Protein cysteine palmitoylation in immunity and inflammation

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.

SMAD2 S-palmitoylation promotes its linker region phosphorylation and TH17 cell differentiation in a mouse model of multiple sclerosis

The transcriptional regulators SMAD2 and SMAD3 share the same primary signaling pathway in response to the cytokine TGFβ. However, whereas SMAD2 stimulates the differentiation of naive CD4+ T cells into proinflammatory T helper 17 cells (TH17 cells), SMAD3 stimulates the differentiation of anti-inflammatory regulatory T cells (Treg cells). Here, we report a dynamic SMAD2-specific posttranslational modification important for TH17 cell differentiation. SMAD2, but not SMAD3, was reversibly S-palmitoylated at cysteine-41 and cysteine-81 by the palmitoyltransferase DHHC7 and depalmitoylated by the acyl protein thioesterase APT2. As a result, SMAD2 was recruited to intracellular membranes where its linker region was phosphorylated, leading to its interaction with the transcriptional regulator STAT3. Nuclear translocation of the SMAD2-STAT3 complex induced the expression of their target genes that promoted TH17 cell differentiation. Perturbation of SMAD2-STAT3 binding by inhibiting the palmitoylation-depalmitoylation cycle suppressed TH17 cell differentiation and reduced disease severity in mice with experimental autoimmune encephalomyelitis, a model of multiple sclerosis (MS). Thus, the S-palmitoylation-depalmitoylation cycle mediated by DHHC7 and APT2 specifically regulates SMAD2, providing insights into the functional differences between SMAD2 and SMAD3 and the distinct role of SMAD2 in TH17 cell differentiation. The findings further highlight DHHC7 and APT2 as potential therapeutic targets for the treatment of TH17 cell-mediated inflammatory diseases, including MS.

An S-acylated N-terminus and a conserved loop regulate the activity of the ABHD17 deacylase

The dynamic addition and removal of long-chain fatty acids modulate protein function and localization. The α/β hydrolase domain-containing (ABHD) 17 enzymes remove acyl chains from membrane-localized proteins such as the oncoprotein NRas, but how the ABHD17 proteins are regulated is unknown. Here, we used cell-based studies and molecular dynamics simulations to show that ABHD17 activity is controlled by two mobile elements-an S-acylated N-terminal helix and a loop-that flank the putative substrate-binding pocket. Multiple S-acylation events anchor the N-terminal helix in the membrane, enabling hydrophobic residues in the loop to engage with the bilayer. This stabilizes the conformation of both helix and loop, alters the conformation of the binding pocket, and optimally positions the enzyme for substrate engagement. S-acylation may be a general feature of acyl-protein thioesterases. By providing a mechanistic understanding of how the lipid modification of a lipid-removing enzyme promotes its enzymatic activity, this work contributes to our understanding of cellular S-acylation cycles.

Dynamic PRDX S-acylation modulates ROS stress and signaling

Peroxiredoxins (PRDXs) are a highly conserved family of peroxidases that serve as the primary scavengers of peroxides. Post-translational modifications play crucial roles modulating PRDX activities, tuning the balance between reactive oxygen species (ROS) signaling and stress. We previously reported that S-acylation occurs at the "peroxidatic" cysteine (Cp) site of PRDX5 and that it inhibits PRDX5 activity. Here, we show that the PRDX family more broadly is subject to S-acylation at the Cp site of all PRDXs and that PRDX S-acylation dynamically responds to cellular ROS levels. Using activity-based fluorescent imaging with DPP-Red, a red-shifted fluorescent indicator for acyl-protein thioesterase (APT) activity, we also discover that the instigation of ROS-stress via exogenous H2O2 activates both the cytosolic and mitochondrial APTs, whereas epidermal growth factor (EGF)-stimulated endogenous H2O2 deactivates the cytosolic APTs. These results indicate that APTs help tune H2O2 signal transduction and ROS protection through PRDX S-deacylation.

The intersection of epigenetics and immune thrombocytopenia: new insights into disease mechanisms and treatments

Immune thrombocytopenia (ITP) is an autoimmune hematologic disorder that arises from an imbalance in immune responses, disrupting the delicate equilibrium of the immune system. An increasing body of research has indicated that immune-related genes hold promise as biomarkers for diagnosis and prognosis, with a particular focus on the roles of B and T cells in ITP pathogenesis. Despite these advancements, a deeper understanding of the underlying regulatory mechanisms governing these immune-related genes remains essential. This review aims to integrate the current body of evidence and provide further insights into the epigenetic regulation of immune pathways involved in ITP development. The problem statement section highlights the complexity of ITP and its intricate connections with immune pathways. It also compares the epigenetic differences between pediatric and adult ITP based on existing evidence. Decoding epigenetic processes could potentially open up new avenues for improving diagnostic methods and therapeutic strategies for ITP.

A pan-cancer analysis of the oncogenic and immunological roles of RGS5 in clear cell renal cell carcinomas based on in vitro experiment validation

BACKGROUND

RGS5, the first gene identified in tumor-resident pericytes, plays a crucial role in angiogenesis. However, its effects on immunology and prognosis in human cancer are still mostly unknown. This study investigates the carcinogenic and immunological roles of RGS5 through a comprehensive pan-cancer analysis.

METHODS

A standardized pan-cancer dataset for RGS5 was obtained from the public database. R software and relevant packages were utilized to analyze the oncogenic and immunological roles. Clinical samples and cellular experiments were conducted to validate RGS5 expression and its biological function in renal cancer.

RESULTS

Bioinformatics analysis revealed that RGS5 is dysregulated in a variety of human malignancies and is significantly associated with patient prognosis. Additionally, RGS5 expression is closely linked to tumor heterogeneity and stemness indicators across different cancer types. Co-expression of RGS5 with genes involved in MHC, immune activation, immunosuppressive proteins, chemokines, and chemokine receptors was observed in various tumors. High expression of RGS5 predicts a good prognosis in patients with renal cancer. In the renal cancer cohort, RGS5 expression strongly correlated with the distribution of tumor-associated fibroblasts. Silencing RGS5 expression can affect the proliferation, migration, and invasion of renal carcinoma cells.

CONCLUSIONS

RGS5 expression in tumors is intricately associated with various clinical features, particularly concerning tumor progression and patient prognosis.

Regulation of pattern recognition receptor signaling by palmitoylation

Pattern recognition receptors (PRRs), consisting of Toll-like receptors, RIG-I-like receptors, cytosolic DNA sensors, and NOD-like receptors, sense exogenous pathogenic molecules and endogenous damage signals to maintain physiological homeostasis. Upon activation, PRRs stimulate the sensitization of nuclear factor κB, mitogen-activated protein kinase, TANK-binding kinase 1-interferon (IFN) regulatory factor, and inflammasome signaling pathways to produce inflammatory factors and IFNs to activate Janus kinase/signal transducer and activator of transcription signaling pathways, resulting in anti-infection, antitumor, and other specific immune responses. Palmitoylation is a crucial type of post-translational modification that reversibly alters the localization, stability, and biological activity of target molecules. Here, we discuss the available knowledge on the biological roles and underlying mechanisms linked to protein palmitoylation in modulating PRRs and their downstream signaling pathways under physiological and pathological conditions. Moreover, recent advances in the use of palmitoylation as an attractive therapeutic target for disorders caused by the dysregulation of PRRs were summarized.

zDHHC-Mediated S-Palmitoylation in Skin Health and Its Targeting as a Treatment Perspective

S-acylation, which includes S-palmitoylation, is the only known reversible lipid-based post-translational protein modification. S-palmitoylation is mediated by palmitoyl acyltransferases (PATs), a family of 23 enzymes commonly referred to as zDHHCs, which catalyze the addition of palmitate to cysteine residues on specific target proteins. Aberrant S-palmitoylation events have been linked to the pathogenesis of multiple human diseases. While there have been advances in elucidating the molecular mechanisms underlying the pathogenesis of various skin conditions, there remain gaps in the knowledge, specifically with respect to the contribution of S-palmitoylation to the maintenance of skin barrier function. Towards this goal, we performed PubMed literature searches relevant to S-palmitoylation in skin to define current knowledge and areas that may benefit from further research studies. Furthermore, to identify alterations in gene products that are S-palmitoylated, we utilized bioinformatic tools such as SwissPalm and analyzed relevant data from publicly available databases such as cBioportal. Since the targeting of S-palmitoylated targets may offer an innovative treatment perspective, we surveyed small molecules inhibiting zDHHCs, including 2-bromopalmitate (2-BP) which is associated with off-target effects, and other targeting strategies. Collectively, our work aims to advance both basic and clinical research on skin barrier function with a focus on zDHHCs and relevant protein targets that may contribute to the pathogenesis of skin conditions such as atopic dermatitis, psoriasis, and skin cancers including melanoma.

Investigation of Protein Fatty Acylation in Virus-Host Interaction

Fatty acylation has a critical impact on antiviral innate immunity. Fatty acylation of virus proteins affects virus virulence and invasion. In contrast, fatty acylation of host cell proteins regulates virus recognition and host-virus interactions, thus affecting antiviral immune responses. Therefore, an emerging need exists to investigate and understand the mechanism and function of protein fatty acylation in regulating antiviral innate immunity. Alkyne probe metabolic labeling and click chemistry assays with biotin-conjugated or fluorophore-conjugated azide provide a simple way to determine the potential fatty-acylated proteins in antiviral innate pathways. Here, we demonstrate comprehensive approaches to determine protein fatty acylation in virus-infected macrophages or protein-overexpressing HEK293T cells in the context of antiviral innate immunity.

Predicting protein interactions of the kinase Lck critical to T cell modulation

Protein-protein interactions (PPIs) play pivotal roles in directing T cell fate. One key player is the non-receptor tyrosine protein kinase Lck that helps to transduce T cell activation signals. Lck is mediated by other proteins via interactions that are inadequately understood. Here, we use the deep learning method AF2Complex to predict PPIs involving Lck, by screening it against ∼1,000 proteins implicated in immune responses, followed by extensive structural modeling for selected interactions. Remarkably, we describe how Lck may be specifically targeted by a palmitoyltransferase using a phosphotyrosine motif. We uncover "hotspot" interactions between Lck and the tyrosine phosphatase CD45, leading to a significant conformational shift of Lck for activation. Lastly, we present intriguing interactions between the phosphotyrosine-binding domain of Lck and the cytoplasmic tail of the immune checkpoint LAG3 and propose a molecular mechanism for its inhibitory role. Together, this multifaceted study provides valuable insights into T cell regulation and signaling.

Related type 2C protein phosphatases Pic3 and Pic12 negatively regulate immunity in tomato to Pseudomonas syringae

Type 2C protein phosphatases (PP2Cs) constitute a large family in most plant species, but relatively few of them have been implicated in immunity. To identify and characterize PP2C phosphatases that affect tomato (Solanum lycopersicum) immunity, we generated loss-of-function mutations in 11 PP2C-encoding genes whose expression is altered in response to immune elicitors or pathogens. We report that 2 closely related PP2C phosphatases, PP2C immunity-associated candidate 3 (Pic3) and Pic12, are involved in regulating resistance to the bacterial pathogen Pseudomonas syringae pv. tomato (Pst). Loss-of-function mutations in Pic3 led to enhanced resistance to Pst in older but not younger leaves, whereas such mutations in Pic12 resulted in enhanced resistance in both older and younger leaves. Overexpression of Pic3 and Pic12 proteins in leaves of Nicotiana benthamiana inhibited resistance to Pst, and this effect was dependent on Pic3/12 phosphatase activity and an N-terminal palmitoylation motif associated with localization to the cell periphery. Pic3, but not Pic12, had a slight negative effect on flagellin-associated reactive oxygen species generation, although their involvement in the response to Pst appeared independent of flagellin. RNA-sequencing analysis of Rio Grande (RG)-PtoR wild-type plants and 2 independent RG-pic3 mutants revealed that the enhanced disease resistance in RG-pic3 older leaves is associated with increased transcript abundance of multiple defense-related genes. RG-pic3/RG-pic12 double-mutant plants exhibited stronger disease resistance than RG-pic3 or RG-pic12 single mutants. Together, our results reveal that Pic3 and Pic12 negatively regulate tomato immunity in an additive manner through flagellin-independent pathways.

The role of S-palmitoylation of C4BPA in regulating murine sperm motility and complement resistance

The epididymis and epididymosomes are crucial for regulating sperm motility, a key factor in male fertility. Palmitoylation, a lipid modification involving the attachment of palmitic acid to cysteine residues, is essential for protein function and localization. Additionally, this modification plays a vital role in the sorting of proteins into exosomes. This study investigates the role of S-palmitoylation at the Cys15 residue of the C4b binding protein alpha chain (C4BPA) in murine sperm motility. Our findings revealed high expression of C4BPA mRNA in the caput epididymis, with the protein present across all regions of the epididymis. Palmitoylation of C4BPA in epididymal epithelial cells was essential for its enrichment in epididymosomes and on sperm, thereby maintaining sperm motility. Inhibition of palmitoylation significantly reduced sperm motility and the localization of C4BPA on sperm. Additionally, palmitoylated C4BPA in exosomes resisted complement C4 attacks, preserving motility, unlike mutated C4BPA (C15S). These results highlight the critical role of palmitoylated C4BPA in protecting sperm from complement attacks and maintaining motility, suggesting that reversible palmitoylation of epididymal proteins could be explored as a therapeutic strategy for male contraception. Our study underscores the importance of post-translational modifications in sperm function and presents new insights into potential male contraceptive methods.

Causal relationship between amino acids and ovarian cancer in the European population: A bidirectional Mendelian randomization study and meta-analysis

In recent years, an increasing number of observational studies have reported the impact of amino acids on ovarian cancer. However, Mendelian randomization studies have not yet been conducted to explore the causal relationship between them in the context of ovarian cancer. This study conducted Mendelian randomization (MR) analysis of 20 amino acids in relation to ovarian cancer data from 2 different sources within the European population, using a two-sample MR approach. The primary results from the inverse variance weighting analysis were then subjected to a meta-analysis, followed by multiple testing correction for the meta-analysis thresholds. Finally, reverse causality testing was performed on the positively associated amino acids and ovarian cancer. MR analyses were conducted for 20 amino acids with ovarian cancer data from both the Finngen R10 and Open genome-wide association study databases. The inverse variance weighted results from these 2 analyses were then combined through meta-analysis, with multiple corrections applied to the significance thresholds of the meta-analysis results. The findings showed that only cysteine had a significant association with ovarian cancer, with an (odds ratio) odds ratio value of 0.507 (95% confidence interval: 0.335-0.767, P = .025). The P-value of the combined MR and meta-analysis, after multiple testing correction, was 0.025, indicating statistical significance (P < .05). Additionally, cysteine did not show a reverse causal relationship with ovarian cancer in either data source. Cysteine is a protective factor for ovarian cancer, potentially reducing the risk of ovarian cancer and slowing the progression of the disease.

2-Bromopalmitate-Induced Intestinal Flora Changes and Testicular Dysfunction in Mice

2-Bromopalmitate (2-BP) is a palmitoylation inhibitor that can prevent the binding of palmitic acid to proteins, thereby exhibiting significant effects in promoting inflammation and regulating the immune system. However, limited research has been conducted regarding the direct effects of 2-BP on the animal organism. Therefore, we probed mice injected with 2-BP for altered expression of inflammatory genes, with a focus on demonstrating changes in the intestinal flora as well as damage to the reproductive system. Our findings indicate that 2-BP can induce substantial inflammatory responses in visceral organs and cause testicular dysfunction. The key changes in the gut microbiota were characterized by an abundance of Firmicutes, Clostridiales, Rikenellaceae_RC9_gut_group, Desulfovibrio, Muribaculaceae, and Alistipes, and their metabolism has been intricately linked to visceral inflammation. Overall, the findings of this study provide a sound scientific basis for understanding the impact of high doses of 2-BP in mammals, while also offering crucial support for the development of preclinical models to suppress palmitoylation.

A palmitoyl transferase chemical-genetic system to map ZDHHC-specific S-acylation

The 23 human zinc finger Asp-His-His-Cys motif-containing (ZDHHC) S-acyltransferases catalyze long-chain S-acylation at cysteine residues across an extensive network of hundreds of proteins important for normal physiology or dysregulated in disease. Here we present a technology to directly map the protein substrates of a specific ZDHHC at the whole-proteome level, in intact cells. Structure-guided engineering of paired ZDHHC 'hole' mutants and 'bumped' chemically tagged fatty acid probes enabled probe transfer to specific protein substrates with excellent selectivity over wild-type ZDHHCs. Chemical-genetic systems were exemplified for five human ZDHHCs (3, 7, 11, 15 and 20) and applied to generate de novo ZDHHC substrate profiles, identifying >300 substrates and S-acylation sites for new functionally diverse proteins across multiple cell lines. We expect that this platform will elucidate S-acylation biology for a wide range of models and organisms.

Exploring Protein S-Palmitoylation: Mechanisms, Detection, and Strategies for Inhibitor Discovery

S-palmitoylation is a reversible and dynamic process that involves the addition of long-chain fatty acids to proteins. This protein modification regulates various aspects of protein function, including subcellular localization, stability, conformation, and biomolecular interactions. The zinc finger DHHC (ZDHHC) domain-containing protein family is the main group of enzymes responsible for catalyzing protein S-palmitoylation, and 23 members have been identified in mammalian cells. Many proteins that undergo S-palmitoylation have been linked to disease pathogenesis and progression, suggesting that the development of effective inhibitors is a promising therapeutic strategy. Reducing the protein S-palmitoylation level can target either the PATs directly or their substrates. However, there are rare clinically effective S-palmitoylation inhibitors. This review aims to provide an overview of the S-palmitoylation field, including the catalytic mechanism of ZDHHC, S-palmitoylation detection methods, and the functional impact of protein S-palmitoylation. Additionally, this review focuses on current strategies for expanding the chemical toolbox to develop novel and effective inhibitors that can reduce the level of S-palmitoylation of the target protein.

Role of novel protein acylation modifications in immunity and its related diseases

The cross-regulation of immunity and metabolism is currently a research hotspot in life sciences and immunology. Metabolic immunology plays an important role in cutting-edge fields such as metabolic regulatory mechanisms in immune cell development and function, and metabolic targets and immune-related disease pathways. Protein post-translational modification (PTM) is a key epigenetic mechanism that regulates various biological processes and highlights metabolite functions. Currently, more than 400 PTM types have been identified to affect the functions of several proteins. Among these, metabolic PTMs, particularly various newly identified histone or non-histone acylation modifications, can effectively regulate various functions, processes and diseases of the immune system, as well as immune-related diseases. Thus, drugs aimed at targeted acylation modification can have substantial therapeutic potential in regulating immunity, indicating a new direction for further clinical translational research. This review summarises the characteristics and functions of seven novel lysine acylation modifications, including succinylation, S-palmitoylation, lactylation, crotonylation, 2-hydroxyisobutyrylation, β-hydroxybutyrylation and malonylation, and their association with immunity, thereby providing valuable references for the diagnosis and treatment of immune disorders associated with new acylation modifications.

Recruitment, regulation, and release: Control of signaling enzyme localization and function by reversible S-acylation

An ever-growing number of studies highlight the importance of S-acylation, a reversible protein-lipid modification, for diverse aspects of intracellular signaling. In this review, we summarize the current understanding of how S-acylation regulates perhaps the best-known class of signaling enzymes, protein kinases. We describe how S-acylation acts as a membrane targeting signal that localizes certain kinases to specific membranes, and how such membrane localization in turn facilitates the assembly of signaling hubs consisting of an S-acylated kinase's upstream activators and/or downstream targets. We further discuss recent findings that S-acylation can control additional aspects of the function of certain kinases, including their interactions and, surprisingly, their activity, and how such regulation might be exploited for potential therapeutic gain. We go on to describe the roles and regulation of de-S-acylases and how extracellular signals drive dynamic (de)S-acylation of certain kinases. We discuss how S-acylation has the potential to lead to "emergent properties" that alter the temporal profile and/or salience of intracellular signaling events. We close by giving examples of other S-acylation-dependent classes of signaling enzymes and by discussing how recent biological and technological advances should facilitate future studies into the functional roles of S-acylation-dependent signaling.

MAVS Cys508 palmitoylation promotes its aggregation on the mitochondrial outer membrane and antiviral innate immunity

Cysteine palmitoylation or S-palmitoylation catalyzed by the ZDHHC family of acyltransferases regulates the biological function of numerous mammalian proteins as well as viral proteins. However, understanding of the role of S-palmitoylation in antiviral immunity against RNA viruses remains very limited. The adaptor protein MAVS forms functionally essential prion-like aggregates upon activation by viral RNA-sensing RIG-I-like receptors. Here, we identify that MAVS, a C-terminal tail-anchored mitochondrial outer membrane protein, is S-palmitoylated by ZDHHC7 at Cys508, a residue adjacent to the tail-anchor transmembrane helix. Using superresolution microscopy and other biochemical techniques, we found that the mitochondrial localization of MAVS at resting state mainly depends on its transmembrane tail-anchor, without regulation by Cys508 S-palmitoylation. However, upon viral infection, MAVS S-palmitoylation stabilizes its aggregation on the mitochondrial outer membrane and thus promotes subsequent propagation of antiviral signaling. We further show that inhibition of MAVS S-palmitoylation increases the host susceptibility to RNA virus infection, highlighting the importance of S-palmitoylation in the antiviral innate immunity. Also, our results indicate ZDHHC7 as a potential therapeutic target for MAVS-related autoimmune diseases.

Palmitoyltransferase ZDHHC6 promotes colon tumorigenesis by targeting PPARγ-driven lipid biosynthesis via regulating lipidome metabolic reprogramming

BACKGROUND

The failure of proper recognition of the intricate nature of pathophysiology in colorectal cancer (CRC) has a substantial effect on the progress of developing novel medications and targeted therapy approaches. Imbalances in the processes of lipid oxidation and biosynthesis of fatty acids are significant risk factors for the development of CRC. Therapeutic intervention that specifically targets the peroxisome proliferator-activated receptor gamma (PPARγ) and its downstream response element, in response to lipid metabolism, has been found to promote the growth of tumors and has shown significant clinical advantages in cancer patients.

METHODS

Clinical CRC samples and extensive in vitro and in vivo experiments were carried out to determine the role of ZDHHC6 and its downstream targets via a series of biochemical assays, molecular analysis approaches and lipid metabolomics assay, etc. RESULTS: To study the effect of ZDHHC6 on the progression of CRC and identify whether ZDHHC6 is a palmitoyltransferase that regulates fatty acid synthesis, which directly palmitoylates and stabilizes PPARγ, and this stabilization in turn activates the ACLY transcription-related metabolic pathway. In this study, we demonstrate that PPARγ undergoes palmitoylation in its DNA binding domain (DBD) section. This lipid-related modification enhances the stability of PPARγ protein by preventing its destabilization. As a result, palmitoylated PPARγ inhibits its degradation induced by the lysosome and facilitates its translocation into the nucleus. In addition, we have identified zinc finger-aspartate-histidine-cysteine 6 (ZDHHC6) as a crucial controller of fatty acid biosynthesis. ZDHHC6 directly interacts with and adds palmitoyl groups to stabilize PPARγ at the Cys-313 site within the DBD domain of PPARγ. Consequently, this palmitoylation leads to an increase in the expression of ATP citrate lyase (ACLY). Furthermore, our findings reveals that ZDHHC6 actively stimulates the production of fatty acids and plays a role in the development of colorectal cancer. However, we have observed a significant reduction in the cancer-causing effects when the expression of ZDHHC6 is inhibited in in vivo trials. Significantly, in CRC, there is a strong positive correlation between the high expression of ZDHHC6 and the expression of PPARγ. Moreover, this high expression of ZDHHC6 is connected with the severity of CRC and is indicative of a poor prognosis.

CONCLUSIONS

We have discovered a mechanism in which lipid biosynthesis is controlled by ZDHHC6 and includes the signaling of PPARγ-ACLY in the advancement of CRC. This finding provides a justification for targeting lipid synthesis by blocking ZDHHC6 as a potential therapeutic approach.

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.

zDHHC20-driven S-palmitoylation of CD80 is required for its costimulatory function

CD80 is a transmembrane glycoprotein belonging to the B7 family, which has emerged as a crucial molecule in T cell modulation via the CD28 or CTLA4 axes. CD80-involved regulation of immune balance is a finely tuned process and it is important to elucidate the underlying mechanism for regulating CD80 function. In this study we investigated the post-translational modification of CD80 and its biological relevance. By using a metabolic labeling strategy, we found that CD80 was S-palmitoylated on multiple cysteine residues (Cys261/262/266/271) in both the transmembrane and the cytoplasmic regions. We further identified zDHHC20 as a bona fide palmitoyl-transferase determining the S-palmitoylation level of CD80. We demonstrated that S-palmitoylation protected CD80 protein from ubiquitination degradation, regulating the protein stability, and ensured its accurate plasma membrane localization. The palmitoylation-deficient mutant (4CS) CD80 disrupted these functions, ultimately resulting in the loss of its costimulatory function upon T cell activation. Taken together, our results describe a new post-translational modification of CD80 by S-palmitoylation as a novel mechanism for the regulation of CD80 upon T cell activation.

The anti-inflammatory role of zDHHC23 through the promotion of macrophage M2 polarization and macrophage necroptosis in large yellow croaker (Larimichthys crocea)

Zinc finger Asp-His-His-Cys motif-containing (zDHHC) proteins, known for their palmitoyltransferase (PAT) activity, play crucial roles in diverse cellular processes, including immune regulation. However, their non-palmitoyltransferase immunomodulatory functions and involvement in teleost immune responses remain underexplored. In this study, we systematically characterized the zDHHC family in the large yellow croaker (Larimichthys crocea), identifying 22 members. Phylogenetic analysis unveiled that each of the 22 LczDHHCs formed distinct clusters with their orthologues from other teleost species. Furthermore, all LczDHHCs exhibited a highly conserved DHHC domain, as confirmed by tertiary structure prediction. Notably, LczDHHC23 exhibited the most pronounced upregulation following Pseudomonas plecoglossicida (P. plecoglossicida) infection of macrophage/monocyte cells (MO/MΦ). Silencing LczDHHC23 led to heightened pro-inflammatory cytokine expression and diminished anti-inflammatory cytokine levels in MO/MΦ during infection, indicating its anti-inflammatory role. Functionally, LczDHHC23 facilitated M2-type macrophage polarization, as evidenced by a significant skewing of MO/MΦ towards the pro-inflammatory M1 phenotype upon LczDHHC23 knockdown, along with the inhibition of MO/MΦ necroptosis induced by P. plecoglossicida infection. These findings highlight the non-PAT immunomodulatory function of LczDHHC23 in teleost immune regulation, broadening our understanding of zDHHC proteins in host-pathogen interactions, suggesting LczDHHC23 as a potential therapeutic target for immune modulation in aquatic species.

The complete assembly of human LAT1-4F2hc complex provides insights into its regulation, function and localisation

The LAT1-4F2hc complex (SLC7A5-SLC3A2) facilitates uptake of essential amino acids, hormones and drugs. Its dysfunction is associated with many cancers and immune/neurological disorders. Here, we apply native mass spectrometry (MS)-based approaches to provide evidence of super-dimer formation (LAT1-4F2hc)2. When combined with lipidomics, and site-directed mutagenesis, we discover four endogenous phosphatidylethanolamine (PE) molecules at the interface and C-terminus of both LAT1 subunits. We find that interfacial PE binding is regulated by 4F2hc-R183 and is critical for regulation of palmitoylation on neighbouring LAT1-C187. Combining native MS with mass photometry (MP), we reveal that super-dimerization is sensitive to pH, and modulated by complex N-glycans on the 4F2hc subunit. We further validate the dynamic assemblies of LAT1-4F2hc on plasma membrane and in the lysosome. Together our results link PTM and lipid binding with regulation and localisation of the LAT1-4F2hc super-dimer.

NLRP3 Cys126 palmitoylation by ZDHHC7 promotes inflammasome activation

Nucleotide oligomerization domain (NOD)-like receptor protein 3 (NLRP3) inflammasome hyperactivation contributes to many human chronic inflammatory diseases, and understanding how NLRP3 inflammasome is regulated can provide strategies to treat inflammatory diseases. Here, we demonstrate that NLRP3 Cys126 is palmitoylated by zinc finger DHHC-type palmitoyl transferase 7 (ZDHHC7), which is critical for NLRP3-mediated inflammasome activation. Perturbing NLRP3 Cys126 palmitoylation by ZDHHC7 knockout, pharmacological inhibition, or modification site mutation diminishes NLRP3 activation in macrophages. Furthermore, Cys126 palmitoylation is vital for inflammasome activation in vivo. Mechanistically, ZDHHC7-mediated NLRP3 Cys126 palmitoylation promotes resting NLRP3 localizing on the trans-Golgi network (TGN) and activated NLRP3 on the dispersed TGN, which is indispensable for recruitment and oligomerization of the adaptor ASC (apoptosis-associated speck-like protein containing a CARD). The activation of NLRP3 by ZDHHC7 is different from the termination effect mediated by ZDHHC12, highlighting versatile regulatory roles of S-palmitoylation. Our study identifies an important regulatory mechanism of NLRP3 activation that suggests targeting ZDHHC7 or the NLRP3 Cys126 residue as a potential therapeutic strategy to treat NLRP3-related human disorders.

Comprehensive metabolomics analysis reveals novel biomarkers and pathways in falsely suspected glutaric aciduria Type-1 newborns

BACKGROUND

Glutaric aciduria type-1 (GA-1) is a rare metabolic disorder due to glutaryl coenzyme A dehydrogenase deficiency, causing elevated levels of glutaryl-CoA and its derivatives. GA-1 exhibits symptoms like macrocephaly, developmental delays, and movement disorders. Timely diagnosis through genetic testing and newborn screening is crucial. However, in some cases, transiently elevated level of glutarylcarnitine (C5DC) challenges accurate diagnosis, highlighting the need for alternative diagnostic methods, like mass spectrometry-based untargeted metabolomics, to identify additional biomarkers for distinguishing falsely suspected GA-1 from healthy newborns.

METHODOLOGY

DBS samples from falsely suspected GA-1 newborns (n = 47) and matched control were collected through the NBS program. Untargeted metabolomics using liquid chromatography-high-resolution mass spectrometry (LC-HRMS) was performed to enable biomarker and pathway investigations for significantly altered metabolites.

RESULTS

582 and 546 were up- and down-regulated metabolites in transient GA-1. 155 endogenous metabolites displayed significant variations compared to the control group. Furthermore, our data identified novel altered metabolic biomarkers, such as N-palmitoylcysteine, heptacarboxyporphyrin, 3-hydroxylinoleoylcarnitine, and monoacylglyceride (MG) (0:0/20:1/0:0), along with perturbed metabolic pathways like sphingolipid and thiamine metabolism associated with the transient elevated C5DC levels in DBS samples.

CONCLUSIONS

A distinct metabolic pattern linked to the transient C5DC elevation in newborns was reported to enhance the prediction of the falsely positive cases, which could help avoiding unnecessary medical treatments and minimizing the financial burdens in the health sector.

Pulsed Electric Fields Induce STING Palmitoylation and Polymerization Independently of Plasmid DNA Electrotransfer

Gene therapy approaches may target skeletal muscle due to its high protein-expressing nature and vascularization. Intramuscular plasmid DNA (pDNA) delivery via pulsed electric fields (PEFs) can be termed electroporation or electrotransfer. Nonviral delivery of plasmids to cells and tissues activates DNA-sensing pathways. The central signaling complex in cytosolic DNA sensing is the cyclic GMP-AMP synthase-stimulator of interferon genes (cGAS-STING). The effects of pDNA electrotransfer on the signaling of STING, a key adapter protein, remain incompletely characterized. STING undergoes several post-translational modifications which modulate its function, including palmitoylation. This study demonstrated that in mouse skeletal muscle, STING was constitutively palmitoylated at two sites, while an additional site was modified following electroporation independent of the presence of pDNA. This third palmitoylation site correlated with STING polymerization but not with STING activation. Expression of several palmitoyl acyltransferases, including zinc finger and DHHC motif containing 1 (zDHHC1), coincided with STING activation. Expression of several depalmitoylases, including palmitoyl protein thioesterase 2 (PPT2), was diminished in all PEF application groups. Therefore, STING may not be regulated by active modification by palmitate after electroporation but inversely by the downregulation of palmitate removal. These findings unveil intricate molecular changes induced by PEF application.

Protein S-palmitoylation modification: implications in tumor and tumor immune microenvironment

Protein S-palmitoylation is a reversible post-translational lipid modification that involves the addition of a 16-carbon palmitoyl group to a protein cysteine residue via a thioester linkage. This modification plays a crucial role in the regulation protein localization, accumulation, secretion, stability, and function. Dysregulation of protein S-palmitoylation can disrupt cellular pathways and contribute to the development of various diseases, particularly cancers. Aberrant S-palmitoylation has been extensively studied and proven to be involved in tumor initiation and growth, metastasis, and apoptosis. In addition, emerging evidence suggests that protein S-palmitoylation may also have a potential role in immune modulation. Therefore, a comprehensive understanding of the regulatory mechanisms of S-palmitoylation in tumor cells and the tumor immune microenvironment is essential to improve our understanding of this process. In this review, we summarize the recent progress of S-palmitoylation in tumors and the tumor immune microenvironment, focusing on the S-palmitoylation modification of various proteins. Furthermore, we propose new ideas for immunotherapeutic strategies through S-palmitoylation intervention.

ZDHHC5-mediated NLRP3 palmitoylation promotes NLRP3-NEK7 interaction and inflammasome activation

The nucleotide-binding domain (NBD), leucine-rich repeat (LRR), and pyrin domain (PYD)-containing protein 3 (NLRP3) inflammasome is a critical mediator of the innate immune response. How NLRP3 responds to stimuli and initiates the assembly of the NLRP3 inflammasome is not fully understood. Here, we found that a cellular metabolite, palmitate, facilitates NLRP3 activation by enhancing its S-palmitoylation, in synergy with lipopolysaccharide stimulation. NLRP3 is post-translationally palmitoylated by zinc-finger and aspartate-histidine-histidine-cysteine 5 (ZDHHC5) at the LRR domain, which promotes NLRP3 inflammasome assembly and activation. Silencing ZDHHC5 blocks NLRP3 oligomerization, NLRP3-NEK7 interaction, and formation of large intracellular ASC aggregates, leading to abrogation of caspase-1 activation, IL-1β/18 release, and GSDMD cleavage, both in human cells and in mice. ABHD17A depalmitoylates NLRP3, and one human-heritable disease-associated mutation in NLRP3 was found to be associated with defective ABHD17A binding and hyper-palmitoylation. Furthermore, Zdhhc5-/- mice showed defective NLRP3 inflammasome activation in vivo. Taken together, our data reveal an endogenous mechanism of inflammasome assembly and activation and suggest NLRP3 palmitoylation as a potential target for the treatment of NLRP3 inflammasome-driven diseases.

CPT1A induction following epigenetic perturbation promotes MAVS palmitoylation and activation to potentiate antitumor immunity

Targeting epigenetic regulators to potentiate anti-PD-1 immunotherapy converges on the activation of type I interferon (IFN-I) response, mimicking cellular response to viral infection, but how its strength and duration are regulated to impact combination therapy efficacy remains largely unknown. Here, we show that mitochondrial CPT1A downregulation following viral infection restrains, while its induction by epigenetic perturbations sustains, a double-stranded RNA-activated IFN-I response. Mechanistically, CPT1A recruits the endoplasmic reticulum-localized ZDHHC4 to catalyze MAVS Cys79-palmitoylation, which promotes MAVS stabilization and activation by inhibiting K48- but facilitating K63-linked ubiquitination. Further elevation of CPT1A incrementally increases MAVS palmitoylation and amplifies the IFN-I response, which enhances control of viral infection and epigenetic perturbation-induced antitumor immunity. Moreover, CPT1A chemical inducers augment the therapeutic effect of combined epigenetic treatment with PD-1 blockade in refractory tumors. Our study identifies CPT1A as a stabilizer of MAVS activation, and its link to epigenetic perturbation can be exploited for cancer immunotherapy.

Refining S-acylation: Structure, regulation, dynamics, and therapeutic implications

With a limited number of genes, cells achieve remarkable diversity. This is to a large extent achieved by chemical posttranslational modifications of proteins. Amongst these are the lipid modifications that have the unique ability to confer hydrophobicity. The last decade has revealed that lipid modifications of proteins are extremely frequent and affect a great variety of cellular pathways and physiological processes. This is particularly true for S-acylation, the only reversible lipid modification. The enzymes involved in S-acylation and deacylation are only starting to be understood, and the list of proteins that undergo this modification is ever-increasing. We will describe the state of knowledge on the enzymes that regulate S-acylation, from their structure to their regulation, how S-acylation influences target proteins, and finally will offer a perspective on how alterations in the balance between S-acylation and deacylation may contribute to 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.

Targeting phenylpyruvate restrains excessive NLRP3 inflammasome activation and pathological inflammation in diabetic wound healing

Moderate inflammation is essential for standard wound healing. In pathological conditions, such as diabetes, protracted and refractory wounds are associated with excessive inflammation, manifested by persistent proinflammatory macrophage states. However, the mechanisms are still unclear. Herein, we perform a metabolomic profile and find a significant phenylpyruvate accumulation in diabetic foot ulcers. Increased phenylpyruvate impairs wound healing and augments inflammatory responses, whereas reducing phenylpyruvate via dietary phenylalanine restriction relieves uncontrolled inflammation and benefits diabetic wounds. Mechanistically, phenylpyruvate is ingested into macrophages in a scavenger receptor CD36-dependent manner, binds to PPT1, and inhibits depalmitoylase activity, thus increasing palmitoylation of the NLRP3 protein. Increased NLRP3 palmitoylation is found to enhance NLRP3 protein stability, decrease lysosome degradation, and promote NLRP3 inflammasome activation and the release of inflammatory factors, such as interleukin (IL)-1β, finally triggering the proinflammatory macrophage phenotype. Our study suggests a potential strategy of targeting phenylpyruvate to prevent excessive inflammation in diabetic wounds.

The Elk-3 target Abhd10 ameliorates hepatotoxic injury and fibrosis in alcoholic liver disease

Alcoholic liver disease (ALD) and other forms of chronic hepatotoxic injury can lead to transforming growth factor β1 (TGFβ1)-induced hepatic fibrosis and compromised liver function, underscoring the need to develop novel treatments for these conditions. Herein, our analyses of liver tissue samples from severe alcoholic hepatitis (SAH) patients and two murine models of ALD reveals that the ALD phenotype was associated with upregulation of the transcription factor ETS domain-containing protein (ELK-3) and ELK-3 signaling activity coupled with downregulation of α/β hydrolase domain containing 10 (ABHD10) and upregulation of deactivating S-palmitoylation of the antioxidant protein Peroxiredoxin 5 (PRDX5). In vitro, we further demonstrate that ELK-3 can directly bind to the ABHD10 promoter to inhibit its transactivation. TGFβ1 and epidermal growth factor (EGF) signaling induce ABHD10 downregulation and PRDX5 S-palmitoylation via ELK-3. This ELK-3-mediated ABHD10 downregulation drives oxidative stress and disrupts mature hepatocyte function via enhancing S-palmitoylation of PRDX5's Cys100 residue. In vivo, ectopic Abhd10 overexpression ameliorates liver damage in ALD model mice. Overall, these data suggest that the therapeutic targeting of the ABHD10-PRDX5 axis may represent a viable approach to treating ALD and other forms of hepatotoxicity.

Palmitoyl transferases act as novel drug targets for pancreatic cancer

BACKGROUND

Pancreatic adenocarcinoma (PAAD) is one of the most leading causes of cancer-related death across the world with the limited efficiency and response rate of immunotherapy. Protein S-palmitoylation, a powerful post-translational lipid modification, is well-known to regulate the stability and cellular distribution of cancer-related proteins, which is mediated by a family of 23 palmitoyl transferases, namely zinc finger Asp-His-His-Cys-type (ZDHHC). However, whether palmitoyl transferases can determine tumor progression and the efficacy of immunotherapy in PAAD remains unknown.

METHODS

Bioinformatics methods were used to identify differential ZDHHCs expression in PAAD. A systematic pan-cancer analysis was conducted to assess the immunological role of ZDHHC3 using RNA sequencing data from The Cancer Genome Atlas database. In vivo Panc 02 subcutaneous tumor model validated the anti-tumor effect of knockdown of ZDHHC3 or intraperitoneal injection of 2-bromopalmitate (2-BP), a typical broad-spectrum palmitoyl transferases inhibitor. Furthermore, we explored therapeutic strategies with combinations of 2-BP with PD-1/PD-L1-targeted immunotherapy in C57BL/6 mice bearing syngeneic Panc 02 pancreatic tumors.

RESULTS

ZDHHC enzymes were associated with distinct prognostic values of pancreatic cancer. We identified that ZDHHC3 expression promotes an immunosuppressive tumor microenvironment in PAAD. 2-BP suppressed pancreatic-tumor cell viability and tumor sphere-forming activities, as well as increased cell apoptosis in vitro, without affecting normal human pancreatic ductal epithelial cells. Furthermore, genetic inactivation of ZDHHC3 or intraperitoneal injection of 2-BP impeded tumor progression in Panc 02 pancreatic tumors with enhanced anti-tumor immunity. 2-BP treatment significantly enhanced the therapeutic efficacy of PD-1/PD-L1 inhibitors in Panc 02 pancreatic tumors.

CONCLUSION

This study revealed some ZDHHC enzyme genes for predicting the prognosis of pancreatic cancer, and demonstrated that ZDHHC3 plays a critical oncogenic role in pancreatic cancer progression, highlighting its potential as an immunotherapeutic target of pancreatic cancer. In addition, combination therapy of 2-BP and PD-1/PD-L1 achieved synergic therapy effects in a mouse model of pancreatic cancer.

CellPalmSeq: A curated RNAseq database of palmitoylating and de-palmitoylating enzyme expression in human cell types and laboratory cell lines

The reversible lipid modification protein S-palmitoylation can dynamically modify the localization, diffusion, function, conformation and physical interactions of substrate proteins. Dysregulated S-palmitoylation is associated with a multitude of human diseases including brain and metabolic disorders, viral infection and cancer. However, the diverse expression patterns of the genes that regulate palmitoylation in the broad range of human cell types are currently unexplored, and their expression in commonly used cell lines that are the workhorse of basic and preclinical research are often overlooked when studying palmitoylation dependent processes. We therefore created CellPalmSeq (https://cellpalmseq.med.ubc.ca), a curated RNAseq database and interactive webtool for visualization of the expression patterns of the genes that regulate palmitoylation across human single cell types, bulk tissue, cancer cell lines and commonly used laboratory non-human cell lines. This resource will allow exploration of these expression patterns, revealing important insights into cellular physiology and disease, and will aid with cell line selection and the interpretation of results when studying important cellular processes that depend on protein S-palmitoylation.

Protein acylation: mechanisms, biological functions and therapeutic targets

Metabolic reprogramming is involved in the pathogenesis of not only cancers but also neurodegenerative diseases, cardiovascular diseases, and infectious diseases. With the progress of metabonomics and proteomics, metabolites have been found to affect protein acylations through providing acyl groups or changing the activities of acyltransferases or deacylases. Reciprocally, protein acylation is involved in key cellular processes relevant to physiology and diseases, such as protein stability, protein subcellular localization, enzyme activity, transcriptional activity, protein-protein interactions and protein-DNA interactions. Herein, we summarize the functional diversity and mechanisms of eight kinds of nonhistone protein acylations in the physiological processes and progression of several diseases. We also highlight the recent progress in the development of inhibitors for acyltransferase, deacylase, and acylation reader proteins for their potential applications in drug discovery.

Post-Translational Modifications by Lipid Metabolites during the DNA Damage Response and Their Role in Cancer

Genomic DNA damage occurs as an inevitable consequence of exposure to harmful exogenous and endogenous agents. Therefore, the effective sensing and repair of DNA damage are essential for maintaining genomic stability and cellular homeostasis. Inappropriate responses to DNA damage can lead to genomic instability and, ultimately, cancer. Protein post-translational modifications (PTMs) are a key regulator of the DNA damage response (DDR), and recent progress in mass spectrometry analysis methods has revealed that a wide range of metabolites can serve as donors for PTMs. In this review, we will summarize how the DDR is regulated by lipid metabolite-associated PTMs, including acetylation, S-succinylation, N-myristoylation, palmitoylation, and crotonylation, and the implications for tumorigenesis. We will also discuss potential novel targets for anti-cancer drug development.

Antitumor potential of PD-L1/PD-1 post-translational modifications

The immune checkpoint programmed death receptor 1 (PD-1) and programmed death ligand 1 (PD-L1) are biologically important immunosuppressive molecules, and the PD-L1/PD-1-mediated signaling pathway is currently considered one of the main mechanisms of tumor escape immune surveillance. PD-L1 is highly expressed on the cytomembrane of tumor cell and binds to PD-1 receptor of activated T cells. This interaction activates PD-L1/PD-1 downstream signal transduction, inhibiting T cells anti-tumor activity. Therefore, inhibitors of PD-L1/PD-1 activation, showing significant efficacy in some types of tumors, have been widely approved in clinical tumor therapy. Recent research on PD-L1/PD-1 signaling pathway regulation has shown post-translational modifications (PTMs) form of PD-L1 or PD-1, including glycosylation, ubiquitination, phosphorylation, and acetylation, which may play an important role in PD-L1/PD-1 signaling pathway regulation and anti-tumor function of T cells. In this review, we focused on PTMs of PD-L1/PD-1 research and potential applications in tumor immunotherapy. This article is protected by copyright. All rights reserved.

A High-Throughput Fluorescent Turn-On Assay for Inhibitors of DHHC Family Proteins

As the "writer" enzymes of protein S-acylation, a dynamic and functionally significant post-translational modification (PTM), DHHC family proteins have emerged in the past decade as both key modulators of cellular homeostasis and as drivers of neoplastic, autoimmune, metabolic, and neurological pathologies. Currently, biological and clinical discovery is hampered by the limitations of existing DHHC family inhibitors, which possess poor physicochemical properties and off-target profiles. However, progress in identifying new inhibitory scaffolds has been meager, in part due to a lack of robust in vitro assays suitable for high-throughput screening (HTS). Here, we report the development of palmitoyl transferase probes (PTPs), a novel family of turn-on pro-fluorescent molecules that mimic the palmitoyl-CoA substrate of DHHC proteins. We use the PTPs to develop and validate an assay with an excellent Z'-factor for HTS. We then perform a pilot screen of 1687 acrylamide-based molecules against zDHHC20, establishing the PTP-based HTS assay as a platform for the discovery of improved DHHC family inhibitors.

Post-Translational Modifications of STING: A Potential Therapeutic Target

Stimulator of interferon genes (STING) is an endoplasmic-reticulum resident protein, playing essential roles in immune responses against microbial infections. However, over-activation of STING is accompanied by excessive inflammation and results in various diseases, including autoinflammatory diseases and cancers. Therefore, precise regulation of STING activities is critical for adequate immune protection while limiting abnormal tissue damage. Numerous mechanisms regulate STING to maintain homeostasis, including protein-protein interaction and molecular modification. Among these, post-translational modifications (PTMs) are key to accurately orchestrating the activation and degradation of STING by temporarily changing the structure of STING. In this review, we focus on the emerging roles of PTMs that regulate activation and inhibition of STING, and provide insights into the roles of the PTMs of STING in disease pathogenesis and as potential targeted therapy.

PRDX6: A protein bridging S-palmitoylation and diabetic neuropathy

Diabetic neuropathy is regarded as one of the most debilitating outcomes of diabetes. It can affect both the peripheral and central nervous systems, leading to pain, decreased motility, cognitive decline, and dementia. S-palmitoylation is a reversible posttranslational lipid modification, and its dysregulation has been implicated in metabolic syndrome, cancers, neurological disorders, and infections. However, the role of S-palmitoylation in diabetic neuropathy remains unclear. Here we demonstrate a potential association between activating protein palmitoylation and diabetic neuropathy. We compared the proteomic data of lumbar dorsal root ganglia (DRG) of diabetes mice and palmitoylome profiling data of the HUVEC cell line. The mapping results identified peroxiredoxin-6 (PRDX6) as a novel target in diabetic neuropathy, whose biological mechanism was associated with S-palmitoylation. Bioinformatic prediction revealed that PRDX6 had two palmitoylation sites, Cys47 and Cys91. Immunofluorescence results indicated PRDX6 translocating between the cytoplasm and cell membrane. Protein function analysis proposed that increased palmitoylation could competitively inhibit the formation of disulfide-bond between Cys47 and Cys91 and change the spatial topology of PRDX6 protein. Cl^-HCO3^- anion exchanger 3 (AE3) was one of the AE family members, which was proved to express in DRG. AE3 activity evoked Cl^- influx in neurons which was generally associated with increased excitability and susceptibility to pain. We demonstrated that the S-palmitoylation status of Cys47 could affect the interaction between PRDX6 and the C-terminal domain of AE3, thereby regulating the activity of AE3 anion exchanger enzyme in the nervous system. The results highlight a central role for PRDX6 palmitoylation in protection against diabetic neuropathy.

Palmitoylation in Crohn's disease: Current status and future directions

S-palmitoylation is one of the most common post-translational modifications in nature; however, its importance has been overlooked for decades. Crohn's disease (CD), a subtype of inflammatory bowel disease (IBD), is an autoimmune disease characterized by chronic inflammation involving the entire gastrointestinal tract. Bowel damage and subsequent disabilities caused by CD are a growing global health issue. Well-acknowledged risk factors for CD include genetic susceptibility, environmental factors, such as a westernized lifestyle, and altered gut microbiota. However, the pathophysiological mechanisms of this disorder are not yet comprehensively understood. With the rapidly increasing global prevalence of CD and the evident role of S-palmitoylation in CD, as recently reported, there is a need to investigate the relationship between CD and S-palmitoylation. In this review, we summarize the concept, detection, and function of S-palmitoylation as well as its potential effects on CD, and provide novel insights into the pathogenesis and treatment of CD.

Differential regulation of lipopolysaccharide-induced IL-1β and TNF-α production in macrophages by palmitate via modulating TLR4 downstream signaling

Diabetic patients are susceptible to infectious diseases. Bacterial invasion activates immune cells such as macrophages through interaction between LPS and TLR4, and induces the expression of inflammatory mediators, including IL-1β and TNF-α, which play key roles in the elimination of infections. Unregulated overproduction or underproduction of these cytokines has been reported as a major factor in the development of septic shock, immune deficiency, and autoimmunity. Recent studies found that metabolic abnormalities of diabetes, such as hyperglycemia and dyslipidemia, played a major role in modulating the immune response. In this study, we studied the effects of palmitic acid (PA) pretreatment on LPS-induced IL-1β and TNF-α production and LPS-TLR4 signaling in macrophages. Compared with control, PA pretreatment significantly increased LPS-induced TNF-α production and secretion in macrophages. In contrast, LPS-induced IL-1β production and secretion was significantly suppressed by PA pretreatment. PA pretreatment did not affect the expression levels of TLR4 or Myd88, or the endocytosis of TLR4 in macrophages. However, PA pretreatment significantly suppressed the phosphorylation level and nuclear translocation of NF-κB, and the phosphorylation level of ERK1/2, whereas increased the phosphorylation levels of p38 and JNK. The activation of IKK which was upstream of NF-κB and ERK1/2 was attenuated, while the activation of TAK1 which was upstream of JNK and p38 was augmented by PA pretreatment. Inhibitors of NF-κB, MEK1/2, and p38 significantly decreased IL-1β expression, while JNK and p38 pathway inhibitors significantly inhibited TNF-α expression. The differential regulation of LPS-induced TNF-α and IL-1β production by PA was associated with cellular metabolism of PA, because inhibiting metabolism of PA with etomoxir or pretreatment with Br-PA which cannot be metabolized reversed these effects. We also showed that PA treatment increased acetylated IKK level which might contribute to the suppressed activation of IKK. The present study showed that LPS-induced production of TNF-α and IL-1β was regulated by different TLR4 downstream pathways in macrophages. PA differentially affected LPS-induced production of TNF-α and IL-1β in macrophages through differentially modulating these pathways. Further experiments will be needed to determine how these phenomena lead to the impaired immune response in patients with diabetes.

Chemical approaches for investigating site-specific protein S-fatty acylation

Protein S-fatty acylation or S-palmitoylation is a reversible and regulated lipid post-translational modification (PTM) in eukaryotes. Loss-of-function mutagenesis studies have suggested important roles for protein S-fatty acylation in many fundamental biological pathways in development, neurobiology, and immunity that are also associated with human diseases. However, the hydrophobicity and reversibility of this PTM have made site-specific gain-of-function studies more challenging to investigate. In this review, we summarize recent chemical biology approaches and methods that have enabled site-specific gain-of-function studies of protein S-fatty acylation and the investigation of the mechanisms and significance of this PTM in eukaryotic biology.

Metabolic Modifications, Inflammation, and Cancer Immunotherapy

Cancer immunotherapy has accomplished significant progresses on treatment of various cancers in the past decade; however, recent studies revealed more and more heterogeneity in tumor microenvironment which cause unneglectable therapy resistance. A central phenomenon in tumor malignancy is metabolic dysfunctionality; it reprograms metabolic homeostasis in tumor and stromal cells thus affecting metabolic modifications on specific proteins. These posttranslational modifications include glycosylation and palmitoylation, which usually alter the protein localization, stability, and function. Many of these proteins participate in acute or chronic inflammation and play critical roles in tumorigenesis and progression. Therefore, targeting these metabolic modifications in immune checkpoints and inflammation provides an attractive therapeutic strategy for certain cancers. In this review, we summarize the recent progresses on metabolic modifications in this field, focus on the mechanisms on how glycosylation and palmitoylation regulate innate immune and inflammation, and we further discuss designing new immunotherapy targeting metabolic modifications. We aim to improve immunotherapy or targeted-therapy response and achieve more accurate individual therapy.

Function of Protein S-Palmitoylation in Immunity and Immune-Related Diseases

Protein S-palmitoylation is a covalent and reversible lipid modification that specifically targets cysteine residues within many eukaryotic proteins. In mammalian cells, the ubiquitous palmitoyltransferases (PATs) and serine hydrolases, including acyl protein thioesterases (APTs), catalyze the addition and removal of palmitate, respectively. The attachment of palmitoyl groups alters the membrane affinity of the substrate protein changing its subcellular localization, stability, and protein-protein interactions. Forty years of research has led to the understanding of the role of protein palmitoylation in significantly regulating protein function in a variety of biological processes. Recent global profiling of immune cells has identified a large body of S-palmitoylated immunity-associated proteins. Localization of many immune molecules to the cellular membrane is required for the proper activation of innate and adaptive immune signaling. Emerging evidence has unveiled the crucial roles that palmitoylation plays to immune function, especially in partitioning immune signaling proteins to the membrane as well as to lipid rafts. More importantly, aberrant PAT activity and fluctuations in palmitoylation levels are strongly correlated with human immunologic diseases, such as sensory incompetence or over-response to pathogens. Therefore, targeting palmitoylation is a novel therapeutic approach for treating human immunologic diseases. In this review, we discuss the role that palmitoylation plays in both immunity and immunologic diseases as well as the significant potential of targeting palmitoylation in disease treatment.

Inhibitors of DHHC family proteins

Protein S-acylation is a prevalent post-translational protein lipidation that is dynamically regulated by 'writer' protein S-acyltransferases and 'eraser' acylprotein thioesterases. The protein S-acyltransferases comprise 23 aspartate-histidine-histidine-cysteine (DHHC)-containing proteins, which transfer fatty acid acyl groups from acyl-coenzyme A onto protein substrates. DHHC proteins are increasingly recognized as critical regulators of S-acylation-mediated cellular processes and pathology. As our understanding of the importance and breadth of DHHC-mediated biology and pathology expands, so too does the need for chemical inhibitors of this class of proteins. In this review, we discuss the challenges and progress in DHHC inhibitor development, focusing on 2-bromopalmitate, the most commonly used inhibitor in the field, and N-cyanomethyl-N-myracrylamide, a new broad-spectrum DHHC inhibitor. We believe that current and ongoing advances in structure elucidation, mechanistic interrogation, and novel inhibitor design around DHHC proteins will spark innovative strategies to modulate these critical proteins in living systems.

S-acylation of Orai1 regulates store-operated Ca2+ entry

Store-operated Ca2+ entry is a central component of intracellular Ca2+ signaling pathways. The Ca2+ release-activated channel (CRAC) mediates store-operated Ca2+ entry in many different cell types. The CRAC channel is composed of the plasma membrane (PM)-localized Orai1 channel and endoplasmic reticulum (ER)-localized STIM1 Ca2+ sensor. Upon ER Ca2+ store depletion, Orai1 and STIM1 form complexes at ER-PM junctions, leading to the formation of activated CRAC channels. Although the importance of CRAC channels is well described, the underlying mechanisms that regulate the recruitment of Orai1 to ER-PM junctions are not fully understood. Here, we describe the rapid and transient S-acylation of Orai1. Using biochemical approaches, we show that Orai1 is rapidly S-acylated at cysteine 143 upon ER Ca2+ store depletion. Importantly, S-acylation of cysteine 143 is required for Orai1-mediated Ca2+ entry and recruitment to STIM1 puncta. We conclude that store depletion-induced S-acylation of Orai1 is necessary for recruitment to ER-PM junctions, subsequent binding to STIM1 and channel activation.