P53-INDEPENDENT APOPTOTIC AND NECROTIC CELL DEATHS INDUCED BY ADENOVIRUS INFECTION - SUPPRESSION BY E1B 19K AND BCL-2 PROTEINS

Adenovirus E1B 19K protein prevents premature death of adenovirus-infe cted cells. Viral mutants (19K mutants) defective in the 19K protein i nduce enhanced cell death, resulting in fragmentation of viral and cel lular DNA. The 19K protein can also suppress the effects of certain ex ternal cell death-inducing stimuli, such as tumor necrosis factor cr a nd various DNA-damaging agents that induce apoptosis. We have examined viral infection of permissive human cells and nonpermissive rat cells to determine if the 19K mutant induces apoptotic or necrotic type of cell death. Infection of normal rat kidney cells with an adenovirus ty pe 2 19K deletion mutant induces internucleosomal DNA fragmentation an d condensation of nuclear chromatin. Electron microscopic examination of these cells revealed the presence of condensed subnuclear bodies ch aracteristic of apoptosis. In contrast, infection of human A549 cells induces random DNA fragmentation, and these cells do not exhibit chara cteristic condensation of the nuclear chromatin but contain enlarged n uclei loaded with virus particles. Therefore, it appears that adenovir us infection induces both apoptotic and necrotic types of cell death, depending on the cell type. Both types of cell death can be suppressed by E1B 19K protein. Similarly, a recombinant adenovirus expressing th e human Bcl-2 protein but lacking the E1B proteins can efficiently sup press both apoptotic and necrotic cell death induced by adenovirus inf ection. The requirement of p53 tumor suppressor protein in adenovirus- induced cell death was investigated by infection of human Saos2 and mo use p53 nullizygous (p53-/-) cells lacking p53 tumor suppressor protei n. In both cell types, the 19K mutant induced enhanced DNA fragmentati on, indicating that the adenovirus-induced cell death program can occu r independently of p53 expression.