Figure 1.

Gene expression signature of c-MYC-immortalized human fibroblasts, “iMYC.” (A) Schematic of the derivation of c-MYC-immortalized cell lines, iMYC, from three independent human foreskin fibroblast (HFF) isolates. HFFs were tranduced with a c-MYC expressing retroviral vector, pBabe-puro, as described previously in reference ¹⁷. Samples of iMYC lines used in the described experiments were collected past the “inflection point” (an event that occurred at >80 population doublings) when cells were uniformly growing as an immortalized population. For comparison, empty vector cells, referred to as HFF-pB and c-MYC expressing HFFs, referred to as eMYC, were collected prior to the “inflection point” within the first 10–30 d in culture (thus “e” for early passage) where cells have undergone fewer than 20 population doublings. (B) Venn diagram indicating the overlap of significantly upregulated (53) and downregulated (263) genes in three independently derived iMYC cells in comparison with eMYC. The p-value of each overlap is shown. (C) K-means clustering analysis identified four groups of genes within the iMYC signature that correctly separated the three cell lines: (1) genes unchanged in eMYC but downregulated in iMYC, (2) genes upregulated in eMYC but downregulated in iMYC to pB levels, (3) genes downregulated in both eMYC and iMYC but more strongly down in iMYC, (4) genes unchanged in eMYC but up in iMYC.