ADAMTS-1 and Syndecan-4 intersect in the regulation of cell migration and angiogenesis

Abstract

The extracellular proteoglycanase ADAMTS-1 has critical roles in organogenesis and angiogenesis. We demonstrate here the functional convergence of ADAMTS-1 and the transmembrane heparan sulfate proteoglycan syndecan-4 in influencing adhesion, migration, and angiogenesis in vitro. Knockdown of ADAMTS-1 in fibroblasts and endothelial cells resulted in a parallel reduction in cell surface syndecan-4 that was not due to altered syndecan-4 expression or internalization, but was attributable to increased expression and activity of matrix metalloproteinase-9 (MMP-9), a known syndecan-4 sheddase. Knockdown of either syndecan-4 or ADAMTS-1 led to enhanced endothelial cell responses to exogenous vascular endothelial growth factor (VEGF), and increased microvessel sprouting in ex vivo aortic ring assays, correlating with reduced ability of the cells to sequester VEGF. On fibronectin but not type 1 collagen matrices, endothelial cells with knockdown of either ADAMTS-1 or syndecan-4 elicited increased migration and showed similarly altered focal adhesion (FA) morphologies, with a higher proportion of larger FAs and formation of long fibrillar integrin 5-containing FAs. However, integrin 5-null endothelial cells also displayed enhanced migration in response to ADAMTS-1/syndecan-4 knockdown, indicating that integrin 5 was not the mediator of the altered migratory behaviour. Plating of naive endothelial cells on cell-conditioned matrix from ADAMTS-1/syndecan-4 knockdown cells demonstrated that the altered behaviour was matrix dependent. Fibulin-1, a known ECM co-factor of ADAMTS-1, was expressed at reduced levels in ADAMTS-1/syndecan-4 knockdown cells. These findings support the notion that ADAMTS-1 and syndecan-4 are functionally interconnected in regulating cell migration and angiogenesis, via the involvement of MMP-9 and fibulin-1 as collaborators