DHHC7 Palmitoylates Glucose Transporter 4 (Glut4) and Regulates Glut4 Membrane Translocation

A comprehensive view of muscle glucose uptake: regulation by insulin, contractile activity, and exercise

Skeletal muscle is the main site of glucose deposition in the body during meals and the major glucose utilizer during physical activity. Although in both instances the supply of glucose from the circulation to the muscle is of paramount importance, in most conditions the rate-limiting step in glucose uptake, storage, and utilization is the transport of glucose across the muscle cell membrane. This step is dependent upon the translocation of the insulin- and contraction-responsive glucose transporter GLUT4 from intracellular storage sites to the sarcolemma and T tubules. Here, we first analyze how glucose can traverse the capillary wall into the muscle interstitial space. We then review the molecular processes that regulate GLUT4 translocation in response to insulin and muscle contractions and the methodologies utilized to unravel them. We further discuss how physical activity and inactivity, respectively, lead to increased and decreased insulin action in muscle and touch upon sex differences in glucose metabolism. Although many key processes regulating glucose uptake in muscle are known, the advent of newer and bioinformatics tools has revealed further molecular signaling processes reaching a staggering level of complexity. Much of this molecular mapping has emerged from cellular and animal studies and more recently from application of a variety of -omics in human tissues. In the future, it will be imperative to validate the translatability of results drawn from experimental systems to human physiology.

Palmitoylation in cardiovascular diseases: Molecular mechanism and therapeutic potential

Cardiovascular disease is one of the leading causes of mortality worldwide, and involves complex pathophysiological mechanisms that encompass various biological processes and molecular pathways. Post-translational modifications of proteins play crucial roles in the occurrence and progression of cardiovascular diseases, among which palmitoylation is particularly important. Various proteins associated with cardiovascular diseases can be palmitoylated to enhance the hydrophobicity of their molecular subdomains. This lipidation can significantly affect some pathophysiological processes, such as metabolism, inflammation by altering protein stability, localization, and signal transduction. In this review, we narratively summarize recent advances in the palmitoylation of proteins related to cardiovascular diseases and discuss its potential as a therapeutic target.

Acid sphingomyelinase recruits palmitoylated CD36 to membrane rafts and enhances lipid uptake

CD36 palmitoylation increases its membrane localization and is required for CD36-mediated uptake of oxidized low-density lipoprotein (oxLDL). Acid sphingomyelinase (ASMase) is transported to the plasma membrane, where it promotes lipid raft clustering, facilitating membrane protein anchoring for biological functions. We here investigated the effects of oxLDL on CD36 palmitoylation and explored the role of ASMase in CD36 membrane translocation. We found that oxLDL increased CD36 palmitoylation and drives its intracellular trafficking from the endoplasmic reticulum to plasma membrane lipid rafts in macrophages. Affinity purification followed by mass spectrometry analysis identified CD36 bound to ASMase in plasma membrane. The CD36/ASMase binding was enhanced by oxLDL treatment. Genetic ablation and pharmacological inhibition of ASMase reduced CD36 recruitment to lipid rafts, and inhibited CD36 intracellular signaling and lipid uptake. Moreover, inhibiting Sortilin to block ASMase intracellular trafficking and reduce membrane ASMase also caused a sharp decrease in amount of membrane CD36. In addition, ASMase overexpression dramatically promoted palmitoylated CD36 membrane localization but not CD36 without palmitoylation, in which the modification was inhibited by 2-bromopalmitate (2-BP) treatment or point mutation at the palmitoylation site. Moreover, ASMase knockout inhibited CD36 membrane recruitment both in peritoneal macrophages and in aorta, and attenuated lipid accumulation in atherosclerotic plaques in mice. Finally, we found oxLDL activated extracellular signal-regulated kinase1/2 (ERK1/2)/specificity protein (SP1) signaling, upregulating ASMase transcription and promoting sphingomyelin catabolism. Therefore, these data demonstrate that ASMase expression induced by oxLDL is required for palmitoylated CD36 membrane translocation during foam cell formation in macrophages.

Identification and validation of palmitoylation-related biomarkers in gestational diabetes mellitus

Palmitoylation plays a crucial role in the pathophysiology of diabetes, and an increase in palmitoylation may inhibit the function of insulin receptors, thereby affecting the progression of gestational diabetes mellitus (GDM). However, its involvement in gestational diabetes mellitus (GDM) remains underexplored. This study analyzed GDM-related datasets and 30 palmitoylation-related genes (PRGs), identifying MNDA, FCGR3B, and AQP9 as significantly upregulated biomarkers in GDM samples. Consistent with the dataset analysis, reverse transcription-polymerase chain reaction (RT-qPCR) confirmed elevated AQP9 expression. Comprehensive analyses, including nomogram construction, enrichment analysis, immune infiltration assessment, molecular regulatory network generation, drug prediction, and molecular docking, were conducted. The biomarker-based nomogram demonstrated excellent predictive performance for GDM risk. MNDA, FCGR3B, and AQP9 were significantly enriched in pathways such as "Myc-targets-v1" and "TNFA signaling via NFkB." Additionally, eosinophil infiltration showed a strong positive correlation with these biomarkers. Regulatory networks involving SH3BP5-AS1-hsa-miR-182-5p-AQP9 and hsa-miR-182-5p-AQP9-ELF5 were identified, and stable binding energies were observed between the biomarkers and corresponding drugs. These findings provide promising avenues for early GDM screening and diagnosis.

The CP123L protein of African swine fever virus is a membrane-associated, palmitoylated protein required for viral replication

African swine fever (ASF) is a highly contagious and often lethal disease caused by African swine fever virus (ASFV) in pigs. Protein palmitoylation is a prevalent posttranslational lipid modification that can modulate viral replication. In this study, we investigated the palmitoylation of ASFV proteins. The results revealed that the CP123L protein (pCP123L) of ASFV was palmitoylated at the cysteine residue at position 18 (C18). To further elucidate the functional significance of this posttranslational modification, abolishing palmitoylation through a cysteine-to-serine mutation at C18 (C18S) of pCP123L (pCP123L/C18S) or treatment with 2-bromopalmitate (2-BP), a palmitoylation inhibitor, led to altered cytomembrane localization and migration rate of pCP123L. Furthermore, depalmitoylation achieved through 2-BP treatment significantly suppressed ASFV replication and exerted a profound impact on virus budding. Remarkably, blocking pCP123L palmitoylation via the C18S mutation resulted in decreased replication of ASFV. Our study represents the first evidence for the presence of palmitoylation in ASFV proteins and underscores its crucial role in viral replication.

IMPORTANCE

African swine fever (ASF) poses a significant threat to the global pig industry. The causative agent of ASF is African swine fever virus (ASFV), which encodes more than 165 proteins. Protein palmitoylation, a common posttranslational lipid modification, can modulate viral infection. To date, the ASFV proteins that undergo palmitoylation and their impacts on viral replication remain elusive. In this study, the CP123L protein (pCP123L) of ASFV was identified as a palmitoylated protein, and the cysteine residue at position 18 of pCP123L is responsible for its palmitoylation. Notably, our findings demonstrate that palmitoylation plays significant roles in ASFV protein functions and facilitates viral replication.

Palmitoylation and regulation of potassium-dependent sodium/calcium exchangers (NCKX)

Cellular Ca2+ homeostasis is critical for normal cell physiology and is regulated by several mechanisms. Two major players in intracellular Ca2+ homeostasis in multiple tissues belong to the SLC8 (Na+/Ca2+ exchangers (NCXs); NCX1-3) and SLC24 (K+ dependent Na+/Ca2+ exchangers (NCKXs); NCKX1-5) families. It has been established that NCXs and NCKX4 are palmitoylated, and that palmitoylation promotes NCX1 inactivation. However, there is still little known about NCKXs' palmitoylation. We found that (1) NCKX3 and NCKX5, but not NCKX1, are palmitoylated, (2) Cys to Ala mutation at position 467 for NCXK3 and 325 for NCKX5 notably diminished palmitoylation and (3) reduced palmitoylation enhanced NCKX3 activity. Our findings bring novel insights into NCKX1, NCKX3 and NCKX5 palmitoylation and establish palmitoylation as an endogenous regulator of NCKX3 activity, paving the way for investigations evaluating the role of palmitoylation in NCKX3 function in health and disease.

Protein posttranslational modifications in metabolic diseases: basic concepts and targeted therapies

Metabolism-related diseases, including diabetes mellitus, obesity, hyperlipidemia, and nonalcoholic fatty liver disease, are becoming increasingly prevalent, thereby posing significant threats to human health and longevity. Proteins, as the primary mediators of biological activities, undergo various posttranslational modifications (PTMs), including phosphorylation, ubiquitination, acetylation, methylation, and SUMOylation, among others, which substantially diversify their functions. These modifications are crucial in the physiological and pathological processes associated with metabolic disorders. Despite advancements in the field, there remains a deficiency in contemporary summaries addressing how these modifications influence processes of metabolic disease. This review aims to systematically elucidate the mechanisms through which PTM of proteins impact the progression of metabolic diseases, including diabetes, obesity, hyperlipidemia, and nonalcoholic fatty liver disease. Additionally, the limitations of the current body of research are critically assessed. Leveraging PTMs of proteins provides novel insights and therapeutic targets for the prevention and treatment of metabolic disorders. Numerous drugs designed to target these modifications are currently in preclinical or clinical trials. This review also provides a comprehensive summary. By elucidating the intricate interplay between PTMs and metabolic pathways, this study advances understanding of the molecular mechanisms underlying metabolic dysfunction, thereby facilitating the development of more precise and effective disease management strategies.

RNAi-mediated glucose transporter 4 (Glut4) silencing inhibits ovarian development and enhances deltamethrin-treated energy depletion in Locusta migratoria

Energy metabolism is essential for insect development, reproduction and detoxification. Insects often reallocate energy and resources to manage external stress, balancing the demands of detoxification and reproduction. Glucose transport 4 (Glut4), a glucose transporter, is involved in glucose and lipid metabolism. However, the specific molecular mechanism of Glut4 in insect reproduction, and its role in the response to insecticide-induced oxidative stress remain unclear. In this study, LmGlut4 was identified and analyzed in Locusta migratoria. Silencing of LmGlut4 significantly reduced vitellogenin (Vg) biosynthesis in the fat body and Vg absorption by oocytes, ultimately hindering ovarian development and oocyte maturation. Knockdown of LmGlut4 also inhibited the biosynthesis of key insect hormones, such as juvenile hormone (JH), 20-hydroxyecdysone (20E) and insulin. Furthermore, LmGlut4 knockdown led to reduced triglyceride (TG) and glycogen content in the fat body and ovary, as well as decreased capacity for trehalose biosynthesis in adipocytes. Additionally, dsLmGlut4-treated locusts showed heightened sensitivity to deltamethrin, leading to increased triglyceride depletion during detoxification. This study sheds light on the biological function of LmGlut4 in the ovary and provides potential target genes for exploring biological pest management strategies.

Mechanisms and functions of protein S-acylation

Over the past two decades, protein S-acylation (often referred to as S-palmitoylation) has emerged as an important regulator of vital signalling pathways. S-Acylation is a reversible post-translational modification that involves the attachment of a fatty acid to a protein. Maintenance of the equilibrium between protein S-acylation and deacylation has demonstrated profound effects on various cellular processes, including innate immunity, inflammation, glucose metabolism and fat metabolism, as well as on brain and heart function. This Review provides an overview of current understanding of S-acylation and deacylation enzymes, their spatiotemporal regulation by sophisticated multilayered mechanisms, and their influence on protein function, cellular processes and physiological pathways. Furthermore, we examine how disruptions in protein S-acylation are associated with a broad spectrum of diseases from cancer to autoinflammatory disorders and neurological conditions.

Genetic deletion of zinc transporter ZnT3 induces progressive cognitive deficits in mice by impairing dendritic spine plasticity and glucose metabolism

Zinc transporter 3 (ZnT3) is abundantly expressed in the brain, residing in synaptic vesicles, where it plays important roles in controlling the luminal zinc levels. In this study, we found that ZnT3 knockout in mice decreased zinc levels in the hippocampus and cortex, and was associated with progressive cognitive impairments, assessed at 2, 6, and 9-month of age. The results of Golgi-Cox staining demonstrated that ZnT3 deficiency was associated with an increase in dendritic complexity and a decrease in the density of mature dendritic spines, indicating potential synaptic plasticity deficit. Since ZnT3 deficiency was previously linked to glucose metabolism abnormalities, we tested the expression levels of genes related to insulin signaling pathway in the hippocampus and cortex. We found that the Expression of glucose transporters, GLUT3, GLUT4, and the insulin receptor in the whole tissue and synaptosome fraction of the hippocampus of the ZnT3 knockout mice were significantly reduced, as compared to wild-type controls. Expression of AKT (A serine/threonine protein kinase) and insulin-induced AKT phosphorylation was also reduced in the hippocampus of ZnT3 knockout mice. We hypothesize that the ZnT3 deficiency and reduced brain zinc levels may cause cognitive impairment by negatively affecting glycose metabolism via decreased expression of key components of insulin signaling, as well as via changes in synaptic plasticity. These finding may provide new therapeutic target for treatments of neurodegenerative disorders.

Tryptophanylation of insulin receptor by WARS attenuates insulin signaling

Increased circulating amino acid levels have been linked to insulin resistance and development of type 2 diabetes (T2D), but the underlying mechanism remains largely unknown. Herein, we show that tryptophan modifies insulin receptor (IR) to attenuate insulin signaling and impair glucose uptake. Mice fed with tryptophan-rich chow developed insulin resistance. Excessive tryptophan promoted tryptophanyl-tRNA synthetase (WARS) to tryptophanylate lysine 1209 of IR (W-K1209), which induced insulin resistance by inhibiting the insulin-stimulated phosphorylation of IR, AKT, and AS160. SIRT1, but not other sirtuins, detryptophanylated IRW-K1209 to increase the insulin sensitivity. Collectively, we unveiled the mechanisms of how tryptophan impaired insulin signaling, and our data suggested that WARS might be a target to attenuate insulin resistance in T2D patients.

STAT3 palmitoylation initiates a positive feedback loop that promotes the malignancy of hepatocellular carcinoma cells in mice

Constitutive activation of the transcription factor STAT3 (signal transducer and activator of transcription 3) contributes to the malignancy of many cancers such as hepatocellular carcinoma (HCC) and is associated with poor prognosis. STAT3 activity is increased by the reversible palmitoylation of Cys108 by the palmitoyltransferase DHHC7 (encoded by ZDHHC7). Here, we investigated the consequences of S-palmitoylation of STAT3 in HCC. Increased ZDHHC7 abundance in HCC cases was associated with poor prognosis, as revealed by bioinformatics analysis of patient data. In HepG2 cells in vitro, DHHC7-mediated palmitoylation enhanced the expression of STAT3 target genes, including HIF1A, which encodes the hypoxia-inducible transcription factor HIF1α. Inhibiting DHHC7 decreased the S-palmitoylation of STAT3 and decreased HIF1α abundance. Furthermore, stabilization of HIF1α by cyclin-dependent kinase 5 (CDK5) enabled it to promote the expression of ZDHHC7, which generated a positive feedback loop between DHHC7, STAT3, and HIF1α. Perturbing this loop reduced the growth of HCC cells in vivo. Moreover, DHHC7, STAT3, and HIF1α were all abundant in human HCC tissues. Our study identifies a pathway connecting these proteins that is initiated by S-palmitoylation, which may be broadly applicable to understanding the role of this modification in cancer.

ZDHHC17 participates in the pathogenesis of polycystic ovary syndrome by affecting androgen conversion to estrogen in granulosa cells

Polycystic ovary syndrome (PCOS) is a prevalent endocrine disorder affecting women of reproductive age and is a significant cause of female subfertility. Our previous research demonstrated that the abnormal palmitoylation of heat shock protein-90α (HSP90α) plays a role in the development of PCOS. However, the palmitoyl acyltransferases in HSP90α palmitoylation remain poorly understood. Herein, we identified ZDHHC17 as a major palmitoyl acyltransferase for HSP90α palmitoylation in granulosa cells. ZDHHC17 protein expression was diminished under excess androgen conditions in vitro and in vivo. Consistently, ovarian ZDHHC17 expression was found to be attenuated in patients with PCOS. ZDHHC17 depletion decreased HSP90α palmitoylation levels and hampered the conversion of androgen to estrogen via CYP19A1. Furthermore, ZDHHC17-mediated regulation of CYP19A1 expression was dependent on HSP90α palmitoylation. Our findings reveal that the regulatory role of HSP90α palmitoylation by ZDHHC17 is critical in PCOS pathophysiology and provide insights into the role of ZDHHC17 in reproductive endocrinology.

Hepatic palmitoyl-proteomes and acyl-protein thioesterase protein proximity networks link lipid modification and mitochondria

Acyl-protein thioesterases 1 and 2 (APT1 and APT2) reverse S-acylation, a potential regulator of systemic glucose metabolism in mammals. Palmitoylation proteomics in liver-specific knockout mice shows that APT1 predominates over APT2, primarily depalmitoylating mitochondrial proteins, including proteins linked to glutamine metabolism. miniTurbo-facilitated determination of the protein-protein proximity network of APT1 and APT2 in HepG2 cells reveals APT proximity networks encompassing mitochondrial proteins including the major translocases Tomm20 and Timm44. APT1 also interacts with Slc1a5 (ASCT2), the only glutamine transporter known to localize to mitochondria. High-fat-diet-fed male mice with dual (but not single) hepatic deletion of APT1 and APT2 have insulin resistance, fasting hyperglycemia, increased glutamine-driven gluconeogenesis, and decreased liver mass. These data suggest that APT1 and APT2 regulation of hepatic glucose metabolism and insulin signaling is functionally redundant. Identification of substrates and protein-protein proximity networks for APT1 and APT2 establishes a framework for defining mechanisms underlying metabolic disease.

S-palmitoylation regulates innate immune signaling pathways: molecular mechanisms and targeted therapies

S-palmitoylation is a reversible posttranslational lipid modification that targets cysteine residues of proteins and plays critical roles in regulating the biological processes of substrate proteins. The innate immune system serves as the first line of defense against pathogenic invaders and participates in the maintenance of tissue homeostasis. Emerging studies have uncovered the functions of S-palmitoylation in modulating innate immune responses. In this review, we focus on the reversible palmitoylation of innate immune signaling proteins, with particular emphasis on its roles in the regulation of protein localization, protein stability, and protein-protein interactions. We also highlight the potential and challenge of developing therapies that target S-palmitoylation or de-palmitoylation for various diseases.

Palmitoylation of solute carriers

Post-translational modifications are an important mechanism in the regulation of protein expression, function, and degradation. Well-known post-translational modifications are phosphorylation, glycosylation, and ubiquitination. However, lipid modifications, including myristoylation, prenylation, and palmitoylation, are poorly studied. Since the early 2000s, researchers have become more interested in lipid modifications, especially palmitoylation. The number of articles in PubMed increased from about 350 between 2000 and 2005 to more than 600 annually during the past ten years. S-palmitoylation, where the 16-carbon saturated (C16:0) palmitic acid is added to free cysteine residues of proteins, is a reversible protein modification that can affect the expression, membrane localization, and function of the modified proteins. Various diseases like Huntington's and Alzheimer's disease have been linked to changes in protein palmitoylation. In humans, the addition of palmitic acid is mediated by 23 palmitoyl acyltransferases, also called DHHC proteins. The modification can be reversed by a few thioesterases or hydrolases. Numerous soluble and membrane-attached proteins are known to be palmitoylated, but among the approximately 400 solute carriers that are classified in 66 families, only 15 found in 8 families have so far been documented to be palmitoylated. Among the best-characterized transporters are the glucose transporters GLUT1 (SLC2A1) and GLUT4 (SLC2A4), the three monoamine transporters norepinephrine transporter (NET; SLC6A2), dopamine transporter (DAT; SLC6A3), and serotonin transporter (SERT; SLC6A4), and the sodium-calcium exchanger NCX1 (SLC8A1). While there is evidence from recent proteomics experiments that numerous solute carriers are palmitoylated, no details beyond the 15 transporters covered in this review are available.

AMPK Phosphorylates ZDHHC13 to Increase MC1R Activity and Suppress Melanomagenesis

Inherited genetic variations in the melanocortin-1 receptor (MC1R) responsible for human red hair color (RHC) variants are associated with impaired DNA damage repair and increased melanoma risk. MC1R signaling is critically dependent on palmitoylation, primarily mediated by the protein acyltransferase zinc finger DHHC-type palmitoyltransferase 13 (ZDHHC13). A better understanding of how ZDHHC13 is physiologically activated could help identify approaches to prevent melanomagenesis in redheads. Here, we report that AMP-activated protein kinase (AMPK) phosphorylates ZDHHC13 at S208 to strengthen the interaction between ZDHHC13 and MC1R-RHC, leading to enhanced MC1R palmitoylation in redheads. Consequently, phosphorylation of ZDHHC13 by AMPK increased MC1R-RHC downstream signaling. AMPK activation and MC1R palmitoylation repressed UVB-induced transformation of human melanocytes in vitro and delayed melanomagenesis in vivo in C57BL/6J-MC1R-RHC mice. The importance of AMPK to MC1R signaling was validated in human melanomas where AMPK upregulation correlated with expression of factors downstream from MC1R signaling and with prolonged patient survival. These findings suggest AMPK activation as a promising strategy to reduce melanoma risk, especially for individuals with red hair.

SIGNIFICANCE

Phosphorylation of ZDHHC13 by AMPK at S208 promotes MC1R activation and suppresses melanocyte transformation, indicating activation of AMPK as a potential approach to prevent melanoma in people with red hair.

Regulation of tumor metabolism by post translational modifications on metabolic enzymes

Metabolic reprogramming is a hallmark of cancer development, progression, and metastasis. Several metabolic pathways such as glycolysis, tricarboxylic acid (TCA) cycle, lipid metabolism, and glutamine catabolism are frequently altered to support cancer growth. Importantly, the activity of the rate-limiting metabolic enzymes in these pathways are specifically modulated in cancer cells. This is achieved by transcriptional, translational, and post translational regulations that enhance the expression, activity, stability, and substrate sensitivity of the rate-limiting enzymes. These mechanisms allow the enzymes to retain increased activity supporting the metabolic needs of rapidly growing tumors, sustain their survival in the hostile tumor microenvironments and in the metastatic lesions. In this review, we primarily focused on the post translational modifications of the rate-limiting enzymes in the glucose and glutamine metabolism, TCA cycle, and fatty acid metabolism promoting tumor progression and metastasis.

Post-translational palmitoylation of metabolic proteins

Numerous cellular proteins are post-translationally modified by addition of a lipid group to their structure, which dynamically influences the proteome by increasing hydrophobicity of proteins often impacting protein conformation, localization, stability, and binding affinity. These lipid modifications include myristoylation and palmitoylation. Palmitoylation involves a 16-carbon saturated fatty acyl chain being covalently linked to a cysteine thiol through a thioester bond. Palmitoylation is unique within this group of modifications, as the addition of the palmitoyl group is reversible and enzyme driven, rapidly affecting protein targeting, stability and subcellular trafficking. The palmitoylation reaction is catalyzed by a large family of Asp-His-His-Cys (DHHCs) motif-containing palmitoyl acyltransferases, while the reverse reaction is catalyzed by acyl-protein thioesterases (APTs), that remove the acyl chain. Palmitoyl-CoA serves an important dual purpose as it is not only a key metabolite fueling energy metabolism, but is also a substrate for this PTM. In this review, we discuss protein palmitoylation in regulating substrate metabolism, focusing on membrane transport proteins and kinases that participate in substrate uptake into the cell. We then explore the palmitoylation of mitochondrial proteins and the palmitoylation regulatory enzymes, a less explored field for potential lipid metabolic regulation.

DHHC17 Is a New Regulator of AMPK Signaling

The association of AMP-activated protein kinase (AMPK) with membranes plays a critical role in the regulation of AMPK activation and function. Protein lipid modification, including palmitoylation, myristoylation, and farnesyation, constitutes a crucial mechanism in the regulation of protein dynamic interactions with membranes. Among the three subunits of the AMPK heterotrimeric complex, the structural subunit AMPKβ is myristoylated and the catalytic subunit AMPKα is palmitoylated. Here, we report the characterization of AMPKα palmitoylation. We found that AMKPα was palmitoylated at Cys209 and Cys543, and this was required for AMPK activation and subcellular membrane compartmentalization. To understand the regulation of AMPKα palmitoylation, we have identified DHHC17 as a candidate palmitoyltransferase for AMPKα and found that DHHC17, by palmitoylating AMPKα, modulated AMPK membrane association and activation in response to energy stress. To determine the role of DHHC17 in cell function, we generated DHHC17 liver-specific knockout mice and found that inactivation of DHHC17 in the mouse liver impaired AMPK activation and hepatic autophagy and caused a type 2 diabetes-like syndrome. Overall, our studies demonstrate that AMPKα palmitoylation plays a critical role in AMPK activation and that DHHC17, through its modulation of AMPK signaling, constitutes a new regulator of hepatic metabolism.

Post-translational Modifications: The Signals at the Intersection of Exercise, Glucose Uptake, and Insulin Sensitivity

Diabetes is a global epidemic, of which type 2 diabetes makes up the majority of cases. Nonetheless, for some individuals, type 2 diabetes is eminently preventable and treatable via lifestyle interventions. Glucose uptake into skeletal muscle increases during and in recovery from exercise, with exercise effective at controlling glucose homeostasis in individuals with type 2 diabetes. Furthermore, acute and chronic exercise sensitizes skeletal muscle to insulin. A complex network of signals converge and interact to regulate glucose metabolism and insulin sensitivity in response to exercise. Numerous forms of post-translational modifications (eg, phosphorylation, ubiquitination, acetylation, ribosylation, and more) are regulated by exercise. Here we review the current state of the art of the role of post-translational modifications in transducing exercise-induced signals to modulate glucose uptake and insulin sensitivity within skeletal muscle. Furthermore, we consider emerging evidence for noncanonical signaling in the control of glucose homeostasis and the potential for regulation by exercise. While exercise is clearly an effective intervention to reduce glycemia and improve insulin sensitivity, the insulin- and exercise-sensitive signaling networks orchestrating this biology are not fully clarified. Elucidation of the complex proteome-wide interactions between post-translational modifications and the associated functional implications will identify mechanisms by which exercise regulates glucose homeostasis and insulin sensitivity. In doing so, this knowledge should illuminate novel therapeutic targets to enhance insulin sensitivity for the clinical management of type 2 diabetes.

KLF10 promotes nonalcoholic steatohepatitis progression through transcriptional activation of zDHHC7

Nonalcoholic steatohepatitis (NASH), characterized by hepatic steatosis, inflammation, and liver injury, has become a leading cause of end-stage liver diseases and liver transplantation. Krüppel-like factors 10 (KLF10) is a Cys2/His2 zinc finger transcription factor that regulates cell growth, apoptosis, and differentiation. However, whether it plays a role in the development and progression of NASH remains poorly understood. In the present study, we found that KLF10 expression was selectively upregulated in the mouse models and human patients with NASH, compared with simple steatosis (NAFL). Gain- and loss-of function studies demonstrated that hepatocyte-specific overexpression of KLF10 aggravated, whereas its depletion alleviated diet-induced NASH pathogenesis in mice. Mechanistically, transcriptomic analysis and subsequent functional experiments showed that KLF10 promotes hepatic lipid accumulation and inflammation through the palmitoylation and plasma membrane localization of fatty acid translocase CD36 via transcriptionally activation of zDHHC7. Indeed, both expression of zDHHC7 and palmitoylation of CD36 are required for the pathogenic roles of KLF10 in NASH development. Thus, our results identify an important role for KLF10 in NAFL-to-NASH progression through zDHHC7-mediated CD36 palmitoylation.

Involvement of glucose transporter 4 in ovarian development and reproductive maturation of Harmonia axyridis (Coleoptera: Coccinellidae)

Glucose is vital to embryogenesis, as are glucose transporters. Glucose transporter 4 (Glut4) is one of the glucose transporters, which is involved in rapid uptake of glucose by various cells and promotes glucose homeostasis. Although energy metabolism in insect reproduction is well known, the molecular mechanism of Glut4 in insect reproduction is poorly understood. We suspect that Glut4 is involved in maintaining glucose concentrations in the ovaries and affecting vitellogenesis, which is critical for subsequent oocyte maturation and insect fertility. Harmonia axyridis (Pallas) is a model organism for genetic research and a natural enemy of insect pests. We studied the influence of the Glut4 gene on the reproduction and development of H. axyridis using RNA interference technology. Reverse transcription quantitative polymerase chain reaction analysis revealed that HaGlut4 was most highly expressed in adults. Knockdown of the HaGlut4 gene reduced the transcript levels of HaGlut4, and the weight and number of eggs produced significantly decreased. In addition, the transcript levels of vitellogenin receptor and vitellogenin in the fat bodies and the ovaries of H. axyridis decreased after the interference of Glut4, and decreased the triglyceride, fatty acid, total amino acid and adenosine triphosphate content of H. axyridis. This resulted in severe blockage of ovary development and reduction of yolk formation; there was no development of ovarioles in the developing oocytes. These changes indicate that a lack of HaGlut4 can impair ovarian development and oocyte maturation and result in decreased fecundity.

Cryo-EM structure of human glucose transporter GLUT4

GLUT4 is the primary glucose transporter in adipose and skeletal muscle tissues. Its cellular trafficking is regulated by insulin signaling. Failed or reduced plasma membrane localization of GLUT4 is associated with diabetes. Here, we report the cryo-EM structures of human GLUT4 bound to a small molecule inhibitor cytochalasin B (CCB) at resolutions of 3.3 Å in both detergent micelles and lipid nanodiscs. CCB-bound GLUT4 exhibits an inward-open conformation. Despite the nearly identical conformation of the transmembrane domain to GLUT1, the cryo-EM structure reveals an extracellular glycosylation site and an intracellular helix that is invisible in the crystal structure of GLUT1. The structural study presented here lays the foundation for further mechanistic investigation of the modulation of GLUT4 trafficking. Our methods for cryo-EM analysis of GLUT4 will also facilitate structural determination of many other small size solute carriers.

Small solute carriers remain difficult to study by single particle cryo-EM. Here, the authors report the cryo-EM structure of human insulin-responsive glucose transporter GLUT4 (55 kDa) without rigid soluble domains or binders.

Lipid-induced S-palmitoylation as a Vital Regulator of Cell Signaling and Disease Development

Lipid metabolites are emerging as pivotal regulators of protein function and cell signaling. The availability of intracellular fatty acid is tightly regulated by glycolipid metabolism and may affect human body through many biological mechanisms. Recent studies have demonstrated palmitate, either from exogenous fatty acid uptake or de novo fatty acid synthesis, may serve as the substrate for protein palmitoylation and regulate protein function via palmitoylation. Palmitoylation, the most-studied protein lipidation, encompasses the reversible covalent attachment of palmitate moieties to protein cysteine residues. It controls various cellular physiological processes and alters protein stability, conformation, localization, membrane association and interaction with other effectors. Dysregulation of palmitoylation has been implicated in a plethora of diseases, such as metabolic syndrome, cancers, neurological disorders and infections. Accordingly, it could be one of the molecular mechanisms underlying the impact of palmitate metabolite on cellular homeostasis and human diseases. Herein, we explore the relationship between lipid metabolites and the regulation of protein function through palmitoylation. We review the current progress made on the putative role of palmitate in altering the palmitoylation of key proteins and thus contributing to the pathogenesis of various diseases, among which we focus on metabolic disorders, cancers, inflammation and infections, neurodegenerative diseases. We also highlight the opportunities and new therapeutics to target palmitoylation in disease development.

CD36 Signal Transduction in Metabolic Diseases: Novel Insights and Therapeutic Targeting

The cluster of differentiation 36 (CD36) is a scavenger receptor present on various types of cells and has multiple biological functions that may be important in inflammation and in the pathogenesis of metabolic diseases, including diabetes. Here, we consider recent insights into how the CD36 response becomes deregulated under metabolic conditions, as well as the therapeutic benefits of CD36 inhibition, which may provide clues for developing strategies aimed at the treatment or prevention of diabetes associated with metabolic diseases. To facilitate this process further, it is important to pinpoint regulatory mechanisms that are relevant under physiological and pathological conditions. In particular, understanding the mechanisms involved in dictating specific CD36 downstream cellular outcomes will aid in the discovery of potent compounds that target specific CD36 downstream signaling cascades.

Protein Lipidation by Palmitoylation and Myristoylation in Cancer

Posttranslational modification of proteins with lipid moieties is known as protein lipidation. The attachment of a lipid molecule to proteins endows distinct properties, which affect their hydrophobicity, structural stability, localization, trafficking between membrane compartments, and influences its interaction with effectors. Lipids or lipid metabolites can serve as substrates for lipidation, and the availability of these lipid substrates are tightly regulated by cellular metabolism. Palmitoylation and myristoylation represent the two most common protein lipid modifications, and dysregulation of protein lipidation is strongly linked to various diseases such as metabolic syndromes and cancers. In this review, we present recent developments in our understanding on the roles of palmitoylation and myristoylation, and their significance in modulating cancer metabolism toward cancer initiation and progression.

Genome wide association study of response to interval and continuous exercise training: the Predict-HIIT study

BACKGROUND

Low cardiorespiratory fitness (V̇O_2peak) is highly associated with chronic disease and mortality from all causes. Whilst exercise training is recommended in health guidelines to improve V̇O_2peak, there is considerable inter-individual variability in the V̇O_2peak response to the same dose of exercise. Understanding how genetic factors contribute to V̇O_2peak training response may improve personalisation of exercise programs. The aim of this study was to identify genetic variants that are associated with the magnitude of V̇O₂peak response following exercise training.

METHODS

Participant change in objectively measured V̇O₂peak from 18 different interventions was obtained from a multi-centre study (Predict-HIIT). A genome-wide association study was completed (n = 507), and a polygenic predictor score (PPS) was developed using alleles from single nucleotide polymorphisms (SNPs) significantly associated (P < 1 × 10^-5) with the magnitude of V̇O₂peak response. Findings were tested in an independent validation study (n = 39) and compared to previous research.

RESULTS

No variants at the genome-wide significance level were found after adjusting for key covariates (baseline V̇O₂peak_, individual study, principal components which were significantly associated with the trait). A Quantile-Quantile plot indicates there was minor inflation in the study. Twelve novel loci showed a trend of association with V̇O₂peak response that reached suggestive significance (P < 1 × 10^-5). The strongest association was found near the membrane associated guanylate kinase, WW and PDZ domain containing 2 (MAGI2) gene (rs6959961, P = 2.61 × 10^-7). A PPS created from the 12 lead SNPs was unable to predict V̇O₂peak response in a tenfold cross validation, or in an independent (n = 39) validation study (P > 0.1). Significant correlations were found for beta coefficients of variants in the Predict-HIIT (P < 1 × 10^-4) and the validation study (P <  × 10^-6), indicating that general effects of the loci exist, and that with a higher statistical power, more significant genetic associations may become apparent.

CONCLUSIONS

Ongoing research and validation of current and previous findings is needed to determine if genetics does play a large role in V̇O₂peak response variance, and whether genomic predictors for V̇O₂peak response trainability can inform evidence-based clinical practice. Trial registration Australian New Zealand Clinical Trials Registry (ANZCTR), Trial Id: ACTRN12618000501246, Date Registered: 06/04/2018, http://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=374601&isReview=true .

The remodel of the "central dogma": a metabolomics interaction perspective

BACKGROUND

In 1957, Francis Crick drew a linear diagram on a blackboard. This diagram is often called the "central dogma." Subsequently, the relationships between different steps of the "central dogma" have been shown to be considerably complex, mostly because of the emerging world of small molecules. It is noteworthy that metabolites can be generated from the diet through gut microbiome metabolism, serve as substrates for epigenetic modifications, destabilize DNA quadruplexes, and follow Lamarckian inheritance. Small molecules were once considered the missing link in the "central dogma"; however, recently they have acquired a central role, and their general perception as downstream products has become reductionist. Metabolomics is a large-scale analysis of metabolites, and this emerging field has been shown to be the closest omics associated with the phenotype and concomitantly, the basis for all omics.

AIM OF REVIEW

Herein, we propose a broad updated perspective for the flux of information diagram centered in metabolomics, including the influence of other factors, such as epigenomics, diet, nutrition, and the gut- microbiome.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Metabolites are the beginning and the end of the flux of information.

Regulation of Dynamic Protein S-Acylation

Protein S-acylation is the reversible addition of fatty acids to the cysteine residues of target proteins. It regulates multiple aspects of protein function, including the localization to membranes, intracellular trafficking, protein interactions, protein stability, and protein conformation. This process is regulated by palmitoyl acyltransferases that have the conserved amino acid sequence DHHC at their active site. Although they have conserved catalytic cores, DHHC enzymes vary in their protein substrate selection, lipid substrate preference, and regulatory mechanisms. Alterations in DHHC enzyme function are associated with many human diseases, including cancers and neurological conditions. The removal of fatty acids from acylated cysteine residues is catalyzed by acyl protein thioesterases. Notably, S-acylation is now known to be a highly dynamic process, and plays crucial roles in signaling transduction in various cell types. In this review, we will explore the recent findings on protein S-acylation, the enzymatic regulation of this process, and discuss examples of dynamic S-acylation.

Regulatory effects of protein S-acylation on insulin secretion and insulin action

Post-translational modifications (PTMs) such as phosphorylation and ubiquitination are well-studied events with a recognized importance in all aspects of cellular function. By contrast, protein S-acylation, although a widespread PTM with important functions in most physiological systems, has received far less attention. Perturbations in S-acylation are linked to various disorders, including intellectual disability, cancer and diabetes, suggesting that this less-studied modification is likely to be of considerable biological importance. As an exemplar, in this review, we focus on the newly emerging links between S-acylation and the hormone insulin. Specifically, we examine how S-acylation regulates key components of the insulin secretion and insulin response pathways. The proteins discussed highlight the diverse array of proteins that are modified by S-acylation, including channels, transporters, receptors and trafficking proteins and also illustrate the diverse effects that S-acylation has on these proteins, from membrane binding and micro-localization to regulation of protein sorting and protein interactions.

A novel quantitative assay for analysis of GLUT4 translocation using high content screening

Insulin resistance is associated with obesity and can lead to several metabolic disorders including type II diabetes, nonalcoholic fatty liver disease and cardiovascular problems. Search for the small molecules which can either induce or mimic the insulin action are of great interest and can be utilized to manage insulin resistance. There are several dietary phytochemicals which can potentially have insulinomimetic action. Nevertheless, high throughput screening methods to test efficiency of small molecules to act as an insulinomimetic are not fully established. In this paper we have performed chemical screen analysis based on GLUT4 translocation using a cell line CHO-HIRC-myc-GLUT4 eGFP that expresses GLUT4-GFP in association with human Insulin receptor. We have established a high content screening-based method which can track and quantify the GLUT4 translocation from perinuclear area to the cell membrane. The assay involves measuring fluorescence intensity in a defined perinuclear area and a defined area along the cell membrane; and the results are expressed as the ratio of fluorescence intensity in the perinuclear to membrane area. The assay could collect real time data of GLUT4 translocation from thousand of cells/ sample and from many such samples in one experiment. We validated the assay using Insulin, insulin mimics/sensitizers and insulin inhibitors. The agonist or antagonists were analyzed for their ability to enhance or block the GLUT4 translocation independent of insulin. The outcome of the assay was correlated by performing glucose uptake assay using differentiated 3T3L1 cells. Using this platform we further identified several plant extracts which had the insulin mimetic action. We confirmed that these plant extracts were non-toxic to the beta cells using RIN mf5cells and 3T3L1 cells. We have identified plant extracts with the potential insulinomimetic action using novel high-content screening approach; these can be further tested for their efficiency in-vivo in pre-clinical trials.

Putative Role of Protein Palmitoylation in Cardiac Lipid-Induced Insulin Resistance

In the heart, inhibition of the insulin cascade following lipid overload is strongly associated with contractile dysfunction. The translocation of fatty acid transporter CD36 (SR-B2) from intracellular stores to the cell surface is a hallmark event in the lipid-overloaded heart, feeding forward to intracellular lipid accumulation. Yet, the molecular mechanisms by which intracellularly arrived lipids induce insulin resistance is ill-understood. Bioactive lipid metabolites (diacyl-glycerols, ceramides) are contributing factors but fail to correlate with the degree of cardiac insulin resistance in diabetic humans. This leaves room for other lipid-induced mechanisms involved in lipid-induced insulin resistance, including protein palmitoylation. Protein palmitoylation encompasses the reversible covalent attachment of palmitate moieties to cysteine residues and is governed by protein acyl-transferases and thioesterases. The function of palmitoylation is to provide proteins with proper spatiotemporal localization, thereby securing the correct unwinding of signaling pathways. In this review, we provide examples of palmitoylations of individual signaling proteins to discuss the emerging role of protein palmitoylation as a modulator of the insulin signaling cascade. Second, we speculate how protein hyper-palmitoylations (including that of CD36), as they occur during lipid oversupply, may lead to insulin resistance. Finally, we conclude that the protein palmitoylation machinery may offer novel targets to fight lipid-induced cardiomyopathy.

Protein palmitoylation and its pathophysiological relevance

Protein palmitoylation, in which C16 fatty acid chains are attached to cysteine residues via a reversible thioester linkage, is one of the most common lipid modifications and plays important roles in regulating protein stability, subcellular localization, membrane trafficking, interactions with effector proteins, enzymatic activity, and a variety of other cellular processes. Moreover, the unique reversibility of palmitoylation allows proteins to be rapidly shuttled between biological membranes and cytoplasmic substrates in a process usually controlled by a member of the DHHC family of protein palmitoyl transferases (PATs). Notably, mutations in PATs are closely related to a variety of human diseases, such as cancer, neurological disorders, and immune deficiency conditions. In addition to PATs, intracellular palmitoylation dynamics are also regulated by the interplay between distinct posttranslational modifications, including ubiquitination and phosphorylation. Understanding the specific mechanisms of palmitoylation may reveal novel potential therapeutic targets for many human diseases.

Structure, function and regulation of mammalian glucose transporters of the SLC2 family

The SLC2 genes code for a family of GLUT proteins that are part of the major facilitator superfamily (MFS) of membrane transporters. Crystal structures have recently revealed how the unique protein fold of these proteins enables the catalysis of transport. The proteins have 12 transmembrane spans built from a replicated trimer substructure. This enables 4 trimer substructures to move relative to each other, and thereby alternately opening and closing a cleft to either the internal or the external side of the membrane. The physiological substrate for the GLUTs is usually a hexose but substrates for GLUTs can include urate, dehydro-ascorbate and myo-inositol. The GLUT proteins have varied physiological functions that are related to their principal substrates, the cell type in which the GLUTs are expressed and the extent to which the proteins are associated with subcellular compartments. Some of the GLUT proteins translocate between subcellular compartments and this facilitates the control of their function over long- and short-time scales. The control of GLUT function is necessary for a regulated supply of metabolites (mainly glucose) to tissues. Pathophysiological abnormalities in GLUT proteins are responsible for, or associated with, clinical problems including type 2 diabetes and cancer and a range of tissue disorders, related to tissue-specific GLUT protein profiles. The availability of GLUT crystal structures has facilitated the search for inhibitors and substrates and that are specific for each GLUT and that can be used therapeutically. Recent studies are starting to unravel the drug targetable properties of each of the GLUT proteins.

DHHC7-mediated palmitoylation of the accessory protein barttin critically regulates the functions of ClC-K chloride channels

Barttin is the accessory subunit of the human ClC-K chloride channels, which are expressed in both the kidney and inner ear. Barttin promotes trafficking of the complex it forms with ClC-K to the plasma membrane and is involved in activating this channel. Barttin undergoes post-translational palmitoylation that is essential for its functions, but the enzyme(s) catalyzing this post-translational modification is unknown. Here, we identified zinc finger DHHC-type containing 7 (DHHC7) protein as an important barttin palmitoyl acyltransferase, whose depletion affected barttin palmitoylation and ClC-K-barttin channel activation. We investigated the functional role of barttin palmitoylation in vivo in Zdhhc7 ^-/- mice. Although palmitoylation of barttin in kidneys of Zdhhc7 ^-/- animals was significantly decreased, it did not pathologically alter kidney structure and functions under physiological conditions. However, when Zdhhc7 ^-/- mice were fed a low-salt diet, they developed hyponatremia and mild metabolic alkalosis, symptoms characteristic of human Bartter syndrome (BS) type IV. Of note, we also observed decreased palmitoylation of the disease-causing R8L barttin variant associated with human BS type IV. Our results indicate that dysregulated DHHC7-mediated barttin palmitoylation appears to play an important role in chloride channel dysfunction in certain BS variants, suggesting that targeting DHHC7 activity may offer a potential therapeutic strategy for reducing hypertension.

mTORC2-AKT signaling to ATP-citrate lyase drives brown adipogenesis and de novo lipogenesis

mTORC2 phosphorylates AKT in a hydrophobic motif site that is a biomarker of insulin sensitivity. In brown adipocytes, mTORC2 regulates glucose and lipid metabolism, however the mechanism has been unclear because downstream AKT signaling appears unaffected by mTORC2 loss. Here, by applying immunoblotting, targeted phosphoproteomics and metabolite profiling, we identify ATP-citrate lyase (ACLY) as a distinctly mTORC2-sensitive AKT substrate in brown preadipocytes. mTORC2 appears dispensable for most other AKT actions examined, indicating a previously unappreciated selectivity in mTORC2-AKT signaling. Rescue experiments suggest brown preadipocytes require the mTORC2/AKT/ACLY pathway to induce PPAR-gamma and establish the epigenetic landscape during differentiation. Evidence in mature brown adipocytes also suggests mTORC2 acts through ACLY to increase carbohydrate response element binding protein (ChREBP) activity, histone acetylation, and gluco-lipogenic gene expression. Substrate utilization studies additionally implicate mTORC2 in promoting acetyl-CoA synthesis from acetate through acetyl-CoA synthetase 2 (ACSS2). These data suggest that a principal mTORC2 action is controlling nuclear-cytoplasmic acetyl-CoA synthesis.

mTORC2 activates Akt, a regulator of cell growth and metabolism, however, the role of mTORC2 in adipocytes is incompletely understood. Here the authors report that a mTORC2-Akt axis specifically activates ACLY to promote lipid synthesis and histone acetylation during brown adipocyte differentiation.

De Novo Lipogenesis as a Source of Second Messengers in Adipocytes

PURPOSE OF REVIEW

Obesity is a major risk factor for type 2 diabetes. Although adipose tissue allows storage of excess calories in periods of overnutrition, in obesity, adipose tissue metabolism becomes dysregulated and can promote metabolic diseases. This review discusses recent advances in understandings how adipocyte metabolism impacts metabolic homeostasis.

RECENT FINDINGS

The ability of adipocytes to synthesize lipids from glucose is a marker of metabolic fitness, e.g., low de novo lipogenesis (DNL) in adipocytes correlates with insulin resistance in obesity. Adipocyte DNL may promote synthesis of special "insulin sensitizing" signaling lipids that act hormonally. However, each metabolic intermediate in the DNL pathway (i.e., citrate, acetyl-CoA, malonyl-CoA, and palmitate) also has second messenger functions. Mounting evidence suggests these signaling functions may also be important for maintaining healthy adipocytes. While adipocyte DNL contributes to lipid storage, lipid precursors may have additional second messenger functions critical for maintaining adipocyte health, and thus systemic metabolic homeostasis.

Metabolites as regulators of insulin sensitivity and metabolism

The cause of insulin resistance in obesity and type 2 diabetes mellitus (T2DM) is not limited to impaired insulin signalling but also involves the complex interplay of multiple metabolic pathways. The analysis of large data sets generated by metabolomics and lipidomics has shed new light on the roles of metabolites such as lipids, amino acids and bile acids in modulating insulin sensitivity. Metabolites can regulate insulin sensitivity directly by modulating components of the insulin signalling pathway, such as insulin receptor substrates (IRSs) and AKT, and indirectly by altering the flux of substrates through multiple metabolic pathways, including lipogenesis, lipid oxidation, protein synthesis and degradation and hepatic gluconeogenesis. Moreover, the post-translational modification of proteins by metabolites and lipids, including acetylation and palmitoylation, can alter protein function. Furthermore, the role of the microbiota in regulating substrate metabolism and insulin sensitivity is unfolding. In this Review, we discuss the emerging roles of metabolites in the pathogenesis of insulin resistance and T2DM. A comprehensive understanding of the metabolic adaptations involved in insulin resistance may enable the identification of novel targets for improving insulin sensitivity and preventing, and treating, T2DM.

Acylation - A New Means to Control Traffic Through the Golgi

The Golgi is well known to act as center for modification and sorting of proteins for secretion and delivery to other organelles. A key sorting step occurs at the trans-Golgi network and is mediated by protein adapters. However, recent data indicate that sorting also occurs much earlier, at the cis-Golgi, and uses lipid acylation as a novel means to regulate anterograde flux. Here, we examine an emerging role of S-palmitoylation/acylation as a mechanism to regulate anterograde routing. We discuss the critical Golgi-localized DHHC S-palmitoyltransferase enzymes that orchestrate this lipid modification, as well as their diverse protein clients (e.g., MAP6, SNAP25, CSP, LAT, β-adrenergic receptors, GABA receptors, and GLUT4 glucose transporters). Critically, for integral membrane proteins, S-acylation can act as new a “self-sorting” signal to concentrate these cargoes in rims of Golgi cisternae, and to promote their rapid traffic through the Golgi or, potentially, to bypass the Golgi. We discuss this mechanism and examine its potential relevance to human physiology and disease, including diabetes and neurodegenerative diseases.

The expression of select genes necessary for membrane-associated estrogen receptor signaling differ by sex in adult rat hippocampus

17β-estradiol can rapidly modulate neuron function via membrane estrogen receptors (ERs) in a sex-specific manner. For example, female rat hippocampal neurons express palmitoylated versions of ERα and ERβ that associate with the plasma membrane. These membrane-associated ERs are organized by caveolin proteins into functional signaling microdomains with metabotropic glutamate receptors (mGluRs). ER/mGluR signaling mediates several sex-specific estradiol actions on hippocampal neuron function. An important unanswered question regards the mechanism by which sex-specific membrane-associated ER signaling is generated, especially since it has been previously demonstrated that mGluR action is not sex-specific. One possibility is that the genes necessary for the ER membrane complex are differentially expressed between males and females, including genes that encode ERα and β, caveolin 1 and 3, and/or the palmitoylacyltransferases DHHC-7 and -21. Thus we used qPCR to test the hypothesis that these genes show sex differences in expression in neonatal and adult rat hippocampus. As an additional control we tested the expression of the 20 other DHHC palmitoylacyltransferases with no known connections to ER. In neonatal hippocampus, no sex differences were detected in gene expression. In adult hippocampus, the genes that encode caveolin 1 and DHHC-7 showed decreased expression in females compared to males. Thus, select genes differ by sex at specific developmental stages, arguing for a more nuanced model than simple widespread perinatal emergence of sex differences in all genes enabling sex-specific estradiol action. These findings enable the generation of new hypotheses regarding the mechanisms by which sex differences in membrane-associated ER signaling are programmed.

S-Palmitoylation Sorts Membrane Cargo for Anterograde Transport in the Golgi

While retrograde cargo selection in the Golgi is known to depend on specific signals, it is unknown whether anterograde cargo is sorted, and anterograde signals have not been identified. We suggest here that S-palmitoylation of anterograde cargo at the Golgi membrane interface is an anterograde signal and that it results in concentration in curved regions at the Golgi rims by simple physical chemistry. The rate of transport across the Golgi of two S-palmitoylated membrane proteins is controlled by S-palmitoylation. The bulk of S-palmitoylated proteins in the Golgi behave analogously, as revealed by click chemistry-based fluorescence and electron microscopy. These palmitoylated cargos concentrate in the most highly curved regions of the Golgi membranes, including the fenestrated perimeters of cisternae and associated vesicles. A palmitoylated transmembrane domain behaves similarly in model systems.

SwissPalm 2: Protein S-Palmitoylation Database

Protein S-palmitoylation is increasingly recognized as an important posttranslational modification, present in all eukaryotic organisms, involved in the regulation of many biological processes. The SwissPalm database centralizes the large and increasing number of published palmitoyl-proteome datasets, provides tools to compare them, and includes curated data from the literature on the identification and analysis of palmitoylated proteins. SwissPalm 2 provides an updated version, with 38 palmitoyl-proteomes at the time of release, from 17 different species, and new features such as the inclusion of orthologs.

Nutrient-Dependent Changes of Protein Palmitoylation: Impact on Nuclear Enzymes and Regulation of Gene Expression

Diet is the main environmental stimulus chronically impinging on the organism throughout the entire life. Nutrients impact cells via a plethora of mechanisms including the regulation of both protein post-translational modifications and gene expression. Palmitoylation is the most-studied protein lipidation, which consists of the attachment of a molecule of palmitic acid to residues of proteins. S-palmitoylation is a reversible cysteine modification finely regulated by palmitoyl-transferases and acyl-thioesterases that is involved in the regulation of protein trafficking and activity. Recently, several studies have demonstrated that diet-dependent molecules such as insulin and fatty acids may affect protein palmitoylation. Here, we examine the role of protein palmitoylation on the regulation of gene expression focusing on the impact of this modification on the activity of chromatin remodeler enzymes, transcription factors, and nuclear proteins. We also discuss how this physiological phenomenon may represent a pivotal mechanism underlying the impact of diet and nutrient-dependent signals on human diseases.

Protein palmitoylation and cancer

Protein S-palmitoylation is a reversible post-translational modification that alters the localization, stability, and function of hundreds of proteins in the cell. S-palmitoylation is essential for the function of both oncogenes (e.g., NRAS and EGFR) and tumor suppressors (e.g., SCRIB, melanocortin 1 receptor). In mammalian cells, the thioesterification of palmitate to internal cysteine residues is catalyzed by 23 Asp-His-His-Cys (DHHC)-family palmitoyl S-acyltransferases while the removal of palmitate is catalyzed by serine hydrolases, including acyl-protein thioesterases (APTs). These enzymes modulate the function of important oncogenes and tumor suppressors and often display altered expression patterns in cancer. Targeting S-palmitoylation or the enzymes responsible for palmitoylation dynamics may therefore represent a candidate therapeutic strategy for certain cancers.

The Absence of DHHC3 Affects Primary and Latent Herpes Simplex Virus 1 Infection

UL20, an essential herpes simplex virus 1 (HSV-1) protein, is involved in cytoplasmic envelopment of virions and virus egress. We reported recently that UL20 can bind to a host protein encoded by the zinc finger DHHC-type containing 3 (ZDHHC3) gene (also known as Golgi-specific DHHC zinc finger protein [GODZ]). Here, we show for the first time that HSV-1 replication is compromised in murine embryonic fibroblasts (MEFs) isolated from GODZ^-/- mice. The absence of GODZ resulted in blocking palmitoylation of UL20 and altered localization and expression of UL20 and glycoprotein K (gK); the expression of gB and gC; and the localization and expression of tegument and capsid proteins within HSV-1-infected MEFs. Electron microscopy revealed that the absence of GODZ limited the maturation of virions at multiple steps and affected the localization of virus and endoplasmic reticulum morphology. Virus replication in the eyes of ocularly HSV-1-infected GODZ^-/- mice was significantly lower than in HSV-1-infected wild-type (WT) mice. The levels of UL20, gK, and gB transcripts in the corneas of HSV-1-infected GODZ^-/- mice on day 5 postinfection were markedly lower than in WT mice, whereas only UL20 transcripts were reduced in trigeminal ganglia (TG). In addition, HSV-1-infected GODZ^-/- mice showed notably lower levels of corneal scarring, and HSV-1 latency reactivation was also reduced. Thus, normal HSV-1 infectivity and viral pathogenesis are critically dependent on GODZ-mediated palmitoylation of viral UL20.IMPORTANCE HSV-1 infection is widespread. Ocular infection can cause corneal blindness; however, approximately 70 to 90% of American adults exposed to the virus show no clinical symptoms. In this study, we show for the first time that the absence of a zinc finger protein called GODZ affects primary and latent infection, as well as reactivation, in ocularly infected mice. The reduced virus infectivity is due to the absence of the GODZ interaction with HSV-1 UL20. These results strongly suggest that binding of UL20 to GODZ promotes virus infectivity in vitro and viral pathogenesis in vivo.

Protein Lipidation: Occurrence, Mechanisms, Biological Functions, and Enabling Technologies

Protein lipidation, including cysteine prenylation, N-terminal glycine myristoylation, cysteine palmitoylation, and serine and lysine fatty acylation, occurs in many proteins in eukaryotic cells and regulates numerous biological pathways, such as membrane trafficking, protein secretion, signal transduction, and apoptosis. We provide a comprehensive review of protein lipidation, including descriptions of proteins known to be modified and the functions of the modifications, the enzymes that control them, and the tools and technologies developed to study them. We also highlight key questions about protein lipidation that remain to be answered, the challenges associated with answering such questions, and possible solutions to overcome these challenges.

Palmitic Acid: Physiological Role, Metabolism and Nutritional Implications

Palmitic acid (PA) has been for long time negatively depicted for its putative detrimental health effects, shadowing its multiple crucial physiological activities. PA is the most common saturated fatty acid accounting for 20–30% of total fatty acids in the human body and can be provided in the diet or synthesized endogenously via de novo lipogenesis (DNL). PA tissue content seems to be controlled around a well-defined concentration, and changes in its intake do not influence significantly its tissue concentration because the exogenous source is counterbalanced by PA endogenous biosynthesis. Particular physiopathological conditions and nutritional factors may strongly induce DNL, resulting in increased tissue content of PA and disrupted homeostatic control of its tissue concentration. The tight homeostatic control of PA tissue concentration is likely related to its fundamental physiological role to guarantee membrane physical properties but also to consent protein palmitoylation, palmitoylethanolamide (PEA) biosynthesis, and in the lung an efficient surfactant activity. In order to maintain membrane phospholipids (PL) balance may be crucial an optimal intake of PA in a certain ratio with unsaturated fatty acids, especially PUFAs of both n-6 and n-3 families. However, in presence of other factors such as positive energy balance, excessive intake of carbohydrates (in particular mono and disaccharides), and a sedentary lifestyle, the mechanisms to maintain a steady state of PA concentration may be disrupted leading to an over accumulation of tissue PA resulting in dyslipidemia, hyperglycemia, increased ectopic fat accumulation and increased inflammatory tone via toll-like receptor 4. It is therefore likely that the controversial data on the association of dietary PA with detrimental health effects, may be related to an excessive imbalance of dietary PA/PUFA ratio which, in certain physiopathological conditions, and in presence of an enhanced DNL, may further accelerate these deleterious effects.