Transfection of the human IGFBP-3 gene into Balb/c fibroblasts: a model for the cellular functions of IGFBPs.

The insulin-like growth factors (IGFs) are potent mitogens with both endocrine and autocrine-paracrine effects on cell growth. The insulin-like growth factor binding proteins (IGFBPs) are found in many human biological fluids and in the conditioned media of many cell cultures. These molecules are ontogenically and hormonally regulated. Nevertheless, the biological role(s) of the IGFBPs remain controversial. Both inhibitory and stimulatory effects of IGFBPs on cell growth have been suggested. In order to evaluate the actions of endogenously produced IGFBPs on cell growth, we have constructed a mammalian expression vector containing the hIGFBP-3 cDNA, and transfected the murine Balb/c cell line. The IGFBP-3 transfected Balb/c cells (Tx-BP-3) expressed readily detectable amounts of hIGFBP-3 protein and its mRNA. Growth of Tx-BP-3 in serum containing media was significantly slower, compared with control plasmid-transfected cells (Tx-P) grown under identical conditions. Fully confluent Tx-BP-3 cells arrested their growth at a cell density that was lower than did Tx-P cells. When transfected cells were grown in insulin-containing media, growth rates of the IGFBP-3 transfected cells were not restored to those observed in control plasmid-transfected cells. These results suggest that in this model, the expression of endogenous IGFBP-3 has an inhibitory effect on cell growth.