P300 BINDING BY E1A COSEGREGATES WITH P53 INDUCTION BUT IS DISPENSABLE FOR APOPTOSIS

E1A expression during adenovirus infection induces apoptosis, E1A expr ession causes accumulation of the p53 tumor suppressor protein, and E1 A-induced apoptosis is p53 mediated in primary rodent cells, implying that p53 induction may be linked to apoptosis induction by E1A. Adenov iruses containing mutations in the EIA gene were tested for the abilit y to trigger both p53 accumulation and the appearance of enhanced cyto pathy (cyt phenotype) and degradation of DNA (deg phenotype), indicati ve of apoptosis in infected HeLa cells, The adenoviruses had mutations which disrupted the pRb- and/or p300-binding activities of E1A so tha t the relationship between p53 induction and apoptosis and binding to these cellular proteins by E1A could be determined, An E1A mutation th at specifically disrupted the p300-binding activity failed to induce p 53 accumulation, whereas mutations in E1A which affected pRb binding i nduced p53 accumulation, Thus, p300 binding was required and pRb bindi ng was dispensable for E1A-mediated accumulation of p53 in HeLa cells, All the EIA mutant viruses, regardless of the ability to induce p53 a ccumulation, induced the cyt and deg phenotypes, suggesting that p53 i nduction in infected HeLa cells was not essential for apoptosis, nor w as binding of E1A to the pRb and/or p300 protein, The possibility that E1A induced a p53-independent apoptosis pathway was tested by analyzi ng the appearance of the cyt and deg phenotypes in Saos-2 cells, which were null for both alleles of p53, upon adenovirus infection, An aden ovirus expressing wild-type 12S E1A induced both the cyt and deg pheno types in Saos-2 cells, as did all the E1A mutant viruses, Thus, E1A ex pression during infection of human cells may trigger redundant p53-ind ependent and dependent apoptotic pathways.