Syndecan-4/PAR-3 signaling regulates focal adhesion dynamics in mesenchymal cells
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2020
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Background: Syndecans regulate cell migration thus having key roles in scarring and wound healing processes.
Our previous results have shown that Thy-1/CD90 can engage both αvβ3 integrin and Syndecan-4 expressed on
the surface of astrocytes to induce cell migration. Despite a well-described role of Syndecan-4 during cell
movement, information is scarce regarding specific Syndecan-4 partners involved in Thy-1/CD90-stimulated cell
migration.
Methods: Mass spectrometry (MS) analysis of complexes precipitated with the Syndecan-4 cytoplasmic tail peptide
was used to identify potential Syndecan-4-binding partners. The interactions found by MS were validated by
immunoprecipitation and proximity ligation assays. The conducted research employed an array of genetic,
biochemical and pharmacological approaches, including: PAR-3, Syndecan-4 and Tiam1 silencing, active Rac1 GEFs
affinity precipitation, and video microscopy.
Results: We identified PAR-3 as a Syndecan-4-binding protein. Its interaction depended on the carboxy-terminal
EFYA sequence present on Syndecan-4. In astrocytes where PAR-3 expression was reduced, Thy-1-induced cell
migration and focal adhesion disassembly was impaired. This effect was associated with a sustained Focal Adhesion
Kinase activation in the siRNA-PAR-3 treated cells. Our data also show that Thy-1/CD90 activates Tiam1, a PAR-3
effector. Additionally, we found that after Syndecan-4 silencing, Tiam1 activation was decreased and it was no
longer recruited to the membrane. Syndecan-4/PAR-3 interaction and the alteration in focal adhesion dynamics
were validated in mouse embryonic fibroblast (MEF) cells, thereby identifying this novel Syndecan-4/PAR-3 signaling
complex as a general mechanism for mesenchymal cell migration involved in Thy-1/CD90 stimulation.
Conclusions: The newly identified Syndecan-4/PAR-3 signaling complex participates in Thy-1/CD90-induced focal
adhesion disassembly in mesenchymal cells. The mechanism involves focal adhesion kinase dephosphorylation and
Tiam1 activation downstream of Syndecan-4/PAR-3 signaling complex formation. Additionally, PAR-3 is defined here
as a novel adhesome-associated component with an essential role in focal adhesion disassembly during polarized
cell migration. These novel findings uncover signaling mechanisms regulating cell migration, thereby opening up
new avenues for future research on Syndecan-4/PAR-3 signaling in processes such as wound healing and scarring