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Antagonistic Relationship between Human Cytomegalovirus pUL27 and pUL97 Activities during Infection.

ABSTRACT:

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Human cytomegalovirus (HCMV) is a member of the betaherpesvirus family. During infection, an array of viral proteins manipulates the host cell cycle. We have previously shown that expression of HCMV pUL27 results in increased levels of the cyclin-dependent kinase (CDK) inhibitor p21(Cip1). In addition, pUL27 is necessary for the full antiviral activity of the pUL97 kinase inhibitor maribavir (MBV). The purpose of this study was to define the relationship between pUL27 and pUL97 and its role in MBV antiviral activity. We observed that expression of wild-type but not kinase-inactive pUL97 disrupted pUL27-dependent induction of p21(Cip1). Furthermore, pUL97 associated with and promoted the phosphorylation of pUL27. During infection, inhibition of the kinase resulted in elevated levels of p21(Cip1) in wild-type virus but not a pUL27-deficient virus. We manipulated the p21(Cip1) levels to evaluate the functional consequence to MBV. Overexpression of p21(Cip1) restored MBV activity against a pUL27-deficient virus, while disruption reduced activity against wild-type virus. We provide evidence that the functional target of p21(Cip1) in the context of MBV activity is CDK1. One CDK-like activity of pUL97 is to phosphorylate nuclear lamin A/C, resulting in altered nuclear morphology and increased viral egress. In the presence of MBV, we observed that infection using a pUL27-deficient virus still altered the nuclear morphology. This was prevented by the addition of a CDK inhibitor. Overall, our results demonstrate an antagonistic relationship between pUL27 and pUL97 activities centering on p21(Cip1) and support the idea that CDKs can complement some activities of pUL97.

Importance

HCMV infection results in severe disease upon immunosuppression and is a leading cause of congenital birth defects. Effective antiviral compounds exist, yet they exhibit high levels of toxicity, are not approved for use during pregnancy, and can result in antiviral resistance. Our studies have uncovered new information regarding the antiviral efficacy of the HCMV pUL97 kinase inhibitor MBV as it relates to the complex interplay between pUL97 and a second HCMV protein, pUL27. We demonstrate that pUL97 functions antagonistically against pUL27 by phosphorylation-dependent inactivation of pUL27-mediated induction of p21(Cip1). In contrast, we provide evidence that p21(Cip1) functions to antagonize overlapping activities between pUL97 and cellular CDKs. In addition, these studies further support the notion that CDK inhibitors or p21(Cip1) activators might be useful in combination with MBV to effectively inhibit HCMV infections.

SUBMITTER: Bigley TM

PROVIDER: S-EPMC4580190 | biostudies-literature | 2015 Oct

REPOSITORIES: biostudies-literature

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Publications

Antagonistic Relationship between Human Cytomegalovirus pUL27 and pUL97 Activities during Infection.

Bigley Tarin M TM Reitsma Justin M JM Terhune Scott S SS

Journal of virology 20150729 20

<h4>Unlabelled</h4>Human cytomegalovirus (HCMV) is a member of the betaherpesvirus family. During infection, an array of viral proteins manipulates the host cell cycle. We have previously shown that expression of HCMV pUL27 results in increased levels of the cyclin-dependent kinase (CDK) inhibitor p21(Cip1). In addition, pUL27 is necessary for the full antiviral activity of the pUL97 kinase inhibitor maribavir (MBV). The purpose of this study was to define the relationship between pUL27 and pUL9 ...[more]

PMID: 26223645

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Project description:UNLABELLED:The mechanisms by which viruses persist and particularly those by which viruses actively contribute to their own latency have been elusive. Here we report the existence of opposing functions encoded by genes within a polycistronic locus of the human cytomegalovirus (HCMV) genome that regulate cell type-dependent viral fates: replication and latency. The locus, referred to as the UL133-UL138 (UL133/8) locus, encodes four proteins, pUL133, pUL135, pUL136, and pUL138. As part of the ULb' region of the genome, the UL133/8 locus is lost upon serial passage of clinical strains of HCMV in cultured fibroblasts and is therefore considered dispensable for replication in this context. Strikingly, we could not reconstitute infection in permissive fibroblasts from bacterial artificial chromosome clones of the HCMV genome where UL135 alone was disrupted. The loss of UL135 resulted in complex phenotypes and could ultimately be overcome by infection at high multiplicities. The requirement for UL135 but not the entire locus led us to hypothesize that another gene in this locus suppressed virus replication in the absence of UL135. The defect associated with the loss of UL135 was largely rescued by the additional disruption of the UL138 latency determinant, indicating a requirement for UL135 for virus replication when UL138 is expressed. In the CD34(+) hematopoietic progenitor model of latency, viruses lacking only UL135 were defective for viral genome amplification and reactivation. Taken together, these data indicate that UL135 and UL138 comprise a molecular switch whereby UL135 is required to overcome UL138-mediated suppression of virus replication to balance states of latency and reactivation. IMPORTANCE:Mechanisms by which viruses persist in their host remain one of the most poorly understood phenomena in virology. Herpesviruses, including HCMV, persist in an incurable, latent state that has profound implications for immunocompromised individuals, including transplant patients. Further, the latent coexistence of HCMV may increase the risk of age-related pathologies, including vascular disease. The key to controlling or eradicating HCMV lies in understanding the molecular basis for latency. In this work, we describe the complex interplay between two viral proteins, pUL135 and pUL138, which antagonize one another in infection to promote viral replication or latency, respectively. We previously described the role of pUL138 in suppressing virus replication for latency. Here we demonstrate a role of pUL135 in overcoming pUL138-mediated suppression for viral reactivation. From this work, we propose that pUL135 and pUL138 constitute a molecular switch balancing states of latency and reactivation.

Dataset Information

Antagonistic Relationship between Human Cytomegalovirus pUL27 and pUL97 Activities during Infection.

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Importance

Publications

Antagonistic Relationship between Human Cytomegalovirus pUL27 and pUL97 Activities during Infection.

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