P53 CONFERS A SELECTIVE ADVANTAGE ON TRANSFECTED HELA-CELLS

The p53 gene, which is frequently mutated in various tumors, encodes a phosphoprotein thought to have a key role in the regulation of cell proliferation. To explore their biological effects, the HeLa carcinoma line, which does not express p53, was co-transfected with plasmid constructs expressing wild-type or mutant p53 proteins, or unrelated proteins, along with a plasmid conferring resistance to a neomycin-kanamycin antibiotic analog (G418). Both wild-type and mutant forms of p53 stimulated the number of G418-resistant colonies between 5- and 36-fold. Further investigation of colony development revealed that p53 enhanced cell survival, leading to increased colony numbers, but did not stimulate cell growth. Nonetheless, we suggest that an initial slowing of cell growth caused by expression of the unintegrated p53 plasmids renders the transfectants resistant to selection with G418, thus causing a higher frequency of G418-resistant colonies. p53 constructs were found to be expressed transiently in HeLa cells as expected, but the G418-resistant colonies frequently failed to express p53. This loss of p53 expression may be due to negative regulatory effects of p53 on the cytomegalovirus promoter that drives the selection marker.