Reversible translocation of acyl-CoA:cholesterol acyltransferase (ACAT) between the endoplasmic reticulum and vesicular structures

by Selleckchem | Jan 16 2024

The enzyme acyl-CoA:cholesterol acyltransferase (ACAT) is normally localized in the endoplasmic reticulum (ER) where it can esterify cholesterol for storage in lipid droplets and/or the formation of lipoproteins. Here, we report that ACAT can translocate from the ER into vesicular structures in response to different ACAT inhibitors. The translocation was fast (within minutes), reversible and occurred in different cell types. Interestingly, oleic acid was able to fasten the re-translocation from vesicles back into the reticular ER network. The process of ACAT translocation could also be induced by cyclodextrins, cholesterol, lanosterol (but not 4-cholestene-3 one), 25-hydroxycholesterol, and by certain stress stimuli such as hyperosmolarity (sucrose treatment), temperature change, or high-density cultivation. In vitro esterification showed that ACAT remains fully active after it has been translocated to vesicles in response to hyperosmotic sucrose treatment of the cells. The translocation process was not accompanied by changes in the electrophoretic mobility of ACAT, even after chemical crosslinking. Interestingly, the protein synthesis inhibitor cycloheximide showed a stimulating effect on ACAT activity and prevented the translocation of ACAT from the ER into vesicles.

Comments:

It seems like you're discussing the translocation behavior of the enzyme ACAT in response to various stimuli and inhibitors. The ability of ACAT to move from the endoplasmic reticulum (ER) into vesicular structures in a reversible and rapid manner in different cell types is quite intriguing. Additionally, the observation that oleic acid facilitates the re-translocation of ACAT from vesicles back to the reticular ER network is noteworthy.

The factors triggering this translocation span a range of compounds and stress stimuli, including cyclodextrins, cholesterol, lanosterol, 25-hydroxycholesterol, as well as stressors like hyperosmolarity, temperature changes, and high-density cultivation. The in vitro esterification studies revealing that ACAT retains full activity after translocating to vesicles due to hyperosmotic sucrose treatment provide valuable insights into its functional behavior under different conditions.

The lack of changes in ACAT's electrophoretic mobility, even after chemical crosslinking during the translocation process, is intriguing and suggests a complex mechanism governing its movement. Moreover, the observation that the protein synthesis inhibitor cycloheximide both stimulates ACAT activity and prevents its translocation into vesicles adds another layer of complexity to the regulation of ACAT function and localization.

This research sheds light on the dynamic nature of ACAT localization and activity in response to various stimuli and inhibitors, emphasizing its adaptability in different cellular environments. The intricate interplay between stimuli, inhibitors, and cellular conditions in modulating ACAT's behavior suggests a finely tuned regulatory mechanism governing cholesterol esterification and lipid metabolism.