J Biol Chem, Vol. 273, Issue 32, 20036-20045, August 7, 1998

Stabilization of p53 by Adenovirus E1A Occurs through Its Amino-terminal Region by Modification of the Ubiquitin-Proteasome Pathway

Takuma Nakajima, Kenichi Morita, Haruki Tsunoda, Shinobu Imajoh-Ohmi^¶, Hirofumi Tanaka, Hideyo Yasuda, and Kinichiro Oda

From the  Department of Biological Science and Technology, Science University of Tokyo, Noda 278, Japan, ^¶ Institute of Medical Science, Tokyo University, 4-6-1 Shiroganedai, Minato-ku 108, Japan, and  School of Life Science, Tokyo University of Pharmacy and Life Science, Hachioji, Tokyo 192-03, Japan

The human epidermoid carcinoma-derived cell line MA1, established by introduction of the adenovirus E1A 12 S cDNA linked to the hormone-inducible promoter, elicits apoptosis after induction of E1A_{12 S} in response to dexamethasone. E1A expression caused accumulation of wild type p53 more than 10-fold within 24 h after dexamethasone treatment. The cell lines that express E1A mutants containing a deletion either in the amino terminus or the conserved region 1 were unable to accumulate p53. p53 accumulated was degraded efficiently in vitro in the S10-0 extract (S10-0) prepared from MA1 cells in an ATP and ubiquitin-dependent manner, but not in S10-24 prepared after treatment with dexamethasone for 24 h. The p53 polyubiquitination activity in S100-0 was calcium-dependent and reduced greatly in S100-24. Ubiquitin affinity chromatography revealed that p53 ubiquitination activity in eluates thought to contain ubiquitin-conjugating enzymes decreased greatly in S100-24 as compared with S100-0. The accumulation of p53 was accompanied by the increase 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 late stage of the apoptotic process. These results indicate that the stabilization of p53 by E1A occurs through modification of a ubiquitin-specific enzyme(s) in the ubiquitin-proteasome pathway.