<tt lang="z9tY8"></tt> Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The VSports app下载. gov means it’s official. Federal government websites often end in . gov or . mil. Before sharing sensitive information, make sure you’re on a federal government site. .

Https

The site is secure. The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely. V体育官网.

. 1999 Oct 26;96(22):12442-7.
doi: 10.1073/pnas.96.22.12442.

SnoN and Ski protooncoproteins are rapidly degraded in response to transforming growth factor beta signaling

Y Sun  1 , X Liu, E Ng-Eaton, H F Lodish, R A Weinberg
Affiliations

SnoN and Ski protooncoproteins are rapidly degraded in response to transforming growth factor beta signaling

V体育2025版 - Y Sun et al. Proc Natl Acad Sci U S A. .

Abstract

Transforming growth factor beta (TGF-beta) regulates a variety of physiologic processes, including growth inhibition, differentiation, and induction of apoptosis. Some TGF-beta-initiated signals are conveyed through Smad3; TGF-beta binding to its receptors induces phosphorylation of Smad3, which then migrates to the nucleus where it functions as a transcription factor. We describe here the association of Smad3 with the nuclear protooncogene protein SnoN VSports手机版. Overexpression of SnoN represses transcriptional activation by Smad3. Activation of TGF-beta signaling leads to rapid degradation of SnoN and, to a lesser extent, of the related Ski protein, and this degradation is likely mediated by cellular proteasomes. These results demonstrate the existence of a cascade of the TGF-beta signaling pathway, which, upon TGF-beta stimulation, leads to the destruction of protooncoproteins that antagonize the activation of the TGF-beta signaling. .

PubMed Disclaimer

Figures

Figure 1
Figure 1
In vitro and in vivo protein–protein interaction between Smad3 and SnoN. (A) In vitro binding of Ski and SnoN proteins to GST-Smad3 recombinant fusion proteins. In vitro-translated HA-tagged human Ski and SnoN proteins were exposed to the various GST-Smad3 recombinant fusion proteins and captured on glutathione beads; 10% of the translation products were directly immunoprecipitated with anti-HA Ab. Proteins bound to the beads were separated by SDS/PAGE and visualized by fluorography. (B) In vivo association of SnoN and Ski with Smad3 protein. HA-SnoN, HA-Ski, and Flag-Smad3 together with the constitutively active type I TGF-β receptor were ectopically expressed in BOSC cells through transient transfection. Lysates prepared from metabolically labeled cells 36 hr after transfection were subjected to immunoprecipitation with anti-HA or anti-Flag Ab. The SnoN and Ski proteins that were associated with Smad3 protein as well as the Smad3 protein associated with SnoN and Ski proteins were retrieved on protein G beads, separated by SDS/PAGE, and visualized through fluorography. The arrowheads denote the slowly migrating Smad3, which most likely is the form phosphorylated by the activated type I TGF-β receptor kinase.
Figure 2
Figure 2
Transcriptional repression by SnoN of the PE2 and 4XSBE (SBE: GTCTAGAG) promoters. (A) HepG2 cells were transfected with PE2-luciferase construct together with 1 μg of Smad3 and SnoN expression plasmids. After incubation for 20 hr in the absence or presence of 100 pM TGF-β, luciferase as well as β-galactosidase activity was determined. (B) HepG2 cells were transfected with 4XSBE-luciferase construct promoter together with 1 μg of Smad3 and 0.25, 1, or 4 μg of SnoN expression plasmids. Luciferase and β-galactosidase activities were determined as in A. In both A and B, relative luciferase activities, whose values are the averages of the duplicate samples, were plotted after normalization with the β-galactosidase, and representative results from three separate experiments are presented. The filled bars represent cells that had been treated with TGF-β, and the open bars represent cells that had not been treated.
Figure 3
Figure 3
TGF-β causes degradation of SnoN and Ski proteins. (A) Mink lung epithelial cells stably expressing SnoN or Ski were pretreated with MG-132 or vehicle (DMSO) for 1 hr before treatment with the indicated concentrations of TGF-β for 30 min. Lysates were immunoprecipitated with the anti-HA Ab; the immunoprecipitates (IP) were collected on protein G beads, separated by SDS/PAGE, transferred to poly(vinylidene difluoride) (PVDF) membrane, and immunoblotted with anti-HA Ab. The amount of lysate used in lanes 4 and 5 was one-third that employed in lanes 1–3. (B) Same as A, except that mink lung epithelial cells stably expressing SnoN protein were treated for different time with TGF-β. (C) Same as A, except an increasing concentration of TGF-β was used with mink lung epithelial cells stably expressing Ski protein. (D and E) Measurement of stability of SnoN (D) and Ski protein (E). (D) Mink lung cells stably expressing HA-SnoN were treated with cycloheximide concomitant with TGF-β. At the indicated times, cells were lysed and the lysate was immunoprecipitated with the anti-HA Ab. The immunoprecipitates were collected on protein G beads, separated by SDS/PAGE, and transferred to PVDF membrane followed by immunoblotting with the anti-HA Ab. (E) Mink lung cells stably expressing Ski were labeled with [35S]methionine for 3 hr, followed by a chase in the presence of 100 μg/ml methionine and cysteine. Cells were lysed and processed as in D, except that the SDS/PAGE gel was dried and exposed to a phosphoimager plate (FUJIX, Tokyo).
See this image and copyright information in PMC

References (VSports注册入口)

    1. Hoodless P A, Wrana J L. Curr Top Microbiol Immunol. 1998;228:235–272. - PubMed
    1. Kingsley D M. Genes Dev. 1994;8:133–146. - "VSports在线直播" PubMed
    1. Massague J. Annu Rev Biochem. 1998;67:753–791. - PubMed
    1. Roberts A B, Flanders K C, Heine U I, Jakowlew S, Kondaiah P, Kim S J, Sporn M B. Philos Trans R Soc London B. 1990;327:145–154. - PubMed
    1. Massague J. Annu Rev Cell Biol. 1990;6:597–641. - PubMed

MeSH terms

Substances

LinkOut - more resources