Investigating the Effect of Tumour Suppressor PTEN/DAF-18 Variants and Mammalian Insulin on the Insulin and Insulin-like Signaling Pathway in Caenorhabditis elegans

Abstract

The insulin and insulin-like growth factor signaling (IIS) pathway is an anabolic, growth stimulating pathway highly conserved among humans and Caenorhabditis elegans (C. elegans). In humans, the tumour suppressor protein Phosphatase and Tensin Homolog (PTEN) inhibits IIS, preventing excessive growth and development. The first aim of this research was to explore the effect of mammalian insulin on the development of C. elegans. A potential treatment for diseases involving hyperactivation of the IIS pathway might involve an engineered antagonistic human insulin which could bind to the insulin receptor and downregulate it through competitive inhibition. However, if C. elegans is to be used as a model to study human insulin, we first need to elucidate the effect of the human insulin on C. elegans. If human insulin can have an agonistic effect on our model organism, then we might be able to use it as an assay to assess the function of human insulin in vivo. In our research, we found that human insulin behaves as an antagonist when expressed transgenically, but agonistically when delivered exogenously. Furthermore, the antagonistic effects of transgenic human insulin were mediated by co-injection of F peptide, a peptide found in agonistic insulins of C. elegans. The second aim of this thesis was to characterize variants of the human tumour suppressor PTEN implicated in autism spectrum disorder (ASD) by looking at the effect of 5 variants in the homologous C. elegans protein DAF-18. By determining the effects of these mutations, we can potentially infer how these variants play a role in human disease formation, such as the development of ASD. We found that variants D66E, L115V, and H168Q are more likely to be benign while variants H138R and T176I are more likely to be pathogenic. Overall, this work reveals the effect of human insulin on the C. elegans IIS pathway and characterizes several variants of unknown significance of the PTEN protein, which has the potential to be clinically relevant when it comes to diseases involving dysregulated insulin signaling such as hyperinsulinemia or cancer.