This Article Full Text Full Text (PDF) Other Versions of this Article: JVI.00247-07v1 81/17/9319    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Lannan, E. Articles by Friesen, P. D. Search for Related Content PubMed PubMed Citation Articles by Lannan, E. Articles by Friesen, P. D.

 Previous Article  |  Next Article 

Journal of Virology, September 2007, p. 9319-9330, Vol. 81, No. 17
0022-538X/07/$08.00+0     doi:10.1128/JVI.00247-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Baculovirus Caspase Inhibitors P49 and P35 Block Virus-Induced Apoptosis Downstream of Effector Caspase DrICE Activation in Drosophila melanogaster Cells

Institute for Molecular Virology, Department of Biochemistry,² Microbiology Doctoral Training Program, Graduate School and College of Agricultural and Life Sciences, University of Wisconsin—Madison, Madison, Wisconsin 53706¹

Received 5 February 2007/ Accepted 11 June 2007

Baculoviruses induce widespread apoptosis in invertebrates. To better understand the pathways by which these DNA viruses trigger apoptosis, we have used a combination of RNA silencing and overexpression of viral and host apoptotic regulators to identify cell death components in the model system of Drosophila melanogaster. Here we report that the principal effector caspase DrICE is required for baculovirus-induced apoptosis of Drosophila DL-1 cells as demonstrated by RNA silencing. proDrICE was proteolytically cleaved and activated during infection. Activation was blocked by overexpression of the cellular inhibitor-of-apoptosis proteins DIAP1 and SfIAP but not by the baculovirus caspase inhibitor P49 or P35. Rather, the substrate inhibitors P49 and P35 prevented virus-induced apoptosis by arresting active DrICE through formation of stable inhibitory complexes. Consistent with a two-step activation mechanism, proDrICE was cleaved at the large/small subunit junction TETD²³⁰-G by a DIAP1-inhibitable, P49/P35-resistant protease and then at the prodomain junction DHTD²⁸-A by a P49/P35-sensitive protease. Confirming that P49 targeted DrICE and not the initiator caspase DRONC, depletion of DrICE by RNA silencing suppressed virus-induced cleavage of P49. Collectively, our findings indicate that whereas DIAP1 functions upstream to block DrICE activation, P49 and P35 act downstream by inhibiting active DrICE. Given that P49 has the potential to inhibit both upstream initiator caspases and downstream effector caspases, we conclude that P49 is a broad-spectrum caspase inhibitor that likely provides a selective advantage to baculoviruses in different cellular backgrounds.

Published ahead of print on 20 June 2007.

This article has been cited by other articles:

• Liu, J., Enomoto, S., Lancto, C. A., Abrahamsen, M. S., Rutherford, M. S. (2008). Inhibition of Apoptosis in Cryptosporidium parvum-Infected Intestinal Epithelial Cells Is Dependent on Survivin. Infect. Immun. 76: 3784-3792 [Abstract] [Full Text]  
• Guy, M. P., Friesen, P. D. (2008). Reactive-Site Cleavage Residues Confer Target Specificity to Baculovirus P49, a Dimeric Member of the P35 Family of Caspase Inhibitors. J. Virol. 82: 7504-7514 [Abstract] [Full Text]  
• Settles, E. W., Friesen, P. D. (2008). Flock House Virus Induces Apoptosis by Depletion of Drosophila Inhibitor-of-Apoptosis Protein DIAP1. J. Virol. 82: 1378-1388 [Abstract] [Full Text]