Syndecan-2 regulation of morphology in breast carcinoma cells is dependent on RhoGTPases

Background: While syndecan-2 is usually considered a mesenchymal transmembrane proteoglycan, it can be up-regulated in some tumour cells, such as the malignant breast carcinoma cell line, MDA-MB231. Depletion of this syndecan by siRNA, but not other syndecans, has a marked effect on cell morphology, increasing spreading, microfilament bundle and focal adhesion formation, with reduced cell migration. Methods: A combination of siRNA transfection, immunofluorescence microscopy, phosphoprotein analysis and migration assays was used to determine how syndecan-2 may influence the cytoskeleton. Results: The altered adhesion upon syndecan-2 depletion was dependent on the RhoGTPases. p190ARhoGAP relocated to the margins of spreading cells, where it codistributed with syndecan-4 and active beta(1)-integrin. This was accompanied by increased RhoGAP tyrosine phosphorylation, indicative of activity and RhoGTPase suppression. Consistent with this, GTP-RhoA was strongly present at the edges of control cells, but lost after syndecan-2 reduction by siRNA treatments. Further, RhoA, but not RhoC was shown to be essential for the anchored phenotype of these breast carcinoma cells that accompanied siRNA-mediated loss of syndecan-2. Conclusions: Syndecan-2 has a key role in promoting the invasive activity of these cells, in part by regulating the RhoGTPases. General significance: Syndecan-2, as a cell surface receptor is accessible for targeting to determine whether breast tumour progression is altered. (C) 2014 Elsevier B.V. All rights reserved.