The insulin-like growth factors (IGFs) are potent mitogens with both endocrine and autocrine-paracrine effects on cell growth. The IGF 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 that endogenously produced IGFBPs have on cell growth, we constructed a mammalian expression vector containing the human IGFBP-3 cDNA and transfected the murine Balb/c cell line. While plasmid-transfected control Balb/c cells (Tx-P) produced only small amounts of a 28-kilodalton IGFBP, the IGFBP-3-transfected Balb/c cells (Tx-BP-3) additionally expressed readily detectable amounts of the characteristic 40- to 44-kilodalton human IGFBP-3 protein doublet and its mRNA. Growth of Tx-BP-3 in serum-containing media was significantly (2.5-fold) slower compared with Tx-P grown under identical conditions. Fully confluent Tx-BP-3 cells arrested their growth at a cell density that was 3-fold lower than did Tx-P cells. When nontransfected cells were grown in the presence of high concentrations of either IGF-I or insulin, growth was equally stimulated. However, when transfected cells were grown in insulin-containing media (5 micrograms/ml), growth rates of the IGFBP-3-transfected cells were not restored to those observed in plasmid-transfected control cells. These results suggest that in this model, the expression of endogenous IGFBP-3 has an inhibitory effect on cell growth.(ABSTRACT TRUNCATED AT 250 WORDS).
ASJC Scopus subject areas
- Molecular Biology