Heparanase is the only mammalian
endoglycosidase which has been widely implicated in
cancer because of its capability to degrade
heparan sulfate chains of
heparan sulfate proteoglycans (
HSPG). Specifically, the cell surface
HSPG syndecan-1 and -4 (SDC1 and SDC4) are modulators of
growth factor action, and SDC4 is implicated in cell adhesion as a key member of focal adhesion complexes. We hypothesized that extracellular
heparanase modulates brain metastatic
breast cancer (BMBC) cell invasiveness by affecting cytoskeletal dynamics, SDC4 carboxy-terminal-associated
proteins, and downstream targets. We used two independently derived human BMBC cell systems (MB-231BR and MB-231BR3), which possess distinct cellular morphologies and properties. Highly aggressive spindle-shaped 231BR3 cells changed to a round cell morphology associated with expression of the
small GTPase guanine nucleotide exchange factor-H1 (GEF-H1). We showed that GEF-H1 is a new component of the SDC4 signaling complex in BMBC cells. Treatment with
heparanase resulted in regulation of the SDC4/
protein kinase C α axis while maintaining a constitutive GEF-H1 level. Third, GEF-H1 knockdown followed by cell exposure to
heparanase caused a significant regulation of activities of Rac1 and RhoA, which are GEF-H1 targets and fundamental effectors in cell plasticity control. Fourth, L-
heparanase augmented expression of β1
integrin in BMBC cells and of
vascular cell adhesion molecule 1 (VCAM1; the major β1
integrin receptor) in human brain microvascular endothelial cells. Finally, using a newly developed blood-brain barrier in vitro model, we show that BMBC cell transmigration was significantly reduced in GEF-H1 knockdown cells. These findings implicate
heparanase in mechanisms of cytoskeletal dynamics and in the cross-talk between
tumor cells and vascular brain endothelium. They are of relevance because they elucidate molecular events in the initial steps leading to BMBC onset and capturing distinct roles of latent and active
heparanase in the brain microenvironment.