Binding of polyunsaturated fatty acids to LXRα and modulation of SREBP‐1 interaction with a specific SCD1 promoter element

Abstract

Stearoyl-CoA desaturase 1 (SCD1) is the rate limiting enzyme in unsaturated fatty acid biosynthesis. This enzyme has an important role in the regulation of hepatic lipogenesis and lipid oxidation, and alterations in these pathways may lead to several diseases. We examined, in HepG2 cell cultures, the mechanism of SCD1 regulation considering the involvement of two transcription factors: liver X receptor alpha (LXRα) and sterol regulatory element-binding protein-1 (SREBP-1), also investigating the effect of dietary polyunsaturated fatty acids (PUFAs) on this process. The analysis of SCD1 promoter allowed to identify a functional SREBP-1 binding site (SRE 1). LXRα activation increased SCD1 protein level through upregulation of SREBP-1 and its consequent binding to SRE 1 sequence. Polyunsaturated docosahexaenoic acid (DHA, C22:6), eicosapentaenoic acid (EPA, C20:5) and arachidonic acid (AA, C20:4) were able to reduce SREBP-1 binding to SCD1 promoter, while saturated stearic acid (SA, C18:0) did not give any effect. Surface plasmon resonance analysis showed a direct binding of DHA, EPA and AA to LXRα. These data indicate a direct inhibitory interaction of PUFAs with LXRα, a consequent reduction of SREBP-1 and of its binding to SCD1 promoter. This information provides a mechanism to explain the regulation of lipogenic pathways induced by PUFAs.

Cyp1b1 deletion and retinol deficiency coordinately suppress mouse liver lipogenic genes and hepcidin expression during post-natal development

“…Srebp-1c and Chrebp / Mlxipl control fatty acid synthesis (Caputo et al, 2014, Flowers and Ntambi, 2008), whereas Srebp2 is selective for cholesterol synthesis (Horton et al, 1998) (Figure 5B). Srebp-1c increased nearly five-fold between birth and weaning, but was unaffected by either GVAD or Cyp1b1 deletion.…”

“…The connections between the 18 genes in the lipogenic pathways (Table 5, Figure 5A) are likely made through the three key regulators, Srebp-1c and Chrebp for fatty acid gene synthesis (Caputo et al, 2014, Eberle et al, 2004, Flowers and Ntambi, 2008) and Srebp-2 for cholesterogenic genes (Horton et al, 1998, Shimano et al, 1997). Each is primarily regulated by proteolytic cleavage by the activator Scap and inhibitory phosphorylation by AMPK (Eberle et al, 2004).…”

Involvement of nutrients and nutritional mediators in mitochondrial 3‐hydroxy‐3‐methylglutaryl‐CoA synthase gene expression

“…After treatments, cells were washed and lysed as previously described (Caputo, De Rosa, et al, ). Thirty micrograms of total proteins from each extract were separated by 10% SDS‐polyacrylamide gels and transferred onto nitrocellulose membranes in a cooling system at 100 V for 1 hr.…”

Effect of Docosahexaenoic Acid on Cell Cycle Pathways in Breast Cell Lines With Different Transformation Degree

“…After treatments, cells were washed and lysed as previously described (Caputo et al, ). Thirty micrograms of total proteins from each extract were separated by 8% or 10% SDS‐polyacrylamide gels and transferred onto nitrocellulose membranes in a cooling system at 100 V for 1 h. Membranes were saturated for 1 h at room temperature with 0.1% Tween‐20, 5% dry milk or BSA in PBS.…”