Cilia play important roles in sensing extracellular signals and directing fluid flow. Ciliary dysfunction is associated with a variety of diseases known as ciliopathies. Histone deacetylase 6 (HDAC6) has recently emerged as a major driver of ciliary disassembly, but little is known about the downstream players. Here we provide the first evidence that HDAC6-mediated deacetylation of α-tubulin and cortactin is critical for its induction of ciliary disassembly. HDAC6 is localized in the cytoplasm and enriched at the centrosome and basal body. Overexpression of HDAC6 decreases the levels of acetylated α-tubulin and cortactin without affecting the expression or localization of known ciliary regulators. We also find that overexpression of α-tubulin or cortactin or their acetylation-deficient mutants enhances the ability of HDAC6 to induce ciliary disassembly. In addition, acetylation-mimicking mutants of α-tubulin and cortactin counteract HDAC6-induced ciliary disassembly. Furthermore, HDAC6 stimulates actin polymerization, and inhibition of actin polymerization abolishes the activity of HDAC6 to trigger ciliary disassembly. These findings provide mechanistic insight into the ciliary role of HDAC6 and underscore the importance of reversible acetylation in regulating ciliary homeostasis.

Cilia are hair-like organelles extending from the cell surface with important sensory and motility functions. Ciliary defects can result in a wide range of human diseases known as ciliopathies. However, the molecular mechanisms controlling ciliogenesis remain poorly defined. Here we show that cylindromatosis (CYLD), a tumor suppressor protein harboring deubiquitinase activity, plays a critical role in the assembly of both primary and motile cilia in multiple organs. CYLD knockout mice exhibit polydactyly and various ciliary defects, such as failure in basal body anchorage and disorganization of basal bodies and axenomes. The ciliary function of CYLD is partially attributed to its deconjugation of the polyubiquitin chain from centrosomal protein of 70 kDa (Cep70), a requirement for Cep70 to interact with γ-tubulin and localize at the centrosome. In addition, CYLD-mediated inhibition of histone deacetylase 6 (HDAC6), which promotes tubulin acetylation, constitutes another mechanism for the ciliary function of CYLD. Small-molecule inhibitors of HDAC6 could partially rescue the ciliary defects in CYLD knockout mice. These findings highlight the importance of protein ubiquitination in the modulation of ciliogenesis, identify CYLD as a crucial regulator of this process, and suggest the involvement of CYLD deficiency in ciliopathies.

Oriented cell division is critical for cell fate specification, tissue organization, and tissue homeostasis, and relies on proper orientation of the mitotic spindle. The molecular mechanisms underlying the regulation of spindle orientation remain largely unknown. Herein, we identify a critical role for cylindromatosis (CYLD), a deubiquitinase and regulator of microtubule dynamics, in the control of spindle orientation. CYLD is highly expressed in mitosis and promotes spindle orientation by stabilizing astral microtubules and deubiquitinating the cortical polarity protein dishevelled. The deubiquitination of dishevelled enhances its interaction with nuclear mitotic apparatus, stimulating the cortical localization of nuclear mitotic apparatus and the dynein/dynactin motor complex, a requirement for generating pulling forces on astral microtubules. These findings uncover CYLD as an important player in the orientation of the mitotic spindle and cell division and have important implications in health and disease.O rientation of the cell division axis offers a critical mechanism for the control of cell type choices and the specification of tissue/organ architecture; this is achieved through accurate orientation of the mitotic spindle relative to the cell cortex (1). Spindle orientation is exquisitely regulated during development as well as in adult life, and defects in this process may have severe consequences, such as developmental disorders and tumor formation (1, 2). A dividing cell can orient its spindle along the planar axis or the apicobasal axis of the tissue, depending on the tissue environment and cell geometry. In most epithelia, such as the intestine crypt epithelium, planar spindle orientation is common to produce two daughter cells side by side. By contrast, apicobasal spindle orientation is frequently associated with asymmetric cell divisions, which result in two daughter cells of distinct identities (2).Astral microtubules play a key role in spindle orientation by linking the spindle to the cell cortex (3). The localization of cell polarity proteins such as dishevelled (Dvl) at the cell cortex is also important for spindle orientation by transmission of extrinsic signals or providing the intrinsic cues. Cortical polarity proteins can recruit the nuclear mitotic apparatus (NuMA) protein and then the microtubule minus end-directed dynein/ dynactin motor complex, which can generate pulling forces on astral microtubules to rotate the spindle (3). Therefore, the dynamic interaction of astral microtubules with the cell cortex via diverse protein complexes constitutes an essential part of the mechanism for spindle orientation. However, it remains elusive how the protein complexes controlling spindle orientation are assembled and activated to make a connection between astral microtubules and the cell cortex.As a posttranslational modification, protein ubiquitination is critical for diverse cellular and biological events, and it is a reversal process mediated by E3 ubiquitin ligases and deubiquitinases, respecti...

Pancreatic cancer is a highly aggressive disease with a grim prognosis, due to its late diagnosis, propensity to rapidly metastasize, and resistance to therapy. The molecular events underlying this remain poorly defined. Here we report the overexpression and gene copy number gain of the microtubule-dependent motor protein Eg5 in human pancreatic cancer samples. We also show that Eg5 expression correlates with clinicopathological parameters of pancreatic cancer and promotes anchorage-independent cell growth and tumour formation in mice. In addition, Eg5 is up-regulated in pancreatic cancer cell lines and enhances cell proliferation in an ATPase activity-dependent manner. Our data further reveal that Eg5 overexpression causes the formation of multipolar spindles and multinucleation and induces the accumulation of polyploid cells. These findings demonstrate a role for Eg5 in pancreatic tumourigenesis and indicate a potential for targeting Eg5 in pancreatic cancer treatment.

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