ENHANCED EXPRESSION OF MULTIPLE FORMS OF VEGF IS ASSOCIATED WITH SPONTANEOUS IMMORTALIZATION OF MURINE FIBROBLASTS

The mechanism(s) involved in immortalization that constitute the first step during malignant transformation has been the subject of our inte rest. By the use of spontaneously immortalized mouse embryonic fibrobl asts we have earlier identified two stages of immortalization which ar e characterized by growth characterisitics of the cells, their conditi oned medium and the protein markers such as p53, p81 and mortalin (Kau l et al. (1994) Biochim. Biophys. Acta, in press). The present study w as planned to purify the mitogenic factors from the conditioned medium of stage II cells. Sequential purification by chromatography followed by peptide sequencing has characterized one of these as vascular endo thelial growth factor (VEGF). Further analysis by RT-PCR suggests that the spontaneously immortalized stage II fibroblasts have enhanced syn thesis and secretion of VEGF as compared to their mortal parent cells. Expression of a novel 304 bp long form of VEGF is identified in immor tal fibroblasts in addition to the three known alternatively spliced f orms. The study points to the involvement of VEGF function during spon taneonus immortalization of mouse, embryonic fibroblasts.