IKKɛ Regulates F Actin Assembly and Interacts with Drosophila IAP1 in Cellular Morphogenesis

SummaryDifferentiated cells assume complex shapes through polarized cell migration and growth. These processes require the restricted organization of the actin cytoskeleton at limited subcellular regions. IKKɛ is a member of the IκB kinase family, and its developmental role has not been clear. Drosophila IKKɛ was localized to the ruffling membrane of cultured cells and was required for F actin turnover at the cell margin. In IKKɛ mutants, tracheal terminal cells, bristles, and arista laterals, which require accurate F actin assembly for their polarized elongation, all exhibited aberrantly branched morphology. These phenotypes were sensitive to a change in the dosage of Drosophila inhibitor of apoptosis protein 1 (DIAP1) and the caspase DRONC without apparent change in cell viability. In contrast to this, hyperactivation of IKKɛ destabilized F actin-based structures. Expression of a dominant-negative form of IKKɛ increased the amount of DIAP1. The results suggest that at the physiological level, IKKɛ acts as a negative regulator of F actin assembly and maintains the fidelity of polarized elongation during cell morphogenesis. This IKKɛ function involves the negative regulation of the nonapoptotic activity of DIAP1.