Physical and Functional Interaction of Murine andXenopus Smad7 with Bone Morphogenetic Protein Receptors and Transforming Growth Factor-β Receptors*
- Serhiy Souchelnytskyi‡,
- Takuya Nakayama§,
- Atsuhito Nakao‡¶,
- Anita Morén‡,
- Carl-Henrik Heldin‡,
- Jan L. Christian§ and
- Peter ten Dijke‡‖
- From the ‡Ludwig Institute for Cancer Research, Biomedical Center, S-751 24 Uppsala, Sweden and the§Department of Cell and Developmental Biology, Oregon Health Sciences University, School of Medicine, Portland, Oregon 97201-3098
Abstract
Members of the transforming growth factor-β (TGF-β) family transmit signals from membrane to nucleus via intracellular proteins known as Smads. A subclass of Smad proteins has recently been identified that antagonize, rather than transduce, TGF-β family signals. Smad7, for example, binds to and inhibits signaling downstream of TGF-β receptors. Here we report that the C-terminal MAD homology domain of murine Smad7 (mSmad7) is sufficient for both of these activities. In addition, we show that mSmad7 interacts with activated bone morphogenetic protein (BMP) type I receptors (BMPR-Is), inhibits BMPR-I-mediated Smad phosphorylation, and phenocopies the effect of known BMP antagonists when overexpressed in ventral cells of Xenopus embryos. Xenopus Smad7 (XSmad7, previously termed Smad8) and mSmad7 are nearly identical within their bioactive C-domain, but have quite distinct N-domains. We found that XSmad7, similar to mSmad7, interacted with BMP and TGF-β type I receptors and inhibited receptor-mediated phosphorylation of downstream signal-transducing Smads. However, XSmad7 is a less efficient inhibitor of TβR-I-mediated responses in mammalian cells than is mSmad7. Furthermore, overexpression of XSmad7 in Xenopus embryos produces patterning defects that are not observed following overexpression of mSmad7, suggesting that mSmad7 and XSmad7 may preferentially target distinct signaling pathways. Our results are consistent with the possibility that the C-domain of antagonistic Smads is an effector domain whereas the N-domain may confer specificity for distinct signaling pathways.
Footnotes
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↵* This work was supported by grants from the National Institutes of Health (to J. L. C.) and the American Heart Association, Oregon Affiliate (to T. N.).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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↵¶ Present address: Dept. of Internal Medicine, Chiba University, School of Medicine, 1-8-1 Inohana, Chiba City, Chiba 260-0856, Japan.
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↵‖ To whom correspondence should be addressed: Ludwig Institute for Cancer Research, Box 595, S751 24 Uppsala, Sweden. Tel.: 46-18-160411; Fax.: 46-18-160420; E-mail:Peter.ten_Dijke{at}LICR.uu.se.
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↵2 Afrakhte, M., Morén, A., Jossan, S., Itoh, S., Westermark, B., Heldin, C.-H., Heldin, N.-E., and ten Dijke, P. (1998) Biochem. Biophys. Res. Commun., in press
- Abbreviations:
- TGF-β
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transforming growth factor-β
- TβR
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TGF-β receptor
- ActR
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activin receptor
- BMP
-
bone morphogenetic protein
- Mad
-
mothers against dpp
- MH2
-
Mad homology 2 domain
- PAGE
-
polyacrylamide gel electrophoresis
- Smad
-
Sma- and Mad-related
- BMPR-I
-
BMP type I receptor
- mSmad7
-
murine Smad7
- XSmad7
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Xenopus Smad7.
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- Received April 6, 1998.
- The American Society for Biochemistry and Molecular Biology, Inc.
