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Published on: October 21, 2012
Induction of apoptosis by adenovirus type 5 E1A in rat cells requires a proliferation block
J S Mymryk1, K Shire, S T Bayley
1Department of Biochemistry, McMaster University, Hamilton, Ontario, Canada.
Abstract:
Infection with Ad5dl520EIB-, an adenovirus producing only the 243 residue E1A protein and lacking the E1B region, caused apoptosis in normal rat kidney (NRK) cells as judged by the production of nucleosomal DNA fragments. Apoptosis occurred only when the cells were growth-inhibited by cell-cell contacts in confluent cultures or by serum starvation and not when they were actively growing. In uninfected cultures, apoptosis also occurred at confluency, but more slowly than after infection. Studies with E1A deletion mutants of dl520E1B- showed that the regions of the E1A 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 defective at inducing baby rat kidney cells to synthesize cellular DNA. In our experiments, cells underwent apoptosis when stimulated by E1A to 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 to induction of apoptosis by c-myc (Evan et al., 1992) are similar and can be interpreted in a similar way.
Insights
Adenovirus infection triggers apoptosis in growth-inhibited normal rat kidney cells. Key regions of the E1A protein, essential for binding p300 and pRb, mediate this apoptotic response.
Area of Science:
- Molecular Biology
- Cell Biology
- Virology
Background:
- Adenoviruses are common viruses that can cause disease.
- Apoptosis, or programmed cell death, is a critical cellular process.
- The E1A protein of adenovirus plays a role in viral replication and cell cycle regulation.
Purpose of the Study:
- To investigate the role of adenovirus E1A protein in inducing apoptosis in normal rat kidney (NRK) cells.
- To identify the specific regions of the E1A protein responsible for apoptosis induction.
- To understand the conditions under which adenovirus-induced apoptosis occurs.
Main Methods:
- Infection of NRK cells with Ad5dl520EIB- adenovirus and its E1A deletion mutants.
- Assay for apoptosis by measuring nucleosomal DNA fragmentation.
- Analysis of E1A protein binding to cellular proteins p300 and pRb.
- Assessment of cellular DNA synthesis in response to E1A mutants.
Main Results:
- Ad5dl520EIB- infection induced apoptosis in NRK cells, particularly when cells were growth-inhibited (confluent or serum-starved).
- Apoptosis was not observed in actively growing cells.
- Specific regions within exon 1 of the E1A protein, crucial for binding p300 and pRb, were essential for inducing apoptosis.
- Mutants defective in apoptosis induction were also defective in stimulating cellular DNA synthesis.
Conclusions:
- Adenovirus E1A protein can induce apoptosis in NRK cells under conditions of growth inhibition.
- The proliferative block opposing E1A-induced proliferation may directly lead to apoptosis.
- The interaction of E1A with p300 and pRb is critical for its apoptotic function, similar to mechanisms involving c-myc.
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