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Regulation of cell proliferation by Smad proteins
Peter Ten Dijke1, Marie-José Goumans, Fumiko Itoh
1Division of Cellular Biochemistry, The Netherlands Cancer Institute, Amsterdam, The Netherlands. p.t.dijke@nki.nl
Abstract:
Transforming growth factor-beta (TGF-beta) family members which include TGF-betas, activins, and bone morphogenetic proteins (BMPs) regulate a broad spectrum of biological responses on a large variety of cell types. TGF-beta family members initiate their cellular responses by binding to distinct receptors with intrinsic serine/threonine kinase activity and activation of specific downstream intracellular effectors termed Smad proteins. Smads relay the signal from the cell membrane to the nucleus, where they affect the transcription of target genes. Smad activation, subcellular distribution, and stability have been found to be intricately regulated and a broad array of transcription factors have been identified as Smad partners. Important activities of TGF-beta are its potent anti-mitogenic and pro-apoptotic effects that, at least in part, are mediated via Smad proteins. Escape from TGF-beta/Smad-induced growth inhibition and apoptosis is frequently observed in tumors. Certain Smads have been found to be mutated in specific types of cancer and gene ablation of particular Smads in mice has revealed increased rate of tumorigenesis. In late stage tumors, TGF-beta has been shown to function as a tumor promoter. TGF-beta can stimulate the de-differentiation of epithelial cells to malignant invasive and metastatic fibroblastic cells. Interestingly, TGF-beta may mediate these effects directly on tumor cells via subverted Smad-dependent and/or Smad-independent pathways.
Insights
Transforming growth factor-beta (TGF-beta) signaling, mediated by Smad proteins, regulates cell growth and apoptosis. Dysregulation of this pathway is linked to cancer development and progression.
Area of Science:
- Cell Biology
- Molecular Biology
- Cancer Research
Background:
- Transforming growth factor-beta (TGF-beta) family members regulate diverse biological responses in various cell types.
- TGF-beta initiates cellular responses via receptors with serine/threonine kinase activity, activating downstream Smad proteins.
- Smads are crucial intracellular effectors that relay signals to the nucleus, influencing gene transcription.
Purpose of the Study:
- To elucidate the role of TGF-beta/Smad signaling in normal cellular processes and its implication in tumorigenesis.
- To investigate how Smad proteins are regulated and interact with other transcription factors.
- To understand the dual role of TGF-beta as an anti-mitogenic factor and a tumor promoter in advanced cancers.
Main Methods:
- Analysis of TGF-beta receptor binding and Smad protein activation pathways.
- Investigation of Smad protein regulation, subcellular localization, and interactions with transcription factors.
- Examination of TGF-beta's effects on cell proliferation, apoptosis, and cellular differentiation in tumor models.
Main Results:
- TGF-beta exerts anti-mitogenic and pro-apoptotic effects, largely mediated by Smad proteins.
- Tumors frequently exhibit escape mechanisms from TGF-beta/Smad-induced growth inhibition and apoptosis.
- Mutations in Smad proteins are observed in specific cancers, and Smad gene ablation increases tumorigenesis.
- In late-stage tumors, TGF-beta can promote tumor progression, invasion, and metastasis through Smad-dependent and -independent pathways.
Conclusions:
- The TGF-beta/Smad pathway is critical for cell growth control and apoptosis, with its dysregulation implicated in cancer.
- Understanding Smad protein regulation and interactions is key to deciphering TGF-beta's complex roles in cancer.
- TGF-beta's dual function as a tumor suppressor and promoter highlights its intricate involvement in cancer biology, particularly in advanced stages.