A novel role of phospho-beta-catenin in microtubule regrowth at centrosome

Beta-catenin is a biologically important molecule playing critical roles in both cell adhesion and transcriptional regulation in the Wnt pathway. Here, we show that phospho-beta-catenin (phosphorylated at Ser33/37/Thr41), which is reported to be degraded immediately after its phosphorylation, accumulated in the centrosome. Whereas phospho-mimicking mutant, S33/37/T41E-beta-catenin, could localize to the centrosome, S33A-beta-catenin that lacks the phosphorylation site lost its localization to the centrosome. Phospho-beta-catenin localized mainly to mother centrosome during the interphase and was recruited to daughter centrosome in M-phase. Depletion of beta-catenin with small interfering RNA or inhibition of its phosphorylation by LiCl treatment caused disruption of radial microtubule (MT) array and retardation of the MT regrowth during the recovery from nocodazole treatment. In addition, these treatments increased the frequency of mono-astral MT reorganization. Furthermore, overexpression of the nonphosphorylatable beta-catenin, but not the phospho-mimicking beta-catenin, markedly disrupted radial MT array and repressed the MT regrowth. In contrast, phospho-mimicking beta-catenin localized to both of the duplicated centrosomes with aberrant larger and denser radial MTs array formation. In addition, some of the cells overexpressing phospho-mimicking beta-catenin had multiple centrosomes. Taken together, this study demonstrates a novel role of phospho-beta-catenin in MT organization at the centrosomes.