Cancer cell invasion and induction of the metastatic cascade are often the consequence of deregulated cell adhesion and migration. There is substantial evidence for the involvement of Stat3 in cell motility, migration, and invasion under normal and pathological situations. Stat3 activation is required for induction of genes encoding MMP‐1, MMP‐2, and MMP‐9, key components of tumor invasion. Through binding to its receptor, cmet, hepatocyte growth factor (HGF) can regulate cell survival, growth, migration, and angiogenesis. cmet is often constitutively active in human tumors and HGF/cmet signaling is at least partially mediated by Stat3. Overall, these observations suggest that positive feedback signals in the HGF/cmet/Stat3 signaling pathway contribute to tumorigenesis.

To explore the role of Stat3 in skin cell malignancy in a human cell culture model, our lab has overexpressed a dominant negative form of Stat3β in the tumorigenic SCC cell line, SRB12‐p9. We established SRB12‐p9 cell clones expressing FLAG‐tagged Stat3β‐Y705F (S3DN). Suppression of Stat3 activity impaired the ability of these cells to scatter upon stimulation with HGF, diminished their capacity to invade, and enhanced adhesion in vitro. S3DN cells also showed suppressed HGF‐induced activation of cmet, as revealed by a phospho‐specific cmet antibody. We next assessed the role of Stat3 in tumor invasion using in vivo mouse tumorigenicity experiments. When injected subcutaneously into immune‐deficient mice, S3DN cells produced tumors that were less locally invasive, though WT tumors were more differentiated as indicated by K10 immunostaining. Upon further examination of these tumors, we found that those arising from WT cells had more intense membrane staining for total cmet and phospho‐cmet than S3DN cells, indicating stronger cmet activity in these tumors. This pattern of cmet staining correlated with increased phospho‐Stat3 membrane staining in the WT tumors. Western blotting revealed a decrease in MMP‐2, MMP‐9, and cmet expression in the S3DN cells. These results are consistent with those from the in vitro experiments. Finally, we show that S3DN may interfere with Stat3/cmet interaction, as evidenced by co‐immunoprecipitation experiments, preventing the activation of cmet at the cell membrane. Ongoing studies will further address the effect of S3DN expression on cmet signaling and the effect this has on the HGF/c‐met/Stat3 signaling loop and tumor cell invasion.

Citation Information: Cancer Prev Res 2010;3(1 Suppl):B40.