The Role Of NudC In Actin Dynamics And Ciliogenesis

Cilia are microtubule-based organelles projecting from the surface of most vertebrate cell types. According to the motion features of cilia, they can be divided into two types: motile cilia and non-motile cilia (primary cilia). Motile cilia can swing regularly, while non-motile cilia play pivotal roles in signals transduction, embryonic development and tissue homeostasis. Defects in ciliary assembly or function lead to a wide range of human diseases termed ciliopathies, including polycystic kidney disease, hydrocephalus and cancer et al. Recently, some studies indicate that actin dynamic is involved in ciliogenesis. Disrupting actin nectwork facilities ciliogenesis by promting the pericentrosomal prediliary compartment (PPC) accumulating at basal body.A number of studies in the filamentous fungus Aspergillus nidulans have demonstrated that the genes in the nuclear distribution (nud) pathway are homologs to components or regulators of the cytoplasmic dynein complex. For example, the NudA, NudG, and NudI genes encode cytoplasmic dynein heavy, light, and intermediate chain, respectively. The NudF gene encodes an Aspergillus ortholog of LIS1, a crucial regulator of dynein. In the filamentous fungus Aspergillus nidulans, NudF, the homology of Lis1 is regulated by NudC which mutation significantly reduces the protein level of NudF. However, the cellular function of NudC remains poorly defined. We and other groups have found that NudC functions as an Hsp90 cochaperone to play vital roles in diverse cellular processes, including cell division and migration, possibly by modulating the LIS1/dynein complex. The mass spectrometry data of the proteins co-immunoprecipitated with NudC suggested that a number of actin binding proteins appear to be candidates for NudC- interacting protein. Moreover, it has been reported that NudC is highly expressed in ciliated epithelia. But, the role of NudC in actin cytoskeleton and ciliogenesis remains unknown.To illustrate the functions of NudC in actin dynamics, we employed lentivirus-mediated RNAi to down regulate the protein level of NudC. Depletion of NudC causes an accumulation of bundled stress fibers and inhibition of cell spreading and lamellipodia formation, resembling the cellular phenotypes induced by knockdown of cofilin 1, resembling the cellular phenotypes induced by knockdown of cofilin 1. Further data show that NudC forms a biochemical complex with cofilin 1 to prevent its degradation. These data indicate for the first time that NudC may stabilize cofilin 1 to regulate actin cytoskeleton and dynamics.Since it has been reported that actin dynamics contributes to ciliogenesis in mammalian cells, we examined the potential role of NudC in primary cilia assembly, n this study, we find that NudC depletion promotes cilia elongation and increases the percentage of ciliated cells in mammalian cells. Furthermore, ectopic expression of cofilin 1 significantly reverses the phenotypes induced by NudC depletion in cultured cells. Thus, our results suggest that NudC acts upstream of cofilin 1 to modulate ciliogenesis and vertebrate development. As inhibition of actin dynamics has been shown to induce ciliogenesis by accumulating ciliogenic membrane vesicles positive for Rablla around the centrosome regions, we tested if NudC depletion promotes ciliogenesis via the similar mechanism. In NudC-depleted RPE1 cells, Rabl la-positive vesicles were more frequently accumulated around the centrosome region compared with the control cells. Furthermore, overexpression of NudC considerably inhibited ciliation in serum-starved RPE-1 cells. Thus, these results suggest that NudC plays an inhibitory role in ciliogenesis in mammalian cells.Cofilin 1 has a central role in controlling actin polymerization and depolymerization through its severing activity. This process has been seen in various pathogeneses including tumor metastasis and inflammation. However, the regulation of cofilin 1 stability is largely unknown. Here we provide strong evidence that NudC forms abiochemical complex with cofilin 1 in mammalian cells. NudC depletion substantially decreased the protein level of cofilin 1, but not its mRNA level. Furether studies show that NudC depletion induces robust degradation of cofilin 1 via the ubiquitin-proteasome pathway, implying a previously uncharacterized machinery formaintaining the stability of cofilin 1.Overall, our functional and biochemical data suggest that NudC regulates actin dynamics, ciliogenesis and developmental processes by stabilizing cofilin 1...