Abrogation of the requirements for added growth factors in 3T3 cells constitutively expressing the p53 and IGF-1 genes.

Two constructs (co-transfected with selectable markers) were used to establish cell lines from BALB/c3T3 cells: a p53 mini-gene under the control of an LTR promoter and a synthetic IGF-1 coding sequence driven by the SV40 early promoter. BALB/c3T3 cells do not grow in plasma or in 1% serum or in soft agar and in defined media require both platelet-derived growth factor (PDGF) and insulin (or IGF-1). Cells carrying only the LTR/p53 mini-gene grew well in plasma (but not in 1% serum), in soft agar and in serum-free medium containing only insulin. Cells carrying only the SV40/IGF-1 gene grew (but not too vigorously) in soft agar and grew well in serum-free medium containing PDGF but no insulin. Cells carrying both constructs grew very well in plasma, in soft agar and in serum-free medium without PDGF nor insulin. The results indicate that the requirements for growth of BALB/c3T3 cells can be reduced to two genes: IGF-1 and a gene replacing PDGF (p53 in our case). An unexpected, but interesting observation was that cells carrying the LTR/p53 gene grew slower in 10% serum than in plasma.