New results from Fielding et al. place a kinase found in focal adhesions on centrosomes. There, the kinase helps arrange microtubules rather than actin.
Focal adhesions contain a mass of proteins that link matrix-bound integrins to the actin cytoskeleton. Within that mass is integrin-linked kinase (ILK), which phosphorylates other focal adhesion proteins during cell spreading and migration. While searching for ILK binding partners, Fielding and colleagues fished out an unexpected class of cytoskeletal proteins—tubulins.
In addition to α- and β-tubulin, several centrosomal microtubule-binding proteins were identified. The localization of active ILK and its partners to centrosomes was necessary for proper spindle formation during mitosis. The absence of ILK disrupted a complex of centrosomal proteins that includes Aurora A. In these cells, microtubules polymerized from only one pole and did not reach the DNA.
Although it is not clear how ILK creates a bipolar spindle, the authors hypothesize that it might be needed for centrosome duplication before mitosis. They are now using a proteomics approach to identify centrosomal targets of the kinase.