Abstract
Syndecans function as co-receptors for integrins on different matrixes. Recently, syndecan-1 has been shown to be important for α2β1 integrin-mediated adhesion to collagen in tumor cells by regulating cell adhesion and migration on two-dimensional collagen. However, the function of syndecans in supporting α2β1 integrin interactions with three-dimensional (3D) collagen is less well studied. Using loss-of-function and overexpression experiments we show that in 3D collagen syndecan-4 supports α2β1-mediated collagen matrix contraction. Cell invasion through type I collagen containing 3D extracellular matrix (ECM) is driven by α2β1 integrin and membrane type-1 matrix metalloproteinase (MT1-MMP). Here we show that mutational activation of K-ras correlates with increased expression of α2β1 integrin, MT1-MMP, syndecan-1, and syndecan-4. While K-ras-induced α2β1 integrin and MT1-MMP are positive regulators of invasion, silencing and overexpression of syndecans demonstrate that these proteins inhibit cell invasion into collagen. Taken together, these data demonstrate the existence of a complex interplay between integrin α2β1, MT1-MMP, and syndecans in the invasion of K-ras mutant cells in 3D collagen that may represent a mechanism by which tumor cells become more invasive and metastatic.