Multiple genetic changes are associated with mammary tumorigenesis in Brca1 conditional knockout mice

Abstract

Germline mutations in the tumor suppressor gene BRCA1 predispose women to breast cancer, however somatic mutations in the gene are rarely detected in sporadic cancers. To understand this phenomenon, we examined mouse models carrying conditional disruption of Brca1 in mammary epithelium in either p53 wild type (wt) or heterozygous backgrounds. Although a p53 +/7 mutation signi®cantly accelerated tumorigenesis, both strains developed mammary tumors in a stochastic fashion, suggesting that multiple factors, in addition to p53 mutations, may be involved in Brca1 related tumorigenesis. A unique feature of Brca1 mammary tumors is their highly diverse histopathology accompanied by severe chromosome abnormalities. The tumors also display extensive genetic/molecular alterations, including overexpression of ErbB2, c-Myc, p27 and Cyclin D1 in the majority of tumors, while they were virtually ERa and p16 negative. Translocations involving p53 were also identi®ed which lead to abnormal RNA and protein products. In addition, we generated cell lines from mammary tumors and found that the cells retained many of the genetic changes found in the primary tumors, suggesting that these genes may be players in Brca1-associated tumorigenesis. Despite their distinct morphology, all cultured tumor cells were Tamoxifen resistant but highly sensitive to Doxorubicin or girradiation, suggesting that these methods would be e ective in treatment of this disease. Oncogene (2001) 20, 7514 ± 7523.

BRCA1 and FOXA1 proteins coregulate the expression of the cell cycle-dependent kinase inhibitor p27Kip1

“…The p27 Kip1 protein expression is decreased in a number of tumor types, including breast, colon, prostate and ovarian tumors (Catzevalos et al, 1997;Ciaparrone et al, 1998;Cordon-Cardo et al, 1998;Masciullo et al, 1999). Conversely in BRCA1 knockout mouse models, reduction of BRCA1 is accompanied by an increase in the expression of p27 Kip1 at the mRNA and protein levels (Brodie et al, 2001;Deans et al, 2004). However, in the conditional BRCA1 knockout model, other cell cycle proteins were also upregulated (Brodie et al, 2001).…”

“…Conversely in BRCA1 knockout mouse models, reduction of BRCA1 is accompanied by an increase in the expression of p27 Kip1 at the mRNA and protein levels (Brodie et al, 2001;Deans et al, 2004). However, in the conditional BRCA1 knockout model, other cell cycle proteins were also upregulated (Brodie et al, 2001). Another recent study showed that using shRNA to decrease BRCA1 expression in MCF7 resulted in an increase in p27 Kip1 mRNA and transfection of the HCC1937 with wild-type BRCA1 resulted in a decrease in p27 Kip1 (Deans et al, 2004).…”

Genistein inhibits Brca1 mutant tumor growth through activation of DNA damage checkpoints, cell cycle arrest, and mitotic catastrophe

“…Four tumor cell lines derived from mammary tumors of Brca1 Ko/Co Wap-Cre;p53 þ /À mice (W525 and W780), MMTV-Neu (Neu), and MMTV-Ras (Ras) 21 were used in this experiment. We plated 10 4 cells into each well of a 24-well plate with varying concentrations of genistein, ranging from 0, 1, 2.5, 5, 7.5, 10, 20, 40 and 80 mM added 24 h later.…”

“…34,35 The DNA damage response serves as a barrier to prevent cell proliferation and eliminate cells with unrepairable DNA damage due to p53-dependent cell cycle arrest and apoptosis. Because all the Brca1 mutant cells used in this study are p53 deficient, 21 the cell cycle arrest and apoptosis caused by genistein treatment are p53 independent. The identity of the factors that are involved in these processes is currently unclear, as ATM and Chk2 can phosphorylate many proteins besides p53.…”

A role of estrogen/ERα signaling in BRCA1-associated tissue-specific tumor formation

“…These cells were maintained in the Dulbecco's modified Eagle's medium (DMEM) with 5 mg/ml bovine insulin and 10 ng/ml mouse epidermal growth factor. BRCA1-mutant mammary tumor cell line, W780, BRCA1 wild-type mammary tumor cells, c-Neu (Brodie et al, 2001) and MCF7 cell were cultured in DMEM with 5-10% fetal bovine serum. For estrogen treatment, cells were plated in dishes at 50% confluence under normal conditions.…”