Expression of growth‐regulated genes in normal and SV40 transformed hamster fibroblasts

Transformation by the oncogenic virus SV40 has been shown to alter the expression of cellular genes at the level of RNA abundance. Many of these genes have yet to be identified. We have determined, by Northern blot analysis, the abundance levels of several growth‐regulated genes in SV40‐transformed cell lines to determine if their expression is altered and correlates with the ability of SV40 transformed cells to grow in low serum containing media. The mRNA abundance levels of the G₁‐specific genes 2A9/calcyclin, 2F1/translocase, and 4F1/vimentin were determined in the parental hamster fibroblast cell line, tk⁻ts13, and in two SV40 transformants, HR5 and HR8 cells, grown in medium containing 10% calf serum (normal medium) and in HR5 and HR8 cells adapted to passage in medium containing low serum. A spontaneous transformant of the parental line capable of growth in low serum in the absence of SV40 transformation (tk⁻ts13/1%), was also included in these studies. The low serum adapted SV40‐transformed cells and the spontaneous tk⁻ts13 transformed cells grew more vigorously than their nonadapted counterparts in medium containing low serum. The low serum adapted cells also grew to higher saturation densities in low serum and to densities comparable to those in high serum, whereas the nonadapted cells grew to low saturation densities in low serum, but not as low as the untransformed parental. These growth‐regulated genes were expressed at lower levels in the SV40 transformed cells growing in medium containing high or low serum, and in the adapted parental cells (tk⁻ts13/1%) grown in medium containing low serum, in comparison with their levels in the nontransformed parental cells (tk⁻ts13/10%) grown in medium containing high serum. Therefore, the decreased levels in the expression of these growth‐regulated genes could not be correlated to the rapid growth of SV40 transformed cells. We conclude that the molecular mechanism(s) that permits low serum adapted growth and SV40 transformed growth is different, at least in part, from the mechanism operating in nontransformed cells.