Rodent and human tumor cell lines secrete a potent vascular permeability factor (VPF) which causes a rapid and substantial increase in microvascular permeability to plasma proteins without causing mast cell degranulation, or endothelial cell damage or without exciting an inflammatory cell infiltrate [D. R. Senger, S. J. Galli, A. M. Dvorak, C. A. Perruzzi, V. S. Harvey, and H. F. Dvorak. Science (Wash. DC), 219: 983–985, 1983; D. R. Senger, C. A. Perruzzi, J. Feder, and H. F. Dvorak. Cancer Res., 46: 5629–5632, 1986]. VPF now has been purified to homogeneity from guinea pig tumor cell culture medium; it is a Mr 34,000–43,000 protein, and a NH2-terminal amino acid sequence has been derived. A synthetic peptide corresponding to amino acid residues 1–24 of the native protein was used to raise rabbit antibodies which bind all of the vessel permeability-increasing activity secreted by guinea pig tumor cells and which stain purified VPF on immunoblots. These findings establish that this NH2-terminal amino acid sequence was derived from the permeability factor. Homology searches found no identity or close similarity between VPF NH2-terminal sequence and database sequences, indicating that VPF is distinct from other proteins for which sequence data are available. In particular, no sequence similarity was found between tumor-secreted VPF and other mediators of increased vessel permeability including plasma and glandular kallikreins.

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This work was supported by USPHS Grant CA 43967 (D.R.S.) awarded by the National Cancer Institute, Department of Health and Human Services, USPHS Grant GM 36812 (L.V.D.W.) awarded by the National Institute of General Medical Sciences, Grant JFRA-198 (L.V.D.W.) from the American Cancer Society, and by a grant from the Monsanto Company.

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