Year: 2017
Type: dissertation
Abstract: Genetic alterations that cooperate with TP53 mutation in breast cancer (BC) are largely unknown. Using a dominant-negative Trp53LSL-R270H/+ mouse strain, I found Trp53 alteration cooperates with Her2/Neu over-expression, but not with hemizygous deletion of Gata3, Runx1, or Nf1. To identify other genes cooperating with mutant Trp53, I completed a Sleeping Beauty (SB) mutagenesis screen in mice. This identified known cooperators such as Met, and other candidates such as Notch1. Cooperation between activated Notch1 and Trp53LSL-R270H/+ was validated in vivo. In addition to coding mutations, chromosomal copy number changes are also important in BC. To identify genes that contribute to mammary tumorigenesis upon copy number alteration, I compared genes targeted by transposons in SB mice carrying Trp53LSL-R270H/+, R26LSL-Pik3ca(Mut)/+, R26LSL-Stat3C/+, or no mutant allele. This enabled me to identify genes altered in all cohorts (e.g. Rasa1), in several but not all backgrounds (e.g. Met), and those that only occurred in the presence of a single driver (e.g. Mll3, Exoc4, and Cul1 loss in Pik3ca-mutant tumors). Importantly, many genes targeted by SB transposons map to loci syntenic with regions commonly gained/lost in human BC. Thus, they likely represent haploinsufficient tumor suppressors or oncogenes. Guided by SB results, the oncogenic interaction between R26LSL-Pik3ca(Mut)/+ and loss/activation of Notch1 was validated in vivo. Additionally, I distinguished genes altered in metastatic lesions from SB mice. This revealed genes previously implicated in BC dissemination (e.g. Hipk2) and novel abnormalities (e.g. loss of Fbxl17). Lastly, to assess the oncogenic potential of ELF3 (which maps to human chromosome 1q and is frequently gained/amplified in human BC), I generated a Cre-conditional Rosa26-targeted Elf3 transgenic strain (R26LSL-Elf3). Using SB mutagenesis, I showed genes such as Cul5 and FoxP1 were disrupted in Elf3 over-expressing SB mammary tumors, while metastases from these mice selected for a distinct set of insertions (e.g. Pard3 disruption).
Source: TSpace (University of Toronto)
Author: Nathan F. Schachter
Language: English
Subfield: Oncology
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W3090796212