Migration-stimulating factor: a genetically truncated onco-fetal fibronectin isoform expressed by carcinoma and tumor-associated stromal cells.

Migration-stimulating factor (MSF) is a 70-kDa motogenic protein previously reported to be expressed by fetal and cancer patient fibroblasts cultured in vitro and present in the serum of breast cancer patients. A 2.2-kb full-length MSF cDNA has been cloned and shown to be a truncated isoform of fibronectin generated from its primary gene transcript by a hitherto unrecognized intron read-through mechanism. MSF cDNA is identical to the 5' end of fibronectin cDNA, up to and including exon III-1a, and terminates in a novel 195-nucleotide 3' sequence. This MSF unique sequence is derived from the intron immediately downstream of exon III-1a in the fibronectin gene and is not found in any previously identified "full-length" fibronectin cDNA. MSF mRNA is 1000-fold less abundant than full-length fibronectin message in fetal fibroblasts and exhibits rapid biphasic decay kinetics previously associated with oncogenes and stress response molecules. MSF recombinant protein exhibits a potent and substratum-dependent motogenic activity, with half-maximal response manifest at 0.1-1.0 pg/ml. This activity is (a) mediated by the IGD amino acid motif; and (b) not expressed by (i.e., cryptic within) full-length fibronectin. In situ hybridization and immunohistochemistry confirm that MSF is expressed by tumor-associated fibroblasts and additionally indicate that it is also expressed by carcinoma cells and tumor-associated vascular endothelial cells. MSF, as a consequence of its potent bioactivities and expression by both stromal and carcinoma cell populations, is well placed to function as an epigenetic effector promoting cancer development.

Evidence of a bi-phasic effect of thrombospondin-1 on angiogenesis.

Contradictory results have been reported regarding the association between vascularity (used as an index of angiogenesis) and thrombospondin-1 (TSP-1) in human tumours. In previous studies, the reported association was based on the estimated average TSP-1 value per tumour, with a sufficient number of specimens collectively analysed per tumour type. Given the extent of intra-tumour heterogeneity, we determined the association between TSP-1 and vascularity within individual specimens, based on the average values of TSP-1 and vascularity in 10-20 pre-selected areas per tumour. Cells expressing TSP-1 mRNA were visualised by in situ hybridisation and quantified by point counting. Vascularity was quantified by point counting and vessel density of von Willebrand Factor-positive vessels. In 10 ductal breast carcinomas, a direct correlation between TSP-1 and vascularity was found in 4 tumours, no correlation in 3 and an inverse correlation in 3. The effect of TSP-1 on endothelial cell migration in vitro was assessed in the Boyden chamber assay. TSP-1 stimulated cell migration at low concentrations (0.1-10 microg/ml) and was inhibitory at high concentrations (25-100 microg/ml). These results suggest that TSP-1 may elicit a concentration-dependent, bi-phasic, effect on angiogenesis.