Doctor of Philosophy

dissertationEwing sarcoma is a devastating pediatric tumor that is particularly aggressive and highly metastatic. The current treatment regimen for this malignancy is aggressive, invasive and toxic, but with limited success. Treatment of metastatic or relapsed Ewing sarcoma is even more dismal with a low 5-year patient survival. My research is focused on identifying new mechanisms that could explain early and extensive metastasis in Ewing sarcoma potentially enabling better disease outcome in the future. In the majority of Ewing sarcoma cases, the causal oncoprotein EWS/FLI develops from the reciprocal chromosomal translocation t(11;22)(q24;q12). For this dissertation, I analyzed the effect of EWS/FLI oncoprotein on the cellular behavior of multiple patient-derived Ewing sarcoma cell lines, and discovered that EWS/FLI compromises the cytoskeletal framework of cells. As a result, Ewing sarcoma cells display small round cell morphology and low cellular adhesion. I further show that these EWS/FLI-dependent changes in cell behavior in vitro are pertinent to tumor cell behavior in vivo and could provide relevant insight into the cell of origin for Ewing sarcoma. Based on these observations, I suggest a new model where the inciting oncogenic event could affect tumor cell adhesion to permit early dissemination of tumor cells or increased colonization of tumor cells at a secondary site, to explain early metastasis of tumor cells. In this dissertation the analysis of the EWS/FLI transcriptome, revealed that focal adhesion proteins, extracellular matrix components, and actin cytoskeletal modulators were most downregulated by EWS/FLI expression. Two focal adhesion proteins namely iv zyxin and the fibronectin receptor α5 integrin were shown to play vital roles in modulating Ewing sarcoma cell morphology, cytoskeletal structure, spreading and adhesion. To adequately study the tumor progression and metastasis of Ewing sarcoma, I developed an intratibial orthotopic mouse model. The Ewing sarcoma tumors grew aggressively in mice and spontaneously metastasized from the tibia to lungs and other bones. This model system recapitulates key features pertinent to the human disease. Taken together, the work described in this dissertation reveals the important role of EWS/FLI mediated downregulation of adhesion proteins in modulating essential cellular features, such as cell adhesion and cytoskeletal structure, to govern oncogenic transformation and metastasis

Molecular dissection of the mechanism by which EWS/FLI expression compromises actin cytoskeletal integrity and cell adhesion in Ewing sarcoma.

Ewing sarcoma is the second-most-common bone cancer in children. Driven by an oncogenic chromosomal translocation that results in the expression of an aberrant transcription factor, EWS/FLI, the disease is typically aggressive and micrometastatic upon presentation. Silencing of EWS/FLI in patient-derived tumor cells results in the altered expression of hundreds to thousands of genes and is accompanied by dramatic morphological changes in cytoarchitecture and adhesion. Genes encoding focal adhesion, extracellular matrix, and actin regulatory proteins are dominant targets of EWS/FLI-mediated transcriptional repression. Reexpression of genes encoding just two of these proteins, zyxin and α5 integrin, is sufficient to restore cell adhesion and actin cytoskeletal integrity comparable to what is observed when the EWS/FLI oncogene expression is compromised. Using an orthotopic xenograft model, we show that EWS/FLI-induced repression of α5 integrin and zyxin expression promotes tumor progression by supporting anchorage-independent cell growth. This selective advantage is paired with a tradeoff in which metastatic lung colonization is compromised

Opposing transcriptional programs of KLF5 and AR emerge during therapy for advanced prostate cancer.

Endocrine therapies for prostate cancer inhibit the androgen receptor (AR) transcription factor. In most cases, AR activity resumes during therapy and drives progression to castration-resistant prostate cancer (CRPC). However, therapy can also promote lineage plasticity and select for AR-independent phenotypes that are uniformly lethal. Here, we demonstrate the stem cell transcription factor Krüppel-like factor 5 (KLF5) is low or absent in prostate cancers prior to endocrine therapy, but induced in a subset of CRPC, including CRPC displaying lineage plasticity. KLF5 and AR physically interact on chromatin and drive opposing transcriptional programs, with KLF5 promoting cellular migration, anchorage-independent growth, and basal epithelial cell phenotypes. We identify ERBB2 as a point of transcriptional convergence displaying activation by KLF5 and repression by AR. ERBB2 inhibitors preferentially block KLF5-driven oncogenic phenotypes. These findings implicate KLF5 as an oncogene that can be upregulated in CRPC to oppose AR activities and promote lineage plasticity

The clone wars - revenge of the metastatic rogue state: the sarcoma paradigm.

Ewing sarcoma (ES) is the second most common bone tumor affecting primarily adolescents and young adults. Despite recent advances in biological understanding, intensification of chemotherapeutic treatments, and progress in local control with surgery and/or radiation therapy, patients with metastatic or recurrent ES continue to have a dismal prognosis with less than 20% overall survival. All ES is likely metastatic at diagnosis although our methods of detection and classification may not account for this. Progressive disease may arise via a combination of: (1) selection of chemotherapy-resistant clones in primary tumor, (2) signaling from bone or lung microenvironments that may attract tumor cells to distant locations, and/or (3) genetic changes within the ES cells themselves due to DNA-damaging chemotherapeutic agents or other "hits." These possibilities and the evidence base to support them are explored

The clone wars - revenge of the metastatic rogue state: the sarcoma paradigm.

Ewing sarcoma (ES) is the second most common bone tumor affecting primarily adolescents and young adults. Despite recent advances in biological understanding, intensification of chemotherapeutic treatments, and progress in local control with surgery and/or radiation therapy, patients with metastatic or recurrent ES continue to have a dismal prognosis with less than 20% overall survival. All ES is likely metastatic at diagnosis although our methods of detection and classification may not account for this. Progressive disease may arise via a combination of: (1) selection of chemotherapy-resistant clones in primary tumor, (2) signaling from bone or lung microenvironments that may attract tumor cells to distant locations, and/or (3) genetic changes within the ES cells themselves due to DNA-damaging chemotherapeutic agents or other "hits." These possibilities and the evidence base to support them are explored

Molecular dissection of the mechanism by which EWS/FLI expression compromises actin cytoskeletal integrity and cell adhesion in Ewing sarcoma.

Ewing sarcoma is the second-most-common bone cancer in children. Driven by an oncogenic chromosomal translocation that results in the expression of an aberrant transcription factor, EWS/FLI, the disease is typically aggressive and micrometastatic upon presentation. Silencing of EWS/FLI in patient-derived tumor cells results in the altered expression of hundreds to thousands of genes and is accompanied by dramatic morphological changes in cytoarchitecture and adhesion. Genes encoding focal adhesion, extracellular matrix, and actin regulatory proteins are dominant targets of EWS/FLI-mediated transcriptional repression. Reexpression of genes encoding just two of these proteins, zyxin and α5 integrin, is sufficient to restore cell adhesion and actin cytoskeletal integrity comparable to what is observed when the EWS/FLI oncogene expression is compromised. Using an orthotopic xenograft model, we show that EWS/FLI-induced repression of α5 integrin and zyxin expression promotes tumor progression by supporting anchorage-independent cell growth. This selective advantage is paired with a tradeoff in which metastatic lung colonization is compromised

A Novel Role for Keratin 17 in Coordinating Oncogenic Transformation and Cellular Adhesion in Ewing Sarcoma

Oncogenic transformation in Ewing sarcoma is caused by EWS/FLI, an aberrant transcription factor fusion oncogene. Glioma-associated oncogene homolog 1 (GLI1) is a critical target gene activated by EWS/FLI, but the mechanism by which GLI1 contributes to the transformed phenotype of Ewing sarcoma was unknown. In this work, we identify keratin 17 (KRT17) as a direct downstream target gene upregulated by GLI1. We demonstrate that KRT17 regulates cellular adhesion by activating AKT/PKB (protein kinase B) signaling. In addition, KRT17 is necessary for oncogenic transformation in Ewing sarcoma and accounts for much of the GLI1-mediated transformation function but via a mechanism independent of AKT signaling. Taken together, our data reveal previously unknown molecular functions for a cytoplasmic intermediate filament protein, KRT17, in coordinating EWS/FLI- and GLI1-mediated oncogenic transformation and cellular adhesion in Ewing sarcoma

Molecular dissection of the mechanism by which EWS/FLI expression compromises actin cytoskeletal integrity and cell adhesion in Ewing sarcoma

Ewing sarcoma is the second-most-common bone cancer in children. Driven by an oncogenic chromosomal translocation that results in the expression of an aberrant transcription factor, EWS/FLI, the disease is typically aggressive and micrometastatic upon presentation. Silencing of EWS/FLI in patient-derived tumor cells results in the altered expression of hundreds to thousands of genes and is accompanied by dramatic morphological changes in cytoarchitecture and adhesion. Genes encoding focal adhesion, extracellular matrix, and actin regulatory proteins are dominant targets of EWS/FLI-mediated transcriptional repression. Reexpression of genes encoding just two of these proteins, zyxin and α5 integrin, is sufficient to restore cell adhesion and actin cytoskeletal integrity comparable to what is observed when the EWS/FLI oncogene expression is compromised. Using an orthotopic xenograft model, we show that EWS/FLI-induced repression of α5 integrin and zyxin expression promotes tumor progression by supporting anchorage-independent cell growth. This selective advantage is paired with a tradeoff in which metastatic lung colonization is compromised