Transformation of late passage insulin-like growth factor-I receptor null mouse embryo fibroblasts by SV40 T antigen

There is evidence that the insulin-like growth factor-I (IGF-I) receptor is required for transformation by a variety of viral and cellular oncogenes in a mouse embryo fibroblast model. To further investigate the IGF-I receptor signaling pathways that are required for the permissive effect of the receptor on transformation by SV40 T antigen, we established three independent fibroblast cell lines each from wild-type and IGF-I receptor null embryos (R−). We transfected the wild-type and R− cell lines with an SV40 T antigen plasmid and selected three clones from each cell line that expressed T antigen. As in previous reports, none of the cloned R− cell lines expressing T antigen were transformed as measured by the ability to form large colonies in soft agar. However, with further passage, all three T antigen–expressing clones from one of the R− cell lines (R−3) formed large colonies in soft agar and the transformation of these T antigen–expressing clones was confirmed by tumorigenesis experiments in immunodeficient mice. DNA microarray analysis comparing gene expression between early passage and late passage R−3/T antigen clones showed, among other changes, an increase in the expression of ErbB-3 mRNA in the late passage clones. Also, the expression of ErbB-3 protein was dramatically increased in the late passage R−3/T antigen clones. We conclude that late passage IGF-I receptor null mouse embryo fibroblasts can be transformed by SV40 T antigen, and that ErbB-3 may play a role in permitting transformation by T antigen. (Cancer Res 2006; 66(8): 4233-9)