INDUCTION OF APOPTOSIS BY ADENOVIRUS TYPE-5 E1A IN RAT-CELLS REQUIRESA PROLIFERATION BLOCK

Infection with Ad5dl520EIB-, an adenovirus producing only the 243 resi due EIA protein and lacking the EIB region, caused apoptosis in normal rat kidney (NRK) cells as judged by the production of nucleosomal DNA fragments. Apoptosis occurred only when the celts were growth-inhibit ed by cell-cell contacts in confluent cultures or by serum starvation and not when they were actively growing. In uninfected cultures, apopt osis also occurred at confluency, but more slowly than after infection . Studies with EIA deletion mutants of dl520E1B- showed that the regio ns of the EIA protein essential for induction of apoptosis were those in exon 1 required for binding to the cellular proteins p300 and pRb. Mutants defective at inducing apoptosis were previously found to be de fective at inducing baby rat kidney cells to synthesize cellular DNA. In our experiments, cells underwent apoptosis when stimulated by E1A t o proliferate under conditions where proliferation was blocked. It is possible that it was the proliferation block opposing the induction of proliferation that led directly to apoptosis. Circumstances leading t o induction of apoptosis by c-myc (Evan et al., 1992) are similar and can be interpreted in a similar way.