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 is 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 is 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.