Inhibition of stearoyl-CoA desaturase 1 expression induces CHOP-dependent cell death in human cancer cells

Background

Cancer cells present a sustained de novo fatty acid synthesis with an increase of saturated and monounsaturated fatty acid (MUFA) production. This change in fatty acid metabolism is associated with overexpression of stearoyl-CoA desaturase 1 (Scd1), which catalyses the transformation of saturated fatty acids into monounsaturated fatty acids (e.g., oleic acid). Several reports demonstrated that inhibition of Scd1 led to the blocking of proliferation and induction of apoptosis in cancer cells. Nevertheless, mechanisms of cell death activation remain to be better understood.

Principal Findings

In this study, we demonstrated that Scd1 extinction by siRNA triggered abolition of de novo MUFA synthesis in cancer and non-cancer cells. Scd1 inhibition-activated cell death was only observed in cancer cells with induction of caspase 3 activity and PARP-cleavage. Exogenous supplementation with oleic acid did not reverse the Scd1 ablation-mediated cell death. In addition, Scd1 depletion induced unfolded protein response (UPR) hallmarks such as Xbp1 mRNA splicing, phosphorylation of eIF2α and increase of CHOP expression. However, the chaperone GRP78 expression, another UPR hallmark, was not affected by Scd1 knockdown in these cancer cells indicating a peculiar UPR activation. Finally, we showed that CHOP induction participated to cell death activation by Scd1 extinction. Indeed, overexpression of dominant negative CHOP construct and extinction of CHOP partially restored viability in Scd1-depleted cancer cells.

Conclusion

These results suggest that inhibition of de novo MUFA synthesis by Scd1 extinction could be a promising anti-cancer target by inducing cell death through UPR and CHOP activation.     

cDNA cloning and the response to overfeeding in the expression of stearoyl-CoA desaturase 1 gene in Landes goose

Stearoyl-CoA desaturase 1 (SCD1) is a rate limiting enzyme in the biosynthesis of monounsaturated fatty acids. It has been cloned from several species: Rattus norvegicus, Mus musculus, Homo Sapiens and Gallus gallus, but not from Anser anser. This study was conducted to isolate the SCD1 cDNA sequence and investigate the effect of overfeeding on SCD1 gene tissue expression in Landes goose. The complete cDNA is 3294 bp in length, with an ORF of 1.083 bp encoding a predicted polypeptide of 360 amino acids and 5′/3′-UTR of 74 and 2137 bp, respectively. Quantitative real time PCR (qPCR) was used to examine SCD1 expression in heart, liver, spleen, lung, kidney, gizzard, glandular stomach, intestine, crureus, pectoral muscle, hypothalamus and adipose tissue (abdominal fat) in both the overfed and control group. SCD1 mRNA was highly expressed in goose fatty liver, and the expression levels of SCD1 in liver and fat of overfeeding group were more than double that of the control group. During the overfeeding period, SCD1 expression in liver and adipose tissue reached the highest level after 70 days, but declined at 79 days. In the control group, after fasting 24 h, the expression level of SCD1 gene in tissues declined sharply. However, SCD1 gene expression in hypothalamus was unaffected. The results of this study provide a theoretical basis to study the relationship between SCD1 gene expression and the formation of fatty liver of Landes goose in response to overfeeding.     

Membrane topology of mouse stearoyl-CoA desaturase 1

Stearoyl-CoA desaturase (SCD) is an integral membrane protein anchored in the endoplasmic reticulum. It catalyzes the biosynthesis of monounsaturated fatty acids that are required for the synthesis of triglycerides, cholesteryl esters, and phospholipids. Four mouse isoforms of SCD (SCD1-4) and two human isoforms have been characterized. In the current study, we characterize the topology of the mouse SCD1 isoform. Hydropathy analysis of the 355-amino acid mouse SCD1 protein predicts that the protein contains four transmembrane domains (TMDs) and three loops connecting the membrane-spanning domains. To define the topology of the protein, recombinant SCD1 constructs containing epitope tags were transiently expressed in HeLa cells and analyzed by indirect immunofluorescence and cysteine derivatization. Our data provide evidence that the N and C termini of SCD1 are oriented toward the cytosol with four transmembrane domains separated by two very short hydrophilic loops in the ER lumen and one large hydrophilic loop in the cytosol. In addition, based on the previous observation that SCD is a thiol enzyme, we sought to investigate whether the cysteine residues were essential for enzyme activity through mutagenesis studies, and our data suggest that the cysteines in SCD are not catalytically essential.     

Thiazole analog as stearoyl-CoA desaturase 1 inhibitor

SCD1 inhibition may represent a novel treatment for obesity, type-2 diabetes and related metabolic disorders. A prototype thiazole amide analog 13 (MF-152) was identified as an excellent tool in the study of SCD biology in animals.     

Discovery of piperidine-aryl urea-based stearoyl-CoA desaturase 1 inhibitors

A series of structurally novel stearoyl-CoA desaturase1 (SCD1) inhibitors has been identified via molecular scaffold manipulation. Preliminary structure–activity relationship (SAR) studies led to the discovery of potent, and orally bioavailable piperidine-aryl urea-based SCD1 inhibitors. 4-(2-Chlorophenoxy)-N-[3-(methyl carbamoyl)phenyl]piperidine-1-carboxamide 4c exhibited robust in vivo activity with dose-dependent desaturation index lowering effects.     

The OLE1 gene of Saccharomyces cerevisiae encodes the delta 9 fatty acid desaturase and can be functionally replaced by the rat stearoyl-CoA desaturase gene

Strains of Saccharomyces cerevisiae bearing the ole1 mutation are defective in unsaturated fatty acid (UFA) synthesis and require UFAs for growth. A previously isolated yeast genomic fragment complementing the ole1 mutation has been sequenced and determined to encode the delta 9 fatty acid desaturase enzyme by comparison of primary amino acid sequence to the rat liver stearoyl-CoA desaturase. The OLE1 structural gene encodes a protein of 510 amino acids (251 hydrophobic) having an approximate molecular mass of 57.4 kDa. A 257-amino acid internal region of the yeast open reading frame aligns with and shows 36% identity and 60% similarity to the rat liver stearoyl-CoA desaturase protein. This comparison disclosed three short regions of high consecutive amino acid identity (greater than 70%) including one 11 of 12 perfect residue match. The predicted yeast enzyme contains at least four potential membrane-spanning regions and several shorter hydrophobic regions that align exactly with similar sequences in the rat liver protein. An ole1 gene-disrupted yeast strain was transformed with a yeast-rat chimeric gene consisting of the promoter region and N-terminal 27 codons of OLE1 fused to the rat desaturase coding sequence. Fusion gene transformants displayed near equivalent growth rates and modest lipid composition changes relative to wild type yeast control implying a significant conservation of delta 9 desaturase tertiary structure and efficient interaction between the rat desaturase and yeast cytochrome b5.     

Advances in regulation and function of stearoyl-CoA desaturase 1 in cancer,from bench to bed

Stearoyl-CoA desaturase 1(SCD1) converts saturated fatty acids to monounsaturated fatty acids. The expression of SCD1 is increased in many cancers, and the altered expression contributes to the proliferation, invasion, stemness and chemoresistance of cancer cells. Recently, more evidence has been reported to further support the important role of SCD1 in cancer, and the regulation mechanism of SCD1 has also been focused. Multiple factors are involved in the regulation of SCD1, including metabolis...     

Lack of stearoyl-CoA desaturase-1 function induces a palmitoyl-CoA Delta6 desaturase and represses the stearoyl-CoA desaturase-3 gene in the preputial glands of the mouse

The mouse preputial gland (PG), a specialized sebaceous structure, is rich in wax esters, triglycerides, and alkyl-2,3-diacylglycerol. We have found that the mouse PG expresses the three gene isoforms (SCD1, SCD2, and SCD3) of the Delta9 stearoyl-CoA desaturase enzyme that catalyzes the biosynthesis of monounsaturated fatty acids mainly, C16:1n-7 and C18:1n-9. However, mice with a targeted disruption in the SCD1 isoform (SCD1(-/-)) have undetectable SCD3 mRNA expression in the PG while the expression of SCD2 isoform was not altered. The levels of C16:1n-7 were reduced by greater than 70% while that of C18:1n-9 were reduced by 28%. The content of the C16:1n-10 (Delta6 hexadecenoic acid) isomer and a major fatty acid of the PG was increased by greater than 2-fold, mainly in the wax ester fraction of the SCD1(-/-) mouse. We demonstrate that the increase in C16:1n-10 is due to induction of a specific palmitoyl-CoA Delta6 desaturase activity. Testosterone administration to the SCD1(-/-) mouse induced SCD3 mRNA expression and resulted in an increase in the Delta9 desaturation of 16:0-CoA, but not of 18:0-CoA. These observations demonstrate that loss of SCD1 function alters the expression of SCD3 and reveal for the first time the presence and regulation of a palmitoyl-CoA Delta6 desaturase enzyme in mammals.     

The aging human orbitofrontal cortex: decreasing polyunsaturated fatty acid composition and associated increases in lipogenic gene expression and stearoyl-CoA desaturase activity

Orbitofrontal cortex (OFC, Brodmann area 10) gray matter volume reductions and selective reductions in docosahexaenoic acid (DHA, 22:6n-3) are observed in adult patients with major depressive disorder (MDD). OFC gray matter volume also decreases with advancing age in healthy subjects. To examine if OFC gray matter DHA composition decreases during normal aging, we determined age-related changes in OFC gray matter fatty acid composition by gas chromatography in subjects aged 29-80 years (n=30). We additionally determined elongase (HELO1), delta-5 desaturase (FASD1), delta-6 desaturase (FASD2), peroxisomal (PEX19), and stearoyl-CoA desaturase (SCD) mRNA expression in the same tissues. Increasing age was associated with a progressive decline in polyunsaturated fatty acid (PUFA) composition, including DHA and arachidonic acid (AA, 20:4n-6), and transient, apparently compensatory, elevations in elongase and desaturase gene expression. The age-related reduction in PUFA composition was inversely correlated with SCD expression and activity resulting in elevations in monounsaturated fatty acid composition. These dynamic age-related changes in OFC gray matter fatty acid composition and biosynthetic gene expression may contribute to the progressive decline in OFC gray matter volume found with advancing age. The implications of age-related reductions in OFC PUFA composition for affective dysregulation in the elderly are discussed.