INSULIN-LIKE GROWTH FACTOR-BINDING PROTEIN-2 INHIBITS PROLIFERATION OF HUMAN EMBRYONIC KIDNEY FIBROBLASTS AND OF ICF-RESPONSIVE COLON-CARCINOMA CELL-LINES

So far, the physiological role of insulin-like growth factor binding p rotein-2 (IGFBP-2) has not been demonstrated directly. Therefore, we t ransfected 293 cells with an expression vector containing the CMV prom oter and the complete cDNA of mouse IGFBP-2, Secretion of bioactive IG FBP-2 into conditioned medium was demonstrated by Western ligand and W estern immunoblotting and quantified by specific RIA, For the analysis of cell proliferation three clones exhibiting either high or low/no I GFBP-2 expression were selected and compared to non-transfected parent al 293 cells. IGFBP-2 secreting clones displayed reduced conversion of thiazolyl blue when compared to negative clones or non-transfected pa rental 293 cells (P < 0.01). The lower growth activity measured in the IGFBP-2 secreting clones was compensated in great part by the adminis tration of exogenous IGF-I or -II. Conditioned media of IGFBP-2 secret ing clones inhibited growth of IGF-responsive colon tumor cell lines ( LS513, MT-29) while those of negative clones did not. In addition, con ditioned medium from a clone expressing high levels of IGFBP-2 inhibit ed anchorage-independent growth of LS513 and MT-29 cells. In contrast, growth of an IGF-unresponsive tumor cell line (Co-115) was not affect ed by the conditioned media. We hypothesize that IGFBP-2 might sequest er the IGFs and thus prevent them from transferring their mitogenic si gnals. (C) 1998 Federation of European Biochemical Societies.