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Updated: Sep 29, 2026
Identifying Caspases and their Motifs that Cleave Proteins During Influenza A Virus Infection
Published on: July 21, 2022
Caspase-mediated cleavage of adenovirus early region 1A proteins
Roger J A Grand1, Katja Schmeiser, Emma M Gordon
1Cancer Research U.K. Institute for Cancer Studies, University of Birmingham, Edgbaston, Birmingham, B15 2TT, United Kingdom. R.J.A.Grand@bham.ac.uk
Abstract:
Adenovirus 2 and 12 early region 1A (Ad2 and Ad12 E1A) proteins were cleaved during cisplatin-induced apoptosis of Ad-transformed rat and human cells. Cleavage was inhibited in the presence of caspase inhibitors such as Z-VAD-FMK. In Ad12 transformants both 13S and 12S E1A proteins were cleaved at a similar rate. In Ad2 transformants the E1A 13S component was appreciably less stable than the 12S component. In in vitro studies Ad2 and Ad12 E1A 13S and Ad2 12S proteins were rapidly cleaved by caspase 3 whereas Ad12 12S E1A and Ad12 13S E1A were rapidly degraded by caspase 7. Cleavage sites in Ad12 13S proteins for caspase 3 have been determined. Initial cleavage occurred at D24 and D150; this was followed by cleavage at D204 and D242. Caspase-3-mediated cleavage of Ad12 13S E1A destroyed its ability to bind to CBP and TBP but interaction between C terminal E1A polypeptides and CtBP was observed. During viral infection Ad5 and Ad12 E1A 12S proteins were markedly more stable than 13S proteins but no difference was observed in Ad E1A levels in the absence or presence of the caspase inhibitors Z-VAD-FMK or Z-D(OMe)-E(OMe)-V-D(OMe)-CH(2)F. Limited caspase 3 and 10 activation occurred during infection with the E1B 19K(-) virus Ad2 pm1722 but little or no activation of caspase 3 was observed during wt virus infection. Examination of protein cleavage during viral infection of A549 cells showed proteolysis of lamin B and PARP in response to Ad5 wt and Ad2 pm1722. Protein degradation in response to both viruses was partially inhibited by Z-VAD-FMK. Following infection of human skin fibroblasts lamin B was degraded, although only limited changes in PARP levels were observed. We have concluded that Ad E1A is cleaved by caspases during apoptosis but not during viral infection. However, some of the processes commonly associated with apoptosis occur during viral infection, particularly with E1B 19K(-) mutants, although apoptosis per se is not evident.
Insights
Adenovirus E1A proteins are cleaved by caspases during apoptosis, but not during viral infection. This cleavage impacts protein interactions and cellular processes, even when full apoptosis is not evident.
Area of Science:
- Molecular Biology
- Virology
- Cellular Biology
Background:
- Adenovirus early region 1A (E1A) proteins play crucial roles in viral replication and cellular transformation.
- Caspases are key executioner proteins in apoptosis, a programmed cell death pathway.
- Understanding the interplay between viral proteins and host cell apoptosis machinery is vital for comprehending viral pathogenesis.
Purpose of the Study:
- To investigate the cleavage of Adenovirus 2 and 12 E1A proteins during cisplatin-induced apoptosis.
- To determine whether E1A proteins are cleaved during adenovirus infection.
- To elucidate the role of caspases in E1A protein degradation and its functional consequences.
Main Methods:
- Treatment of adenovirus-transformed cells with cisplatin to induce apoptosis.
- Use of caspase inhibitors (e.g., Z-VAD-FMK) to assess caspase involvement.
- In vitro cleavage assays using purified caspases (caspase 3 and 7).
- Analysis of E1A protein cleavage sites and their impact on protein-protein interactions (CBP, TBP, CtBP).
- Infection of human cells with wild-type and mutant adenoviruses, followed by analysis of protein degradation (lamin B, PARP).
Main Results:
- Adenovirus 2 and 12 E1A proteins were cleaved by caspases during cisplatin-induced apoptosis.
- Cleavage was inhibited by caspase inhibitors.
- Specific cleavage sites in Ad12 13S E1A by caspase 3 were identified (D24, D150, D204, D242).
- Caspase-3-mediated cleavage disrupted E1A binding to CBP and TBP.
- During viral infection, E1A proteins were more stable, and significant caspase activation was limited, except in E1B 19K(-) mutant infections.
- Proteolysis of lamin B and PARP occurred during viral infection, partially inhibited by Z-VAD-FMK.
Conclusions:
- Adenovirus E1A proteins are substrates for caspases during apoptosis.
- E1A cleavage by caspases during apoptosis affects its interaction with host factors.
- Adenovirus E1A proteins are generally resistant to caspase-mediated cleavage during productive viral infection.
- Apoptosis-associated protein degradation can occur during viral infection, particularly with E1B 19K-deficient mutants, independent of overt apoptosis.
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