Genome-Wide Screen for Context-Dependent Tumor Suppressors Identified Using in Vivo Models for Neoplasia in Drosophila.

Genetic approaches in Drosophila have successfully identified many genes involved in regulation of growth control as well as genetic interactions relevant to the initiation and progression of cancer in vivo Here, we report on large-scale RNAi-based screens to identify potential tumor suppressor genes that interact with known cancer-drivers: the Epidermal Growth Factor Receptor and the Hippo pathway transcriptional cofactor Yorkie. These screens were designed to identify genes whose depletion drove tissue expressing EGFR or Yki from a state of benign overgrowth into neoplastic transformation in vivo We also report on an independent screen aimed to identify genes whose depletion suppressed formation of neoplastic tumors in an existing EGFR-dependent neoplasia model. Many of the positives identified here are known to be functional in growth control pathways. We also find a number of novel connections to Yki and EGFR driven tissue growth, mostly unique to one of the two. Thus, resources provided here would be useful to all researchers who study negative regulators of growth during development and cancer in the context of activated EGFR and/or Yki and positive regulators of growth in the context of activated EGFR. Resources reported here are available freely for anyone to use.

Warburg Effect Metabolism Drives Neoplasia in a Drosophila Genetic Model of Epithelial Cancer.

Cancers develop in a complex mutational landscape. Genetic models of tumor formation have been used to explore how combinations of mutations cooperate to promote tumor formation in vivo. Here, we identify lactate dehydrogenase (LDH), a key enzyme in Warburg effect metabolism, as a cooperating factor that is both necessary and sufficient for epidermal growth factor receptor (EGFR)-driven epithelial neoplasia and metastasis in a Drosophila model. LDH is upregulated during the transition from hyperplasia to neoplasia, and neoplasia is prevented by LDH depletion. Elevated LDH is sufficient to drive this transition. Notably, genetic alterations that increase glucose flux, or a high-sugar diet, are also sufficient to promote EGFR-driven neoplasia, and this depends on LDH activity. We provide evidence that increased LDHA expression promotes a transformed phenotype in a human primary breast cell culture model. Furthermore, analysis of publically available cancer data showed evidence of synergy between elevated EGFR and LDHA activity linked to poor clinical outcome in a number of human cancers. Altered metabolism has generally been assumed to be an enabling feature that accelerates cancer cell proliferation. Our findings provide evidence that sugar metabolism may have a more profound role in driving neoplasia than previously appreciated.

Oncogenic cooperation between Yorkie and the conserved microRNA miR-8 in the wing disc of Drosophila.

Tissue growth has to be carefully controlled to generate well-functioning organs. MicroRNAs are small non-coding RNAs that modulate the activity of target genes and play a pivotal role in animal development. Understanding the functions of microRNAs in development requires the identification of their target genes. Here, we find that miR-8, a conserved microRNA in the miR-200 family, controls tissue growth and homeostasis in the Drosophila wing imaginal disc. Upregulation of miR-8 causes the repression of Yorkie, the effector of the Hippo pathway in Drosophila, and reduces tissue size. Remarkably, co-expression of Yorkie and miR-8 causes the formation of neoplastic tumors. We show that upregulation of miR-8 represses the growth inhibitor brinker, and depletion of brinker cooperates with Yorkie in the formation of neoplastic tumors. Hence, miR-8 modulates a positive growth regulator, Yorkie, and a negative growth regulator, brinker Deregulation of this network can result in the loss of tissue homeostasis and the formation of tumors.

Yorkie and JNK Control Tumorigenesis in Drosophila Cells with Cytokinesis Failure.

Cytokinesis failure may result in the formation of polyploid cells, and subsequent mitosis can lead to aneuploidy and tumor formation. Tumor suppressor mechanisms limiting the oncogenic potential of these cells have been described. However, the universal applicability of these tumor-suppressive barriers remains controversial. Here, we use Drosophila epithelial cells to investigate the consequences of cytokinesis failure in vivo. We report that cleavage defects trigger the activation of the JNK pathway, leading to downregulation of the inhibitor of apoptosis DIAP1 and programmed cell death. Yorkie overcomes the tumor-suppressive role of JNK and induces neoplasia. Yorkie regulates the cell cycle phosphatase Cdc25/string, which drives tumorigenesis in a context of cytokinesis failure. These results highlight the functional significance of the JNK pathway in epithelial cells with defective cytokinesis and elucidate a mechanism used by emerging tumor cells to bypass this tumor-suppressive barrier and develop into tumors.

Cancer in Drosophila: Imaginal Discs as a Model for Epithelial Tumor Formation.

Cancer genomics has greatly increased our understanding of the complexity of the genetic and epigenetic changes found in human tumors. Understanding the functional relationships among these elements calls for the use of flexible genetic models. We discuss the use of Drosophila models to study cooperation among genetic factors that contribute to disease progression.

Cell Competition Drives the Formation of Metastatic Tumors in a Drosophila Model of Epithelial Tumor Formation.

Cell competition is a homeostatic process in which proliferating cells compete for survival. Elimination of otherwise normal healthy cells through competition is important during development and has recently been shown to contribute to maintaining tissue health during organismal aging. The mechanisms that allow for ongoing cell competition during adult life could, in principle, contribute to tumorigenesis. However, direct evidence supporting this hypothesis has been lacking. Here, we provide evidence that cell competition drives tumor formation in a Drosophila model of epithelial cancer. Cells expressing EGFR together with the conserved microRNA miR-8 acquire the properties of supercompetitors. Neoplastic transformation and metastasis depend on the ability of these cells to induce apoptosis and engulf nearby cells. miR-8 expression causes genome instability by downregulating expression of the Septin family protein Peanut. Cytokinesis failure due to downregulation of Peanut is required for tumorigenesis. This study provides evidence that the cellular mechanisms that drive cell competition during normal tissue growth can be co-opted to drive tumor formation and metastasis. Analogous mechanisms for cytokinesis failure may lead to polyploid intermediates in tumorigenesis in mammalian cancer models.