The O’Donnell laboratory is focused on understanding the mechanisms that contribute to tumor initiation, progression, and metastasis. Our laboratory has made significant contributions to the development and utilization of ex vivo and in vivo transposon mutagenesis systems for the discovery of new cancer genes. Using these systems, we have identified novel genes that promote liver cancer, leukemia, and non-small cell lung cancer. These approaches enabled our discovery of oncogenic cell surface receptors in lung cancer, which we are currently investigating using molecular and biochemical studies, and mouse models. These studies may provide new therapeutic approaches to target cancer cells.

Functional annotation of cancer genomes through transposon mutagenesis

A Sleeping Beauty-mediated transposon mutagenesis screen previously performed in our laboratory identified mutations that cooperate with MYC to accelerate liver tumorigenesis in vivo (O’Donnell et al, PNAS, 2012). This revealed a tumor suppressor role for Steroid Receptor Coactivator 2/Nuclear Receptor Coactivator 2 (Src-2/Ncoa2) in liver cancer. In contrast, SRC-2 promotes survival and metastasis in prostate cancer cells, suggesting a tissue-specific and context-dependent role for SRC-2 in tumorigenesis. To determine if genetic loss of SRC-2 is sufficient to accelerate MYC-mediated liver tumorigenesis, we bred Src-2 -/- mice with a MYC-induced liver tumor model and observed a significant increase in liver tumor burden. RNA sequencing of liver tumors and in vivo chromatin immunoprecipitation assays revealed a set of direct target genes that are bound by SRC-2 and exhibit downregulated expression in Src-2 -/- liver tumors. We recently demonstrated that activation of SHP (Small Heterodimer Partner), DKK4 (Dickkopf-4), and CADM4 (Cell Adhesion Molecule 4) by SRC-2 suppresses tumorigenesis in vitro and in vivo (Suresh et al, PLoS Genetics, 2017). These studies suggest that SRC-2 may exhibit oncogenic or tumor suppressor activity depending on the target genes and nuclear receptors that are expressed in distinct tissues and illuminate the mechanisms of tumor suppression by SRC-2 in liver.

Establishment of an ex vivo mutagenesis system

Aberrant signaling through cytokine receptors and their downstream signaling pathways is a major oncogenic mechanism underlying hematopoietic malignancies. To better understand how these pathways become pathologically activated and to potentially identify new drivers of hematopoietic cancers, we developed a high-throughput functional screening approach using ex vivo mutagenesis with the Sleeping Beauty transposon (Guo et al, Cancer Research, 2016). We analyzed over 1100 transposon-mutagenized pools of Ba/F3 cells, an IL-3-dependent pro-B cell line, which acquired cytokine independence and tumor-forming ability. Recurrent transposon insertions could be mapped to genes in the JAK/STAT and MAPK pathways, confirming the ability of this strategy to identify known oncogenic components of cytokine signaling pathways. Additionally, recurrent insertions were identified in a large set of genes that have been found to be mutated in leukemia or associated with survival, but were not previously linked to the JAK/STAT or MAPK pathways nor shown to functionally contribute to leukemogenesis. Forced expression of these novel genes resulted in IL-3-independent growth in vitro and tumorigenesis in vivo, validating this mutagenesis-based approach for identifying new genes that promote cytokine signaling and leukemogenesis. Taken together, these findings provided a broadly applicable approach for classifying functionally relevant genes in diverse malignancies and offer new insights into the impact of cytokine signaling on leukemia development.

Investigating the regulation and function of cell surface receptors in lung cancer pathogenesis

Non-small cell lung cancer (NSCLC) is the leading cause of cancer-associated deaths worldwide. Given the exciting potential of targeting membrane proteins in human malignancies using therapeutic antibodies, we sought to identify cell-surface receptors that act as drivers of lung tumorigenesis. We recently reported that PROTOCADHERIN 7 (PCDH7), a transmembrane receptor and member of the Cadherin superfamily, is frequently overexpressed in NSCLC tumors, and high expression of PCDH7 is associated with poor clinical outcome (Zhou et al, Cancer Research, 2017). PCDH7 overexpression synergizes with KRAS and EGFR to induce MAPK signaling and tumorigenesis. Moreover, PCDH7 depletion suppressed ERK activation, sensitized cells to MEK inhibitors, and reduced tumor growth. PCDH7 potentiates ERK signaling by facilitating interaction of Protein Phosphatase 2A (PP2A) with its potent inhibitor, the SET oncoprotein. These findings establish a previously uncharacterized oncogenic role for PCDH7 in lung tumorigenesis and provide proof-of-concept support for the development of novel therapies that target PCDH7 at the cell surface of NSCLC cells. Our lab is currently investigating the mechanisms through which several cell surface receptors including PCDH7 promote lung cancer pathogenesis.