DOWN-REGULATION OF VASCULAR ENDOTHELIAL GROWTH-FACTOR IN A HUMAN COLON-CARCINOMA CELL-LINE TRANSFECTED WITH AN ANTISENSE EXPRESSION VECTOR SPECIFIC FOR C-SRC

Vascular endothelial growth factor (VEGF) is implicated in the angioge nesis of human colon cancer. Recent evidence suggests that factors tha t regulate VEGF expression may partially depend on c-src-mediated sign al transduction pathways. The tyrosine kinase activity of Src is activ ated in most colon tumors and cell lines, We established stable subclo nes of the human colon adenocarcinoma cell line HT29 in which Src expr ession and activity are decreased specifically as a result of a transf ected antisense expression vector. This study determined whether VEGF expression is decreased in these cell lines and whether the smaller si ze and reduced growth rate of antisense vector-transfected cell lines in vivo might result, in part, from reduced vascularization of tumors. Northern blot analysis of these cell lines revealed that VEGF mRNA ex pression was decreased in proportion to the decrease in Src kinase act ivity. Under hypoxic conditions, cells with decreased Src activity had a <2-fold increase in VEGF expression, whereas parental cells had a > 50-fold increase. VEGF protein in the supernatants of cells was also r educed in antisense transfectants compared with that from parental cel ls, In nude mice, subcutaneous tumors from antisense transfectants sho wed a significant reduction in vascularity. These results suggest that Src activity regulates the expression of VEGF in colon tumor cells.