C3H strain of mouse mammary tumour virus, like GR strain, infects human mammary epithelial cells, albeit less efficiently than murine mammary epithelial cells

Mouse mammary tumor-like virus (MMTV) is present in human breast tissue before development of virally associated breast cancer

“…The evidence suggestive of a role for an MMTV–like virus in human breast cancer is as follows: (i) a meta-analysis of 22 studies concluded that the identification of MMTV–like gene sequences in breast cancer tissues, was associated with a 15 fold increase in breast cancer [9], (ii) MMTV-like env gene sequences were identified in 38% of US human breast tumors but were extremely uncommon in healthy breast tissues [3, 6], (iii) the near complete proviral structure of MMTV-like virus that was 95-98% homologous to MMTV has been identified in human breast tumors [4, 10], (iv) MMTV viral proteins have been identified in human breast cancer [11], (v) Wnt-1 oncogene expression is significantly higher in MMTV-like positive compared to MMTV-like negative breast cancer specimens, which parallels high Wnt-1 expression in MMTV positive mouse mammary tumors [12, 13], (vi) MMTV can infect human cells and randomly integrate its genomic information [14, 15], and produce virus particles [16] (vii) there is increased prevalence of MMTV-like viral sequences in healthy breast tissues (nil), healthy tissue adjacent to breast cancer (19%), breast hyperplasia (27%), ductal carcinoma in situ (82%) [17], (viii) the age standardized rates for breast cancers in five countries of Asia are less frequent (29–43 per 100,000) than in seven countries of Europe, the Americas, and Australia (47–92) [18]. These findings correlate with different burdens of MMTV-like infection in human breast cancers, 0-20% in Asia vs. 27-60%, in the seven countries which are associated with different prevalence of MMTV in the indigenous mouse species [18, 19].…”

Polypyrimidine tract‐binding protein binds to the 5′ untranslated region of the mouse mammary tumor virus mRNA and stimulates cap‐independent translation initiation

“…In a previous study, we showed that the full‐length mRNA of MMTV harbors an IRES within its 5′ UTR . Considering reports showing that MMTV can infect and replicate in human cell lines , in this new study we sought to determine if the MMTV‐IRES is modulated by cellular proteins in the context of a human cell line. To this end, we used human embryonic kidney fibroblast 293T (HEK 293T) cells derived from human embryonic kidney cells.…”

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

“…Using both a wild-type and a recombinant egfp -containing virus carrying MMTV(C3H) Env, we have recently shown that MMTV(C3H), like other strains, is able to infect human cells, albeit less efficiently than mouse cells [ 31 ]. The established infection was, however, sufficient to enable virus spread to every cell in culture.…”

“…The established infection was, however, sufficient to enable virus spread to every cell in culture. Infectivity of the wild-type and MMTV(C3H)-Env-carrying MMTV recombinant virions was blocked by heat-inactivation and an inhibitor of reverse transcription, 3′-azido-3′-deoxythymidine (AZT), ruling out a non-specific mechanism of viral transfer [ 31 ]. Furthermore, infection requires an intact MMTV envelope protein, since neutralizing anti-MMTV antibodies blocked infectivity of both the wild-type and MMTV(C3H)-Env-carrying MMTV recombinant virions.…”