title: Cytoplasmic location of α1A voltage-gated calcium channel C-terminal fragment (Cav2.1-CTF) aggregate is sufficient to cause cell death.
abstract: The human α1A voltage-dependent calcium channel (Cav2.1) is a pore-forming essential subunit embedded in the plasma membrane. Its cytoplasmic carboxyl(C)-tail contains a small poly-glutamine (Q) tract, whose length is normally 4∼19 Q, but when expanded up to 20∼33Q, the tract causes an autosomal-dominant neurodegenerative disorder, spinocerebellar ataxia type 6 (SCA6). A recent study has shown that a 75-kDa C-terminal fragment (CTF) containing the polyQ tract remains soluble in normal brains, but becomes insoluble mainly in the cytoplasm with additional localization to the nuclei of human SCA6 Purkinje cells. However, the mechanism by which the CTF aggregation leads to neurodegeneration is completely elusive, particularly whether the CTF exerts more toxicity in the nucleus or in the cytoplasm. We tagged recombinant (r)CTF with either nuclear-localization or nuclear-export signal, created doxycyclin-inducible rat pheochromocytoma (PC12) cell lines, and found that the CTF is more toxic in the cytoplasm than in the nucleus, the observations being more obvious with Q28 (disease range) than with Q13 (normal-length). Surprisingly, the CTF aggregates co-localized both with cAMP response element-binding protein (CREB) and phosphorylated-CREB (p-CREB) in the cytoplasm, and Western blot analysis showed that the quantity of CREB and p-CREB were both decreased in the nucleus when the rCTF formed aggregates in the cytoplasm. In human brains, polyQ aggregates also co-localized with CREB in the cytoplasm of SCA6 Purkinje cells, but not in other conditions. Collectively, the cytoplasmic Cav2.1-CTF aggregates are sufficient to cause cell death, and one of the pathogenic mechanisms may be abnormal CREB trafficking in the cytoplasm and reduced CREB and p-CREB levels in the nuclei.
authors.affiliation: Department of Neurology and Neurological Science, Graduate School, Tokyo Medical and Dental University, Yushima, Bunkyo-ku, Tokyo, Japan.
authors.forename: Makoto
authors.initials: M
authors.lastname: Takahashi
authors.forename: Masato
authors.initials: M
authors.lastname: Obayashi
authors.forename: Taro
authors.initials: T
authors.lastname: Ishiguro
authors.forename: Nozomu
authors.initials: N
authors.lastname: Sato
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Niimi
authors.forename: Kokoro
authors.initials: K
authors.lastname: Ozaki
authors.forename: Kaoru
authors.initials: K
authors.lastname: Mogushi
authors.forename: Yasen
authors.initials: Y
authors.lastname: Mahmut
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Tanaka
authors.forename: Fuminori
authors.initials: F
authors.lastname: Tsuruta
authors.forename: Ricardo
authors.initials: R
authors.lastname: Dolmetsch
authors.forename: Mitsunori
authors.initials: M
authors.lastname: Yamada
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Takahashi
authors.forename: Takeo
authors.initials: T
authors.lastname: Kato
authors.forename: Osamu
authors.initials: O
authors.lastname: Mori
authors.forename: Yoshinobu
authors.initials: Y
authors.lastname: Eishi
authors.forename: Hidehiro
authors.initials: H
authors.lastname: Mizusawa
authors.forename: Kinya
authors.initials: K
authors.lastname: Ishikawa
mesh_terms: D000818:Animals; D015220:Calcium Channels / Q000737:chemistry / Q000235:genetics / Q000378:metabolism* / Q000633:toxicity; D016923:Cell Death; D002460:Cell Line; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism*; D004318:Doxycycline / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D042541:Intracellular Space / Q000378:metabolism; D049790:Nuclear Export Signals / Q000235:genetics; D019913:Nuclear Localization Signals / Q000737:chemistry / Q000235:genetics; D011485:Protein Binding; D021381:Protein Transport; D011689:Purkinje Cells / Q000378:metabolism / Q000473:pathology; D051381:Rats; D020864:Calcium Channels, N-Type
chemical_list: D015220:Calcium Channels; D017362:Cyclic AMP Response Element-Binding Protein; D004318:Doxycycline; D049790:Nuclear Export Signals; D019913:Nuclear Localization Signals; C105656:CACNA1A protein, human; D020864:Calcium Channels, N-Type