The
integrin VLA-4 is important for the metastatic dissemination of
melanoma cells. We could recently show that
heparin can block
VLA-4 binding, which contributes, next to blocking P- and
L-selectin, to the understanding of antimetastatic activities of
heparin. The matricellular
ligand Cyr61, secreted by numerous tumours, is responsible for increased tumourigenicity and
metastasis. This has been attributed to Cyr61 binding to, and thus activating
integrins. However, a VLA-4/Cyr61 axis has not yet been reported. Since Cyr61 possesses
heparin binding capabilities, Cyr61 can be supposed as potential target for
heparin to indirectly interfere with
integrin functions. The present in vitro studies address (i) the existence of a Cyr61/VLA-4 axis and (ii) the functional relevance of
heparin interference via Cyr61. The C-terminal module III of Cyr61 could be exposed as nanomolar affine binding site for
VLA-4. A
shRNA-based knockdown of Cyr61 in MV3 human
melanoma cells reduced VLA-4-mediated cell binding to
VCAM-1, migration on
fibronectin, and
integrin signalling functions significantly. Using a biosensor approach we provide insight into
heparin interference with this process. The
low-molecular-weight heparin tinzaparin, but not the pentasaccharide
fondaparinux, binds module IV of Cyr61 with micromolar affinity. But
tinzaparin cannot interfere with Cyr61 accumulation onto
syndecan-4, indicating different Cyr61 binding sites for
heparin and other GAGs. Nonetheless,
tinzaparin affects the
VLA-4 binding and signalling functions selectively via Cyr61 already at very low concentration most likely by blocking the cellular secreted free Cyr61. This study emphasises Cyr61 as promising, and hitherto not considered target for
heparin to selectively influence
integrin functions.