Matriptase is an epithelial-derived, cell surface
serine protease. This
protease activates
hepatocyte growth factor (HGF) and
urokinase plasminogen activator (uPA), two
proteins thought to be involved in the growth and motility of
cancer cells, particularly
carcinomas, and in the vascularization of
tumors. Thus,
matriptase may play an important role in the progression of
carcinomas, such as
breast cancer. We examined the regulation of activation of
matriptase in human
breast cancer cells, in comparison to non-transformed mammary epithelial cells 184A1N4 and MCF-10A. Results clearly indicated that unlike non-transformed mammary epithelial cells,
breast cancer cells do not respond to the known activators of
matriptase, serum and
sphingosine 1-phosphate (S1P). Similar levels of activated
matriptase were detected in
breast cancer cells, grown in the presence or absence of S1P. However, up to five-fold higher levels of activated
matriptase were detected in the
conditioned media from the
cancer cells grown in the absence of serum and S1P, when compared to non-transformed mammary epithelial cells. S1P also induces formation of cortical actin structures in non-transformed cells, but not in
breast cancer cells. These results show that in non-transformed cells, S1P induces a rearrangement of the actin cytoskeleton and stimulates proteolytic activity on cell surfaces. In contrast, S1P treatment of
breast cancer cells does not activate
matriptase, and instead these cells constitutively activate the
protease. In addition,
breast cancer cells respond differently to S1P in terms of the regulation of actin cytoskeletal structures.
Matriptase and its cognate inhibitor,
HGF activator inhibitor 1 (HAI-1) colocalize on the cell periphery of
breast cancer cells and form stable complexes in the extracellular milieu, suggesting that the inhibitor serves to prevent undesired proteolysis in these cells. Finally, we demonstrate that treatment of T-47D cells with
epidermal growth factor (
EGF), which promotes cell ruffling, stimulates increased accumulation of activated
matriptase at the sites of membrane ruffling, suggesting a possible functional role at these sites.