T antigen transformation reveals Tp53/RB-dependent route to PLAC1 transcription activation in primary fibroblasts

PLAC1 (placenta-specific 1) is a gene that is placenta specific and transcribed very little, if at all, in any somatic tissue. It is nevertheless expressed in many cancer cell lines. To understand how cancer cells may activate the gene in nonexpressing cells, we found that a model is provided by classical transformation of normal fibroblasts by SV40 T antigen. T antigen derepressed the PLAC1 P1 promoter, with Tp53 and RB exerting critical and opposing actions and nuclear receptors, retinoid X receptor and liver X receptor, sharply increasing the level of expression.