title: TNF-α Induces Caspase-1 Activation Independently of Simultaneously Induced NLRP3 in 3T3-L1 Cells.
abstract: The intracellular cysteine protease caspase-1 is critically involved in obesity-induced inflammation in adipose tissue. A substantial body of evidence from immune cells, such as macrophages, has shown that caspase-1 activation depends largely on a protein complex, called the NLRP3 inflammasome, which consists of the NOD-like receptor (NLR) family protein NLRP3, the adaptor protein ASC, and caspase-1 itself. However, it is not fully understood how caspase-1 activation is regulated within adipocytes upon inflammatory stimuli. In this study, we show that TNF-α-induced activation of caspase-1 is accompanied by robust induction of NLRP3 in 3T3-L1 adipocytes but that caspase-1 activation may not depend on the NLRP3 inflammasome. Treatment of 3T3-L1 cells with TNF-α induced mRNA expression and activation of caspase-1. Although the basal expression of NLRP3 and ASC was undetectable in unstimulated cells, TNF-α strongly induced NLRP3 expression but did not induce ASC expression. Interestingly, inhibitors of the ERK MAP kinase pathway strongly suppressed NLRP3 expression but did not suppress the expression and activation of caspase-1 induced by TNF-α, suggesting that NLRP3 is dispensable for TNF-α-induced caspase-1 activation. Moreover, we did not detect the basal and TNF-α-induced expression of other NLR proteins (NLRP1a, NLRP1b, and NLRC4), which do not necessarily require ASC for caspase-1 activation. These results suggest that TNF-α induces caspase-1 activation in an inflammasome-independent manner in 3T3-L1 cells and that the ERK-dependent expression of NLRP3 may play a role independently of its canonical role as a component of inflammasomes. J. Cell. Physiol. 231: 2761-2767, 2016. © 2016 Wiley Periodicals, Inc.
authors.affiliation: Department of Cell Regulation, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Japan.
authors.forename: Mana
authors.initials: M
authors.lastname: Furuoka
authors.affiliation: Department of Cell Regulation, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Japan.
authors.forename: Kei-Ichi
authors.initials: K
authors.lastname: Ozaki
authors.affiliation: Department of Cell Regulation, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Japan.
authors.forename: Daichi
authors.initials: D
authors.lastname: Sadatomi
authors.affiliation: Department of Cell Regulation, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Japan.
authors.forename: Sayaka
authors.initials: S
authors.lastname: Mamiya
authors.affiliation: Department of Pharmacology and Therapeutic Innovation, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Japan.
authors.forename: Tomo
authors.initials: T
authors.lastname: Yonezawa
authors.affiliation: Department of Cell Regulation, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Japan.
authors.forename: Susumu
authors.initials: S
authors.lastname: Tanimura
authors.affiliation: Department of Cell Regulation, Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, Japan.
authors.forename: Kohsuke
authors.initials: K
authors.lastname: Takeda
mesh_terms: D041721:3T3-L1 Cells; D000818:Animals; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D053468:CARD Signaling Adaptor Proteins; D020170:Caspase 1 / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D020935:MAP Kinase Signaling System / Q000187:drug effects; D051379:Mice; D008810:Mice, Inbred C57BL; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
chemical_list: D051017:Apoptosis Regulatory Proteins; D053468:CARD Signaling Adaptor Proteins; D000071199:NLR Family, Pyrin Domain-Containing 3 Protein; C492716:Nlrp3 protein, mouse; C498534:Pycard protein, mouse; D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha; D020170:Caspase 1