(1) IL-3-independent cells were readily isolated after LISN infection when either IGF-1 or supraphysiologic concentrations of insulin were included in the culture medium.
(2) Stimulation by insulin-like growth factor-I (IGF-I) of LISN C4 cells, a mouse fibroblast cell line that overexpresses human IGF-I receptors, led to an increase in the amount of a phosphatidylinositol kinase that could be immunoprecipitated by anti-IGF-I receptor or anti-phosphotyrosine antibodies.
(3) In contrast, when LISN-infected cells were plated in medium without exogenously supplied IGF-1 or insulin, factor-independent cells were rarely isolated.
(4) To further examine the effects of IGF-1 on hematopoietic cells, FDC-P1 cells were infected with a retroviral construct (LISN) containing the human IGF-1 receptor (hIGF-1R) and neo genes.