Urinary trypsin inhibitor (UTI) has a multipotent inhibitory effect on
proteases such as
trypsin,
chymotrypsin,
plasmin, human
leukocyte elastase, or
hyaluronidase. UTI can bind easily to its receptors on various types of
tumor cells (human
ovarian cancer HOC-I cells, human
choriocarcinoma SMT-cc1 cells, and murine
Lewis lung carcinoma 3LL cells). Our results show that the
UTI receptors of some
tumor cells have a possible role in modulating
plasmin activity on the cell surface and prevention of
tumor cell invasion and
metastasis (H. Kobayashi et al., J. Biol. Chem., 269; 20642-20647, 1994). UTI interacts with
tumor cells as a negative modulator of the invasive cells. We investigated whether this effect may be mediated by UTI binding to the
cell surface receptors. In addition, the role of
peptide sequences from each UTI domain and their interaction with
tumor cells were investigated. UTI derivatized with
biotin or
FITC was taken up by
tumor cells in a dose-dependent manner. This cell association was inhibited with a
monoclonal antibody D1, which specifically recognizes NH2 terminus (domain I) of UTI. The binding was inhibited by fluid phase UTI, but not HI-8, COOH terminus (domain II) of UTI, suggesting that UTI binds to cells through a site in the UTI domain I. Furthermore, we found that UTI, HI-8 and a number of
peptides containing
Arg-Gly-Pro-Cys-Arg-
Ala-Phe-Ile promoted the inhibition of
tumor cell invasion. This site corresponds to the
plasmin-inhibiting domain within HI-8. The possibility that UTI binding to
tumor cells might be involved in the prevention of
tumor cell invasion in vitro was excluded since HI-8, lacking domain I, promotes the inhibition of
tumor cell invasion with essentially the same affinity as UTI. All these data allow us to conclude that inhibition of
tumor cell invasion is mediated by domain II, which possesses anti-
plasmin activity.