The cell's resistance to cell death by adhesion loss to extracellular matrix (anoikis), contributes to
tumor progression and
metastasis. Various adhesion molecules are involved in the anoikis resistance, including the
syndecan-4 (SDC4), a
heparan sulfate proteoglycan (
HSPG) present on the cell surface. Changes in the expression of SDC4 have been observed in
tumor and transformed cells, indicating its involvement in
cancer. In previous works, we demonstrated that acquisition of anoikis resistance resistance by blocking adhesion to the substrate up-regulates
syndecan-4 expression in endothelial cells. This study investigates the role of SDC4 in the transformed phenotype of anoikis resistant endothelial cells. Anoikis-resistant endothelial cells (Adh1-EC) were transfected with
micro RNA interference (miR RNAi) targeted against
syndecan-4. The effect of SDC4 silencing was analyzed by real-time PCR, western blotting and immunofluorescence. Transfection with miRNA-SDC4 resulted in a sequence-specific decrease in
syndecan-4 mRNA and
protein levels. Furthermore, we observed a reduction in the number of heparan and
chondroitin sulfate chains in the
cell extract and culture medium. The SDC4 silencing led to downregulation of proliferative and invasive capacity and angiogenic abilities of anoikis-resistant endothelial cells. Compared with the parental cells (Adh1-EC), SDC4 silenced cells (SDC4 miR-Syn-4-1-Adh1-EC e miR-Syn-4-2-Adh1-EC) exhibited an increase in adhesion to
collagen and
laminin and also in the apoptosis rate. Moreover, transfection with miRNA-SDC4 caused a decrease in the number of cells in the S phase of the cell cycle. This is accompanied by an increase in the
heparan sulfate synthesis after 12 h of simulation with
fetal calf serum (FCS). SDC4 silencing cells are more dependent of
growth factors present in the FCS to synthesize
heparan sulfate than parental cells. Similar data were obtained for the wild-type cell line (EC). Our results indicated that downregulation of SDC4 expression reverses the transformed phenotype of anoikis resistant endothelial cells. These and other findings suggest that
syndecan-4 is suitable for pharmacological intervention, making it an attractive target for
cancer therapy.