Mouse Mammary Tumor Virus p75 and p110 CUX1 Transgenic Mice Develop Mammary Tumors of Various Histologic Types

Abstract

The p75 and p110 isoforms of the CUX1 homeodomain protein are overexpressed in breast tumors and cancer cell lines. To assess and compare the ability of these short CUX1 isoforms in driving mammary tumor development, we used site-specific transgenesis into the Hprt locus to generate transgenic mice expressing p75 or p110 CUX1 under the control of the mouse mammary tumor virus-long terminal repeat. We report that mammary tumors developed after a long latency period, and although various histopathologies were observed, the proportion of adenosquamous carcinomas was significantly higher in p75 CUX1 than in p110 CUX1 transgenic mice. Metastasis to the lung was observed in three p75 CUX1 transgenic mice. Comparisons between tumors and adjacent normal mammary glands revealed that transgenes were overexpressed in most but not all tumors, yet in all cases tested, CUX1 DNA binding was increased, suggesting that both higher expression and changes in post-translational modifications can contribute to stimulate transgene activity. Interestingly, higher expression of erbB2 mRNA was seen in most tumors, not only solid carcinomas but also adenosquamous carcinomas, whereas higher expression of various Wnt genes and activation of the B-catenin pathway was observed primarily in adenosquamous carcinomas. Activation of erbB2 expression appeared to represent a cooperating event that occurred independently of CUX1. In contrast, chromatin immunoprecipitation, short hairpin RNA-mediated knockdown, and reporter assays established that CUX1 is involved in the transcriptional regulation of several Wnt genes. Together, these results support the notion that oncogenic activity of CUX1 can facilitate the establishment of a Wnt/B-catenin autocrine loop. [Cancer Res 2009;69(18):7188-97]

CUX1, a haploinsufficient tumour suppressor gene overexpressed in advanced cancers

“…Transgenic mouse models have established that higher expression of several CUX1 isoforms increases cancer incidence 16,17,61 and that cytokinesis failure cooperates with the p75 and p110 CUX1 transcription factors in tumorigenicity 19 , whereas a Kras oncogene cooperates with the p200 CUX1 DNA repair accessory factor 18 . A hemizygous mouse knockout model should be used in the future to verify that inactivation of one Cux1 allele promotes tumorigenicity, particularly in the myeloid compartment, and to identify molecular events that cooperate with Cux1 hemizygosity in tumour development.…”

“…Consistent with this, transgenic mice expressing various CUX1 isoforms exhibit multiorgan hyperplasia 15 and develop myelo proliferative disease (MPD)-like myeloid leukaemias 16 and tumours in the mammary gland [17][18][19] , the lung 18 and the uterus 20 . Many cell lines with CUX1 LOH that are listed on the Sanger cancer cell line website (see Further information) harbour amplification of the remaining allele, illustrating the dual role of CUX1 in cancer (TABLE 1).…”

“…This transcript was found to be aberrantly expressed in many breast tumour cells lines and breast tumours, in which a significant association was established with a diffuse infiltrative growth pattern 24 . Indeed, transgenic mice expressing this transcript in mammary epithelial cells were shown to develop mammary tumours with metastasis to the lung 17 .…”

“…Functional analysis showed that p200 CUX1 is directly involved in DNA repair and prevents RAS-induced senescence by accelerating the repair of oxidative DNA damage 18 . Transgenic mice expressing the p75 CUX1 or p110 CUX1 isoform under the control of the MMTV-LTR regulatory sequences and integrated into the hypoxanthine guanine phosphoribosyl transferase (Hprt) locus also developed mammary tumours after a long latency period, and metastasis to the lung was observed in a small proportion of p75 CUX1 transgenic mice 17 . However, activating mutations in Kras were found in less than 10% of these tumours, and no mutation was found in Hras or Nras (Z.M.R.…”

“…In addition, p200 CUX1 promotes genome stability through its role in base excision repair 18 . Such functions would not predict a role as an oncogene, but overexpression of either p200 or p110 CUX1 contributes to tumorigenicity in cell culture models 21,24 and in transgenic mice 16,17,19,20,61 (reviewed in REFS 28,67). Two studies showed that cancer cells are acutely dependent on the multiple roles of CUX1 in maintaining genome integrity 18,19 .…”