Genes affected by mouse mammary tumor virus (MMTV) proviral insertions in mouse mammary tumors are deregulated or mutated in primary human mammary tumors

Abstract

The accumulation of mutations is a contributing factor in the initiation of premalignant mammary lesions and their progression to malignancy and metastasis. We have used a mouse model in which the carcinogen is the mouse mammary tumor virus (MMTV) which induces clonal premalignant mammary lesions and malignant mammary tumors by insertional mutagenesis. Identification of the genes and signaling pathways affected in MMTV-induced mouse mammary lesions provides a rationale for determining whether genetic alteration of the human orthologues of these genes/pathways may contribute to human breast carcinogenesis. A high-throughput platform for inverse PCR to identify MMTV-host junction fragments and their nucleotide sequences in a large panel of MMTV-induced lesions was developed. Validation of the genes affected by MMTV-insertion was carried out by microarray analysis. Common integration site (CIS) means that the gene was altered by an MMTV proviral insertion in at least two independent lesions arising in different hosts. Three of the new genes identified as CIS for MMTV were assayed for their capability to confer on HC11 mouse mammary epithelial cells the ability for invasion, anchorage independent growth and tumor development in nude mice. Analysis of MMTV induced mammary premalignant hyperplastic outgrowth (HOG) lines and mammary tumors led to the identification of CIS restricted to 35 loci. Within these loci members of the Wnt, Fgf and Rspo gene families plus two linked genes (Npm3 and Ddn) were frequently activated in tumors induced by MMTV. A second group of 15 CIS occur at a low frequency (2-5 observations) in mammary HOGs or tumors. In this latter group the expression of either Phf19 or Sdc2 was shown to increase HC11 cells invasion capability. Foxl1 expression conferred on HC11 cells the capability for anchorage-independent colony formation in soft agar and tumor development in nude mice. The published transcriptome and nucleotide sequence analysis of gene expression in primary human breast tumors was interrogated. Twenty of the human orthologues of MMTV CIS associated genes are deregulated and/or mutated in human breast tumors.

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

“…We consider the data generated in this study to be valid for the following reasons: (i) The study was conducted by PCR with primers based on MMTV-like envelope gene sequences as described by Wang et al [13]. These MMTV env gene sequences are unique to the MMTV genome and are not present in human endogenous retrovirus sequences (HERV) and which are commonly identified in studies of the human genome.…”

“…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].…”

Therapeutic Targeting of Tumor-Derived R-Spondin Attenuates β-Catenin Signaling and Tumorigenesis in Multiple Cancer Types

“…The identification of Rspo2 and Rspo3 as sites of integration for MMTV-induced mammary tumors in mice supported a role as breast cancer oncogenes (26)(27)(28). Ectopic expression of Rspo2 was shown to increase tumorigenic and invasive properties of mouse breast cell lines (25).…”

MicroRNA-195-5p acts as an anti-oncogene by targeting PHF19 in hepatocellular carcinoma

“…This correlates with increased recruitment of eZH2 and accumulation of H3K27me3 and PRC1 components on the INK4A promoter, suggesting a potential oncogenic role for PHF19 (26). In addition, Callahan et al (27) showed that PHF19 increased HC11 mouse mammary epithelial cell invasion capability. PHF19 was shown to confer properties associated with malignant transformation in HC11 mammary epithelial cells (27).…”

“…In addition, Callahan et al (27) showed that PHF19 increased HC11 mouse mammary epithelial cell invasion capability. PHF19 was shown to confer properties associated with malignant transformation in HC11 mammary epithelial cells (27). In the present study, PHF19 was increased in the hCC tissues compared to that in the adjacent non-tumor tissues.…”