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Toxicol Appl Pharmacol. 2018 Jun 15;349:1-7. doi: 10.1016/j.taap.2018.04.020. Epub 2018 Apr 22.

Pharmacologic inhibition of S1P attenuates ATF6 expression, causes ER stress and contributes to apoptotic cell death.

Author information

1
Department of Medicine, Division of Nephrology, McMaster University, St. Joseph's Healthcare Hamilton, Hamilton Centre for Kidney Research, Hamilton, Ontario L8N 4A6, Canada.
2
Department of Medicine, Division of Nephrology, McMaster University, St. Joseph's Healthcare Hamilton, Hamilton Centre for Kidney Research, Hamilton, Ontario L8N 4A6, Canada. Electronic address: austinr@taari.ca.

Abstract

Mammalian cells express unique transcription factors embedded in the endoplasmic reticulum (ER) membrane, such as the sterol regulatory element-binding proteins (SREBPs), that promote de novo lipogenesis. Upon their release from the ER, the SREBPs require proteolytic activation in the Golgi by site-1-protease (S1P). As such, inhibition of S1P, using compounds such as PF-429242 (PF), reduces cholesterol synthesis and may represent a new strategy for the management of dyslipidemia. In addition to the SREBPs, the unfolded protein response (UPR) transducer, known as the activating transcription factor 6 (ATF6), is another ER membrane-bound transcription factor that requires S1P-mediated activation. ATF6 regulates ER protein folding capacity by promoting the expression of ER chaperones such as the 78-kDa glucose-regulated protein (GRP78). ER-resident chaperones like GRP78 prevent and/or resolve ER polypeptide accumulation and subsequent ER stress-induced UPR activation by folding nascent polypeptides. Here we report that pharmacological inhibition of S1P reduced the expression of ATF6 and GRP78 and induced the activation of UPR transducers inositol-requiring enzyme-1α (IRE1α) and protein kinase RNA-like ER kinase (PERK). As a consequence, S1P inhibition also increased the susceptibility of cells to ER stress-induced cell death. Our findings suggest that S1P plays a crucial role in the regulation of ER folding capacity and also identifies a compensatory cross-talk between UPR transducers in order to maintain adequate ER chaperone expression and activity.

KEYWORDS:

ATF6; ER stress; PF-429242; S1P inhibition; SREBP; UPR inhibition

PMID:
29689241
DOI:
10.1016/j.taap.2018.04.020

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