Open AccessSelective Abrogation of BiP/GRP78 Blunts Activation of NF-κB through the ATF6 Branch of the UPR: Involvement of C/EBPβ and mTOR-Dependent Dephosphorylation of Akt
Author(s) -
Shotaro Nakajima,
Naoki Hiramatsu,
Kunihiro Hayakawa,
Youhei Saito,
Hironori Kato,
Tao Huang,
Jian Yao,
Adrienne W. Paton,
James C. Paton,
Masanori Kitamura
Publication year - 2011
Publication title -
molecular and cellular biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.14
H-Index - 327
eISSN - 1067-8824
pISSN - 0270-7306
DOI - 10.1128/mcb.00939-10
Subject(s) - dephosphorylation , biology , protein kinase b , unfolded protein response , pi3k/akt/mtor pathway , phosphorylation , nf κb , microbiology and biotechnology , cancer research , endoplasmic reticulum , signal transduction , phosphatase
Subtilase cytotoxin (SubAB) that selectively cleaves BiP/GRP78 triggers the unfolded protein response (UPR) and protects mice from endotoxic lethality and collagen arthritis. We found that pretreatment of cells with SubAB suppressed tumor necrosis alpha (TNF-α)-induced activation of NF-κB and NF-κB-dependent chemokine expression. To elucidate underlying mechanisms, the involvement of C/EBP and Akt, putative regulators of NF-κB, was investigated. Among members of the C/EBP family, SubAB preferentially induced C/EBPβ. Overexpression of C/EBPβ suppressed TNF-α-induced NF-κB activation, and knockdown of C/EBPβ attenuated the suppressive effect of SubAB on NF-κB. We identified that the ATF6 branch of the UPR plays a crucial role in the induction of C/EBPβ. In addition to this effect, SubAB depressed basal and TNF-α-induced phosphorylation of Akt via the UPR. It was mediated by the induction of ATF6 and consequent activation of mTOR that dephosphorylated Akt. Inhibition of Akt attenuated activation of NF-κB by TNF-α, suggesting that the mTOR-Akt pathway is another target for SubAB-initiated, UPR-mediated NF-κB suppression. These results elucidated that SubAB blunts activation of NF-κB through ATF6-dependent mechanisms, i.e., preferential induction of C/EBPβ and mTOR-dependent dephosphorylation of Akt.