Oncogenic Signaling & Development

Hyperactivation of the mitogen-activated kinase (MAPK) signaling pathway is one of the most common events in many cancers. This signaling pathway requires input from transmembrane receptors that transduce signals via the small GTPase Ras (LET-60 in C. elegans), which regulates transcription factors that control a variety of cellular processes such as proliferation, differentiation, and cell survival. Although much is known about the consequences of Ras/MAPK pathway activation in cancer very little is known about mechanisms that establish and maintain signaling thresholds under normal conditions. We first became interested in how the Ras/MAPK pathway is regulated after showing that the insulin-like growth factor receptor (DAF-2) is required for proper MAPK activity necessary for eliminating cells in the germline that have been exposed to genotoxic stress (Perrin et al., 2013). Using the C. elegans germline and vulva as model systems we are taking advantage of genetics, proteomics and cell biology techniques to defining the mechanisms by which Ras/MAPK signaling is regulated during normal development and in response to cellular stress. In parallel, we are actively investigating if these genes and mechanisms are conserved in the regulation of MAPK in human cells and vertebrate models.

Aishwarya Subramanian - postdoctoral fellowAishwarya (postdoctoral fellow) is leading a project using C. elegans as well as patient-derived cancer cell lines to identify new genes and pathways that are required to sustain oncogenic Ras/MAPK activity. Constitutive activation of the mitogen-activated kinase (MAPK) pathway is predominant in many cancers, with mutations leading to activation of the small GTPase Ras. Oncogenic gain-of-function (gf) mutations in Ras/let-60 cause a multivulva (Muv) phenotype, where worms develop ectopic vulvae along their hypodermis. This phenotype is a highly sensitive readout for Ras activity and has been used to identify key regulators of Ras signaling. Although numerous studies have provided insights into the genetics of Ras signaling, there remain significant gaps in our understanding of how Ras maintains cells in the transformed state.

Efforts to target Ras for cancer therapy have also been largely unsuccessful. Through collaborations with Mads Daugaard (University of British Columbia,) Michael Wilson (SickKids), and Meredith Irwin (SickKids), she is using RNA sequencing to survey the transcriptome to determine how changes in RNA processing, such as alternative polyadenylation, cooperate with oncogenic Ras/LET-60 to regulate cell proliferation and differentiation. Using C. elegans as an in vivo model system, we have uncovered a novel mechanism whereby alterations in mRNA processing contribute to Ras-driven oncogenesis. Our aim is to translate these findings into human cancers using both established and patient-derived cancer cell lines in order to identify novel transcripts that sustain oncogenic Ras activity.

Vulva

Cell Fate

Multicellular organisms can contain trillions of cells and hundreds of different cell types that precisely sculpt a variety of tissues and organs during development. One question we are interested in is how cells know when and whether to divide to generate the appropriate number of progeny required to build an organ. Additionally, how is their growth, migration and differentiation, and in some cases suicide, controlled to meet the precise physical morphology of an organ?

Matthew ErogluMatthew’s (PhD candidate) research focuses on identifying novel genes that regulate organ development and how cell fate decisions are made during development of the C. elegans vulva. A single fertilized egg cell gives rise to all the tissues and organs of multicellular organisms. Yet, how does this cell know precisely what to do at each step? Scientists have historically used model organisms such as C. elegans to uncover fundamental signaling networks that orchestrate cell proliferation, migration, differentiation, and programmed death to precisely sculpt all the tissues and organs of an organism.

Whereas loss-of-function mutations in Ras lead to ablation of the vulva, gain-of-function mutations in Ras analogous to cancer-causing mutations in humans lead to development of multiple vulva-like protrusions in C. elegans. Wild-type worms always develop a single functional vulva, however, indicating precise regulation of Ras signaling. He recently identified an uncharacterized gene family that is required for cell fate determination in different tissues, as well as a novel role for these genes in organism lifespan. Overall, this project will inform how Ras signaling is fine-tuned during normal development to ensure proper tissue and cellular function as well as how aberrations in it can lead to deleterious outcomes. Matthew is currently using genomics and proteomics to understand how these genes and their protein products are organized into genetic and physical networks. Some techniques Matthew uses include RNAi and forward genetic screens, gene editing using CRISPR/Cas9, immunoprecipitation-mass spectrometry, next generation sequencing, and time-lapse confocal microscopy.

Anson (MSc candidate) is working with Aishwarya on the alternative polyadenylation (APA) project. He is specifically interested in how cfim-1 (NUDT21 in humans) and other components of the APA machine modulate Ras/MAPK signaling in worms and in neuroblastoma, an aggressive pediatric cancer. Anson is using genetics and high resolution imaging to investigate the role of cfim-1 in vulva and germline development. Although NUDT21 is an essential gene in mammals, cfim-1 mutants are viable in C. elegans but lethal under stressful conditions. Because of this, Anson is conducting a selection screen using mutagen to identify suppressors of cfim-1.