| Mitochondria are dynamic organelles, and the opposing processes of fusion and fission that mediate mitochondrial morphology have been linked to both the metabolic state and health of the cell. Programmed cell death, or apoptosis, is regulated at the mitochondria by the Bcl-2 family of proteins, which consists of both pro- and anti-apoptotic members. Apoptosis is an important host defense mechanism against viruses that can be subverted by viral gene products. Human cytomegalovirus encodes "viral mitochondria-localized inhibitor of apoptosis" (vMIA; pUL37x1), which targets to mitochondria where it functions as a potent cell death suppressor. The mechanism by which vMIA functions to block cytochrome c release from the mitochondria has not been fully elucidated. I show that Bax and Bak play a role in regulating mitochondrial fusion in healthy cells. Also, since vMIA is able to interact with and inhibit the pro-apoptotic function of both these proteins, I propose that vMIA may fragment mitochondria through inhibition of Bax and Bak maintenance of mitochondrial morphology in addition to blocking their pro-apoptotic activity.;Bax and Bak have been proposed to regulate mitochondrial fusion through the large GTPase Mfn2, a key mitochondrial fusion protein. My results show that vMIA is also able to interact with Mfn2, and this interaction is independent of both Bax and Bak, which may bind both mitofusins and vMIA. Surprisingly, I demonstrate that vMIA fails to inhibit apoptosis in cells lacking Mfn2. The lack of protection by vMIA in cells lacking Mfn2 suggests that neutralization of Bax and Bak activity by vMIA may occur through the formation of a functional complex with Mfn2, providing new insights into the mechanism of apoptosis inhibition by vMIA. These results also indicate an essential role of Mfn2 in mediating apoptosis inhibition by vMIA, further connecting mitochondrial morphology machinery and apoptosis regulation. |
