Regulation of Mitotic Cytoskeleton Dynamics and Cytokinesis by Integrin-Linked Kinase in Retinoblastoma Cells

During cell division integrin-linked kinase (ILK) has been shown to regulate microtubule dynamics and centrosome clustering, processes involved in cell cycle progression, and malignant transformation. In this study, we examine the effects of downregulating ILK on mitotic function in human retinoblastoma cell lines. These retinal cancer cells, caused by the loss of function of two gene alleles (Rb1) that encode the retinoblastoma tumour suppressor, have elevated expression of ILK. Here we show that inhibition of ILK activity results in a concentration-dependent increase in nuclear area and multinucleated cells. Moreover, inhibition of ILK activity and expression increased the accumulation of multinucleated cells over time. In these cells, aberrant cytokinesis and karyokinesis correlate with altered mitotic spindle organization, decreased levels of cortical F-actin and centrosome de-clustering. Centrosome de-clustering, induced by ILK siRNA, was rescued in FLAG-ILK expressing Y79 cells as compared to those expressing FLAG-tag alone. Inhibition of ILK increased the proportion of cells exhibiting mitotic spindles and caused a significant G2/M arrest as early as 24 hours after exposure to QLT-0267. Live cell analysis indicate ILK downregulation causes an increase in multipolar anaphases and failed cytokinesis (bipolar and multipolar) of viable cells. These studies extend those indicating a critical function for ILK in mitotic cytoskeletal organization and describe a novel role for ILK in cytokinesis of Rb deficient cells.