TonEBP degradation is essential for microtubule nucleation and regrowth.

TonEBP is a transcription factor known for its involvement in diverse physiological processes, including cell cycle, mitosis, migration, and cytoskeletal remodeling. However, the role of TonEBP regarding microtubules, essential structural components of the cytoskeleton, remains unclear. Here, we introduce a novel function for TonEBP as a regulator of microtubule nucleation. Our initial findings reveal that Nocodazole, a well-known microtubule depolymerizing agent, significantly downregulates the protein level of TonEBP. Moreover, microtubule depolymerization induces rapid degradation of TonEBP through the ubiquitin-proteasome pathway. Knockdown of TonEBP results in enhanced microtubule polymerization and regrowth, whereas the presence of TonEBP impairs microtubule nucleation. Collectively, our data suggest that TonEBP negatively regulates microtubule nucleation.

TonEBP inhibits ciliogenesis by controlling aurora kinase A and regulating centriolar satellite integrity.

BACKGROUND: Primary cilia on the surface of eukaryotic cells serve as sensory antennas for the reception and transmission in various cell signaling pathways. They are dynamic organelles that rapidly form during differentiation and cell cycle exit. Defects in these organelles cause a group of wide-ranging disorders called ciliopathies. Tonicity-responsive enhancer-binding protein (TonEBP) is a pleiotropic stress protein that mediates various physiological and pathological cellular responses. TonEBP is well-known for its role in adaptation to a hypertonic environment, to which primary cilia have been reported to contribute. Furthermore, TonEBP is involved in a wide variety of other signaling pathways, such as Sonic Hedgehog and WNT signaling, that promote primary ciliogenesis, suggesting a possible regulatory role. However, the functional relationship between TonEBP and primary ciliary formation remains unclear. METHODS: TonEBP siRNAs and TonEBP-mCherry plasmids were used to examine their effects on cell ciliation rates, assembly and disassembly processes, and regulators. Serum starvation was used as a condition to induce ciliogenesis. RESULTS: We identified a novel pericentriolar localization for TonEBP. The results showed that TonEBP depletion facilitates the formation of primary cilia, whereas its overexpression results in fewer ciliated cells. Moreover, TonEBP controlled the expression and activity of aurora kinase A, a major negative regulator of ciliogenesis. Additionally, TonEBP overexpression inhibited the loss of CP110 from the mother centrioles during the early stages of primary cilia assembly. Finally, TonEBP regulated the localization of PCM1 and AZI1, which are necessary for primary cilia formation. CONCLUSIONS: This study proposes a novel role for TonEBP as a pericentriolar protein that regulates the integrity of centriolar satellite components. This regulation has shown to have a negative effect on ciliogenesis. Investigations into cilium assembly and disassembly processes suggest that TonEBP acts upstream of the aurora kinase A - histone deacetylase 6 signaling pathway and affects basal body formation to control ciliogenesis. Taken together, our data proposes previously uncharacterized regulation of primary cilia assembly by TonEBP.