Vascular permeability factor (VPF) is one of the most potent known inducers of microvascular hyperpermeability; in addition, it is a selective endothelial cell growth factor, hence its alternate name, vascular endothelial growth factor. VPF exerts its actions on the microvasculature by interacting with specific endothelial cell receptors. VPF is expressed by many transplantable animal tumors, by tumor cell lines in culture, and by certain normal cells in situ. The purpose of the present investigation was to determine whether and with what consistency VPF and its endothelial cell receptors are expressed in primary autochthonous human tumors of gastrointestinal tract origin, as determined by in situ hybridization and immunohistochemistry. Twenty-one primary adenocarcinomas (17 colon, 2 stomach, 1 small bowel, and 1 pancreas) were studied. The malignant epithelial cells expressed VPF mRNA strongly, in contrast to normal epithelium, hyperplastic polyps, and adenomas, which expressed little or no VPF mRNA. VPF expression was further increased in tumor cells immediately adjacent to zones of tumor necrosis; in such areas, occasional stromal cells also expressed VPF mRNA. In the ten colon carcinomas studied, tumor cells stained for VPF protein by immunohistochemistry. The endothelial cells of nearby stromal blood vessels also stained for VPF by immunohistochemistry and in addition expressed mRNAs encoding the VPF receptors flt~l and kdr as determined by in situ hybridization. Endothelial cells away from the tumor did not stain for VPF and no definite mRNA expression for flt-1 or kdr was detected by in situ hybridization. The ganglion cells of the myenteric plexus of normal bowel expressed VPF mRNA and protein. These data indicate that primary autochthonous human tumors of gastrointestinal origin regularly express both VPF mRNA and VPF protein and that adjacent stromal vessels express mRNAs for both known VPF receptors. VPF is likely to contribute to tumor growth by promoting angiogenesis and stroma formation, both directly, through its action as an endothelial cell growth factor, and indirectly, by increasing vascular permeability, thereby leading to plasma protein extravasation, fibrin deposition, and the eventual replacement of the resulting matrix with vascularized stroma.
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This work was supported by USPHS Research Grants CA-50453 and CA-58845 (to H. F. D.), and by CA-43967 (to D. R. S.) awarded by the National Cancer Institute, Department of Health and Human Services, and under terms of a contract from the National Foundation for Cancer Research, and by grants from the BIH Pathology Foundation, Inc.