STABILIZATION OF P53 BY ADENOVIRUS E1A OCCURS THROUGH ITS AMINO-TERMINAL REGION BY MODIFICATION OF THE UBIQUITIN-PROTEASOME PATHWAY

The human epidermoid carcinoma-derived cell line MA1, established by i ntroduction of the adenovirus E1A 12 S cDNA linked to the hormone-indu cible promoter, elicits apoptosis after induction of EIA,,, in respons e to dexamethasone. E1A expression caused accumulation of wild type p5 3 more than 10-fold within 24 h after dexamethasone treatment. The cel l lines that express E1A mutants containing a deletion either in the a mino terminus or the conserved region 1 were unable to accumulate p53, p53 accumulated was degraded efficiently in vitro in the S10-0 extrac t (S10-0) prepared from MA1 cells in an ATP and ubiquitin-dependent ma nner, but not in S10-24 prepared after treatment with dexamethasone fo r 24 h, The p53 polyubiquitination activity in S100-0 was calcium-depe ndent and reduced greatly in S100-24, Ubiquitin affinity chromatograph y revealed that p53 ubiquitination activity in eluates thought to cont ain ubiquitin-conjugating enzymes decreased greatly in S100-24 as comp ared with S100-0, The accumulation of p53 was accompanied by the incre ase in the level of Mdm2, which has been shown to degrade p53 through binding to it. The high p53 level, however, was maintained until the l ate stage of the apoptotic process, These results indicate that the st abilization of p53 by E1A occurs through modification of a ubiquitin-s pecific enzyme(s) in the ubiquitin-proteasome pathway.