Inactive Type II and Type I Receptors for TGF Are Dominant Inhibitors of TGF-dependent Transcription

doi:10.1074/jbc.270.14.8274

Inactive Type II and Type I Receptors for TGF Are Dominant Inhibitors of TGF-dependent Transcription (*)

From the Molecular Cardiology Unit, Departments of Medicine, Cell Biology, and Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, Texas 77030

^¶To whom correspondence should be addressed:
Molecular Cardiology Unit, One Baylor Plaza, Rm. 506C, Baylor College of Medicine, Houston, TX 77030.
Tel.: 713-798-6683; Fax: 713-798-7437.

↵^§ Fellow of the Deutsche Forschungsgemeinschaft. Present address: Institut für Biochemie und Biotechnologie, Abteilung für Zell- und Molekularbiologie, Technische Universität Braunschweig, D-38108 Braunschweig, Federal Republic of Germany.

Abstract

Although transforming growth factor-β (TGFβ) is implicated in differentiation and disease, proof of in vivo function requires specific inhibitors of the TGFβ cascade. TGFβ binds a family of type I and type II receptors (TβRI, TβRII), containing a cytoplasmic serine/threonine kinase domain. We previously reported that kinase-deficient TβRII (ΔkTβRII) blocks TGFβ-dependent transcription in cardiac myocytes. It is controversial whether both receptors are needed in all cells for gene regulation by TGFβ or whether they mediate distinct subsets of TGFβ-dependent events. To resolve this uncertainty, TGFβ-dependent transcription was investigated in cardiac myocytes versus mink lung epithelial cells. 1) ΔkTβRII inhibits induction of a TGFβ-responsive reporter gene, in both cell backgrounds. 2) Charged-to-alanine mutations of key residues of the TβRII kinase, including consensus ATP binding and amino acid recognition motifs, are competent for binding but not transcriptional activation. Each inactive receptor inhibits TGFβ-dependent transcription in both cell types. 3) Kinase-deficient TβRI (ΔkTβRI) likewise impairs TGFβ-dependent transcription, less completely than ΔkTβRII; kinase-deficient activin type I receptor has no effect. 4) TGFβ-binding proteins in cardiac cells and Mv1Lu cells are comparable by affinity labeling and immunoprecipitation; however, Mv1Lu cells express up to 3-fold higher levels of TβRII and TβRI. Thus, the model inferred from TGFβ-resistant cell lines (that TβRII and TβRI are necessary in tandem for the TGFβ-signaling complex to regulate transcription) is valid for cardiac myocytes, the cell type most prominently affected in TGFβ-deficient animals.

Footnotes

↵* This work was supported in part by National Institutes of Health Grants R01 HL47567, P01 HL49953, and T32 HL07706 (to M. D. S.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¹ The abbreviations used are:

TGFβ

type β transforming growth factor

TβRI

type I TGFβ receptor

TβRII

type II TGFβ receptor

ΔkTβRI

kinase-deficient truncation of TβRI

ΔkTβRII

kinase-deficient truncation of TβRII

PAI-1

plasminogen activator inhibitor-1

PCR

polymerase chain reaction

DMEM

Dulbecco's modified Eagle's medium.
↵²T. Brand and M. D. Schneider, unpublished results.
- Received November 28, 1994.