Related Experiment Video

Updated: Aug 18, 2026

Studying TGF-β Signaling and TGF-β-induced Epithelial-to-mesenchymal Transition in Breast Cancer and Normal Cells
06:54

Studying TGF-β Signaling and TGF-β-induced Epithelial-to-mesenchymal Transition in Breast Cancer and Normal Cells

Published on: October 27, 2020

Nuclear targeting of transforming growth factor-beta-activated Smad complexes

Hong Bing Chen1, Jonathan G Rud, Kai Lin

  • 1Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, Massachusetts 01605, USA.

The Journal of Biological Chemistry
|April 1, 2005
PubMed

Insights

Transforming growth factor beta (TGF-beta) signaling activates Smad3/Smad4 complexes for nuclear import via an importin-independent pathway. Phospho-Smad3 guides nuclear entry, suppressing Smad4 export and promoting target gene regulation.

Area of Science:

  • Cellular Biology
  • Molecular Biology
  • Signal Transduction

Background:

  • Transforming growth factor beta (TGF-beta) signaling is crucial for cellular processes.
  • Smad proteins (Smad2, Smad3, Smad4) are key mediators of TGF-beta signaling.
  • Nuclear translocation of Smad complexes regulates gene expression.

Purpose of the Study:

  • To elucidate the nuclear import mechanism of TGF-beta-activated Smad3/Smad4 complexes.
  • To investigate the role of phospho-Smad3 in guiding nuclear import.
  • To understand how Smad4 nuclear export is regulated during TGF-beta signaling.

Main Methods:

  • Co-immunoprecipitation assays to study protein interactions.
  • Nuclear import/export assays in cell culture models.
  • Analysis of Smad complex formation and localization.
  • Investigation of the role of importin and nucleoporins.

Main Results:

  • The TGF-beta-activated phospho-Smad3/Smad4 complex uses an importin-independent nuclear import pathway.
  • Phospho-Smad3, rather than Smad4, dominates the nuclear import process.
  • The binding of phospho-Smad3 to Smad4 inhibits Smad4 interaction with the nuclear export receptor CRM1.
  • Tumorigenic Smad4 mutations disrupt its nuclear accumulation in response to TGF-beta.

Conclusions:

  • TGF-beta signaling utilizes a unique importin-independent mechanism for Smad3/Smad4 nuclear import.
  • Phospho-Smad3 plays a critical role in directing the Smad complex to the nucleus.
  • TGF-beta signaling actively suppresses Smad4 nuclear export, ensuring its nuclear presence.
  • Dysregulation of Smad4 nuclear import/export is implicated in tumorigenesis.

More Related Videos

Live Cell Imaging of the TGF- β/Smad3 Signaling Pathway In Vitro and In Vivo Using an Adenovirus Reporter System11:06

Live Cell Imaging of the TGF- β/Smad3 Signaling Pathway In Vitro and In Vivo Using an Adenovirus Reporter System

Published on: July 30, 2018

Visualization and Quantification of TGFβ/BMP/SMAD Signaling under Different Fluid Shear Stress Conditions using Proximity-Ligation-Assay11:38

Visualization and Quantification of TGFβ/BMP/SMAD Signaling under Different Fluid Shear Stress Conditions using Proximity-Ligation-Assay

Published on: September 14, 2021

Related Concept Videos

TGF - β Signaling Pathway01:16

TGF - β Signaling Pathway

The TGF-β signaling pathway regulates cell growth, differentiation, adhesion, motility, and development. TGF-β ligands that induce TGF-β signaling are synthesized in their latent form. Several proteases or cell surface receptors such as integrins act upon the latent form, releasing the active ligand. There are three types of mammalian TGF-βs: (TGF-β1, TGF-β2, and TGF-β3) that bind as homodimers or heterodimers to TGF-β receptors. The TGF-β receptors are of three kinds RI, RII, and RIII. The RI...
PI3K/mTOR/AKT Signaling Pathway01:22

PI3K/mTOR/AKT Signaling Pathway

The mammalian target of rapamycin  (mTOR) is a serine/threonine kinase that regulates growth, proliferation, and cell survival in response to hormones, growth factors, or nutrient availability. This kinase exists in two structurally and functionally distinct forms: mTOR complex 1  (mTORC1) and mTOR complex 2  (mTORC2). The first form (mTORC1) is composed of a rapamycin-sensitive Raptor and proline-rich Akt substrate, PRAS40. In contrast,  mTORC2 consists of a rapamycin-insensitive companion...
Receptor Downregulation in MVBs01:15

Receptor Downregulation in MVBs

Multivesicular bodies (MVBs) are mature endosomes that sort ubiquitinated proteins and then fuse with lysosomes to degrade the sorted proteins. Epidermal growth factor (EGF) and its receptor (EGFR) form a complex that can be internalized through endocytosis, sorted into an MVB, and later degraded.
The EGFR can initiate signaling pathways that  lead to cell proliferation, migration, and differentiation. Overexpression of EGFR  stimulates cells to proliferate. Excessive  EGFR activation may...
MAPK Signaling Cascades01:07

MAPK Signaling Cascades

Mitogen-activated protein kinase, or MAPK pathway, activates three sequential kinases to regulate cellular responses such as proliferation, differentiation, survival, and apoptosis. The canonical MAPK pathway starts with a mitogen or growth factor binding to an RTK. The activated RTKs stimulate Ras, which recruits Raf or MAP3 Kinase (MAPKKK), the first kinase of the MAPK signaling cascade. Raf further phosphorylates and activates MEK or MAP2 Kinases (MAPKK), which in turn phosphorylates MAP...
Regulation of Nuclear Protein Sorting01:45

Regulation of Nuclear Protein Sorting

Nuclear protein sorting regulates nucleus composition and gene expression, crucial for determining the fate of a eukaryotic cell. Hence, the entry and exit of molecules across the nuclear envelope is a tightly controlled process. Nuclear protein sorting can be inhibited by one of the following ways: 1) masking cargo signal sequences, 2) modifying the nuclear receptor's affinity for cargo, 3) controlling the nuclear pore size, 4) retaining the cargo during its transit to the cytosol or the...
mTOR Signaling and Cancer Progression03:03

mTOR Signaling and Cancer Progression

The mammalian target of rapamycin or mTOR protein was discovered in 1994 due to its direct interaction with rapamycin. The protein gets its name from a yeast homolog called TOR. The mTOR protein complex in mammalian cells plays a major role in balancing anabolic processes such as the synthesis of proteins, lipids, and nucleotides and catabolic processes, such as autophagy in response to environmental cues, such as availability of nutrients and growth factors.
The mTOR pathway or the...