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Association between the cellular p53 and the adenovirus 5 E1B‐55kd proteins reduces the oncogenicity of Ad‐transformed cells.

The association of the cellular p53 protein with the E1B‐55kd protein of adenovirus 5 (Ad5) is thought to result in inactivation of the p53 recessive oncogene product. Here we show that Ad5 E1‐transformed 3Y1 rat cells which express low levels of the 55 kd E1B protein do not contain the p53‐E1B 55kd complex. These cells have nuclearly located p53 and are highly oncogenic in nude mice. In 3Y1 cells expressing the E1B protein at a sufficiently high level, association between p53 and E1B‐55kd occurs, resulting in an almost complete trapping of p53 into a discrete cytoplasmic body. These cells only form tumors after a very long latency period and in the tumors that eventually appear selection has occurred in favor of cells lacking the complex and containing free nuclear p53. Comparable results were found when highly oncogenic Ad12‐transformed cells were supertransfected with the Ad5 E1B region. In none of the Ad‐transformed mouse, rat and human cell lines examined, could we detect p53 of abnormal molecular weight or association with hsc70, neither could we immunoprecipitate p53 by the mutant specific antibody PAb240. These data suggest that a high level of nuclear p53 with a wild‐type conformation contributes to the oncogenicity of Ad transformed cells.