Role of VN and the uPAR–VN interaction in xenograft tumor growth. (A) Absence of macro-metastasis foci in the lungs of SCID mice xenografted with HEK293 cells expressing mouse uPAR. Primary tumors and lungs were collected from killed mice, fixed in PFA, and imaged using an inverted fluorescence microscope. Representative images of primary tumors (upper panel) and front and back views of lungs (lower panels) are shown. (B) Expression of uPAR reduces tumor latency. Anesthetized 8-week-old SCID mice were inoculated in the fourth mammary fat pad with mock (black), muPAR (red), muPAR^W32A (blue), and muPAR^ΔD1 (green) transfected cells. The appearance of tumors was monitored by palpation. Kaplan-Meier curves show the fraction of tumor-free mice. The total number of mice analyzed with each cell line is indicated and includes complete data from 3 to 5 independent experiments. (C) VN deficiency impairs MDA-MB-231 tumor formation in immunodeficient RAG^−/− mice. MDA-MB-231 cells were injected into the fourth mammary fat pad of RAG^−/−/VN^+/+, RAG^−/−/VN^−/−, or RAG^−/−/VN^+/− mice and tumor formation monitored. The graph shows data pooled from 2 independent experiments and indicates the number of tumor-bearing mice and total number of mice injected. At the end of the observational period (4 months), none of the remaining mice (RAG^−/−/VN^−/−, n = 22; RAG^−/−/VN^+/+, n = 3; and RAG^−/−/VN^+/−, n = 5) had palpable tumors.