Author ORCID Identifier

https://orcid.org/0000-0001-7474-7156

Date of Graduation

8-2019

Document Type

Dissertation (PhD)

Program Affiliation

Human and Molecular Genetics

Degree Name

Doctor of Philosophy (PhD)

Advisor/Committee Chair

Dung-Fang Lee

Committee Member

Louise C. Strong

Committee Member

Dihua Yu

Committee Member

M. James You

Committee Member

Chad Huff

Abstract

Li-Fraumeni syndrome (LFS) is an autosomal dominant disease caused by germline mutations in the gene TP53, which predispose individuals to a wide range of malignancies, including osteosarcoma and breast cancer. In the previous study, our group developed a novel disease model platform by reprograming LFS patients' fibroblasts to induced pluripotent stem cells (iPSCs), and further differentiate these iPSCs into mesenchymal stem cells (MSCs) then to osteoblasts (OBs), the cells from which osteosarcomas originate. Interestingly, LFS iPSC-derived osteoblasts recapitulated the osteosarcoma phenotype, creating “a bone tumor in a dish”. This “tumor in a dish” platform proved that LFS is an ideal model system to study and modeling LFS associated malignancies.

In this study, we applied whole exome deep sequencing in LFS iPSCs derived samples carrying different tumorigenic potential (MSCs, OBs, OB derived tumors) to identify cancer drivers that contribute to LFS associated osteosarcomagenesis. We found that LFS patient derived OBs exhibit both in vitro and in vivo oncogenic properties. We also observed increased somatic mutation prevalence in LFS OBs derived tumors compare to LFS OBs. Genes that are commonly mutated between LFS OBs derived tumors and genes carrying truncating or frameshift mutations in LFS OBs derived tumors were identified, including USP34, ANAPC1, ESPL1, MYLK, SLC35G2, FAM160A2, SLC25A32, SYNE2, RPL8, and FAM20A. These genes are potential candidate driver genes during early osteosarcoma development.

Breast cancer is the most common tumor among women with germline TP53 mutations. In this study, we also generated iPSC lines from LFS breast cancer patient and healthy family member. Using precise genome editing tools, we created TP53 mutation (delG) in unaffected relative derived the iPSCs, generating isogenic controls to facilitate studying of mutant p53 related phenotypic differences. We also demonstrated differentiation of LFS iPSCs to non-neural ectoderm using a chemical based protocol. Further establishment of mammary organoids differentiation protocol will provide in vitro platform in modeling LFS associated breast cancer.

In addition, we successfully corrected TP53 mutation (Y205C) in LFS patient derived iPSCs using TALEN-mediated precise gene editing. Similar approach was used to generate two H1 human embryonic stem cells (hESCs) carrying homozygous TP53 R282W and TP53 R248W mutation. These engineered iPSCs/hESCs offers exciting opportunities for studying mechanisms of mutant p53 associated malignancies and testing existing or potential compounds targeting mutant p53-associated pathway.

In summary, our studies demonstrated the potential of LFS patient derived iPSCs in cancer modeling.

Keywords

Li–Fraumeni syndrome, pluripotent stem cells, cancer disease modeling, osteosarcoma, mutant p53, genome editing

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