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

While syndecan-2 is usually considered a mesenchymal transmembrane proteoglycan, it can be upregulated 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. A combination of siRNA transfection, immunofluorescence microscopy, phosphoprotein analysis and migration assays was used to determine how syndecan-2 may influence the cytoskeleton. 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 β1-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. Syndecan-2 has a key role in promoting the invasive activity of these cells, in part by regulating the RhoGTPases. Syndecan-2, as a cell surface receptor is accessible for targeting to determine whether breast tumour progression is altered. This article is part of a Special Issue entitled Matrix-mediated cell behaviour and properties.