EFFECT OF A NULL MUTATION OF THE INSULIN-LIKE GROWTH-FACTOR-I RECEPTOR GENE ON GROWTH AND TRANSFORMATION OF MOUSE EMBRYO FIBROBLASTS

Fibroblast cell lines, designated R(-) and W cells, were generated, re spectively, from mouse embryos homozygous for a targeted disruption of the Igf1r gene, encoding the type 1 insulin-like growth factor recept or, and from their wild-type littermates. W cells grow normally in ser um-free medium supplemented with various combinations of purified grow th factors, while pre and postcrisis R(-) cells cannot grow, as they a re arrested before entering the S phase. R(-) cells are able to grow i n 10% serum, albeit more slowly than W cells, and with all phases of t he cell cycle being elongated. An activated Ha-ras expressed from a st ably transfected plasmid is unable to overcome the inability of R(-) c ells to grow in serum-free medium supplemented with purified growth fa ctors but stimulates their growth in 10% serum and also induces the fo rmation of small foci in some clones. Nevertheless, even in the presen ce of serum, R(-) cells stably transfected with Ha-ras, alone or in co mbination with simian virus 40 large T antigen, fail to form colonies in soft agar. Reintroduction into R(-) cells (or their derivatives) of a plasmid expressing the human insulin-like growth factor I receptor RNA and protein restores their ability to grow with purified growth fa ctors or in soft agar. The signaling pathways participating in cell gr owth and transformation are discussed on the basis of these results.