Oncogenes and Angiogenesis: down-regulation of thrombospondin-1 in normal fibroblasts exposed to factors from cancer cells harboring mutant ras.
The onset of angiogenesis in cancer often involves down-regulation of endogenous angiogenesis inhibitors, of which thrombospondin-1 (TSP-1) is a paradigm. As this effect is thought to occur under the influence of transforming genetic lesions (e.g., expression of the mutant ras oncogene), its nature is regarded as intrinsic to cancer cells themselves. Here, we show that ras-transformed cancer cells can also induce TSP-1 down-regulation in their adjacent nontransformed stromal fibroblasts, but not in endothelial cells, in a paracrine and distance-dependent manner. Indeed, several H-ras-expressing fibrosarcoma (528ras1, B6ras, and NIH3T3Ras) and carcinoma (DLD-1 and IEC18Ras3) cells were found to release soluble factors capable of suppressing TSP-1 protein, mRNA, and promoter activity in nontumorigenic, immortalized dermal fibroblastic cell lines in culture (e.g., in fibroblasts expressing enhanced green fluorescent protein/TSP-1 reporter). This effect was abrogated in Id1-/- fibroblasts. At least two low molecular weight (<3 kDa), heat-labile, and trypsin-resistant mediators of TSP-1 suppression were found to be released from 528ras1 cells. Their effects on normal fibroblasts were inhibited (albeit to different extents) by pertussis toxin and, in one case, by dimethylsphingosine, none of which affected TSP-1 expression by 528ras1 cells. Collectively, our study suggests that the effect of mutant ras on tumor neovascularization is not limited to changes in angiogenic properties of cancer cells themselves. Rather, mutant ras, through a different signaling mechanism, may modulate the properties of the adjacent normal stroma, thus eliciting a proangiogenic field effect.
Kalas
Wojciech
W
Henderson Research Centre, McMaster University, Hamilton, Ontario, Canada.
Yu
Joanne L
JL
Milsom
Chloe
C
Rosenfeld
Jack
J
Benezra
Robert
R
Bornstein
Paul
P
Rak
Janusz
J
D000818:Animals; D045744:Cell Line, Tumor; D002471:Cell Transformation, Neoplastic / Q000235:genetics; D015536:Down-Regulation; D005347:Fibroblasts / Q000378:metabolism* / Q000502:physiology; D005354:Fibrosarcoma / Q000098:blood supply / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000037:antagonists & inhibitors / Q000378:metabolism; D011905:Genes, ras / Q000235:genetics*; D006801:Humans; D051798:Inhibitor of Differentiation Protein 1 / Q000096:biosynthesis / Q000235:genetics; D008055:Lipids / Q000502:physiology; D051379:Mice; D009154:Mutation; D041681:NIH 3T3 Cells; D009389:Neovascularization, Pathologic / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D011401:Promoter Regions, Genetic; D015398:Signal Transduction; D019700:Thrombospondin 1 / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D014020:Tissue Extracts / Q000378:metabolism / Q000494:pharmacology
C497455:Idb1 protein, mouse; D051798:Inhibitor of Differentiation Protein 1; D008055:Lipids; D019700:Thrombospondin 1; D014020:Tissue Extracts; D019206:GTP-Binding Protein alpha Subunits, Gi-Go