Quantitative live-cell imaging and computational modeling shed new light on endogenous WNT/CTNNB1 signaling dynamics

WNT/CTNNB1 signaling regulates tissue development and homeostasis in all multicellular animals, but the underlying molecular mechanism remains incompletely understood. Specifically, quantitative insight into endogenous protein behavior is missing. Here, we combine CRISPR/Cas9-mediated genome editing and quantitative live-cell microscopy to measure the dynamics, diffusion characteristics and absolute concentrations of fluorescently tagged, endogenous CTNNB1 in human cells under both physiological and oncogenic conditions. State-of-the-art imaging reveals that a substantial fraction of CTNNB1 resides in slow-diffusing cytoplasmic complexes, irrespective of the activation status of the pathway. This cytoplasmic CTNNB1 complex undergoes a major reduction in size when WNT/CTNNB1 is (hyper)activated. Based on our biophysical measurements, we build a computational model of WNT/CTNNB1 signaling. Our integrated experimental and computational approach reveals that WNT pathway activation regulates the dynamic distribution of free and complexed CTNNB1 across different subcellular compartments through three regulatory nodes: the destruction complex, nucleocytoplasmic shuttling, and nuclear retention.

Automated summary

WNT/CTNNB1 signaling regulates tissue development and homeostasis in multicellular animals by affecting the dynamic distribution of CTNNB1 through regulatory nodes including the destruction complex, nucleocytoplasmic shuttling, and nuclear retention, as revealed by an integrated experimental and computational approach. The study found that a substantial fraction of CTNNB1 resides in slow-diffusing cytoplasmic complexes, which undergo a major reduction in size when the pathway is hyperactivated. The research provides quantitative insight into endogenous protein behavior and sheds light on the molecular mechanism underlying WNT/CTNNB1 signaling.