Canine Distemper Virus Matrix Protein Influences Particle Infectivity, Particle Composition, and Envelope Distribution in Polarized Epithelial Cells and Modulates Virulence

Abstract

In paramyxoviruses, the matrix (M) protein mediates the interaction between the envelope and internal proteins during particle assembly and egress. In measles virus (MeV), M mutations, such as those found in subacute sclerosing panencephalitis (SSPE) strains, and differences in vaccine and wild-type M proteins can affect the strength of interaction with the envelope glycoproteins, assembly efficiency, and spread. However, the contribution of the M protein to the replication and pathogenesis of the closely related canine distemper virus (CDV) has not been characterized. To this end this, we generated a recombinant wild-type CDV carrying a vaccine strain M protein. The recombinant virus retained the parental growth phenotype in VerodogSLAMtag cells, but displayed an increased particle-to-infectivity ratio very similar to that of the vaccine strain, likely due to inefficient H protein incorporation. Even though infectious virus was released only from the apical surface, consistent with the release polarity of the wild-type CDV strain, envelope protein distribution in polarized epithelial cells reproduced the bipolar pattern seen in vaccine strain-infected cells. Most notably, the chimeric virus was completely attenuated in ferrets and caused only a mild and transient leukopenia, indicating that the differences in particle infectivity and envelope protein sorting mediated by the vaccine M protein contribute importantly to vaccine strain attenuation.Morbilliviruses are enveloped negative-strand RNA viruses that cause severe disease in their respective hosts. Pathogenesis studies of measles virus (MeV) in nonhuman primates and canine distemper virus (CDV) in ferrets reveal that wild-type strains initially target immune cells and then spread to epithelia and in some cases to the central nervous system (6,23,34). This dissemination requires the transition of the respiratory mucosa at the initial infection stage, subsequent spread to lymphoid and epithelial tissues throughout the body, and finally virus release via the epithelia of the respiratory, gastrointestinal, and urinary tracts for shedding and transmission.Polarized epithelia form barriers that separate compartments within the organism, as well as the organism and the environment (22). Consequently, replication in epithelia constitutes an integral part of the life cycle of many viruses. The polarization of the epithelial layer results in distinct apical and basolateral domains that are separated by tight junctions, and membrane proteins are transported to the apical or basolateral surface based on sorting signals in their sequences (14). Many viruses exploit this polarization by recognizing receptor molecules that are localized at the respective site of contact with the epithelial layer (7,11,32). It is further speculated that virus dissemination either by lateral cell-to-cell fusion or by polarized virus release from epithelia contributes to virulence (5, 9, 13, 30).The matrix (M) protein plays an essential role in paramyxovirus assembly by mediating the interac...

Nipah Virus Matrix Protein Influences Fusogenicity and Is Essential for Particle Infectivity and Stability

“…Despite their conserved role in assembly and budding, there are genus-and strain-specific differences between paramyxoviral matrix proteins that do not allow exchanging M proteins even between closely related viruses without affecting virus growth (36)(37)(38). In line with these studies, a recent crosscomplementation study by Yun et al (26) demonstrated that introduction of the Hendra virus M gene into NiV increased the replicative titers, likely as a result of an increased budding activity of HeV M.…”

Nipah Virus Entry and Egress from Polarized Epithelial Cells

“…Late in infection, ongoing cell-to-cell fusion and virus replication cause extensive cytopathic effects and likely disrupt all basolateral trafficking pathways. The consecutive accumulation of the glycoproteins at apical surfaces might be triggered by an apical G/F retargeting promoted by the M protein, as proposed previously for other viruses (25,29,30,34,68,69). However, there is no evidence so far that G, F, and M meet and interact intracellularly before reaching the plasma membrane.…”

“…Envelope proteins can even be expressed at opposing membranes. Here, partial retargeting of the glycoproteins by the matrix protein to the site of budding is believed to be required for virus release (25,29,30,34,68,69). Resembling measles virus (29), NiV M, F, and G proteins possess opposing targeting signals.…”

Morbillivirus and henipavirus attachment protein cytoplasmic domains differently affect protein expression, fusion support and particle assembly

“…Paramyxovirus HN/H/G and F protein cytoplasmic domains also contain tyrosine motifs, which result in transport of proteins to the basolateral surface of polarized cells (Runkler et al, 2009;Weise et al, 2010). These signals, however, are overridden by the homologous matrix (M) protein, resulting in direction of the glycoproteins to the appropriate cellular compartment for virus assembly (Dietzel et al, 2011;Naim et al, 2000).…”