Yuichi Watanabe, Takashi Sasaki, Shoko Miyoshi, Makoto Shimizu, Yoshio Yamauchi, and Ryuichiro Sato *


Insulin-induced genes (INSIGs) encode endoplasmic reticulum (ER)-resident proteins that regulate intracellular cholesterol metabolism. Oxysterols are oxygenated derivatives of cholesterol, some of which orchestrate lipid metabolism via interaction with INSIGs. Recently, it was reported that expression of activating transcription factor-4 (ATF4) was induced by certain oxysterols; the precise of mechanism is unclear. Herein, we show that INSIGs mediate ATF4 upregulation upon interaction with oxysterol. Oxysterols that possess a high affinity for INSIG, such as 27- and 25-hydroxycholesterol (25HC), markedly induced the increase of ATF4 protein when compared with other oxysterols. In addition, ATF4 upregulation by these oxysterols was attenuated in INSIG1/2-deficient CHO cells and was recovered by either INSIG1 or INSIG2 rescue. Mechanistic studies revealed that the binding of 25HC to INSIG is critical for increased ATF4 protein via activation of PERK and eIF2α. Knockout of INSIG1 or INSIG2 in human hepatoma Huh7 cells attenuated ATF4 protein upregulation, indicating that only one of the endogenous INSIGs, unlike overexpression of intrinsic INSIG1 or INSIG2, was insufficient for ATF4 induction. Furthermore, ATF4 proactively upregulated the cell death inducible genes expression, such as Chop, Chac1, and Trb3, thereby markedly reducing cell viability with 25-hydroxycholesterol. These findings support a model whereby that INSIGs sense an increase in oxysterol in the ER and induce an increase of ATF4 protein via the PERK/eIF2α pathway, thereby promoting cell death.

Paper Information

: The Journal of Biological Chemistry
: 10.1016/j.jbc.2021.100989