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Quantitative phosphoproteomics of transforming growth factor-β signaling in colon cancer cells
1Department of Chemistry and Biomolecular Sciences, Macquarie University, Sydney, Australia.
Abstract:
The transforming growth factor-β (TGF-β) signaling pathway progresses through a series of protein phosphorylation regulated steps. Smad4 is a key mediator of the classical TGF-β signaling pathway; however, reports suggest that TGF-β can activate other cellular pathways independent of Smad4. By investigating the TGF-β-regulated phosphoproteome, we aimed to uncover new functions controlled by TGF-β. We applied titanium dioxide to enrich phosphopeptides from stable isotope labeling with amino acids in cell culture (SILAC)-labeled SW480 cells stably expressing Smad4 and profiled them by mass spectrometry. TGF-β stimulation for 30 min resulted in the induction of 17 phosphopeptides and the repression of 8 from a total of 149 unique phosphopeptides. Proteins previously not known to be phosphorylated by TGF-β including programmed cell death protein 4, nuclear ubiquitous casein and cyclin-dependent kinases substrate, hepatoma-derived growth factor and cell division kinases amongst others were induced following TGF-β stimulation, while the phosphorylation of TRAF2 and NCK-interacting protein kinase are examples of proteins whose phosphorylation status was repressed. This phosphoproteomic screen has identified new TGF-β-modulated phosphorylation responses in colon carcinoma cells.
Insights
Transforming growth factor-β (TGF-β) signaling regulates cell functions. This study identified novel TGF-β-modulated phosphorylation events in colon cancer cells, expanding our understanding of TGF-β pathway independent of Smad4.
Area of Science:
- Cellular Biology
- Molecular Biology
- Biochemistry
Background:
- The transforming growth factor-β (TGF-β) pathway is crucial for cellular processes, involving protein phosphorylation.
- Smad4 is a central mediator, but TGF-β can activate Smad4-independent pathways.
- Understanding these alternative routes is key to uncovering new TGF-β functions.
Purpose of the Study:
- To investigate the TGF-β-regulated phosphoproteome to identify novel TGF-β-controlled cellular functions.
- To explore Smad4-independent TGF-β signaling mechanisms.
Main Methods:
- Utilized Stable Isotope Labeling with Amino acids in Cell culture (SILAC) for quantitative phosphoproteomics.
- Employed titanium dioxide for phosphopeptide enrichment.
- Analyzed phosphopeptide profiles using mass spectrometry in SW480 colon carcinoma cells.
Main Results:
- Identified 149 unique phosphopeptides, with 17 induced and 8 repressed upon TGF-β stimulation.
- Discovered novel TGF-β-phosphorylated proteins, including programmed cell death protein 4 and hepatoma-derived growth factor.
- Observed repression of phosphorylation for proteins like TRAF2 and NCK-interacting protein kinase.
Conclusions:
- This phosphoproteomic screen reveals new TGF-β-modulated phosphorylation events in colon carcinoma cells.
- Highlights the complexity of TGF-β signaling beyond the classical Smad4 pathway.
- Provides a foundation for further research into non-canonical TGF-β functions.
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