Abstract
The Δ9-fatty acid desaturase introduces a double bond at the Δ9 position of the acyl moiety of acyl-CoA and regulates the cellular levels of unsaturated fatty acids. However, it is unclear how Δ9-desaturase expression is regulated in response to changes in the levels of fatty acid desaturation. In this study, we found that the degradation of DESAT1, the sole Δ9-desaturase in the Drosophila cell line S2, was significantly enhanced when the amounts of unsaturated acyl chains of membrane phospholipids were increased by supplementation with unsaturated fatty acids, such as oleic and linoleic acids. In contrast, inhibition of DESAT1 activity remarkably suppressed its degradation. Of note, removal of the DESAT1 N-terminal domain abolished the responsiveness of DESAT1 degradation to the level of fatty acid unsaturation. Further truncation and amino acid replacement analyses revealed that two sequential prolines, the second and third residues of DESAT1, were responsible for the unsaturated fatty acid-dependent degradation. Although degradation of mouse stearoyl-CoA desaturase 1 (SCD1) was unaffected by changes in fatty acid unsaturation, introduction of the N-terminal sequential proline residues into SCD1 conferred responsiveness to unsaturated fatty acid-dependent degradation. Furthermore, we also found that the Ca2+-dependent cysteine protease calpain is involved in the sequential proline-dependent degradation of DESAT1. In light of these findings, we designated the sequential prolines at the second and third positions of DESAT1 as a "di-proline motif," which plays a crucial role in the regulation of Δ9-desaturase expression in response to changes in the level of cellular unsaturated fatty acids.
Highlights
The ⌬9-fatty acid desaturase introduces a double bond at the ⌬9 position of the acyl moiety of acyl-CoA and regulates the cellular levels of unsaturated fatty acids
We found that the degradation of DESAT1, the sole ⌬9-desaturase in the Drosophila cell line S2, was significantly enhanced when the amounts of unsaturated acyl chains of membrane phospholipids were increased by supplementation with unsaturated fatty acids, such as oleic and linoleic acids
The expression of stearoyl-CoA desaturase 1 (SCD1) is mainly regulated by SREBP1, a master regulator of lipid biosynthesis at the transcriptional level [6], whereas the degradation of SCD1 is mediated by the ubiquitin–proteasome system irrespective of the cellular levels of unsaturated fatty acids that regulate Scd1 gene expression [7]
Summary
To explore the regulatory mechanisms of DESAT1 expression, we raised polyclonal antibodies against DESAT1 and examined the effect of exogenously added fatty acids on the expression of DESAT1. Truncation of residues 2– 6 of DESAT1 decreased the degradation rate of the mutant protein (Fig. 5, A and B) and abolished the effect of C18:1 and DESAT1 inhibitor on the expression levels of the mutant protein (Fig. 5, C–F). These results suggest that residues 2– 6 contain residues required for the unsaturated fatty acid-induced degradation of DESAT1 protein. Introduction of proline at the third residue of mouse SCD1 conferred responsiveness to C18:1-sensitive and DESAT1 inhibitor-sensitive degradation (Fig. 7, C and D, and supplemental Fig. 7, G and H) Taken together, these results suggest that the di-proline motif in the N-terminal. The amount of exogenously expressed DESAT1-FLAGC was increased by calpeptin treatment, whereas the expression level of DESAT1 (P2A/P3A)-FLAGC protein was not affected, implying that the di-proline motif is required for calpain-mediated degradation of DESAT1 (Fig. 8C, supplemental Fig. 8, C and D)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
