The small intestine epithelium is one of the most proliferative tissues in the human body, renewing every 3-5 days. The rapid turnover is sustained by stem cells under the control of Wnt signalling, dictating critical cell behaviours during both embryonic development and adult tissue homeostasis. Deregulation of this pathway is linked to a plethora of diseases including tumorigenesis.
Leucine rich repeat G–protein coupled receptor 5 (Lgr5) is a Wnt pathway receptor that serves as a molecular determinant of stem cells with its ligand R-spondin (RSPO). Despite its importance as a marker for this critical niche, little is known about Lgr5 trafficking and it’s signalling which may be intimately linked. This information is crucial to understand how stem cells perceive and respond to their environment and ultimately for developing specific and successful anticancer strategies.
The key objective of this project was to resolve early critical molecular details that drive Wnt signalling in stem and cancer cells. Utilizing a novel tool, SNAP-tagged Lgr5, we were able to exclusively track the cell membrane subpopulation of the Lgr5 from early molecular events that occur immediately after receptor activation such as endocytosis through to late events such as lysosomal degradation. These experiments led to formulation of a trafficking model of Lgr5 in an unbound and a ligand-bound state. Moreover, insights into interactions with Wnt signalling players, such as RNF43 and Wnt receptor complex components, have been gained. Future studies based on our findings will help detailed characterization of the stem cell marker Lgr5 and may provide further understanding of the molecular mechanism of Lgr5-RSPO-induced Wnt pathway activation in stem cells and cancer.
