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The mechanism whereby some lymphomas invade liver extensively has not been fully investigated. There is no basement membrane under the sinusoidal endothelium of the liver, and hepatocytes produce fibronectin (FN); therefore, adhesion to this FN may be particularly important for liver infiltration by lymphoma cells. A mouse lymphoma cell line, RL-male1, adhered to FN. However, this cell line did not express classical FN receptors such as very late antigen (VLA)-4 and VLA-5, as estimated by immunofluorescent staining. We have generated monoclonal antibodies (mAbs) that inhibit adhesion of RL-male1 cells to FN. Western blot and immunoprecipitation analyses showed that the new mAbs recognize a protein with an approximate molecular weight of 55,000 (p55). This antigenic protein was highly purified by immunoprecipitation and processed for microsequencing. From NH2-terminal sequence results, the p55 antigen was not identical to known FN receptors. Radioisotope-labeled RL-male1 cells, when injected i.v. into mice, rapidly infiltrated the liver (30-35% of injected cells), as measured by a gamma counter. Intravenous injection of the new mAbs partially (20%) blocked the infiltration of i.v.-injected lymphoma cells into the liver, whereas control rat IgG and an anti-CD11a mAb did not. These results demonstrate that the mouse lymphoma cell line RL-male1 nses a novel FN receptor for liver infiltration.

The recently discovered tumor suppressor gene maspin has been shown to inhibit tumor cell motility, invasion, and metastasis in breast cancer by our laboratories. Nonetheless, the exploitation of maspin as a potential diagnostic and/or therapeutic tool has remained limited due to the lack of knowledge concerning its molecular and biological mechanism(s) of action. The work reported here demonstrates that recombinant maspin (rMaspin) has the ability to induce higher cell surface levels of alpha5- and alpha3-containing integrins and reduced levels of alpha2-, alpha4-, alpha6-, alpha(v)-, and some beta1-containing integrins in the metastatic human breast carcinoma cell line MDA-MB-435 concomitant with its ability to inhibit the invasive process in vitro. Furthermore, treatment of MDA-MB-435 cells with rMaspin results in the selective adhesion of the cell to a fibronectin matrix and conversion from a fibroblastic to a more epithelial-like phenotype. In addition, the ability of rMaspin to inhibit the invasive process can be abrogated with a blocking antibody to the alpha5beta1 integrin, which diminishes the ability of the cells to invade through a fibronectin matrix-containing barrier in vitro. Taken together, these data address the hypothesis that rMaspin reduces the invasive phenotype of MDA-MB-435 cells by altering their integrin profile, particularly alpha5, which in turn converts these cells to a more benign epithelial phenotype, with less invasive ability. These data provide new insights into the biological significance of this tumor suppressor gene found in normal mammary epithelium and may form the basis of novel therapeutic strategies in the management of breast carcinoma.

Our previous study showed that human peritoneal conditioned medium (CM) increased the matrix metalloproteinase-9 (MMP-9) secretion and invasiveness of ovarian cancer cells (NOM1). In an effort to identify this MMP-9-stimulating factor, we examined the effects of extracellular matrix components, such as type IV collagen, laminin, and fibronectin, on ovarian cancer cells. We found that fibronectin increased the MMP-9 activity of NOM1 cell CM in a concentration-dependent manner and that the peritoneal CM contained high level of fibronectin. An increase of MMP-9 activity in NOM1 cell CM by the peritoneal CM was almost completely blocked by 20 microg/ml of anti-integrin alpha5/FnR antibody and RGD polypeptides. Furthermore, after immunoprecipitation by antifibronectin antibody supernatant of the peritoneal CM did not increase MMP-9 activity in NOM1 cells. Fibronectin and the peritoneal CM also increased MMP-9 activity and expression in NOM1 cell lysate, and these effects were blocked by anti-integrin alpha5/FnR antibody. Invasiveness of NOM1 cells was enhanced by fibronectin and the peritoneal CM in a concentration-dependent manner, and anti-integrin alpha5/FnR antibody blocked these effects. These results suggested that fibronectin secreted from peritoneum increased MMP-9 activity and expression, and, in turn, invasiveness of ovarian cancer cells.