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Mechanism and Consequences of the Interplay between Mitosis and Human Papillomavirus Initial Infection

Periodic Reporting for period 4 - MitoVin (Mechanism and Consequences of the Interplay between Mitosis and Human Papillomavirus Initial Infection)

Reporting period: 2021-04-01 to 2022-09-30

Several important virus families can only establish an infection, if they invade dividing cells. They require cell division in order to deliver their genome in a replication competent form into the nuclei of cells, as during cell division the nuclear envelope, a protective border to the cytosol, is removed during cell division giving these viruses access to the nuclear lumen. In this project, we have followed up two main questions: On the one hand how do small DNA tumor viruses of the papillomavirus family, i.e. viruses that lead to malignant cancers, mechanistically use host cell division to enter host cells, a mechanism of viral invasion that is barely understood. On the other hand, we used such papilloma viruses as a model virus to address how intrinsic and extrinsic changes to cellular context (such as (chronic) inflammation, wounding, prior infection, and ageing) affect this process and thus the outcome of infection. The latter has been documented but why these processes affect virus infection is not understood.

Since infections of human papillomaviruses pose a severe health risk through the development of anogenital and oropharyngeal cancers, our work may allow the development of better preventative and possibly personalised treatment options.

The overall objectives aim at understanding of these human papillomaviruses infect cells under a variety of conditions, but also to experimentally establish systems that allow to study how viruses in general are impacted by physiological and pathophysiological changes that arise during our life time. The latter implies that besides our genetic background, the way our lives have been influences our susceptibility to viral infections, a feature that has been observed in epidemiological studies, but that remains mostly inaccessible to experimentation. But as long as we cannot understand the underlying cause for different susceptibility, we may not be able to protect ourselves from infections depending on our personal history.
Investigations into how papillomaviruses exploit host cell division to gain access to the nuclear space for infection have identified cellular targets that are hijacked for this purpose. We have established a principal four step mechanism for this, which involves an activation step through master mitotic kinases that set the cue, a transport step involving a previously unknown cellular complex, a tethering step to mitotic chromatin, and a deactivation step, once cell division occurred. Moreover, we have identified on the viral side a peptide in a crucial viral protein that mediates these interactions, Besides a more thorough understanding of viral infection, we found that the presence of the viral peptide concentration-dependently allows to stall mitosis and eventually induce cell death, so that this may provide an avenue for anti.cancer treatments. Finally, we have delineated how epithelial tissue wounding determines tropism and efficacy of infection for specific cells within the tissue on a molecular level.
The most surprising finding of our research has probably been that by learning about a mechanism, we observed that the interactions of a viral protein with cellular proteins to achieve nuclear delivery can lead to misrouting of the cellular proteins. Changing the location of the cellular proteins, in turn, apparently changes the physiological function with dire consequences for cell division and subsequent cell fate. This effect depends solely on the concentration of viral protein. In low concentrations, no profound consequences are observable, at medium concentrations cell division is perturbed and may react by abnormal cell division with malignant changes, while at high concentrations the cells undergo cell death. If the latter could be induced, it may provide a new strategy to target cancer cells themselves to induce cell death. Thus, a virus that can lead to cancer induction may also be used to treat cancer itself.
Papillomavirus DNA dynamics (green) in relation to cellular chromatin (red) during cytokinesis