The regulatory role of cyclin-dependent protein kinases in human cytomegalovirus replication

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Replication of human cytomegalovirus (HCMV) is characterized by a tight virus-host cell interaction, as in particular cyclin-dependent protein kinases (CDKs) are functionally integrated into efficient viral gene expression and protein modification. CDK1, -2, -7 and -9 were identified as main HCMV-regulating kinases, albeit the underlying regulatory mechanisms are still under investigation. We and others reported that pharmacological inhibition of CDK activity induces intranuclear aggregation of the viral regulatory protein pUL69. Interaction analyses showed protein association between pUL69 and CDK/cyclin complexes. Importantly, we demonstrated that CDKs as well as the viral protein kinase pUL97, recently described as a viral CDK ortholog, possess the ability to specifically phosphorylate this viral protein. The functional significance of pUL69 phoshorylation was indicated by the finding that CDK inhibitors reduced its known mRNA export activity. This is the first example defining a specific contact point of the interregulation between CDKs and HCMV replication. The present project will concentrate on the question which functional consequences arise from the CDK inhibitor-induced intranuclear aggregate formation and whether there are further aspects of CDK-HCMV interregulation connected with this finding. In this context, it is suggestive that more viral proteins are involved in the viral CDK interaction, as concluded from preliminary results. Specific experiments will address the compository and functional analysis of heteromeric protein complexes which are associated with CDK inhibitor-induced aggregates. Moreover, mutant viral proteins will be generated to address the question of altered phosphorylation characteristics and the impact of CDK-specific phosphorylation on the activities of these viral proteins. The study will provide a detailed description of the molecular events which recruit CDK activities as an internal pathway of HCMV replication.