Conserved mode of nuclear lamina distortion by primate cytomegaloviruses: importance of the pSer22 motif, viral kinase and cis/trans isomerase Pin1 activity

Human cytomegalovirus (HCMV) is a ubiquitous human pathogen of high clinical relevance. In terms of pathogenic determination, the regulatory factors of HCMV-host interaction play a crucial role, and recently we reported on virus-supportive functions of the cellular peptidyl-prolyl <i>cis</i>/<i>trans</i> isomerase Pin1. Notably, Pin1 is able to recognize phosphorylated serine/threonine-proline motifs and regulate the structural conformation, stability and function of its substrate proteins. During HCMV replication, Pin1 facilitates viral nuclear egress by inducing site-specific rearrangements of the nuclear lamina through the <i>cis</i>/<i>trans</i> conversion of lamin type A/C. To this end, we developed readout systems to decipher details of HCMV-Pin1 regulatory interaction. Notably, together with primary human foreskin fibroblasts (HFFs) and recombinant lamin-modified cell populations, the molecular mechanisms of Pin1 interaction with both the nuclear lamina and viral proteins were illustrated. Our new results demonstrate the following: (i) currently available Pin1-inhibitory small molecules, similar to the antiviral drug maribavir (MBV), exert an antiviral activity against human and non-human primate cytomegaloviruses (CMVs); (ii) site-specific phosphorylation at serine 22, a Pin1 recognition motif within lamin A/C, is consistently mediated by the pUL97 kinase homologs of these viruses; (iii) the phosphorylation of serine 22 is sensitive to the virus-specific kinase inhibitor MBV; (iv) a doxycycline-inducible expression of autofluorescent lamin A/C-red fluorescent protein (RFP) fusion constructs in HFFs supports the productive HCMV replication; (v) these lamin A/C-RFP reporter cells indicated a virus-induced formation of lamina-depleted areas (LDAs), dependent on serine 22 but independent of the infecting CMV species; and (vi) treatment of CMV-infected cells with kinase or Pin1 inhibitors exerted distinct effects on the magnitude of LDA formation. Combined, the study is consistent with our concept that the mode of nuclear egress shows parallels between human and non-human primate CMVs. Thus, the role of Pin1 may play an important regulatory role in determining virus infection and replication efficiency.