The role of upar deficiency in induction of cancer dormancy. w

uPAR on the surface of cancer cells has been linked with increased cell migration, invasiveness and early cancer recurrence. We now show that a fiill complement of uPAR is required for tumorigenicity of a squamous cell carcinoma and that a reduction in uPAR leads to its dormancy in vivo. In contrast, the uPAR-dcficient cells grow in culture as well as the control cells, suggesting a specific role for this receptor in vivo. Following inoculation on CAMs, clones of carcinoma cells with uPAR level reduced up to 70% by an antisense-expressing construct, remain viable but do not increase in mass for up to 5 months. After this prolonged period, and in spite a persistently low level of uPAR, all clones emerge from dormancy and begin to grow, suggesting that uPAR deficiency can be bypassed. Our data show that the dormancy of the uPAR-deficient cells is caused by a reduced rate (more than 70%) of proliferation and not by enhanced rate of cell death. Although the reduced uPAR, and thus a reduced surface uPA, may be directly responsible for the lack of mitogenic stimulus, this is only a remote possibility, and we postulate that the effect of uPAR is indirect Since uPAR has been shown to interact with integrins (both in function enhancing and blocking capacity), we tested whether the difference in uPAR level has an effect on adhesion of the tumorigenic and dormant cells to matrix proteins such as fibronectin (FN) and vitronectin (VN). The adhesion to VN did not correlate with the uPAR level and was always lower than the adhesion to FN. However, cells with "normal" level of uPAR adhered to FN -2 to 3 fold more efficiently than the dormant, uPARdeficient cells. A FACS analysis of the FN-binding integrins (a3,a5 and av) revealed that all cells, regardless of their adhesion efficiency to FN expressed similar levels of these integrins. This suggested that it is the state of activation of the FN-binding integrins that determines the ability of cells to adhere to FN. Indeed, l-activating antibody (TS2/16) stimulated the adhesion of the dormant cells to FN by 85% but not the adhesion of the tumorigenic cells. Experiments are in progress to determine whether there are differences in the interactions between uPAR and the l integrins in cells with different uPAR levels, and what is the consequence, in addition to the enhanced adhesion to FN, of the active conformation of l family of integrins on the ability of cells to proliferate in vivo.