Dynamic localization of α-tubulin acetyltransferase ATAT1 through the cell cycle in human fibroblastic KD cells.

Acetylation of α-tubulin is a well-studied posttranscriptional modification, which is mostly catalyzed by α-tubulin N-acetyltransferase (ATAT1). ATAT1 possibly affects various cellular functions related with microtubules, such as intracellular transport, cell motility, cilia formation, and neuronal signaling. Here, we analyzed the subcellular localization of immunolabeled ATAT1 in human fibroblast KD cells through the cell cycle using confocal laser scanning microscopy. ATAT1 dramatically changed its localization through the cell cycle, depending on the mitotic phase. In interphase, immunolabeled ATAT1 was observed in centrioles, nuclei, and basal bodies if the cells projected primary cilia. ATAT1 was intensely detected as clusters in the nuclei in the G1-G2 phase. In telophase, ATAT1 colocalized with chromatids and spindle poles, and ultimately migrated to the daughter nucleus, newly synthesized centrioles, and midbody. The nucleolus is a core region of ribosomal RNA transcription, and the midbody is associated with severing and depolymerizing of microtubules in the stembody. The specific distributions of ATAT1 through the cell cycle suggest multiple functions of ATAT1, which could include acetylation of microtubules, RNA transcription activity, severing microtubules, and completion of cytokinesis.

ATAT1 is essential for regulation of homeostasis-retaining cellular responses in corticotrophs along hypothalamic-pituitary-adrenal axis.

The production and secretion of adrenocorticotropin, a proopiomelanocortin (POMC)-derived hormone, by corticotrophs in the anterior pituitary, is regulated by corticotrophin-releasing hormone (CRH) and glucocorticoids. We have previously demonstrated that adrenalectomy induces α-tubulin N-acetyltransferase 1 (ATAT1) expression and α-tubulin acetylation in corticotrophs. However, the regulatory mechanism of ATAT1 expression and the function of acetylated microtubules in corticotrophs are unclear. Here, we analyze the effect of CRH or dexamethasone on Atat1 expression in the mouse corticotroph AtT20 cell line. The expression of Atat1 was increased by CRH and decreased by dexamethasone in AtT20 cells. We examined the effect of Atat1 knockdown on the expression of POMC-associated genes and the dexamethasone-induced nuclear translocation of glucocorticoid receptor (GR) by real-time polymerase chain reaction and Western blot analysis, respectively. Atat1 knockdown resulted in a significant increase in the expression of ACTH-producing genes and decreased the dexamethasone-induced nuclear translocation of GR accompanied with a reduction in α-tubulin acetylation. Atat1 overexpression resulted in a significant increase in α-tubulin acetylation and the dexamethasone-induced nuclear translocation of GR. These results suggest that the acetylated microtubules function as the rail-line for the transportation of GR into the nucleus. We conclude that ATAT1 finely tunes the cellular responses of corticotrophs to hormonal stimulation through an intracellular feedback circuit.

Expression and localization of forkhead box protein FOXJ1 in S100ß-positive multiciliated cells of the rat pituitary.

S100ß-positive cells exist in the marginal cell layer (MCL) of the adenohypophysis and follicle structure in the parenchyma of anterior lobe (ALFS) in pituitary. They have multiple functions as phagocytes or cells that regulate hormone secretion. Majority of S100ß-positive cells in the adenohypophysis express sex determining region Y-box 2 protein (SOX2), a stem cell marker; therefore, S100ß/SOX2 double positive cells are also considered as one type of stem/progenitor cells. MCL and ALFS are consisting of morphologically two types of cells, i.e., multiciliated cells and non-ciliated cells. However, the relationship between the S100ß-positive cells and multiciliated cells in the pituitary is largely unknown. In the present study, we first immunohistochemically verified the feature of multiciliated cells in MCL and ALFS. We then examined the expression patterns of FOXJ1, an essential expression factor for multiciliated cell-differentiation, and SOX2 in the S100ß-positive multiciliated cells by in situ hybridization and immunohistochemistry. We identified anew the S100ß/SOX2/FOXJ1 triple positive multiciliated cells, and revealed that they were dispersed throughout the MCL and ALFS. These results indicate that the MCL and ALFS are consisting of morphologically and functionally distinct two types of cells, i.e., S100ß/SOX2 double positive non-ciliated cells and S100ß/SOX2/FOXJ1 triple positive multiciliated cells.

Adrenalectomy facilitates ATAT1 expression and α-tubulin acetylation in ACTH-producing corticotrophs.

Microtubules play an important role in the intracellular transport of secretory granules in endocrine cells and in mitosis and the maintenance of cell morphology and are composed of heterodimers of α- and ß-tubulin. α-Tubulin N-acetyltransferase 1 (ATAT1), which acetylates the lysine residue at position 40 of α-tubulin, functions not only in stabilizing microtubule structures and forming the primary cilium assembly but also in vesicular trafficking in neurons. However, the localization of ATAT1 and the role of α-tubulin acetylation in endocrine cells in the pituitary are still poorly understood. Corticotrophs in the anterior lobe of the pituitary produce and secrete adrenocorticotropin (ACTH). Although removal of the adrenal gland, a target organ of ACTH, is reported to promote the synthesis and secretion of ACTH in corticotrophs and to induce structural alterations in their organelles, uncertainty remains as to whether the acetylation of α-tubulin is involved in such intracellular events of corticotrophs. We investigate the expression and localization of ATAT1 and the acetylation of α-tubulin in the pituitary of normal and adrenalectomized rats. We find that ATAT1 is localized to the Golgi apparatus of endocrine cells in the anterior lobe of normal pituitary and that the expression levels of ATAT1 and acetylation levels of α-tubulin increase following adrenalectomy. These results agree with the hypothesis that the acetylation of α-tubulin by ATAT1 regulates the intracellular transport of secretory granules in corticotrophs.

Intracellular localization of α-tubulin acetyltransferase ATAT1 in rat ciliated cells.

Cilia are microtubule-based hair-like organelles on basal bodies located beneath the cell membrane in various tissues of multicellular animals, and are usually classified into motile cilia and primary cilia. Microtubules are assembled from the heterodimers of α- and ß-tubulin. The lysine residue at position 40 (K40) of α-tubulin is an important site for acetylation, and this site is acetylated in the cilium. α-Tubulin N-acetyltransferase 1 (ATAT1) is an acetyltransferase specific to the K40 residue of α-tubulin; however, its intracellular distribution in mammalian tissues remains unclear. In this study, we analyzed ATAT1 localization in rat trachea, oviduct, kidney, retina, testis and the third ventricle of the brain by immunohistochemical techniques using a specific antibody against ATAT1. ATAT1 was distributed to the motile cilia of multiciliated cells of the trachea, third ventricle of the brain and oviduct, and in the primary cilia of the renal medullary collecting duct. ATAT1 also localized to the primary cilia, inner and outer segments of retinal photoreceptor cells, and at the Golgi apparatus of spermatocytes and spermatids of testis. These results indicated that α-tubulin acetylation by ATAT1 at distinct subcellular positions may influence the functional regulation of microtubules and cilia in a variety of ciliated cells.

The elongation of primary cilia via the acetylation of α-tubulin by the treatment with lithium chloride in human fibroblast KD cells.

Primary cilium, an organelle found on nearly every cell in the human body, typically serves as the mechanical sensor of the cell. Lithium ion is known to promote the elongation of primary cilia in a variety of cell types, but it is unknown whether lithium is involved in the acetylation of α-tubulin which is essential for the assembly of primary cilia. In order to reveal the relationship between the elongation of primary cilia with lithium and the acetylation of α-tubulin, we first observed the formation and structure of primary cilia in KD cells, a cell line deriving fibroblasts in human labium. Subsequently, by immunohistochemical and western blot analysis we elucidated that the length of primary cilia and acetylation of α-tubulin are regulated by lithium chloride (LiCl) in the medium in a time- and concentration-dependent manner. We next performed the RT-PCR, RNAi-based experiments and biochemical study using an inhibitor of glycogen synthase kinase-3ßGSK-3ß). We found that LiCl mobilizes the α-tubulin N-acetyltransferase 1 (αTAT1) in the signaling pathway mediating GSK-3ß and adenylate cyclase III. In conclusion, our results suggested that LiCl treatments activate αTAT1 by the inhibition of GSK-3ß and promote the α-tubulin acetylation, and then elongate the primary cilia.