Mechanisms of epithelial cell cancer generation: genetic risk factors on cancer progression investigated using in vivo models and at a single cell level

Abstract

Loss of Brca1, loss of p53, AIB1/AIB1delta3 over-expression, and ERalpha; over-expression, are risk factors for breast cancer development. These risk factors influence on mammary gland development and breast cancer risk were investigated using two techniques: mouse models and single cell tracking of primary mammary epithelial cell cultures. Also, the impact of the PPARgamma; agonist CS7017 in a mouse model of loss of Brca1 function was evaluated.

The impact of combining expression of either AIB1 or AIB1delta3 with ERalpha; overexpression in the mammary gland was investigated in vivo. Overexpression of AIB1 or AIB1delta3 with and without ERalpha; increased HAN prevalence. Older AIB1/CERM and AIB1delta3/CERM mice developed a significant increase in mammary gland collagen content. 17beta-estradiol/progesterone treatment increased collagen in the AIB1delta3/CERM mice. After hormonal exposure in the AIB1delta3 and AIB1delta3/CERM mice, multilayered epithelial structures and expression levels of PR and downstream genes were increased. AIB1delta3 is a more potent inducer of mammary pathological and gene expression changes, especially in response to hormonal stimulation.

The impact of the PPARgamma agonist CS7017 on promotion and progression of mammary cancer in Brca1f11/f11/MMTV-Cre/p53+/- mice was examined. Mammary tissue from CS7017-treated mice had increased PPARgamma; target genes, and reduced levels of pAkt, cell proliferation and HAN prevalence. Cancer prevalence at 12 months of age was unchanged with CS7017 treatment. However, differentiated cancer histologies, papillary and in situ cancers, lobular cancerization, and focal squamous metaplasia, appeared only in the CS7017-treated group. Levels of pAkt and pErk and Cdk6 were reduced in the cancers that appeared in the CS7017 treatment group. CS1707 treatment significantly altered cancer progression in a genetically engineered mouse model of BRCA1 mutation.

Single cell tracking was performed on primary mammary epithelial cell (PMEC) cultures from three different models: Brca1f11/f11/MMTV-Cre, Brca1f11/f11/MMTV-Cre/p53+/- and Brca1f11/f11/p53+/-/MMTV-Cre/Tet-op-ER/MMTV-rtTA mice at 10-12 months of age. Mean cell lifetime were significantly shorter in primary mammary epithelial cell cultures from Brca1f11/f11/MMTV-Cre and Brca1f11/f11/MMTV-Cre/p53+/- mice. A higher percentage of dividing cells were found in cultures from all genotypes as compared to wild-type mice. Brca1f11/f11/MMTV-Cre/p53+/- mice showed the lowest level of colony formation. Single cell tracking revealed genotype-specific differences in primary mammary epithelial cell behavior.