Breast cancer is an age-related disease, with higher incidence in elder women and worse prognosis in younger women. Most breast tumors are of epithelial origin. The mammary epithelium consists of an outer basal myoepithelial layer of cells and an inner luminal cell layer. Studies have described the existence of cytokeratin protein 5 (K5) marked bipotent progenitors giving rise to both basal and luminal cells, and cytokeratin protein 8 (K8) marked unipotent progenitors that produce luminal cells only. Surprisingly, despite the long history of breast cancer research, how age impacts breast cancer, and whether and how breast tumors initiated from K5 or K8 positive (K5+ or K8+) progenitors exhibit intrinsic differences remain unclear. Answering these questions may provide new avenues for improved diagnostics and personalized therapeutics that could prolong the lives of patients. The most frequent genetic alterations in breast cancer occur in the tumor suppressor p53, with arginine 248 being the top mutational hotspot. The newly published conditional p53wm-R245W mouse allele, which allows conversion of wild type p53 to p53R245W (corresponding to human p53 arginine to tryptophan mutation at codon 248) in response to Cre recombinase, is a potentially valuable tool for studying the age-dependence and cell-specificity of breast cancer driven by mutant p53. As a prelude for future mechanistic and therapeutic studies, this pilot project will utilize the p53wm-R245W allele to model breast cancer and compare mouse mammary tumors initiated at different ages or from different cellular origins, which are hypothesized to exhibit differences at the histological, molecular or genomic levels. This hypothesis will be tested in three specific aims.
The first aim i s to compare p53R245W mutant driven mammary tumors initiated in young and old mice. Adenoviruses expressing Cre (Ad-Cre), will be injected into the mammary ducts of 2 months- or 10 months old female p53wm-R245W/+ mice. Tumor incidence, latency and growth rate, animal survival, metastasis, and the spectra of histological and molecular subtypes of tumors will be compared between mice injected with Ad-Cre at the respective ages.
The second aim i s to compare p53R245W driven mammary tumors initiated from either K5+ or K8+ progenitor cells. p53wm-R245W/+ female mice will receive mammary intraductal injection of adenoviruses AdK5-Cre or AdK8-Cre that express Cre led by the K5 or K8 promoter, respectively. The same parameters as described in Aim 1 will be compared between the mice receiving AdK5-Cre or AdK8-Cre. The last aim is to investigate the age-dependence and cell-specificity of mammary tumors at the genomic level. Whole-exome sequencing (WES) will be performed on tumors produced in Aims 1 and 2. Genes with recurrent alterations will be compared between mammary tumors initiated from the 2 months- and 10 months old mice, as well as between tumors initiated from the K5+ or K8+ progenitor cells. The WES data will also be compared to the human breast cancer sequencing data.
This proposed study will lay the groundwork for understanding the impact of age in breast cancer, and the contribution of different types of mammary epithelial progenitor cells towards the intrinsic biological diversity of breast cancer. It may eventually lead to improved diagnosis and personalized treatment that could prolong the lives of breast cancer patients.