The emerging role of receptor trafficking in signalosome formation and sustained long-term Wnt/ β -catenin signaling

Despite its central role in development, cell homeostasis, and cancer, the mechanisms that induce and transduce Wnt signaling, particularly the role and impact of receptor internalization, have been under discussion for almost two decades. To integrate seemingly contradictory experimental observations into a coherent explanatory framework, we developed a mechanistic computational model that dissects the spatiotemporal regulation of canonical Wnt signaling. For this, a newly optimized multi-level rule-based modeling and simulation approach is employed to describe and simulate the compartmental distribution of extracellular, intracellular, and membrane-associated signaling molecules, as well as a concise representation of the receptor life cycle, including internalization, degradation, and recycling processes.

Our simulations show that cells can compensate for the partial immobilization of receptor complexes by internalization (the movement of molecules into the cell) and rapid recycling (the return of these molecules to the cell membrane). This process ensures the formation of larger and more stable protein-receptor complexes (signalosomes) and the continuation of the signaling process. Our results imply that degradation and recycling are essentially required for stable, long-term signaling (in terms of beta-catenin aggregation). This process is often overlooked in its importance for stable, long-term signal maintenance, and it provides a possible explanation for why excessive signal activation in cancer cells is highly dependent on internalization and recycling processes. Having integrated the concept of rebinding (the process by which proteins return to their original location) and residence time (how long a protein stays in a particular location), the model illustrates the pivotal role of ordered membrane domains (lipid rafts) in the recruitment of proteins such as DVL (Disheveled) to the membrane and their aggregation. This study highlights the complex interplay of cellular processes involved in Wnt signaling, including lateral diffusion, internalization, recycling, and the role of ordered membrane domains. Integrating such a multitude of experimental measurements based on varying cell lines/tissues, experimental approaches, and treatments into a simulation model enables comprehensive and in-depth insights into the mechanistic regulation of canonical Wnt signaling, which will open up new possibilities for modulating Wnt signaling in disease contexts.