1,*

Department of Pharmacology and Cancer Biology1 and Department of Immunology,2 Duke University Medical Center, Durham, North Carolina 27710

Received 18 September 1998/Returned for modification 26 October 1998/Accepted 22 December 1998

The Smads are a family of nine related proteins which function as signaling intermediates for the transforming growth factor beta  (TGF-beta ) superfamily of ligands. To discern the in vivo functions of one of these Smads, Smad3, we generated mice harboring a targeted disruption of this gene. Smad3 null mice, although smaller than wild-type littermates, are viable, survive to adulthood, and exhibit an early phenotype of forelimb malformation. To study the cellular functions of Smad3, we generated Smad3 null mouse embryonic fibroblasts (MEFs) and dermal fibroblasts. We demonstrate that null MEFs have lost the ability to form Smad-containing DNA binding complexes and are unable to induce transcription from the TGF-beta -responsive promoter construct, p3TP-lux. Using the primary dermal fibroblasts, we also demonstrate that Smad3 is integral for induction of endogenous plasminogen activator inhibitor 1. We subsequently demonstrate that Smad3 null MEFs are partially resistant to TGF-beta 's antiproliferative effect, thus firmly establishing a role for Smad3 in TGF-beta -mediated growth inhibition. We next examined cells in which Smad3 is most highly expressed, specifically cells of immune origin. Although no specific developmental defect was detected in the immune system of the Smad3 null mice, a functional defect was observed in the ability of TGF-beta to inhibit the proliferation of splenocytes activated by specific stimuli. In addition, primary splenocytes display defects in TGF-beta -mediated repression of cytokine production. These data, taken together, establish a role for Smad3 in mediating the antiproliferative effects of TGF-beta and implicate Smad3 as a potential effector for TGF-beta in modulating immune system function.

* Corresponding author. Mailing address: Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, NC 27710. Phone: (919) 681-4861. Fax: (919) 681-7152. E-mail: wang{at}galactose.mc.duke.edu.

Molecular and Cellular Biology, April 1999, p. 2495-2504, Vol. 19, No. 4
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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