U24 from Roseolovirus interacts strongly with Nedd4 WW Domains

Abstract

U24 is a protein found in both roseoloviruses Human Herpes Virus type 6 and 7 (HHV-6 and HHV-7), with an N-terminus that is rich in prolines (PY motif in both HHV-6A and 7; PxxP motif in HHV-6A). Previous work has shown that the interaction between U24 and WW domains is important for endocytic recycling of T-cell receptors, but a cognate ligand was never identified. In this contribution, data was obtained from pull-downs, ITC, NMR and molecular dynamics simulations to show that a specific interaction exists between U24 and Nedd4 WW domains. ITC experiments were also carried out for U24 from HHV-6A phosphorylated at Thr6 (pU24-6A) and a peptide containing the PY motif from Nogo-A, a protein implicated in both the initial inflammatory and the neurodegenerative phases of multiple sclerosis (MS). The results suggest that phosphorylation of U24 from HHV-6A may be crucial for its potential role in MS.Roseoloviruses, which include human herpes virus type 6A (HHV-6A), HHV-6B and HHV-7, are ubiquitous and highly prevalent. They have been found to be implicated in several neurological diseases, including encephalitis, epilepsy, and multiple sclerosis (MS) [1][2][3][4] . MS is a neurological inflammatory disease in the central nervous system (CNS). The exact cause of MS is unknown, but it has been suggested that one or more viruses may be possible triggers 2,5,6 . U24 is a putative tail-anchored membrane protein that is unique to roseoloviruses 7 . It is expressed in infected cells during the early stages of viral infection 8 . Although the exact function of U24 has not been identified, a number of studies have demonstrated a potential link between U24 and MS 9,10 .One possible way in which U24 may be implicated in MS is through the mimicry of myelin basic protein (MBP) because the two proteins share a seven amino acid stretch that contains a PxxP motif (Fig. 1a). This segment is essential for MBP to participate in Fyn-mediated signalling pathways by a direct but non-canonical association with the Fyn-SH3 domain 11 . Disruption of these signalling pathways has a large impact on oligodendrocyte differentiation and maturation, processes that are perturbed in MS patients. Within this PxxP motif and just before it are two threonine residues (T95 and T98), which can be phosphorylated. Phosphorylation has been shown to affect the local structure of MBP and its disposition on the membrane surface 12 . U24-6A shares with MBP both the PxxP motif and a threonine at an analogous position to T98 (Fig. 1a). Recent work has demonstrated that U24-6A can be phosphorylated by MAPK, albeit less effectively than MBP 13 . It has also been shown that U24-6A can associate with Fyn SH3, but again does so more weakly than MBP (K D = 5 mM for U24-6A 14 versus 4-8 μ M for MBP 15 ). These findings suggested that although U24-6A may mimic MBP, it most likely does not interfere directly with MBP function.Within the proline rich region of U24 is a PY motif that is conserved in both HHV-6A and HHV-7 (Fig. 1a). This motif was found to be responsible for ...

Herpesviruses possess conserved proteins for interaction with Nedd4 family ubiquitin E3 ligases

“…The PY motif of U24 is able to associate with Itch (Fig. 3 ) and the WW domain of Nedd4 25 . As the PY motif of U24 is responsible for CD3ε down-regulation, we examined whether this function is conserved among all viral proteins.…”

“…Sang et al . reported that the PY motifs of U24 proteins are able to interact with the WW domains of Nedd4 proteins in an acellular system 25 . In addition, the m42 gene product of mouse cytomegalovirus (MCMV), a homolog of HCMV UL42, down-regulates CD45 expression on the MCMV-infected macrophage surface and induces the lysosomal degradation of CD45 30 .…”

Viruses go modular

“…The roseoloviral protein U24 is a C-tail-anchored membrane protein shown to affect recycling and endocytosis of cell-surface receptors (131,132). In addition, U24 function may be linked to MS, as it has been found to mimic the interaction of myelin basic protein's function with its binding partner Fyn (133,134). The N-terminal region of U24 encoded by HHV-6A and HHV-7 contains a PPxY motif that was shown to interact with HECTfamily E3 ligases SMURF2 and Nedd4, albeit more strongly with WW domain 3 of Nedd4 (135).…”

“…Importantly, because sodium channels have been found to be associated with MS lesions, investigators speculated that U24 may interfere with the endosomal recycling of sodium channels known to be regulated by Nedd4. Although still speculative, results from Sang et al (133) suggest that the PPxY motif of U24 and its strong interaction with WW domain 3 of Nedd4 may play a role in MS or other related demyelinating diseases.…”

Role of PML-Nuclear Bodies in Human Herpesvirus 6A and 6B Genome Integration

“…However, in immunocompromised individuals, HHV-6B reactivation can be problematic and occasionally life-threatening (5),(6),(7). In case of HHV-6A, several reports have associated the virus with neurodegenerative diseases such as multiple sclerosis and more recently with Alzheimer’s disease (8), (9), (10), (11). In spite of their pathological differences, both HHV-6A and HHV6B can readily integrate their genomes into host chromosomes (12), (13), (14).…”