title: Homeotic factor ATBF1 induces the cell cycle arrest associated with neuronal differentiation.
abstract: The present study aimed to elucidate the function of AT motif-binding factor 1 (ATBF1) during neurogenesis in the developing brain and in primary cultures of neuroepithelial cells and cell lines (Neuro 2A and P19 cells). Here, we show that ATBF1 is expressed in the differentiating field in association with the neuronal differentiation markers beta-tubulin and MAP2 in the day E14.5 embryo rat brain, suggesting that it promotes neuronal differentiation. In support of this, we show that ATBF1 suppresses nestin expression, a neural stem cell marker, and activates the promoter of Neurod1 gene, a marker for neuronal differentiation. Furthermore, we show that in Neuro 2A cells, overexpressed ATBF1 localizes predominantly in the nucleus and causes cell cycle arrest. In P19 cells, which formed embryonic bodies in the floating condition, ATBF1 is mainly cytoplasmic and has no effect on the cell cycle. However, the cell cycle was arrested when ATBF1 became nuclear after transfer of P19 cells onto adhesive surfaces or in isolated single cells. The nuclear localization of ATBF1 was suppressed by treatment with caffeine, an inhibitor of PI(3)K-related kinase activity of ataxa-telangiectasia mutated (ATM) gene product. The cytoplasmic localization of ATBF1 in floating/nonadherent cells is due to CRM1-dependent nuclear export of ATBF1. Moreover, in the embryonic brain ATBF1 was expressed in the cytoplasm of proliferating stem cells on the ventricular zone, where cells are present at high density and interact through cell-to-cell contact. Conversely, in the differentiating field, where cell density is low and extracellular matrix is dense, the cell-to-matrix interaction triggered nuclear localization of ATBF1, resulting in the cell cycle arrest. We propose that ATBF1 plays an important role in the nucleus by organizing the neuronal differentiation associated with the cell cycle arrest.
authors.affiliation: Department of Neurophysiology and Brain Science, Graduate School of Medical Sciences, Nagoya City University, Mizuhoku, Nagoya 467-8601, Japan.
authors.forename: Cha-Gyun
authors.initials: CG
authors.lastname: Jung
authors.forename: Hye-Jung
authors.initials: HJ
authors.lastname: Kim
authors.forename: Makoto
authors.initials: M
authors.lastname: Kawaguchi
authors.forename: Kum Kum
authors.initials: KK
authors.lastname: Khanna
authors.forename: Hideki
authors.initials: H
authors.lastname: Hida
authors.forename: Kiyofumi
authors.initials: K
authors.lastname: Asai
authors.forename: Hitoo
authors.initials: H
authors.lastname: Nishino
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Miura
mesh_terms: D021581:Active Transport, Cell Nucleus; D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002450:Cell Communication; D002453:Cell Cycle; D002454:Cell Differentiation; D002478:Cells, Cultured; D004622:Embryo, Mammalian / Q000166:cytology; D047108:Embryonic Development; D018507:Gene Expression Regulation, Developmental / Q000502:physiology; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D028884:Karyopherins / Q000502:physiology; D009474:Neurons / Q000166:cytology*; D051381:Rats; D017208:Rats, Wistar; D018160:Receptors, Cytoplasmic and Nuclear / Q000502:physiology; D000097606:Exportin 1 Protein
chemical_list: D002110:Caffeine; D018398:Homeodomain Proteins; D028884:Karyopherins; D018160:Receptors, Cytoplasmic and Nuclear; D000097606:Exportin 1 Protein; C071660:ZFHX3 protein, human