title: Proinflammatory cytokines downregulate connexin 43-gap junctions via the ubiquitin-proteasome system in rat spinal astrocytes.
abstract: Astrocytic gap junctions formed by connexin 43 (Cx43) are crucial for intercellular communication between spinal cord astrocytes. Various neurological disorders are associated with dysfunctional Cx43-gap junctions. However, the mechanism modulating Cx43-gap junctions in spinal astrocytes under pathological conditions is not entirely clear. A previous study showed that treatment of spinal astrocytes in culture with pro-inflammatory cytokines tumor necrosis factor-α (TNF-α) and interferon-γ (IFN-γ) decreased both Cx43 expression and gap junction intercellular communication (GJIC) via a c-jun N-terminal kinase (JNK)-dependent pathway. The current study further elaborates the intracellular mechanism that decreases Cx43 under an inflammatory condition. Cycloheximide chase analysis revealed that TNF-α (10 ng/ml) alone or in combination with IFN-γ (5 ng/ml) accelerated the degradation of Cx43 protein in cultured spinal astrocytes. The reduction of both Cx43 expression and GJIC induced by a mixture of TNF-α and IFN-γ were blocked by pretreatment with proteasome inhibitors MG132 (0.5 μM) and epoxomicin (25 nM), a mixture of TNF-α and IFN-γ significantly increased proteasome activity and Cx43 ubiquitination. In addition, TNF-α and IFN-γ-induced activation of ubiquitin-proteasome systems was prevented by SP600125, a JNK inhibitor. Together, these results indicate that a JNK-dependent ubiquitin-proteasome system is induced under an inflammatory condition that disrupts astrocytic gap junction expression and function, leading to astrocytic dysfunction and the maintenance of the neuroinflammatory state.
authors.affiliation: Department of Pharmacology, Hiroshima University Graduate School of Biomedical & Health Sciences, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8553, Japan.
authors.forename: Fang Fang
authors.initials: FF
authors.lastname: Zhang
authors.affiliation: Department of Pharmacology, Hiroshima University Graduate School of Biomedical & Health Sciences, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8553, Japan. Electronic address: mnori@hiroshima-u.ac.jp.
authors.forename: Norimitsu
authors.initials: N
authors.lastname: Morioka
authors.affiliation: Department of Pharmacology, Hiroshima University Graduate School of Biomedical & Health Sciences, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8553, Japan.
authors.forename: Tomoya
authors.initials: T
authors.lastname: Kitamura
authors.affiliation: Department of Pharmacology, Hiroshima University Graduate School of Biomedical & Health Sciences, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8553, Japan.
authors.forename: Kazue
authors.initials: K
authors.lastname: Hisaoka-Nakashima
authors.affiliation: Department of Pharmacology, Hiroshima University Graduate School of Biomedical & Health Sciences, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8553, Japan.
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Nakata
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000166:cytology / Q000276:immunology*; D002478:Cells, Cultured; D018031:Connexin 43 / Q000276:immunology*; D016207:Cytokines / Q000276:immunology*; D015536:Down-Regulation / Q000276:immunology; D017629:Gap Junctions / Q000276:immunology*; D007155:Immunologic Factors / Q000276:immunology; D051381:Rats; D017208:Rats, Wistar; D013116:Spinal Cord / Q000166:cytology / Q000276:immunology*; D043743:Ubiquitin-Protein Ligase Complexes / Q000276:immunology*; D054875:Ubiquitination
chemical_list: D018031:Connexin 43; D016207:Cytokines; C500216:GJA1 protein, human; D007155:Immunologic Factors; D043743:Ubiquitin-Protein Ligase Complexes
keywords: Astrocyte; Connexin 43; Cycloheximide; Cytokine; Neuroinflammation; Ubiquitin-proteasome system