Functional characterization of genetic alterations in cancer

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Functional characterization of genetic alterations in cancer

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Title: Functional characterization of genetic alterations in cancer
Author: Kim, Eejung
Citation: Kim, Eejung. 2016. Functional characterization of genetic alterations in cancer. Doctoral dissertation, Harvard University, Graduate School of Arts & Sciences.
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Abstract: The comprehensive identification of genetic alterations is critical to understanding the pathophysiology of cancer. Recent advances in sequencing technology have enabled the detailed description of cancer genomes. However, to translate these findings into a deeper understanding of cancer biology, analyzing the functional impact of cancer-associated genetic aberration is essential. Here I investigate how to accelerate the functional characterization of two classes of genetic alterations, point mutations and amplifications.

The wide spectrum of point mutations that arise in cancer makes them challenging to study comprehensively. I have developed a scalable systematic method to experimentally infer the functional impact of cancer-associated gene variants. I performed pooled in vivo tumor formation assays and gene expression profiling using 474 mutant alleles curated from 5,338 human tumors. I identified 12 transforming alleles including two in genes (PIK3CB, POT1) that have not been previously shown to be tumorigenic. One rare KRAS allele, D33E, displayed tumorigenicity and constitutive activation of RAS effector pathways. By correlating gene expression changes induced upon expression of wild type and mutant alleles, I could infer the activity of specific alleles. These approaches enable the interrogation of cancer-associated alleles at scale and demonstrate that rare alleles may be functionally important.

Frequently amplified regions in cancer often harbor oncogenic drivers. However, identifying the driver gene among many other amplified genes is challenging. In high-grade serous ovarian cancer (HGSOC), 1,825 genes are amplified across 63 amplicons. We employed systematic loss-of-function RNAi data to identify amplified genes that were essential in the ovarian lineage. We identified 50 amplified and essential genes and validated FRS2, an adaptor protein in FGFR pathway. FRS2-amplified cancer cell lines were dependent on FRS2 expression and FRS2 overexpression in immortalized cell lines was sufficient to promote anchorage independent growth and tumorigenesis in nude mice. This approach demonstrates that intersecting structural genomics with functional genomics can facilitate the discovery of driver genes in recurrently amplified regions. Collectively, the methods I present here provide a framework to study point mutations and amplifications to accelerate the interpretation of the cancer genome.
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