Weisbach H, Schablowsky C, Vetter B, Gruska I, Hagemeier C, Wiebusch L. Synthetic lethal mutations in the cyclin A interface of human cytomegalovirus.
PLoS Pathog 2017;
13:e1006193. [PMID:
28129404 DOI:
10.1371/journal.ppat.1006193]
[Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2016] [Revised: 02/08/2017] [Accepted: 01/19/2017] [Indexed: 11/29/2022] Open
Abstract
Generally, the antagonism between host restriction factors and viral countermeasures decides on cellular permissiveness or resistance to virus infection. Human cytomegalovirus (HCMV) has evolved an additional level of self-imposed restriction by the viral tegument protein pp150. Depending on a cyclin A-binding motif, pp150 prevents the onset of viral gene expression in the S/G2 cell cycle phase of otherwise fully permissive cells. Here we address the physiological relevance of this restriction during productive HCMV infection by employing a cyclin A-binding deficient pp150 mutant virus. One consequence of unrestricted viral gene expression in S/G2 was the induction of a G2/M arrest. G2-arrested but not mitotic cells supported viral replication. Cyclin A destabilization by the viral gene product pUL21a was required to maintain the virus-permissive G2-arrest. An HCMV double-point mutant where both pp150 and pUL21a are disabled in cyclin A interaction forced mitotic entry of the majority of infected cells, with a severe negative impact on cell viability and virus growth. Thus, pp150 and pUL21a functionally cooperate, together building a cell cycle synchronization strategy of cyclin A targeting and avoidance that is essential for productive HCMV infection.
Efficient virus replication depends on continuous, uninterrupted supply with metabolites and replication factors from the host cell. This is difficult to achieve in actively dividing cells, especially for a slowly replicating virus like HCMV, a widespread pathogen of major medical importance in immunocompromised patients. To ensure that viral replication is not disturbed by cell division, HCMV has developed a twofold strategy of cyclin A targeting and avoidance. First, HCMV employs the viral cyclin A substrate pp150 to synchronize the onset of replication with G1, a cell cycle phase of low cyclin A expression. Then, HCMV expresses the cyclin A destabilizing factor pUL21a to maintain the G1 cell cycle state until the successful release of virus progeny. While this strategy is based on two viral proteins, a cyclin A sensor and effector, it relies on one and the same type of cyclin A interaction motif, making HCMV vulnerable to binding site disruption.
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