Single amino acid substitution (G42E) in the receptor binding domain of mouse mammary tumour virus envelope protein facilitates infection of non-murine cells in a transferrin receptor 1-independent manner

Abstract

BackgroundMouse mammary tumour virus (MMTV) is a betaretrovirus that infects rodent cells and uses mouse tranferrin receptor 1 (TfR1) for cell entry. Several MMTV strains have been shown to productively infect, in addition to murine cells, various heterologous cell lines including those of human origin, albeit less efficiently than murine cells. Furthermore, there have been reports that the continued passage of MMTV in heterologous cell lines gives rise to novel variants that are able to infect naive non-murine cells with higher efficiency than the parental virus.ResultsWe show that MMTV(C3H), like other MMTV strains, that had undergone a number of replication cycles in non-murine cells displayed an increased replication kinetic, as compared to parental virus, when applied on naive human cells. Sequence analysis of several replication kinetic variants and the parental virus, together with calculation of the ratio of non-synonymous to synonymous mutations at individual codons, revealed that several regions within the viral genome were under strong positive selection pressure during viral replication in human cells. The mutation responsible, at least in part, for the phenotypic change was subsequently mapped to the segment of env encoding the receptor binding site (F40HGFR44). Introduction of the identified mutation, leading to single amino acid substitution (G42E), into egfp-containing recombinant MMTV virions enhanced their ability to bind to and infect human cells. Interestingly, neither the replication kinetic mutant nor the parental virus required human TfR1 for infection. Knock-out of TFR1 gene from the human genome did not decrease the susceptibility of Hs578T cells to virus infection. Furthermore, the expression of human TfR1, in contrast to mouse TfR1, did not enhance the susceptibility of MMTV-resistant Chinese hamster ovary cells. Thus, human TfR1 is dispensable for infection and another cell surface molecule mediates the MMTV entry into human cells.ConclusionTaken together, our data explain the mechanism enabling MMTV to form ‘host-range variants’ in non-murine cells that has been known for a long time, the basis of which remained obscure. Our findings may expand our understanding of how viruses gain capability to cross species-specific barriers to infect new hosts.Electronic supplementary materialThe online version of this article (doi:10.1186/s12977-015-0168-2) contains supplementary material, which is available to authorized users.

Retroviral host range extension is coupled with Env-activating mutations resulting in receptor-independent entry

“…Mutations leading to host range extension have been described in envelope glycoproteins of other retroviruses (mouse mammary tumor virus, Moloney murine leukemia virus) (47,48). Although these mutations are located in the SU part of Env and the authors hypothesize that they could be associated with a new host receptor binding, we cannot exclude the possibility that such mutations Fig.…”

Human saliva as route of inter-human infection for mouse mammary tumor virus

“…Notwithstanding the strong similarities between mouse and human tumors, the efforts to demonstrate a viral origin for HSBC were unsuccessful. However, nowadays there is a substantial amount of data supporting this possibility, such as: the presence of MMTV sequences in a percentage between 30% and 40% of infiltrating HSBC [ 5 , 6 ]; the presence of MMTV sequences shown by CISH in the nucleus of tumor cells [ 10 ]; the demonstration of a strict relationship between the presence of MMTV sequence and the progression of HSBC (normal gland, atypical ductal epithelial hyperplasia, ductal carcinoma in situ) [ 10 ]; the production of viral particles in primary cultures of human breast cancer [ 7 ]; the ability of MMTV to infect human cells in culture [ 8 , 20 ]; the identification of a molecular mechanism that facilitates entrance of MMTV in non-murine cells [ 21 ].…”

Is MMTV associated with human breast cancer? Maybe, but probably not

“…Many publications have reported on the successful infection of human cells by MMTV, albeit less efficiently than human cells [ 22 – 26 ]. Further, studies indicate that the MMTV receptor in rodent cells is different than in human cells [ 27 ]. Over the past two decades this debate has intensified with claims ranging from a high to no prevalence rates being described by conflicting reports.…”