Molecular Determinants for the Inactivation of the Retinoblastoma Tumor Suppressor by the Viral Cyclin-dependent Kinase UL97

Iwahori, Satoko; Hakki, Morgan; Chou, Sunwen; Kalejta, Robert F.

doi:10.1074/jbc.m115.660043

Cited by 28 publications

(58 citation statements)

References 90 publications

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“…Interestingly, CDKs are also functionally integrated into the replication of herpesviruses. Notably, the HCMV-encoded protein kinase pUL97 shares important structural and functional features with CDKs, such as structural similarities in the N-and C-terminal lobe of the kinase domain, interaction with cyclins, phosphorylation of identical substrates, and functional complementation in heterologous systems (Chou et al, 2006;Romaker et al, 2006;Chou, 2008;Hume et al, 2008;Hamirally et al, 2009;Kamil et al, 2009;Thomas et al, 2009;Kuny et al, 2010;Graf et al, 2013;Iwahori et al, 2015;Oberstein et al, 2015;Steingruber et al, 2015). A combined regulatory impact of CDK and pUL97 activity on the viral mRNA export factor pUL69 was demonstrated Thomas et al, 2009;Feichtinger et al, 2011;Oberstein et al, 2015) and, very recently, additional posttranslational modification by methylation proved to be similarly important (Thomas et al, 2015).…”

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confidence: 99%

New insight into the phosphorylation-regulated intranuclear localization of human cytomegalovirus pUL69 mediated by cyclin-dependent kinases (CDKs) and viral CDK orthologue pUL97

Graf

Feichtinger

Naing

et al. 2016

Journal of General Virology

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Cyclin-dependent kinases (CDKs) are multifaceted regulators involved in the replication of human cytomegalovirus. Recently, we demonstrated an interaction of CDK9-cyclin T1 as well as viral CDK orthologue pUL97 with the viral regulator pUL69, thereby leading to pUL69-activating phosphorylation. Here, we demonstrate that colocalization and direct pUL69-cyclin T1 interaction is independent of viral strains and host cell types. In vitro phosphorylation of pUL69 by CDK9 or pUL97 did not occur in a single site-specific manner, but at multiple sites. The previously described fine-speckled nuclear aggregation of pUL69 was assigned to the late phase of viral replication. CDK inhibitors, including a novel inhibitor of the CDK-activating kinase CDK7, massively intensified this fine-speckled accumulation. Interestingly, we also observed spontaneous pUL69 accumulation in the absence of inhibitors at a lower frequency. These findings provide new insight into pUL69 kinase interregulation and emphasize the importance of pUL69 phosphorylation for correct intranuclear localization.

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confidence: 99%

New insight into the phosphorylation-regulated intranuclear localization of human cytomegalovirus pUL69 mediated by cyclin-dependent kinases (CDKs) and viral CDK orthologue pUL97

Graf

Feichtinger

Naing

et al. 2016

Journal of General Virology

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“…UL97 is a v-Cdk that phosphorylates and inactivates Rb (55,59,60). UL97 also phosphorylates lamin proteins to induce partial lamina breakdown at the inner nuclear envelope (61) that theoretically promotes nuclear capsid egress and thus efficient HCMV productive replication.…”

Section: Resultsmentioning

confidence: 99%

“…Rb accumulates in phosphorylated forms during HCMV infection (31,55,60). Classically, phosphorylated Rb is considered inactive (73); thus, it was surprising that HCMV replication was inefficient in the absence of a posttranslationally modified form of a protein already considered to be devoid of activity.…”

Section: Discussionmentioning

confidence: 99%

Deficiencies in Cellular Processes Modulated by the Retinoblastoma Protein Do Not Account for Reduced Human Cytomegalovirus Replication in Its Absence

VanDeusen

Kalejta

2015

J Virol

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Despite encoding multiple viral proteins that modulate the retinoblastoma (Rb) protein in a manner classically defined as inactivation, human cytomegalovirus (HCMV) requires the presence of the Rb protein to replicate efficiently. In uninfected cells, Rb controls numerous pathways that the virus also commandeers during infection. These include cell cycle progression, senescence, mitochondrial biogenesis, apoptosis, and glutaminolysis. We investigated whether a potential inability of HCMV to regulate these Rb-controlled pathways in the absence of the Rb protein was the reason for reduced viral productive replication in Rb knockdown cells. We found that HCMV was equally able to modulate these pathways in the parental Rb-expressing and Rb-depleted cells. Our results suggest that Rb may be required to enhance a specific viral process during HCMV productive replication. R etinoblastoma (Rb) protein function is modified by multiple viruses (1-3). Through transcriptional repression of the E2F-responsive genes required for DNA replication, hypophosphorylated (active) Rb impedes cell cycle transit through G 1 and into S phase (4). Rb can also induce the formation of heterochromatin at E2F responsive genes, leading to permanent transcriptional silencing and replicative senescence (5, 6), providing a tumor suppressive function. As the role of Rb as a mediator of senescence and restrictor of cell cycle progression has long been acknowledged, the prevailing model in the field of DNA virology has associated viral targeting of Rb with maintaining a cell cycle state conducive to viral replication (7). Specifically, it was proposed that viruses alter the function of Rb to provide an S-phase-like environment where the enzymes and small molecule precursors necessary for DNA synthesis would be readily available for viral DNA replication. Indeed, the ability of the E7 protein of the high-risk human papillomavirus strain 16 to bind Rb is necessary for viral DNA replication (8).However, we recently reported that transient and stable Rb knockdown reduces the efficiency of human cytomegalovirus (HCMV) DNA synthesis and productive replication (9). This result was unexpected as HCMV encodes at least four viral proteins reported to modify several biological functions of Rb (2). Therefore, the relationship between viruses and Rb appears more complicated than the current paradigm allows.In recent years Rb has been shown to affect many facets of mitochondrial function in addition to its critical role in controlling the cell cycle. These include mitochondrial biogenesis, apoptosis, and the utilization of glutamine for the tricarboxylic acid (TCA) cycle and the production of glutathione. In the absence of Rb, cells have lower ratios of mitochondrial to cellular DNA, and this has been ascribed to defects in mitochondrial biogenesis (10,11). Rb regulates apoptosis directly at the mitochondria by binding to Bax (12,13). Interestingly, it is a phosphorylated form of Rb that interacts with Bax, and loss of this form can trigger apoptosis (12...

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“…Rb proteins form transcriptionally repressive complexes that arrest cell cycle progression. Phosphorylation on specific serine and threonine residues followed by a proline, the consensus motif targeted by cellular CDKs and UL97, disrupts these complexes, and thereby inactivates the Rb proteins (Iwahori et al, 2015; Rubin, 2013). Rb proteins can also be inactivated without phosphorylation when bound by virally encoded oncoproteins such as Adenovirus E1A, SV40 T antigen, and Papillomavirus E7 (Felsani et al, 2006; Helt and Galloway, 2003; Lee and Cho, 2002).…”

Section: Introductionmentioning

confidence: 99%

“…UL97 utilizes an LXCXE motif (termed L1) to target the Rb family members for phosphorylation and inactivation, disrupting Rb-E2F1, Rb-E2F2, Rb-E2F3a, and Rb-E2F3b complexes (Iwahori et al, 2015; Iwahori et al, 2017). Interestingly, while UL97 inactivates both p130 and p107 through phosphorylation, it does not disrupt their complexes with E2F4 (Iwahori et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

Phosphorylation of transcriptional regulators in the retinoblastoma protein pathway by UL97, the viral cyclin-dependent kinase encoded by human cytomegalovirus

Iwahori

Kalejta

2017

Virology

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Human cytomegalovirus (HCMV) encodes a viral cyclin-dependent kinase (v-CDK), the UL97 protein. UL97 phosphorylates Rb, p107 and p130, thereby inactivating all three retinoblastoma (Rb) family members. Rb proteins function through regulating the activity of transcription factors to which they bind. Therefore, we examined whether the UL97-mediated regulation of the Rb tumor suppressors also extended to their binding partners. We observed that UL97 phosphorylates LIN52, a component of p107- and p130-assembled transcriptionally repressive DREAM complexes that control transcription during the G0/G1 phases, and the Rb-associated E2F3 protein that activates transcription through G1 and S phases. Intriguingly, we also identified FoxM1B, a transcriptional regulator during the S and G2 phases, as a UL97 substrate. This survey extends the influence of UL97 beyond simply the Rb proteins themselves to their binding partners, as well as past the G1/S transition into later stages of the cell cycle.

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Molecular Determinants for the Inactivation of the Retinoblastoma Tumor Suppressor by the Viral Cyclin-dependent Kinase UL97

Cited by 28 publications

References 90 publications

New insight into the phosphorylation-regulated intranuclear localization of human cytomegalovirus pUL69 mediated by cyclin-dependent kinases (CDKs) and viral CDK orthologue pUL97

New insight into the phosphorylation-regulated intranuclear localization of human cytomegalovirus pUL69 mediated by cyclin-dependent kinases (CDKs) and viral CDK orthologue pUL97

Deficiencies in Cellular Processes Modulated by the Retinoblastoma Protein Do Not Account for Reduced Human Cytomegalovirus Replication in Its Absence

Phosphorylation of transcriptional regulators in the retinoblastoma protein pathway by UL97, the viral cyclin-dependent kinase encoded by human cytomegalovirus

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