Abstract
The human adenovirus type 5 (HAdV5) infects epithelial cells of the upper and lower respiratory tract. The virus causes lysis of infected cells and thus enables spread of progeny virions to neighboring cells for the next round of infection. The mechanism of adenovirus virion egress across the nuclear barrier is not known. The human adenovirus death protein (ADP) facilitates the release of virions from infected cells and has been hypothesized to cause membrane damage. Here, we set out to answer whether ADP does indeed increase nuclear membrane damage. We analyzed the nuclear envelope morphology using a combination of fluorescence and state-of-the-art electron microscopy techniques, including serial block-face scanning electron microscopy and electron cryo-tomography of focused ion beam-milled cells. We report multiple destabilization phenotypes of the nuclear envelope in HAdV5 infection. These include reduction of lamin A/C at the nuclear envelope, large-scale membrane invaginations, alterations in double membrane separation distance and small-scale membrane protrusions. Additionally, we measured increased nuclear membrane permeability and detected nuclear envelope lesions under cryoconditions. Unexpectedly, and in contrast to previous hypotheses, ADP did not have an effect on lamin A/C reduction or nuclear permeability.
Highlights
Human adenovirus type 5 (HAdV5) belongs to the species C of mastadenoviruses and is a nonenveloped double-stranded DNA virus
We have shown that our adenovirus death protein (ADP)+ virus strain displayed those characteristics when comparing its virus titer growth curve to the ADP− strain (Figure 1b)
This hypothesis was derived from the fact that after addition of the inhibitor nelfinavir, which blocks ADP function, the protein still localized to the nuclear envelope but not cytoplasmic vesicles
Summary
Human adenovirus type 5 (HAdV5) belongs to the species C of mastadenoviruses and is a nonenveloped double-stranded DNA virus. No exact mechanism has described how the mature adenovirus particles are released from infected cells. There are two processes present, the first to allow mature virions to cross the nuclear envelope and the second to exit the cell across the plasma membrane, both of which are possibly interlinked. Multiple cell-death pathways have been suggested to be the cause of ultimate host cell lysis. The process was initially described as apoptosis, a lack of membrane blebbing and DNA fragmentation hinted against apoptosis and another necroptosis-like cell death was suggested [1,2,3]. In HAdV infection, nuclear membrane damage has been proposed to be induced by the adenovirus death protein (ADP) preceding total cell lysis [1,9]
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