# Regulatory Mechanisms of Sterol Regulatory Element-Binding Protein-Dependent Human ELOVL6 Expression in Response to Free Fatty Acids

## TL;DR

This study explores how free fatty acids regulate the ELOVL6 gene through SREBP proteins, revealing a transient and tightly controlled mechanism important for lipid balance.

## Contribution

The study identifies and characterizes two functional SREs in the human ELOVL6 promoter that mediate SREBP-dependent fatty acid-responsive transcription.

## Key findings

- Palmitic acid induces a transient upregulation of ELOVL6 mRNA in human hepatoma cells.
- Both SRE1 and SRE2 are essential for fatty acid-responsive transcription of ELOVL6.
- Nuclear SREBP accumulation peaks early after PA stimulation and declines, correlating with transient ELOVL6 induction.

## Abstract

ELOVL6 is a key microsomal enzyme that catalyzes the elongation of C16 saturated and monounsaturated fatty acids into C18 species and plays a pivotal role in lipid homeostasis. Although ELOVL6 is recognized as a downstream target of sterol regulatory element-binding proteins (SREBPs), the promoter architecture and the functional contribution of individual sterol regulatory elements (SREs) within the human ELOVL6 gene remain poorly characterized. In this study, we investigated the transcriptional regulation of human ELOVL6 in response to free fatty acids, focusing on SREBP-mediated mechanisms. A 1.6 kb genomic region encompassing the human ELOVL6 promoter and first intron was cloned, and two putative SREs, designated SRE1 and SRE2, were identified. Using human hepatoma Huh7 cells, we found that palmitic acid (PA), but not oleic acid (OA), induced a transient upregulation of ELOVL6 mRNA expression at 24 h, which diminished by 48 h. Electrophoretic mobility shift assays and chromatin immunoprecipitation analyses demonstrated specific binding of SREBP to both SRE1 and SRE2, with enhanced recruitment following PA stimulation. Luciferase reporter assays revealed that site-directed mutagenesis of either SRE significantly reduced basal promoter activity, while simultaneous disruption of both elements resulted in profound suppression, indicating that both elements are essential for fatty acid-responsive transcription. Consistent with these findings, PA stimulation caused a rapid but transient accumulation of nuclear SREBP, peaking at 4 h and declining thereafter, suggesting that the short nuclear half-life of active SREBP contributes to the transient induction of ELOVL6. Collectively, these results delineate the cis-regulatory framework of the human ELOVL6 gene and demonstrate that SRE1 and SRE2 cooperatively mediate SREBP-dependent, fatty acid-responsive transcription. This tightly regulated and transient activation of ELOVL6 may represent an adaptive mechanism to acute lipid-derived stress, the dysregulation of which could contribute to metabolic disorders and cancer-associated lipid remodeling.