Developmentally regulated endothelial cell locus I (Del I) is a new angiogenic molecules expressed specifically in early embryonic endothelial cells. We investigated the relationship between Dell and tumor cell-derived vascular endothelial growth factor (VEGF). Dunn osteosarcoma cells and high- and low-metastatic murine sarcoma cells did not express Dell. However, the expression of Del I was observed in these primary tumor tissues and the pulmonary metastatic tissues after subcutaneous inoculation in vivo. Every tumor cell-conditioned medium containing VEGF induced the expression of Dell in murine lung microvascular endothelial (MLE) cells, although control MLE cells did not express Del I. The anti-mouse VEGF monoclonal antibody inhibited the induction of the Dell expression. In addition, mouse recombinant interleukin-lot and tumor necrosis factor-alpha also induced Dell in MLE cells. Dell may play an important role in tumor angiogenesis through the effects of tumor-derived factors including VEGF. (c) 2005 Elsevier Inc. All rights reserved.