MAPK9: A New Regulator of Triglyceride Metabolism revealed by siRNA Screening

Lipid homeostasis is an essential factor for proper function both at the level of a cell and of an organism. Dysregulation of this process is responsible for some of the major health concerns of our societies such as obesity and atherosclerosis. Considering the wide variety of lipids and the high dynamic of the system, it is clear that regulation is required to keep the appropriate balance between the different lipids. Although a few regulation pathways are already characterized, some others still wait to be discovered. In order to unravel new players involved in lipid regulation, a screening procedure was developed combining RNA interference in Hela cells and thin layer chromatography. Thereby, it is possible to monitor modifications of lipid composition resulting from siRNA knock-down. Furthermore, the potential of mass spectrometry as a lipid analysis tool in large-scale studies was evaluated. This method was then applied to an essential family of regulatory proteins, the kinases. Lipid composition of 600 kinases knock-downs was analyzed. Mostly, variations in triglyceride and cholesterol levels were observed, suggesting that these lipids are more subject to variation in the cells. Unfortunately, it appears that the screen suffered from a high-rate of off-targets effects, implying that most of the phenotypes observed can’t reliably be linked to the corresponding kinase knock-downs. However, several interesting conclusions can still be derived from this screen. First, it was observed that several siRNA induce a decrease in cholesterol, which is coupled to accumulation of a new lipid. Several lines of evidence suggest that this new lipid is in fact a methylated sterol precursor such as lanosterol or demethyllanosterol. Previously, HMG-CoA reductase was considered as the rate-limiting enzyme of cholesterol biosynthesis and the major regulated step of this process. These data show that another major regulation step occurs more downstream in the pathway at the level of methylated cholesterol precursors. Furthermore, MAPK9 was identified as a new regulator of triglyceride homeostasis at the cellular level. Upon MAPK9 knock-down, an increase in triglyceride content was observed both by thin layer chromatography and mass spectrometry. Accordingly, these cells present an increase in lipid droplets, the cellular organelles responsible for triglyceride storage. Sty1 was also identified as the functional homolog of MAPK9 in S. pombe for this process, as similar increase in triglyceride and lipid droplets is observed in a deletion strain for this gene. Although more detailed studies will be necessary to unravel the molecular mechanism of this process, these data suggest the evolutionary conserved implication of the MAP kinase pathway in the regulation of lipid storage both in humans and in yeasts

OSBPL10, a novel candidate gene for high triglyceride trait in dyslipidemic Finnish subjects, regulates cellular lipid metabolism

Analysis of variants in three genes encoding oxysterol-binding protein (OSBP) homologues (OSBPL2, OSBPL9, OSBPL10) in Finnish families with familial low high-density lipoprotein (HDL) levels (N = 426) or familial combined hyperlipidemia (N = 684) revealed suggestive linkage of OSBPL10 single-nucleotide polymorphisms (SNPs) with extreme end high triglyceride (TG; >90th percentile) trait. Prompted by this initial finding, we carried out association analysis in a metabolic syndrome subcohort (Genmets) of Health2000 examination survey (N = 2,138), revealing association of multiple OSBPL10 SNPs with high serum TG levels (>95th percentile). To investigate whether OSBPL10 could be the gene underlying the observed linkage and association, we carried out functional experiments in the human hepatoma cell line Huh7. Silencing of OSBPL10 increased the incorporation of [3H]acetate into cholesterol and both [3H]acetate and [3H]oleate into triglycerides and enhanced the accumulation of secreted apolipoprotein B100 in growth medium, suggesting that the encoded protein ORP10 suppresses hepatic lipogenesis and very-low-density lipoprotein production. ORP10 was shown to associate dynamically with microtubules, consistent with its involvement in intracellular transport or organelle positioning. The data introduces OSBPL10 as a gene whose variation may contribute to high triglyceride levels in dyslipidemic Finnish subjects and provides evidence for ORP10 as a regulator of cellular lipid metabolism

MAPK9: A New Regulator of Triglyceride Metabolism revealed by siRNA Screening

Lipid homeostasis is an essential factor for proper function both at the level of a cell and of an organism. Dysregulation of this process is responsible for some of the major health concerns of our societies such as obesity and atherosclerosis. Considering the wide variety of lipids and the high dynamic of the system, it is clear that regulation is required to keep the appropriate balance between the different lipids. Although a few regulation pathways are already characterized, some others still wait to be discovered. In order to unravel new players involved in lipid regulation, a screening procedure was developed combining RNA interference in Hela cells and thin layer chromatography. Thereby, it is possible to monitor modifications of lipid composition resulting from siRNA knock-down. Furthermore, the potential of mass spectrometry as a lipid analysis tool in large-scale studies was evaluated. This method was then applied to an essential family of regulatory proteins, the kinases. Lipid composition of 600 kinases knock-downs was analyzed. Mostly, variations in triglyceride and cholesterol levels were observed, suggesting that these lipids are more subject to variation in the cells. Unfortunately, it appears that the screen suffered from a high-rate of off-targets effects, implying that most of the phenotypes observed can’t reliably be linked to the corresponding kinase knock-downs. However, several interesting conclusions can still be derived from this screen. First, it was observed that several siRNA induce a decrease in cholesterol, which is coupled to accumulation of a new lipid. Several lines of evidence suggest that this new lipid is in fact a methylated sterol precursor such as lanosterol or demethyllanosterol. Previously, HMG-CoA reductase was considered as the rate-limiting enzyme of cholesterol biosynthesis and the major regulated step of this process. These data show that another major regulation step occurs more downstream in the pathway at the level of methylated cholesterol precursors. Furthermore, MAPK9 was identified as a new regulator of triglyceride homeostasis at the cellular level. Upon MAPK9 knock-down, an increase in triglyceride content was observed both by thin layer chromatography and mass spectrometry. Accordingly, these cells present an increase in lipid droplets, the cellular organelles responsible for triglyceride storage. Sty1 was also identified as the functional homolog of MAPK9 in S. pombe for this process, as similar increase in triglyceride and lipid droplets is observed in a deletion strain for this gene. Although more detailed studies will be necessary to unravel the molecular mechanism of this process, these data suggest the evolutionary conserved implication of the MAP kinase pathway in the regulation of lipid storage both in humans and in yeasts

MAPK9: A New Regulator of Triglyceride Metabolism revealed by siRNA Screening

Lipid homeostasis is an essential factor for proper function both at the level of a cell and of an organism. Dysregulation of this process is responsible for some of the major health concerns of our societies such as obesity and atherosclerosis. Considering the wide variety of lipids and the high dynamic of the system, it is clear that regulation is required to keep the appropriate balance between the different lipids. Although a few regulation pathways are already characterized, some others still wait to be discovered. In order to unravel new players involved in lipid regulation, a screening procedure was developed combining RNA interference in Hela cells and thin layer chromatography. Thereby, it is possible to monitor modifications of lipid composition resulting from siRNA knock-down. Furthermore, the potential of mass spectrometry as a lipid analysis tool in large-scale studies was evaluated. This method was then applied to an essential family of regulatory proteins, the kinases. Lipid composition of 600 kinases knock-downs was analyzed. Mostly, variations in triglyceride and cholesterol levels were observed, suggesting that these lipids are more subject to variation in the cells. Unfortunately, it appears that the screen suffered from a high-rate of off-targets effects, implying that most of the phenotypes observed can’t reliably be linked to the corresponding kinase knock-downs. However, several interesting conclusions can still be derived from this screen. First, it was observed that several siRNA induce a decrease in cholesterol, which is coupled to accumulation of a new lipid. Several lines of evidence suggest that this new lipid is in fact a methylated sterol precursor such as lanosterol or demethyllanosterol. Previously, HMG-CoA reductase was considered as the rate-limiting enzyme of cholesterol biosynthesis and the major regulated step of this process. These data show that another major regulation step occurs more downstream in the pathway at the level of methylated cholesterol precursors. Furthermore, MAPK9 was identified as a new regulator of triglyceride homeostasis at the cellular level. Upon MAPK9 knock-down, an increase in triglyceride content was observed both by thin layer chromatography and mass spectrometry. Accordingly, these cells present an increase in lipid droplets, the cellular organelles responsible for triglyceride storage. Sty1 was also identified as the functional homolog of MAPK9 in S. pombe for this process, as similar increase in triglyceride and lipid droplets is observed in a deletion strain for this gene. Although more detailed studies will be necessary to unravel the molecular mechanism of this process, these data suggest the evolutionary conserved implication of the MAP kinase pathway in the regulation of lipid storage both in humans and in yeasts

Top-down lipidomic screens by multivariate analysis of high-resolution survey mass spectra.

Direct profiling of total lipid extracts on a hybrid LTQ Orbitrap mass spectrometer by high-resolution survey spectra clusters species of 11 major lipid classes into 7 groups, which are distinguished by their sum compositions and could be identified by accurately determined masses. Rapid acquisition of survey spectra was employed as a "top-down" screening tool that, together with the computational method of principal component analysis, revealed pronounced perturbations in the abundance of lipid precursors within the entire series of experiments. Altered lipid precursors were subsequently identified either by accurately determined masses or by in-depth MS/MS characterization that was performed on the same instrument. Hence, the sensitivity, throughput and robustness of lipidomics screens were improved without compromising the accuracy and specificity of molecular species identification. The top-down lipidomics strategy lends itself for high-throughput screens complementing ongoing functional genomics efforts.Journal ArticleResearch Support, Non-U.S. Gov'tinfo:eu-repo/semantics/publishe

How lipids influence the activity of β2-adrenergic receptor

The lipidic composition of the membrane bilayer has been proven to be a critical player in the modulation of many membrane protein structure and function. Several studies have proposed a functional role for lipids, especially cholesterol, on the biological behavior of GPCRs. Our studies will focus on the human b2-adrenergic receptor (b2AR), which is involved mostly in the modulation of the sympathetic nervous system. Since b2AR is widely expressed in the organism, the question of the receptor regulation in different tissues arises. It has been suggested that a tissue-specific regulation of b2AR is possible in relation to its environment. The effect of cholesterol on b2AR stability and function has been clearly shown in some publications. However, very few studies tackle the role of other membrane lipids on GPCRs activity. Thus our work was aimed to understand the effect of lipids on b2AR function. We have developed a method to examine the interaction between lipids in biological membranes and the receptor using mass spectrometry. We were thus able to identify the lipid species bound to the purified receptor. We have also tested the effect of lipid environment on the functionality of the receptor. Using different lipid species individually, we have reconstituted b2AR in HDL particles of phosphatidylcholine (PC), phosphatydilethanolamine (PE), phosphatidylglycerol (PG), phosphatydylserine (PS), PC/Cholesteryl hemisuccinate (PC/CHS) and PC/sphingomyelin (PC/SM). We show the choice of lipids strongly modulate the affinity of the receptor towards its ligands as well as liguand-induced conformational changes. Some lipid species, like PE favor an inactive state of the receptor, whereas others like PG promote the activation of the protein. Cholesterol analogue CHS enhances the affinity of b2AR towards its ligands (agonist and antagonist). We have also monitored the effect of fatty acid chain length on the receptor activity.The results presented here constitute a significant step towards understanding the relationship between b2AR and the lipids in biological membrane.info:eu-repo/semantics/publishe

A new experimental approach to detect long-range conformational changes transmitted between the membrane and cytosolic domains of LmrA, a bacterial multidrug transporter

info:eu-repo/semantics/publishe

Structures of P-glycoprotein reveal its conformational flexibility and an epitope on the nucleotide-binding domain

P-glycoprotein (P-gp) is one of the best-known mediators of drug efflux-based multidrug resistance in many cancers. This validated therapeutic target is a prototypic, plasma membrane resident ATPBinding Cassette transporter that pumps xenobiotic compounds out of cells. The large, polyspecific drug-binding pocket of P-gp recognizes a variety of structurally unrelated compounds. The transport of these drugs across the membrane is coincident with changes in the size and shape of this pocket during the course of the transport cycle. Here, we present the crystal structures of three inward-facing conformations of mouse P-gp derived from two different crystal forms. One structure has a nanobody bound to the C-terminal side of the first nucleotide-binding domain. This nanobody strongly inhibits the ATP hydrolysis activity of mouse Pgp by hindering the formation of a dimeric complex between the ATP-binding domains, which is essential for nucleotide hydrolysis. Together, these inward-facing conformational snapshots of P-gp demonstrate a range of flexibility exhibited by this transporter, which is likely an essential feature for the binding and transport of large, diverse substrates. The nanobody-bound structure also reveals a unique epitope on P-gp.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Phosphorylation-induced conformational changes of cystic fibrosis transmembrane conductance regulator monitored by attenuated total reflection-Fourier transform IR spectroscopy and fluorescence spectroscopy.

Cystic fibrosis transmembrane conductance regulator (CFTR) is a member of the ABC protein superfamily. Phosphorylation of a regulatory domain of this protein is a prerequisite for activity. We analyzed the effect of protein kinase A (PKA) phosphorylation on the structure of purified and reconstituted CFTR protein. 1H/2H exchange monitored by attenuated total reflection Fourier transform IR spectroscopy demonstrates that CFTR is highly accessible to aqueous medium. Phosphorylation of the regulatory (R) domain by PKA further increases this accessibility. More specifically, fluorescence quenching of cytosolic tryptophan residues revealed that the accessibility of the cytoplasmic part of the protein is modified by phosphorylation. Moreover, the combination of polarized IR spectroscopy with 1H/2H exchange suggested an increase of the accessibility of the transmembrane domains of CFTR. This suggests that CFTR phosphorylation can induce a large conformational change that could correspond either to a displacement of the R domain or to long range conformational changes transmitted from the phosphorylation sites to the nucleotide binding domains and the transmembrane segments. Such structural changes may provide better access for the solutes to the nucleotide binding domains and the ion binding site.Journal ArticleResearch Support, Non-U.S. Gov'tinfo:eu-repo/semantics/publishe