Identification of a Role for β-Catenin in the Establishment of a Bipolar Mitotic Spindle

β-Catenin is a multifunctional protein that is known to participate in two well defined cellular processes, cell-cell adhesion and Wnt-stimulated transcriptional activation. Here we report that β-catenin participates in a third cellular process, the establishment of a bipolar mitotic spindle. During mitosis, β-catenin relocalizes to mitotic spindle poles and to the midbody. Furthermore, biochemical fractionation demonstrates the presence of β-catenin in purified centrosome preparations. Reduction of cellular β-catenin by RNA interference leads to the failure of centrosomes to fully separate, resulting in a marked increase in the frequency of monoastral mitotic spindles. Our results define a new and important function for β-catenin in mitosis and demonstrate that β-catenin is involved in vital biological processes beyond cell adhesion and Wnt signaling.