A Novel Human Cytomegalovirus Locus Modulates Cell Type-Specific Outcomes of Infection

Abstract

Clinical strains of HCMV encode 20 putative ORFs within a region of the genome termed ULb′ that are postulated to encode functions related to persistence or immune evasion. We have previously identified ULb′-encoded pUL138 as necessary, but not sufficient, for HCMV latency in CD34+ hematopoietic progenitor cells (HPCs) infected in vitro. pUL138 is encoded on polycistronic transcripts that also encode 3 additional proteins, pUL133, pUL135, and pUL136, collectively comprising the UL133-UL138 locus. This work represents the first characterization of these proteins and identifies a role for this locus in infection. Similar to pUL138, pUL133, pUL135, and pUL136 are integral membrane proteins that partially co-localized with pUL138 in the Golgi during productive infection in fibroblasts. As expected of ULb′ sequences, the UL133-UL138 locus was dispensable for replication in cultured fibroblasts. In CD34+ HPCs, this locus suppressed viral replication in HPCs, an activity attributable to both pUL133 and pUL138. Strikingly, the UL133-UL138 locus was required for efficient replication in endothelial cells. The association of this locus with three context-dependent phenotypes suggests an exciting role for the UL133-UL138 locus in modulating the outcome of viral infection in different contexts of infection. Differential profiles of protein expression from the UL133-UL138 locus correlated with the cell-type dependent phenotypes associated with this locus. We extended our in vitro findings to analyze viral replication and dissemination in a NOD-scid IL2Rγc null-humanized mouse model. The UL133-UL138 NULL virus exhibited an increased capacity for replication and/or dissemination following stem cell mobilization relative to the wild-type virus, suggesting an important role in viral persistence and spread in the host. As pUL133, pUL135, pUL136, and pUL138 are conserved in virus strains infecting higher order primates, but not lower order mammals, the functions encoded likely represent host-specific viral adaptations.

Interaction between the human cytomegalovirus-encoded UL142 and cellular Snapin proteins

“…During extensive passage in vitro, a 15 kb sequence in the UL/b' region (UL133-UL151) was deleted from the widely used HCMV laboratory strain AD169 compared with the low passage Toledo strain (8). In recent studies, the UL/b' region has been demonstrated to be important for the dissemination, latency and virulence of HCMV in human hosts (9)(10)(11)(12). The UL142 ORF, located within the UL/b' region, is 921 bp in length and is predicted to encode a protein, presumably an important component in the inhibition of natural killer (NK) cell killing and the innate defense against HCMV (13).…”

An Endothelial Cell-Specific Requirement for the UL133-UL138 Locus of Human Cytomegalovirus for Efficient Virus Maturation

“…This locus encodes four proteins, pUL133, pUL135, pUL136, and pUL138, from polycistronic transcripts (59,60). Like the entire ULb= region, the UL133-UL138 locus is dispensable for viral replication in fibroblasts (60).…”

The susceptibility of primary cultured rhesus macaque kidney epithelial cells to rhesus cytomegalovirus strains

“…In HCMV, clinical strains contain a UL/b¢ region (UL128-UL150) that encodes multiple ORFs involved in cell-type dependent replication, intra-host dissemination, latency and immune evasion (Bradley et al, 2009;Cheung et al, 2005;Goodrum et al, 2007;Hahn et al, 2004;Penfold et al, 1999;Prod'homme et al, 2010;Ryckman et al, 2006Ryckman et al, , 2008Sinzger et al, 2008;Stanton et al, 2010;Tomasec et al, 2005;Umashankar et al, 2011). As viral determinants for HCMV entry of EP, UL128L-encoded proteins, form a pentamer with gH and gL mediating HCMV entry into EP via an endocytotic pathway (Bodaghi et al, 1999;Ryckman et al, 2008;Wang & Shenk, 2005;Wang et al, 2007).…”