Growth inhibition of vascular smooth muscle cells derived from urokinase receptor (u-PAR)-deficient mice in the presence of carcinoma cells

Abstract The growth rate of vascular smooth muscle cells (VSMCs), which were derived from aorta of mice deficient in the fibrinolytic factors tissue-type plasminogen activator (t-PA −/− ), urokinase (u-PA −/− ), u-PA receptor (u-PAR −/− ) and type 1 plasminogen activator inhibitor (PAI-1 −/− ), as well as wild-type (WT) mice, was investigated in the presence of mouse melanoma cells (B16). In the VSMCs cultured with a basal medium supplemented with 10% fetal calf serum (FCS), there was no difference in the growth rate among the gene-lacking VSMCs and WT VSMCs, indicating that these fibrinolytic factors were not involved in the FCS-mediated cell proliferation. On the other hand, when these VSMCs were cultured with B16 cells in either the mixed culture or a double-chamber, only u-PAR −/− VSMCs showed a significantly lower growth rate. In addition, these suppressive effects on u-PAR −/− VSMCs were also observed in the presence of B16-derived conditioned medium (B16/CM). The growth rate of all the VSMCs except u-PAR −/− VSMCs was increased in the presence of B16/CM. The degree of the increase in cell number was comparable to that obtained with FCS. These effects on growth activity were partially associated with the levels of mitogen-activated protein kinase (MAPK, p42/p44) activity. The findings suggest that u-PAR plays an important role in the proliferative response of VSMCs and that without u-PAR, there is no intracellular signaling for cell proliferation.