Beta-catenin A molecular multiplayer

Beta-catenin (CTNNB1) plays a dual role in the cell, functioning both in cell adhesion and WNT signalling. In cell adhesion, CTNNB1 binds to cadherins in adherens junctions and anchors them to the cytoskeleton. This is crucial for reinforcing cell-cell junctions and maintaining structural integrity. In WNT signalling, CTNNB1 accumulates in the cytoplasm and nucleus in response to WNT stimulation, where it activates target gene transcription essential for processes like embryonic development and adult tissue homeostasis. This thesis delves into the complex balance CTNNB1 must maintain between these two crucial functions. While earlier research has explored the functions of CTNNB1 separately, only a few studies have investigated how the balance between these functions is regulated or if there is interaction between the two functions. We used advanced microscopy techniques were used to visualize the behaviour of endogenously tagged fluorescent CTNNB1 in live cells. Quantification of CTNNB1 levels in different cellular compartments revealed that CTNNB1 accumulates not only in the nucleus and cytoplasm but also at the membrane upon WNT stimulation. As CTNNB1 increases at the membrane were highest at low overall levels of CTNNB1, we propose a model in which the membrane might act as a buffer to regulate nuclear CTNNB1 levels under low levels of WNT activation. Additionally, we explored the impact of matrix stiffness on CTNNB1 distribution and WNT signalling activity. We show that while stiffness affects CTNNB1 distribution, it does not necessarily alter WNT target gene expression. Finally, we propose a set of point mutations in CTNNB1 to affect its interactions with cadherins or alpha-catenin (CTNNA1) as a means to further experimentally shift the balance of CTNNB1 between its functions.