Investigation of the Anti-apoptotic Function and Regulation of Vaccinia Virus F1L

• Author / Creator

  Campbell, Stephanie D

• Apoptosis, an evolutionarily conserved cell death programme, is a potent barrier against virus infection. Central to this process are mitochondria, which harbour cytochrome c and other apoptosis-inducing factors. Once released, these factors activate a caspase cascade that culminates in cell death. Mitochondrial integrity is tightly regulated by the Bcl-2 family of proteins, which are united by the presence of one or more conserved Bcl-2 homology, or BH, domains that are critical for protein interactions and function. Bak and Bax are the key pro-apoptotic members that engage the mitochondrial death machinery to release cytochrome c. These proteins are activated by pro-apoptotic BH3-only proteins and inhibited by anti-apoptotic family members, such as Mcl-1. Due to the importance of Bak and Bax, many viruses, including poxviruses, have adapted strategies to interfere with the activation of these two proteins. In the prototypic poxvirus vaccinia virus, this is accomplished by a unique anti-apoptotic protein, F1L. F1L localizes to mitochondria and prevents apoptosis induced by a variety of stimuli. This is achieved by direct binding to Bak, while Bax inhibition is believed to occur by the binding of F1L to the BH3-only protein, BimL. However, the way in which F1L binds Bak and BimL is unknown, since F1L lacks sequence homology to Bcl-2 proteins. Here, we show that F1L functions in a manner that resembles Mcl-1, the major cellular regulator of Bak. Moreover, we have identified divergent BH domains within F1L that are critical for Bak binding and anti-apoptotic activity. Given the importance of the Bcl-2 family of proteins, many members are regulated by ubiquitination, which targets the proteins for proteasomal degradation. Similarly, we have discovered that F1L is tightly regulated by the ubiquitin-proteasome system. Our studies on F1L ubiquitination have also revealed a potential role for F1L in the regulation of mitochondrial morphology. Thus, despite divergence at the sequence level, F1L interacts with Bak in a manner nearly identical to cellular Bcl-2 family members, and, additionally, F1L is governed by the same regulatory mechanisms that control members of the Bcl-2 family.

• Subjects / Keywords

  • Poxvirus
  • Apoptosis

• Graduation date

  Spring 2012

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3NW3V

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.