Abstract 919: A genome-wide screen in C. elegans identifies cell non-autonomous suppressors of let-60/RAS mediated oncogenic over-proliferation
Authors: Rambani Komal , Kladney Raleigh , Chang Serena , Harrigan Markus , Dowdle James , Tang Xing , Liu Huayang , Brunner Elizabeth , Chamberlin Helen , Leone Gustavo 
Published: July 2016

Coordinated proliferative signals from the mesenchymal cells play a crucial role in the regulation of proliferation of epithelial cells during normal development, wound healing and several other normal physiological conditions. However, when epithelial cells acquire a set of malignant mutations, they respond differently to these extrinsic proliferative signals leading to enhanced abnormal proliferation of mutant epithelial cells and hence tumor growth. Despite mounting evidence that stromal cells influence the growth of tumors and cancer progression, it is unclear which specific genes in these mesenchymal cells regulate the molecular signals that promote the over-proliferation of the adjacent mutant cells. The complexity of several cell types and their interactions in vivo in the cancer mouse models and human tumor samples limits our ability to identify mesenchymal genes important in this process. Thus, we took a cross species approach to use C. elegans vulval development as a model to better understand the impact of mesenchymal (mesodermal) cells on the proliferation of the epithelial (epidermal) cells. This model includes well-described signaling interactions between mesodermal (anchor cell, gonad, and muscle) cells and epidermal (vulva precursor cells, VPCs) cells. In this system, three of the six equipotent VPCs normally acquire vulva fates (termed 1° and 2°) upon receiving coordinated EGF and Wnt signals from the mesodermal cells, and lateral Notch signaling between the VPCs. Then, they divide 3 times to produce a symmetric vulva comprised of 22 daughter cells. Abnormal activation of the EGF pathway, such as by introducing gain-of-function (gf) mutations in let-60/Ras, leads to the promotion of vulval fates in the remaining three VPCs, which then divide inappropriately resulting in development of multiple vulval protrusions (Muv phenotype).To identify genes that function in mesodermal cells to inhibit the proliferation of Ras-activated epidermal cells, we genetically engineered C. elegans to develop a strain that possesses let-60(gf)/Ras mediated over-proliferation (Muv phenotype) and RNA interference (RNAi) competence specific to the mesodermal tissues. This strain was subjected to a genome-wide RNAi screen. Our screen identified 47 genes that, upon RNAi knock-down of a gene in mesodermal cells, suppress over-proliferation of let-60(gf)/Ras epithelial cells in a genotype-specific manner. Notably, these genes encode chromatin remodeling proteins, ribosomal proteins, proteins involved in vesicle transport, and metabolic factors, rather than secreted molecules. Importantly, candidate genes emerged from this screen are significantly enriched for the conserved genes from C. elegans to humans. These results form an initial understanding of molecular factors in mesenchymal cells that impact oncogenic cell proliferation.

Citation Format: Komal Rambani, Raleigh Kladney, Serena Chang, Markus Harrigan, James Dowdle, Xing Tang, Huayang Liu, Elizabeth Brunner, Helen Chamberlin, Gustavo Leone. A genome-wide screen in C. elegans identifies cell non-autonomous suppressors of let-60/RAS mediated oncogenic over-proliferation. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 919.