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Cytoplasmic interactions of syndecan-4 orchestrate adhesion receptor and growth factor receptor signalling
Mark D Bass1, Martin J Humphries
1Wellcome Trust Centre for Cell-Matrix Research, School of Biological Sciences, University of Manchester, Manchester M13 9PT, U.K.
Abstract:
Syndecan-4 is a ubiquitous transmembrane proteoglycan that localizes to the focal adhesions of adherent cells and binds to a range of extracellular ligands, including growth factors and extracellular-matrix proteins. Engagement of syndecan-4 is essential for adhesion formation in cells adhering via certain integrins, and for cell proliferation and migration in response to growth factors. The cytoplasmic domain of syndecan-4 interacts with a number of signalling and structural proteins, and both extracellular and cytoplasmic domains are necessary for regulated activation of associated transmembrane receptors. PDZ domain-containing scaffold proteins (syntenin and CASK) bind to the C-terminus of the syndecan-4 cytoplasmic domain and co-ordinate clustering of receptors and connection to the actin cytoskeleton. Syndecan-4 also binds and activates protein kinase Calpha in the presence of phosphatidylinositol 4,5-bisphosphate, and regulates signalling by Rho-family GTPases and focal adhesion kinase. This review discusses the cytoplasmic interactions of syndecan-4 and how they affect cell behaviour as a consequence of the interaction with extracellular ligands. These conclusions also offer an insight into the role of syndecan-4 in vivo, and are consistent with phenotypes generated as a consequence of abnormal syndecan-4 expression in pathologies and gene disruption studies.
Insights
Syndecan-4, a cell adhesion molecule, regulates cell behavior through its interactions with extracellular ligands and intracellular proteins. Its cytoplasmic domain is crucial for coordinating cell adhesion, migration, and signaling pathways.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Syndecan-4 is a transmembrane proteoglycan found at cell focal adhesions.
- It interacts with extracellular ligands like growth factors and matrix proteins.
- Syndecan-4 plays roles in cell adhesion, proliferation, and migration.
Purpose of the Study:
- To review the cytoplasmic interactions of syndecan-4.
- To understand how these interactions affect cell behavior in response to extracellular signals.
- To provide insights into syndecan-4's in vivo functions and roles in disease.
Main Methods:
- Literature review of studies on syndecan-4.
- Analysis of molecular interactions involving syndecan-4's cytoplasmic domain.
- Integration of findings on signaling pathways regulated by syndecan-4.
Main Results:
- Syndecan-4's cytoplasmic domain interacts with signaling and structural proteins.
- Scaffold proteins like syntenin and CASK bind syndecan-4, organizing receptor clusters and cytoskeletal connections.
- Syndecan-4 activates protein kinase Calpha and regulates Rho GTPases and focal adhesion kinase.
Conclusions:
- Cytoplasmic interactions of syndecan-4 are critical for mediating its effects on cell behavior.
- These interactions link extracellular ligand binding to intracellular signaling cascades.
- Understanding syndecan-4's cytoplasmic functions is key to comprehending its in vivo roles and pathological implications.