title: 24(S)-Hydroxycholesterol induces RIPK1-dependent but MLKL-independent cell death in the absence of caspase-8.
abstract: 24(S)-Hydroxycholesterol (24S-OHC), which is enzymatically produced in the brain, is known to play an important role in maintaining brain cholesterol homeostasis. We have previously reported that 24S-OHC induces a type of non-apoptotic programmed necrosis in neuronal cells expressing little caspase-8. Necroptosis has been characterized as a type of programmed necrosis in which activation of receptor-interacting protein kinase 1 (RIPK1), RIPK3, and mixed lineage kinase domain-like (MLKL) is involved in the signaling pathway. In the present study, we investigated the involvement of these three proteins in 24S-OHC-induced cell death. We found that RIPK1 but neither RIPK3 nor MLKL was expressed in human neuroblastoma SH-SY5Y cells, while all three proteins were expressed in human T lymphoma caspase-8-deficient Jurkat (Jurkat(Cas8-/-)) cells. In Jurkat(Cas8-/-) cells, tumor necrosis factor α (TNFα)-induced cell death was significantly suppressed by treatment with respective inhibitors of RIPK1, RIPK3, and MLKL. In contrast, only RIPK1 inhibitor showed significant suppression of 24S-OHC-induced cell death, and even this was less prominent than was observed in TNFα-induced cell death. In Jurkat(Cas8-/-) cells, knockdown of either RIPK1 or RIPK3 caused moderate but significant suppression of 24S-OHC-induced cell death, but no such effect was observed as a result of knockdown of MLKL. Collectively, these results suggest that, for both SH-SY5Y cells and Jurkat(Cas8-/-) cells, 24S-OHC-induced cell death is dependent on RIPK1 but not on MLKL. We therefore conclude that, in the absence of caspase-8 activity, 24S-OHC induces a necroptosis-like cell death which is RIPK1-dependent but MLKL-independent.
authors.affiliation: Systems Life Sciences Laboratory, Department of Medical Life Systems, Faculty of Life and Medical Sciences, Doshisha University, 1-3 Miyakodani, Tatara, Kyotanabe, Kyoto 610-0394, Japan.
authors.forename: Diep-Khanh Ho
authors.initials: DK
authors.lastname: Vo
authors.affiliation: Systems Life Sciences Laboratory, Department of Medical Life Systems, Faculty of Life and Medical Sciences, Doshisha University, 1-3 Miyakodani, Tatara, Kyotanabe, Kyoto 610-0394, Japan. Electronic address: yurano@mail.doshisha.ac.jp.
authors.forename: Yasuomi
authors.initials: Y
authors.lastname: Urano
authors.affiliation: Systems Life Sciences Laboratory, Department of Medical Life Systems, Faculty of Life and Medical Sciences, Doshisha University, 1-3 Miyakodani, Tatara, Kyotanabe, Kyoto 610-0394, Japan.
authors.forename: Wakako
authors.initials: W
authors.lastname: Takabe
authors.affiliation: Systems Life Sciences Laboratory, Department of Medical Life Systems, Faculty of Life and Medical Sciences, Doshisha University, 1-3 Miyakodani, Tatara, Kyotanabe, Kyoto 610-0394, Japan.
authors.forename: Yoshiro
authors.initials: Y
authors.lastname: Saito
authors.affiliation: Systems Life Sciences Laboratory, Department of Medical Life Systems, Faculty of Life and Medical Sciences, Doshisha University, 1-3 Miyakodani, Tatara, Kyotanabe, Kyoto 610-0394, Japan. Electronic address: nnoguchi@mail.doshisha.ac.jp.
authors.forename: Noriko
authors.initials: N
authors.lastname: Noguchi
mesh_terms: D053181:Caspase 8 / Q000378:metabolism*; D016923:Cell Death / Q000187:drug effects; D045744:Cell Line, Tumor; D055785:Gene Knockdown Techniques; D006801:Humans; D006888:Hydroxycholesterols / Q000494:pharmacology*; D008954:Models, Biological; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011494:Protein Kinases / Q000378:metabolism*; D053422:Receptor-Interacting Protein Serine-Threonine Kinases / Q000378:metabolism*
chemical_list: D006888:Hydroxycholesterols; D047428:Protein Kinase Inhibitors; C044563:24-hydroxycholesterol; C570693:MLKL protein, human; D011494:Protein Kinases; C506249:RIPK1 protein, human; C119705:RIPK3 protein, human; D053422:Receptor-Interacting Protein Serine-Threonine Kinases; C505530:CASP8 protein, human; D053181:Caspase 8
keywords: 24S-Hydroxycholesterol; Cell death; Mixed lineage kinase domain-like; Necroptosis; Receptor-interacting protein kinase 1