Trafficking and signaling by fatty-acylated and prenylated proteins

Next generation antimitotic β-carboline derivatives modulate microtubule dynamics and downregulate NF-κB, ERK 1/2 and phospho HSP 27

AIM

Exploring the efficacy of β-carboline-based molecular inhibitors in targeting microtubules for the development of novel anticancer therapeutics.

MATERIALS AND METHODS

We synthesized a series of 1-Aryl-N-substituted-β-carboline-3-carboxamide compounds and evaluated their cytotoxicity against human lung carcinoma (A549) cells using the MTT assay. Normal lung fibroblast cells (WI-38) were used to assess compound selectivity. The mechanism of action of MJ-211 was elucidated through Western blot analysis of key pro-apoptotic and cell cycle regulatory proteins. Additionally, the inhibitory effect of MJ-211 on multicellular 3D spheroid growth of A549 cells was evaluated.

KEY FINDINGS

Lead compound MJ-211 exhibited remarkable cytotoxicity against A549 cells with an IC50 of 4.075 μM at 24 h treatment and IC50 of 1.7 nM after 72 h of treatment, while demonstrating selectivity towards normal WI-38 cells. MJ-211 activated pro-apoptotic factors Bim and p53, and suppressed Cyclin B1, Phospho HSP 27, BubR1, Mad 2, ERK1/2, and NF-κB, indicating its potent antimitotic and pro-apoptotic effects. MJ-211 significantly suppressed the migration of cells and inhibited the growth of A549 cell-derived multicellular 3D spheroids, highlighting its efficacy in a more physiologically relevant model.

SIGNIFICANCE

Cytotoxic effect of MJ-211 against cancer cells, selectivity towards normal cells, and ability to modulate key regulatory proteins involved in apoptosis and cell cycle progression underscore its potential as a promising template for further anticancer lead optimization. Moreover, the inhibitory effect of MJ-211 on multicellular spheroid growth suggests its efficacy in combating tumor heterogeneity and resistance mechanisms, thereby offering a promising avenue for future anticancer drug development.

ZDHHC1 downregulates LIPG and inhibits colorectal cancer growth via IGF2BP1 Palmitoylation

Alteration in lipid metabolism is recognized as a hallmark feature of colorectal cancer (CRC). Protein S-palmitoylation plays a critical role in many different cellular processes including protein-lipid interaction. Zinc Finger DHHC-Type Containing 1 (ZDHHC1, also known as ZNF377) belongs to the palmitoyl-transferase ZDHHC family, and is a potential tumor suppressor. However, our knowledge of the functional roles of ZDHHC1 in CRC is limited. We discovered that ZDHHC1 expression was downregulated in CRC tissues and that low levels of ZDHHC1 were associated with unfavorable prognosis. Functional studies showed that ZDHHC1 inhibited CRC cell proliferation and invasion in vitro and in vivo. We also found that lipase G (LIPG) is negatively regulated by ZDHHC1 and plays a key role in CRC cell growth through lipid storage. Additionally, we demonstrated that ZDHHC1 functions as a IGF2BP1-palmitoylating enzyme that induces S-palmitoylation at IGF2BP1-C337, which results in downregulated LIPG expression via m6A modification. Mechanistic investigations revealed that the ZDHHC1/IGF2BP1/LIPG signaling axis is associated with inhibition of CRC cell growth. Our study uncovers the potential role of ZDHHC1 in CRC, including inhibition of CRC growth by reducing the stability of LIPG mRNA in an m6A dependent-manner by palmitoylation of IGF2BP1.

Interplay of CD36, autophagy, and lipid metabolism: insights into cancer progression

CD36, a scavenger receptor B2 that is dynamically distributed between cell membranes and organelle membranes, plays a crucial role in regulating lipid metabolism. Abnormal CD36 activity has been linked to a range of metabolic disorders, such as obesity, nonalcoholic fatty liver disease, insulin resistance and cardiovascular disease. CD36 undergoes various modifications, including palmitoylation, glycosylation, and ubiquitination, which greatly affect its binding affinity to various ligands, thereby triggering and influencing various biological effects. In the context of tumors, CD36 interacts with autophagy to jointly regulate tumorigenesis, mainly by influencing the tumor microenvironment. The central role of CD36 in cellular lipid homeostasis and recent molecular insights into CD36 in tumor development indicate the applicability of CD36 as a therapeutic target for cancer treatment. Here, we discuss the diverse posttranslational modifications of CD36 and their respective roles in lipid metabolism. Additionally, we delve into recent research findings on CD36 in tumors, outlining ongoing drug development efforts targeting CD36 and potential strategies for future development and highlighting the interplay between CD36 and autophagy in the context of cancer. Our aim is to provide a comprehensive understanding of the function of CD36 in both physiological and pathological processes, facilitating a more in-depth analysis of cancer progression and a better development and application of CD36-targeting drugs for tumor therapy in the near future.

Library Screening, In Vivo Confirmation, and Structural and Bioinformatic Analysis of Pentapeptide Sequences as Substrates for Protein Farnesyltransferase

Protein farnesylation is a post-translational modification where a 15-carbon farnesyl isoprenoid is appended to the C-terminal end of a protein by farnesyltransferase (FTase). This process often causes proteins to associate with the membrane and participate in signal transduction pathways. The most common substrates of FTase are proteins that have C-terminal tetrapeptide CaaX box sequences where the cysteine is the site of modification. However, recent work has shown that five amino acid sequences can also be recognized, including the pentapeptides CMIIM and CSLMQ. In this work, peptide libraries were initially used to systematically vary the residues in those two parental sequences using an assay based on Matrix Assisted Laser Desorption Ionization-Mass Spectrometry (MALDI-MS). In addition, 192 pentapeptide sequences from the human proteome were screened using that assay to discover additional extended CaaaX-box motifs. Selected hits from that screening effort were rescreened using an in vivo yeast reporter protein assay. The X-ray crystal structure of CMIIM bound to FTase was also solved, showing that the C-terminal tripeptide of that sequence interacted with the enzyme in a similar manner as the C-terminal tripeptide of CVVM, suggesting that the tripeptide comprises a common structural element for substrate recognition in both tetrapeptide and pentapeptide sequences. Molecular dynamics simulation of CMIIM bound to FTase further shed light on the molecular interactions involved, showing that a putative catalytically competent Zn(II)-thiolate species was able to form. Bioinformatic predictions of tetrapeptide (CaaX-box) reactivity correlated well with the reactivity of pentapeptides obtained from in vivo analysis, reinforcing the importance of the C-terminal tripeptide motif. This analysis provides a structural framework for understanding the reactivity of extended CaaaX-box motifs and a method that may be useful for predicting the reactivity of additional FTase substrates bearing CaaaX-box sequences.

Role of microRNAs and their putative mechanism in regulating potato (Solanum tuberosum L.) life cycle and response to various environmental stresses

The exponentially increasing population and the demand for food is inextricably linked. This has shifted global attention to improving crop plant traits to meet global food demands. Potato (Solanum tuberosum L.) is a major non-grain food crop that is grown all over the world. Currently, some of the major global potato research work focuses on the significance of microRNAs (miRNAs) in potato. miRNAs are a type of non-coding RNAs that regulate the gene expression of their target mRNA genes by cleavage and/or their translational inhibition. This suggests an essential role of miRNAs in a multitude of plant biological processes, including maintenance of genome integrity, plant growth, development and maturation, and initiation of responses to various stress conditions. Therefore, engineering miRNAs to generate stress-resistant varieties of potato may result in high yield and improved nutritional qualities. In this review, we discuss the potato miRNAs specifically known to play an essential role in the various stages of the potato life cycle, conferring stress-resistant characteristics, and modifying gene expression. This review highlights the significance of the miRNA machinery in plants, especially potato, encouraging further research into engineering miRNAs to boost crop yields and tolerance towards stress.

Inhibition of N-myristoyltransferase activity promotes androgen receptor degradation in prostate cancer

BACKGROUND

Even though prostate cancer (PCa) patients initially respond to androgen deprivation therapy, some will eventually develop castration resistant prostate cancer (CRPC). Androgen receptor (AR) mediated cell signaling is a major driver in the progression of CRPC while only a fraction of PCa becomes AR negative. This study aimed to understand the regulation of AR levels by N-myristoyltransferase in PCa cells.

METHODS

Two enantiomers, (1S,2S)- d-NMAPPD and (1R,2R)- d-NMAPPD (LCL4), were characterized by various methods (1 H and 13 C NMR, UHPLC, high-resolution mass spectra, circular dichroism) and evaluated for the ability to bind to N-myristoyltransferase 1 (NMT1) using computational docking analysis. structure-activity relationship analysis of these compounds led to the synthesis of (1R,2R)-LCL204 and evaluation as a potential NMT1 inhibitor utilizing the purified full length NMT1 enzyme. The NMT inhibitory activity wase determined by Click chemistry and immunoblotting. Regulation of NMT1 on tumor growth was evaluated in a xenograft tumor model.

RESULTS

(1R,2R)- d-NMAPPD, but not its enantiomer (1S,2S)- d-NMAPPD, inhibited NMT1 activity and reduced AR protein levels. (1R,2R)-LCL204, a derivative of (1R,2R)- d-NMAPPD, inhibited global protein myristoylation. It also suppressed protein levels, nuclear translocation, and transcriptional activity of AR full-length or variants in PCa cells. This was due to enhanced ubiquitin and proteasome-mediated degradation of AR. Knockdown of NMT1 levels inhibited tumor growth and proliferation of cancer cells.

CONCLUSION

Inhibitory efficacy on N-myristoyltransferase activity by d-NMAPPD is stereospecific. (1R,2R)-LCL204 reduced global N-myristoylation and androgen receptor protein levels at low micromolar concentrations in prostate cancer cells. pharmacological inhibition of NMT1 enhances ubiquitin-mediated proteasome degradation of AR. This study illustrates a novel function of N-myristoyltransferase and provides a potential strategy for treatment of CRPC.

Targeting of Specialized Metabolites Biosynthetic Enzymes to Membranes and Vesicles by Posttranslational Palmitoylation: A Mechanism of Non-Conventional Traffic and Secretion of Fungal Metabolites

In nature, the formation of specialized (secondary) metabolites is associated with the late stages of fungal development. Enzymes involved in the biosynthesis of secondary metabolites in fungi are located in distinct subcellular compartments including the cytosol, peroxisomes, endosomes, endoplasmic reticulum, different types of vesicles, the plasma membrane and the cell wall space. The enzymes traffic between these subcellular compartments and the secretion through the plasma membrane are still unclear in the biosynthetic processes of most of these metabolites. Recent reports indicate that some of these enzymes initially located in the cytosol are later modified by posttranslational acylation and these modifications may target them to membrane vesicle systems. Many posttranslational modifications play key roles in the enzymatic function of different proteins in the cell. These modifications are very important in the modulation of regulatory proteins, in targeting of proteins, intracellular traffic and metabolites secretion. Particularly interesting are the protein modifications by palmitoylation, prenylation and miristoylation. Palmitoylation is a thiol group-acylation (S-acylation) of proteins by palmitic acid (C16) that is attached to the SH group of a conserved cysteine in proteins. Palmitoylation serves to target acylated proteins to the cytosolic surface of cell membranes, e.g., to the smooth endoplasmic reticulum, whereas the so-called toxisomes are formed in trichothecene biosynthesis. Palmitoylation of the initial enzymes involved in the biosynthesis of melanin serves to target them to endosomes and later to the conidia, whereas other non-palmitoylated laccases are secreted directly by the conventional secretory pathway to the cell wall space where they perform the last step(s) of melanin biosynthesis. Six other enzymes involved in the biosynthesis of endocrosin, gliotoxin and fumitremorgin believed to be cytosolic are also targeted to vesicles, although it is unclear if they are palmitoylated. Bioinformatic analysis suggests that palmitoylation may be frequent in the modification and targeting of polyketide synthetases and non-ribosomal peptide synthetases. The endosomes may integrate other small vesicles with different cargo proteins, forming multivesicular bodies that finally fuse with the plasma membrane during secretion. Another important effect of palmitoylation is that it regulates calcium metabolism by posttranslational modification of the phosphatase calcineurin. Mutants defective in the Akr1 palmitoyl transferase in several fungi are affected in calcium transport and homeostasis, thus impacting on the biosynthesis of calcium-regulated specialized metabolites. The palmitoylation of secondary metabolites biosynthetic enzymes and their temporal distribution respond to the conidiation signaling mechanism. In summary, this posttranslational modification drives the spatial traffic of the biosynthetic enzymes between the subcellular organelles and the plasma membrane. This article reviews the molecular mechanism of palmitoylation and the known fungal palmitoyl transferases. This novel information opens new ways to improve the biosynthesis of the bioactive metabolites and to increase its secretion in fungi.

Targeting LYPLAL1-mediated cGAS depalmitoylation enhances the response to anti-tumor immunotherapy

Cyclic GMP-AMP synthase (cGAS) binds pathogenic and other cytoplasmic double-stranded DNA (dsDNA) to catalyze the synthesis of cyclic GMP-AMP (cGAMP), which serves as the secondary messenger to activate the STING pathway and innate immune responses. Emerging evidence suggests that activation of the cGAS pathway is crucial for anti-tumor immunity; however, no effective intervention method targeting cGAS is currently available. Here we report that cGAS is palmitoylated by ZDHHC9 at cysteines 404/405, which promotes the dimerization and activation of cGAS. We further identified that lysophospholipase-like 1 (LYPLAL1) depalmitoylates cGAS to compromise its normal function. As such, inhibition of LYPLAL1 significantly enhances cGAS-mediated innate immune response, elevates PD-L1 expression, and enhances anti-tumor response to PD-1 blockade. Our results therefore reveal that targeting LYPLAL1-mediated cGAS depalmitoylation contributes to cGAS activation, providing a potential strategy to augment the efficacy of anti-tumor immunotherapy.

ARF6 plays a general role in targeting palmitoylated proteins from the Golgi to the plasma membrane

Protein palmitoylation is a post-translational lipid modification of proteins. Accumulating evidence reveals that palmitoylation functions as a sorting signal to direct proteins to destinations; however, the sorting mechanism remains largely unknown. Here, we show that ARF6 plays a general role in targeting palmitoylated proteins from the Golgi to the plasma membrane (PM). Through shRNA screening, we identified ARF6 as the key small GTPase in targeting CD36, a palmitoylated protein, from the Golgi to the PM. We found that the N-terminal myristoylation of ARF6 is required for its binding with palmitoylated CD36, and the GTP-bound form of ARF6 facilitates the delivery of CD36 to the PM. Analysis of stable isotope labeling by amino acids in cell culture revealed that ARF6 might facilitate the sorting of 359 of the 531 palmitoylated PM proteins, indicating a general role of ARF6. Our study has thus identified a sorting mechanism for targeting palmitoylated proteins from the Golgi to the PM.

Use of alkyne-tagged myristic acid to detect N-terminal myristoylation

Protein N-terminal myristoylation is a lipidic modification typically occurring to the α-amino group of N-terminal glycine residues of proteins. It is catalyzed by the N-myristoyltransferase (NMT) enzyme family. Many studies in the past three decades have highlighted the importance of N-terminal glycine myristoylation as it affects protein localization, protein-protein interaction, and protein stability, thereby regulating multiple biological processes, including immune cell signaling, cancer progression, and infections. This book chapter will present protocols for using alkyne-tagged myristic acid to detect the N-myristoylation of targeted proteins in cell lines and compare global N-myristoylation levels. We then described a protocol of SILAC proteomics that compare the levels of N-myristoylation on a proteomic scale. These assays allow for the identification of potential NMT substrates and the development of novel NMT inhibitors.

Myristic acid as a checkpoint to regulate STING-dependent autophagy and interferon responses by promoting N-myristoylation

Stimulator of interferon gene (STING)-triggered autophagy is crucial for the host to eliminate invading pathogens and serves as a self-limiting mechanism of STING-induced interferon (IFN) responses. Thus, the mechanisms that ensure the beneficial effects of STING activation are of particular importance. Herein, we show that myristic acid, a type of long-chain saturated fatty acid (SFA), specifically attenuates cGAS-STING-induced IFN responses in macrophages, while enhancing STING-dependent autophagy. Myristic acid inhibits HSV-1 infection-induced innate antiviral immune responses and promotes HSV-1 replication in mice in vivo. Mechanistically, myristic acid enhances N-myristoylation of ARF1, a master regulator that controls STING membrane trafficking. Consequently, myristic acid facilitates STING activation-triggered autophagy degradation of the STING complex. Thus, our work identifies myristic acid as a metabolic checkpoint that contributes to immune homeostasis by balancing STING-dependent autophagy and IFN responses. This suggests that myristic acid and N-myristoylation are promising targets for the treatment of diseases caused by aberrant STING activation.

S-Palmitoylation of Tyrosinase at Cysteine500 Regulates Melanogenesis

Palmitoylation is a lipid modification involving the attachment of palmitic acid to a cysteine residue, thereby affecting protein function. We investigated the effect of palmitoylation of tyrosinase, the rate-limiting enzyme in melanin synthesis, using a human three-dimensional skin model system and melanocyte culture. The palmitoylation inhibitor, 2-bromopalmitate, increased melanin content and tyrosinase protein levels in melanogenic cells by suppressing tyrosinase degradation. The palmitoylation site was Cysteine⁵⁰⁰ in the C-terminal cytoplasmic tail of tyrosinase. The nonpalmitoylatable mutant, tyrosinase (C500A), was slowly degraded and less ubiquitinated than wild-type tyrosinase. Screening for the Asp-His-His-Cys (DHHC) family of proteins for tyrosinase palmitoylation suggested that DHHC2, 3, 7, and 15 are involved in tyrosinase palmitoylation. Knockdown of DHHC2, 3, or 15 increased tyrosinase protein levels and melanin content. Determination of their subcellular localization in primary melanocytes revealed that DHHC2, 3, and 15 were localized in the endoplasmic reticulum, Golgi apparatus, and/or melanosomes, whereas only DHHC2 was localized in the melanosomes. Immunoprecipitation showed that DHHC2 and DHHC3 predominantly bind to mature and immature tyrosinase, respectively. Taken together, tyrosinase palmitoylation at Cysteine⁵⁰⁰ by DHHC2, 3, and/or 15, especially DHHC2 in trans-Golgi apparatus and melanosomes and DHHC3 in the endoplasmic reticulum and cis-Golgi apparatus, regulate melanogenesis by modulating tyrosinase protein levels.

Miniaturized Synthetic Palmitoylation Motifs for Small-Molecule Localization in Living Cells

Conjugating small-molecule ligands to synthetic motifs that can localize to specific organelles or membranes in living cells is a practical approach to develop compounds as chimeric tools or drugs that can manipulate biological processes in a subcellular site-specific manner. However, the number of available organelle-targeted synthetic motifs for small-molecule localization is limited. We have recently developed a synthetic myristoyl-^DCys motif for small-molecule localization that undergoes S-palmitoylation via the cellular palmitoylation machinery and localizes to the Golgi surface. Herein, we show that the lipid acyl chain of the myristoyl (C14)-^DCys motif can be as short as 10-carbons and still retain the palmitoylation-dependent Golgi localization property in cells. This discovery led to the identification of four new derivatives for small-molecule localization: tridecanoyl (C13)-, dodecanoyl (C12)-, undecanoyl (C11)-, and decanoyl (C10)-^DCys motifs. We demonstrated that even the short decanoyl-^DCys palmitoylation motif could be used to generate small-molecule ligand conjugates that functioned as chemical tools for controlling protein localization and cell signaling. The miniaturized synthetic palmitoylation motifs identified in this work may find applications in creating various Golgi-localizable chimeric molecules for use in chemical biology and drug development.

PDE6D Mediates Trafficking of Prenylated Proteins NIM1K and UBL3 to Primary Cilia

Mutations in PDE6D impair the function of its cognate protein, phosphodiesterase 6D (PDE6D), in prenylated protein trafficking towards the ciliary membrane, causing the human ciliopathy Joubert Syndrome (JBTS22) and retinal degeneration in mice. In this study, we purified the prenylated cargo of PDE6D by affinity proteomics to gain insight into PDE6D-associated disease mechanisms. By this approach, we have identified a specific set of PDE6D-interacting proteins that are involved in photoreceptor integrity, GTPase activity, nuclear import, or ubiquitination. Among these interacting proteins, we identified novel ciliary cargo proteins of PDE6D, including FAM219A, serine/threonine-protein kinase NIM1 (NIM1K), and ubiquitin-like protein 3 (UBL3). We show that NIM1K and UBL3 localize inside the cilium in a prenylation-dependent manner. Furthermore, UBL3 also localizes in vesicle-like structures around the base of the cilium. Through affinity proteomics of UBL3, we confirmed its strong interaction with PDE6D and its association with proteins that regulate small extracellular vesicles (sEVs) and ciliogenesis. Moreover, we show that UBL3 localizes in specific photoreceptor cilium compartments in a prenylation-dependent manner. Therefore, we propose that UBL3 may play a role in the sorting of proteins towards the photoreceptor outer segment, further explaining the development of PDE6D-associated retinal degeneration.

Blockade of NMT1 enzymatic activity inhibits N-myristoylation of VILIP3 protein and suppresses liver cancer progression

Hepatocellular carcinoma (HCC) is one of the most common malignant tumors. Identification of the underlying mechanism of HCC progression and exploration of new therapeutic drugs are urgently needed. Here, a compound library consisting of 419 FDA-approved drugs was taken to screen potential anticancer drugs. A series of functional assays showed that desloratadine, an antiallergic drug, can repress proliferation in HCC cell lines, cell-derived xenograft (CDX), patient-derived organoid (PDO) and patient-derived xenograft (PDX) models. N-myristoyl transferase 1 (NMT1) was identified as a target protein of desloratadine by drug affinity responsive target stability (DARTS) and surface plasmon resonance (SPR) assays. Upregulation of NMT1 expression enhanced but NMT1 knockdown suppressed tumor growth in vitro and in vivo. Metabolic labeling and mass spectrometry analyses revealed that Visinin-like protein 3 (VILIP3) was a new substrate of NMT1 in protein N-myristoylation modification, and high NMT1 or VILIP3 expression was associated with advanced stages and poor survival in HCC. Mechanistically, desloratadine binds to Asn-246 in NMT1 and inhibits its enzymatic activity, disrupting the NMT1-mediated myristoylation of the VILIP3 protein and subsequent NFκB/Bcl-2 signaling. Conclusively, this study demonstrates that desloratadine may be a novel anticancer drug and that NMT1-mediated myristoylation contributes to HCC progression and is a potential biomarker and therapeutic target in HCC.

Remodeling of the Plasma Membrane by Surface-Bound Protein Monomers and Oligomers: The Critical Role of Intrinsically Disordered Regions

The plasma membrane (PM) of cells is a dynamic structure whose morphology and composition is in constant flux. PM morphologic changes are particularly relevant for the assembly and disassembly of signaling platforms involving surface-bound signaling proteins, as well as for many other mechanochemical processes that occur at the PM surface. Surface-bound membrane proteins (SBMP) require efficient association with the PM for their function, which is often achieved by the coordinated interactions of intrinsically disordered regions (IDRs) and globular domains with membrane lipids. This review focuses on the role of IDR-containing SBMPs in remodeling the composition and curvature of the PM. The ability of IDR-bearing SBMPs to remodel the Gaussian and mean curvature energies of the PM is intimately linked to their ability to sort subsets of phospholipids into nanoclusters. We therefore discuss how IDRs of many SBMPs encode lipid-binding specificity or facilitate cluster formation, both of which increase their membrane remodeling capacity, and how SBMP oligomers alter membrane shape by monolayer surface area expansion and molecular crowding.

Targeting EGFR-dependent tumors by disrupting an ARF6-mediated sorting system

Aberrant activation of EGFR due to overexpression or mutation is associated with poor prognosis in many types of tumors. Here we show that blocking the sorting system that directs EGFR to plasma membrane is a potent strategy to treat EGFR-dependent tumors. We find that EGFR palmitoylation by DHHC13 is critical for its plasma membrane localization and identify ARF6 as a key factor in this process. N-myristoylated ARF6 recognizes palmitoylated EGFR via lipid-lipid interaction, recruits the exocyst complex to promote EGFR budding from Golgi, and facilitates EGFR transporting to plasma membrane in a GTP-bound form. To evaluate the therapeutic potential of this sorting system, we design a cell-permeable peptide, N-myristoylated GKVL-TAT, and find it effectively disrupts plasma membrane localization of EGFR and significantly inhibits progression of EGFR-dependent tumors. Our findings shed lights on the underlying mechanism of how palmitoylation directs protein sorting and provide an potential strategy to manage EGFR-dependent tumors.

EGFR is aberrantly activated in many cancer types. Here the authors show that small GTPase ARF6 mediates the trafficking of palmitoylated EGFR from Golgi to plasma membrane and the blockade of this sorting system inhibits the growth of EGFR overexpression tumours.

Inhibition of vaccinia virus L1 N-myristoylation by the host N-myristoyltransferase inhibitor IMP-1088 generates non-infectious virions defective in cell entry

We have recently shown that the replication of rhinovirus, poliovirus and foot-and-mouth disease virus requires the co-translational N-myristoylation of viral proteins by human host cell N-myristoyltransferases (NMTs), and is inhibited by treatment with IMP-1088, an ultrapotent small molecule NMT inhibitor. Here, we examine the importance of N-myristoylation during vaccinia virus (VACV) infection in primate cells and demonstrate the anti-poxviral effects of IMP-1088. N-myristoylated proteins from VACV and the host were metabolically labelled with myristic acid alkyne during infection using quantitative chemical proteomics. We identified VACV proteins A16, G9 and L1 to be N-myristoylated. Treatment with NMT inhibitor IMP-1088 potently abrogated VACV infection, while VACV gene expression, DNA replication, morphogenesis and EV formation remained unaffected. Importantly, we observed that loss of N-myristoylation resulted in greatly reduced infectivity of assembled mature virus particles, characterized by significantly reduced host cell entry and a decline in membrane fusion activity of progeny virus. While the N-myristoylation of VACV entry proteins L1, A16 and G9 was inhibited by IMP-1088, mutational and genetic studies demonstrated that the N-myristoylation of L1 was the most critical for VACV entry. Given the significant genetic identity between VACV, monkeypox virus and variola virus L1 homologs, our data provides a basis for further investigating the role of N-myristoylation in poxviral infections as well as the potential of selective NMT inhibitors like IMP-1088 as broad-spectrum poxvirus inhibitors.

Structural and large-scale analysis unveil the intertwined paths promoting NMT-catalyzed lysine and glycine myristoylation

N-myristoyltransferases (NMTs) catalyze protein myristoylation, a lipid modification crucial for cell survival and a range of pathophysiological processes. Originally thought to modify only N-terminal glycine α-amino groups (G-myristoylation), NMTs were recently shown to also modify lysine ε-amino groups (K-myristoylation). However, the clues ruling NMT-dependent K-myristoylation and the full range of targets are currently unknown. Here we combine mass spectrometry, kinetic studies, in silico analysis, and crystallography to identify the specific features driving each modification. We show that direct interactions between the substrate's reactive amino group and the NMT catalytic base promote K-myristoylation but with poor efficiency compared to G-myristoylation, which instead uses a water-mediated interaction. We provide evidence of depletion of proteins with NMT-dependent K-myristoylation motifs in humans, suggesting evolutionary pressure to prevent this modification in favor of G-myristoylation. In turn, we reveal that K-myristoylation may only result from post-translational events. Our studies finally unravel the respective paths towards K-myristoylation or G-myristoylation, which rely on a very subtle tradeoff embracing the chemical landscape around the reactive group.

S-acylation regulates the membrane association and activity of Calpain-5

Calpain-5 (CAPN5) is a member of the calpain family of calcium-activated neutral thiol proteases. CAPN5 is partly membrane associated, despite its lack of a transmembrane domain. Unlike classical calpains, CAPN5 contains a C-terminal C2 domain. C2 domains often have affinity to lipids, mediating membrane association. We recently reported that the C2 domain of CAPN5 was essential for its membrane association and the activation of its autolytic activity. However, despite the removal of the C2 domain by autolysis, the N-terminal fragment of CAPN5 remained membrane associated. S-acylation, also referred to as S-palmitoylation, is a reversible post-translational lipid modification of cysteine residues that promotes membrane association of soluble proteins. In the present study several S-acylated cysteine residues were identified in CAPN5 with the acyl-PEG exchange method. Data reported here demonstrate that CAPN5 is S-acylated on up to three cysteine residues including Cys-4 and Cys-512, and likely Cys-507. The D589N mutation in a potential calcium binding loop within the C2 domain interfered with the S-acylation of CAPN5, likely preventing initial membrane association. Mutating specific cysteine residues of CAPN5 interfered with both its membrane association and the activation of CAPN5 autolysis. Taken together, our results suggest that the S-acylation of CAPN5 is critical for its membrane localization which appears to favor its enzymatic activity.

The HIV-1 Gag Protein Displays Extensive Functional and Structural Roles in Virus Replication and Infectivity

Once merely thought of as the protein responsible for the overall physical nature of the human immunodeficiency virus type 1 (HIV-1), the Gag polyprotein has since been elucidated to have several roles in viral replication and functionality. Over the years, extensive research into the polyproteins’ structure has revealed that Gag can mediate its own trafficking to the plasma membrane, it can interact with several host factors and can even aid in viral genome packaging. Not surprisingly, Gag has also been associated with HIV-1 drug resistance and even treatment failure. Therefore, this review provides an extensive overview of the structural and functional roles of the HIV-1 Gag domains in virion integrity, functionality and infectivity.

Protein Farnesylation on Nasopharyngeal Carcinoma, Molecular Background and Its Potential as a Therapeutic Target

Simple Summary

Nasopharyngeal carcinoma is distinguished from other head and neck carcinomas by the association of its carcinogenesis with the Epstein–Barr virus. It is highly metastatic, and a novel therapeutic modality for metastatic nasopharyngeal carcinoma is keenly awaited. Protein farnesylation is a C-terminal lipid modification of proteins and was initially investigated as a key process in activating the RAS oncoprotein through its association with the cellular membrane structure. Since then, more and more evidence has accumulated to indicate that proteins other than RAS are also farnesylated and have significant roles in carcinogenesis. This review delineates molecular pathogenesis through protein farnesylation in the context of nasopharyngeal carcinoma and discusses the potential of farnesylation as a therapeutic target.

Abstract

Nasopharyngeal carcinoma (NPC) is one of the Epstein–Barr virus (EBV)-associated malignancies. NPC is highly metastatic compared to other head and neck carcinomas, and evidence has shown that the metastatic features of NPC are involved in EBV infection. The prognosis of advanced cases, especially those with distant metastasis, is still poor despite advancements in molecular research and its application to clinical settings. Thus, further advancement in basic and clinical research that may lead to novel therapeutic modalities is needed. Farnesylation is a lipid modification in the C-terminus of proteins. It enables proteins to attach to the lipid bilayer structure of cellular membranes. Farnesylation was initially identified as a key process of membrane association and activation of the RAS oncoprotein. Farnesylation is thus expected to be an ideal therapeutic target in anti-RAS therapy. Additionally, more and more molecular evidence has been reported, showing that proteins other than RAS are also farnesylated and have significant roles in cancer progression. However, although several clinical trials have been conducted in cancers with high rates of ras gene mutation, such as pancreatic carcinomas, the results were less favorable than anticipated. In contrast, favorable outcomes were reported in the results of a phase II trial on head and neck carcinoma. In this review, we provide an overview of the molecular pathogenesis of NPC in terms of the process of farnesylation and discuss the potential of anti-farnesylation therapy in the treatment of NPC.

Harnessing the Therapeutic Potential of Biomacromolecules through Intracellular Delivery of Nucleic Acids, Peptides, and Proteins

Biomacromolecules have long been at the leading edge of academic and pharmaceutical drug development and clinical translation. With the clinical advances of new therapeutics, such as monoclonal antibodies and nucleic acids, the array of medical applications of biomacromolecules has broadened considerably. A major on-going effort is to expand therapeutic targets within intracellular locations. Owing to their large sizes, abundant charges, and hydrogen-bond donors and acceptors, advanced delivery technologies are required to deliver biomacromolecules effectively inside cells. In this review, strategies used for the intracellular delivery of three major forms of biomacromolecules: nucleic acids, proteins, and peptides, are highlighted. An emphasis is placed on synthetic delivery approaches and the major hurdles needed to be overcome for their ultimate clinical translation.

Local and substrate-specific S-palmitoylation determines subcellular localization of Gαo

Peripheral membrane proteins (PMPs) associate with cellular membranes through post-translational modifications like S-palmitoylation. The Golgi apparatus is generally viewed as the transitory station where palmitoyl acyltransferases (PATs) modify PMPs, which are then transported to their ultimate destinations such as the plasma membrane (PM). However, little substrate specificity among the many PATs has been determined. Here we describe the inherent partitioning of Gαo - α-subunit of heterotrimeric Go proteins - to PM and Golgi, independent from Golgi-to-PM transport. A minimal code within Gαo N-terminus governs its compartmentalization and re-coding produces G protein versions with shifted localization. We establish the S-palmitoylation at the outer nuclear membrane assay ("SwissKASH") to probe substrate specificity of PATs in intact cells. With this assay, we show that PATs localizing to different membrane compartments display remarkable substrate selectivity, which is the basis for PMP compartmentalization. Our findings uncover a mechanism governing protein localization and establish the basis for innovative drug discovery.

Protein Lipidation Types: Current Strategies for Enrichment and Characterization

Post-translational modifications regulate diverse activities of a colossal number of proteins. For example, various types of lipids can be covalently linked to proteins enzymatically or non-enzymatically. Protein lipidation is perhaps not as extensively studied as protein phosphorylation, ubiquitination, or glycosylation although it is no less significant than these modifications. Evidence suggests that proteins can be attached by at least seven types of lipids, including fatty acids, lipoic acids, isoprenoids, sterols, phospholipids, glycosylphosphatidylinositol anchors, and lipid-derived electrophiles. In this review, we summarize types of protein lipidation and methods used for their detection, with an emphasis on the conjugation of proteins with polyunsaturated fatty acids (PUFAs). We discuss possible reasons for the scarcity of reports on PUFA-modified proteins, limitations in current methodology, and potential approaches in detecting PUFA modifications.

Traceless antibiotic-crosslinked micelles for rapid clearance of intracellular bacteria

Effective delivery of antimicrobial agents to intracellular pathogens represents a major bottleneck for a wide variety of infectious diseases. To address this, we developed SIR-micelles(+), as a new delivery vehicle comprising antibiotic-loaded micelles with rapid self-immolation within cells for targeted delivery to macrophages, where most intracellular bacterial reside. After phagocytosis, SIR-micelles(+) rapidly release the pristine antibiotic after the cleavage of the disulfide bonds by intracellular reducing agents such as glutathione (GSH). Colistin, a hydrophilic and potent "last-resort" antibiotic used for the treatment of drug-resistant bacterial infection, was encapsulated in SIR-micelles with 40% yield and good short-term storage stability. Hydrophobic moieties and mannose ligands in SIR-micelles(+) enhanced the delivery of colistin into macrophages. The traceless and thiol-responsive release of colistin effectively eliminated intracellular Escherichia coli within twenty minutes. In a murine pneumonia model, SIR-micelles(+) significantly reduced bacterial lung burden of multidrug-resistant Klebsiella pneumoniae. Furthermore, SIR-micelles(+) improved the survival rate and reduced the bacterial burden of organs infected by intracellular bacteria transferred from donor mice. Using this formulation approach, the nephrotoxicity and neurotoxicity induced by antibiotic were reduced by about 5- 15 fold. Thus, SIR-micelles(+) represent a new class of material that can be used for targeting treatment of intracellular and drug-resistant pathogens.

MALDI-MS Analysis of Peptide Libraries Expands the Scope of Substrates for Farnesyltransferase

Protein farnesylation is a post-translational modification where a 15-carbon farnesyl isoprenoid is appended to the C-terminal end of a protein by farnesyltransferase (FTase). This modification typically causes proteins to associate with the membrane and allows them to participate in signaling pathways. In the canonical understanding of FTase, the isoprenoids are attached to the cysteine residue of a four-amino-acid CaaX box sequence. However, recent work has shown that five-amino-acid sequences can be recognized, including the pentapeptide CMIIM. This paper describes a new systematic approach to discover novel peptide substrates for FTase by combining the combinatorial power of solid-phase peptide synthesis (SPPS) with the ease of matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS). The workflow consists of synthesizing focused libraries containing 10-20 sequences obtained by randomizing a synthetic peptide at a single position. Incubation of the library with FTase and farnesyl pyrophosphate (FPP) followed by mass spectrometric analysis allows the enzymatic products to be clearly resolved from starting peptides due to the increase in mass that occurs upon farnesylation. Using this method, 30 hits were obtained from a series of libraries containing a total of 80 members. Eight of the above peptides were selected for further evaluation, reflecting a mixture that represented a sampling of diverse substrate space. Six of these sequences were found to be bona fide substrates for FTase, with several meeting or surpassing the in vitro efficiency of the benchmark sequence CMIIM. Experiments in yeast demonstrated that proteins bearing these sequences can be efficiently farnesylated within live cells. Additionally, a bioinformatics search showed that a variety of pentapeptide CaaaX sequences can be found in the mammalian genome, and several of these sequences display excellent farnesylation in vitro and in yeast cells, suggesting that the number of farnesylated proteins within mammalian cells may be larger than previously thought.

ANKRD22 is an N-myristoylated hairpin-like monotopic membrane protein specifically localized to lipid droplets

The membrane topology and intracellular localization of ANKRD22, a novel human N-myristoylated protein with a predicted single-pass transmembrane domain that was recently reported to be overexpressed in cancer, were examined. Immunofluorescence staining of COS-1 cells transfected with cDNA encoding ANKRD22 coupled with organelle markers revealed that ANKRD22 localized specifically to lipid droplets (LD). Analysis of the intracellular localization of ANKRD22 mutants C-terminally fused to glycosylatable tumor necrosis factor (GLCTNF) and assessment of their susceptibility to protein N-glycosylation revealed that ANKRD22 is synthesized on the endoplasmic reticulum (ER) membrane as an N-myristoylated hairpin-like monotopic membrane protein with the amino- and carboxyl termini facing the cytoplasm and then sorted to LD. Pro98 located at the center of the predicted membrane domain was found to be essential for the formation of the hairpin-like monotopic topology of ANKRD22. Moreover, the hairpin-like monotopic topology, and positively charged residues located near the C-terminus were demonstrated to be required for the sorting of ANKRD22 from ER to LD. Protein N-myristoylation was found to positively affect the LD localization. Thus, multiple factors, including hairpin-like monotopic membrane topology, C-terminal positively charged residues, and protein N-myristoylation cooperatively affected the intracellular targeting of ANKRD22 to LD.

Protein Sorting in Plasmodium Falciparum

Plasmodium falciparum is a unicellular eukaryote with a very polarized secretory system composed of micronemes rhoptries and dense granules that are required for host cell invasion. P. falciparum, like its relative T. gondii, uses the endolysosomal system to produce the secretory organelles and to ingest host cell proteins. The parasite also has an apicoplast, a secondary endosymbiotic organelle, which depends on vesicular trafficking for appropriate incorporation of nuclear-encoded proteins into the apicoplast. Recently, the central molecules responsible for sorting and trafficking in P. falciparum and T. gondii have been characterized. From these studies, it is now evident that P. falciparum has repurposed the molecules of the endosomal system to the secretory pathway. Additionally, the sorting and vesicular trafficking mechanism seem to be conserved among apicomplexans. This review described the most recent findings on the molecular mechanisms of protein sorting and vesicular trafficking in P. falciparum and revealed that P. falciparum has an amazing secretory machinery that has been cleverly modified to its intracellular lifestyle.

Inhibition of the miR-155 and protein prenylation feedback loop alleviated acute graft-versus-host disease through regulating the balance between T helper 17 and Treg cells

MicroRNA-155(miR-155) and protein prenylation have been reported to participate in acute graft-versus-host disease (aGVHD) through modulating T lymphocyte differentiation, however the mechanism remains elusive. In this study, we found that the expression of miR-155 and protein prenyltransferases in peripheral blood T lymphocytes of aGVHD mice was significantly increased. Suppression of miR-155 by antagomir-155 could remarkably reduce prenyltransferases mRNA and protein expression in T lymphocytes of aGVHD mice. Conversely, prenyltransferase inhibitors significantly reduced the level of miR-155. Inhibition of this feedback loop of miR-155 and protein prenylation in aGVHD mice led to improved survival and lower aGVHD histopathology scores and significantly induced T cell deficient differentiation towards T helper 17 (Th17) cells and titled differentiation towards CD4⁺CD25^hi regulatory T (Treg) cells. Furthermore, the immunoregulatory effects and protection from aGVHD of prenyltransferase inhibitors could be reversed by the addition of miR-155. The dual treatment of prenylation inhibitors and antagomir-155 showed synergistic effects on T polarization and protection from aGVHD. Consistent with the in vivo changes, inhibition of this feedback loop of miR-155 and protein prenylation affected Th17 and Treg cell polarization in vitro. Our data suggest that miR-155 and protein prenylation may constitute a feedback loop that amplifies immune and inflammatory responses in subjects with aGVHD, and they may serve as potential targets for aGVHD prophylaxis and treatment.

Demyristoylation of the Cytoplasmic Redox Protein Trx-h2 Is Critical for Inducing a Rapid Cold Stress Response in Plants

In Arabidopsis, the cytosolic redox protein thioredoxin h2 (Trx-h2) is anchored to the cytoplasmic endomembrane through the myristoylated second glycine residue (Gly²). However, under cold stress, the cytosolic Trx-h2 is rapidly translocated to the nucleus, where it interacts with and reduces the cold-responsive C-repeat-binding factors (CBFs), thus activating cold-responsive (COR) genes. In this study, we investigated the significance of fatty acid modification of Trx-h2 under cold conditions by generating transgenic Arabidopsis lines in the trx-h2 mutant background, overexpressing Trx-h2 (Trx-h2^OE/trx-h2) and its point mutation variant Trx-h2(G/A) [Trx-h2(G/A)^OE/trx-h2], in which the Gly² was replaced by alanine (Ala). Due to the lack of Gly², Trx-h2(G/A) was incapable of myristoylation, and a part of Trx-h2(G/A) localized to the nucleus even under warm temperature. As no time is spent on the demyristoylation and subsequent nuclear translocation of Trx-h2(G/A) under a cold snap, the ability of Trx-h2(G/A) to protect plants from cold stress was greater than that of Trx-h2. Additionally, COR genes were up-regulated earlier in Trx-h2(G/A)2^OE/trx-h2 plants than in Trx-h2^OE/trx-h2 plants under cold stress. Consequently, Trx-h2(G/A)2^OE/trx-h2 plants showed greater cold tolerance than Col-0 (wild type) and Trx-h2^OE/trx-h2 plants. Overall, our results clearly demonstrate the significance of the demyristoylation of Trx-h2 in enhancing plant cold/freezing tolerance.

Chemically modified and conjugated antimicrobial peptides against superbugs

Antimicrobial resistance (AMR) is one of the greatest threats to human health that, by 2050, will lead to more deaths from bacterial infections than cancer. New antimicrobial agents, both broad-spectrum and selective, that do not induce AMR are urgently required. Antimicrobial peptides (AMPs) are a novel class of alternatives that possess potent activity against a wide range of Gram-negative and positive bacteria with little or no capacity to induce AMR. This has stimulated substantial chemical development of novel peptide-based antibiotics possessing improved therapeutic index. This review summarises recent synthetic efforts and their impact on analogue design as well as their various applications in AMP development. It includes modifications that have been reported to enhance antimicrobial activity including lipidation, glycosylation and multimerization through to the broad application of novel bio-orthogonal chemistry, as well as perspectives on the direction of future research. The subject area is primarily the development of next-generation antimicrobial agents through selective, rational chemical modification of AMPs. The review further serves as a guide toward the most promising directions in this field to stimulate broad scientific attention, and will lead to new, effective and selective solutions for the several biomedical challenges to which antimicrobial peptidomimetics are being applied.

Lysine Fatty Acylation: Regulatory Enzymes, Research Tools, and Biological Function

Post-translational acylation of lysine side chains is a common mechanism of protein regulation. Modification by long-chain fatty acyl groups is an understudied form of lysine acylation that has gained increasing attention recently due to the characterization of enzymes that catalyze the addition and removal this modification. In this review we summarize what has been learned about lysine fatty acylation in the approximately 30 years since its initial discovery. We report on what is known about the enzymes that regulate lysine fatty acylation and their physiological functions, including tumorigenesis and bacterial pathogenesis. We also cover the effect of lysine fatty acylation on reported substrates. Generally, lysine fatty acylation increases the affinity of proteins for specific cellular membranes, but the physiological outcome depends greatly on the molecular context. Finally, we will go over the experimental tools that have been used to study lysine fatty acylation. While much has been learned about lysine fatty acylation since its initial discovery, the full scope of its biological function has yet to be realized.

Discovery of lipid profiles of type 2 diabetes associated with hyperlipidemia using untargeted UPLC Q-TOF/MS-based lipidomics approach

The incidence of type 2 diabetes (T2D) is rising rapidly and has become an important public health problem. According to reports, people with T2D often have hyperlipidemia. Hence, in the current study, a plasma non-targeted lipidomics method was used to study the differences in lipid profile between 36 T2D-associated hyperlipidemia patients and 43 healthy controls by ultra-performance liquid chromatography coupled with quadrupole time-of-flight high-definition mass spectrometry (UPLC Q-TOF/MS). Furthermore, we studied the differences in lipid profile between 36 T2D-associated hyperlipidemia patients and 41 T2D patients. Principal component analysis (PCA), orthogonal partial least squares-discriminant analysis (OPLS-DA), S-plot and heatmap were used to analyze the lipid changes between the groups. Compared with the healthy control group, 37 lipids were significantly altered in the T2D-associated hyperlipidemia group, and when compared with the T2D group, 22 lipids were significantly altered in the T2D-associated hyperlipidemia group. Of all the detected lipids categories which included sphingolipids, glycerolipids, glycerophospholipids, prenol lipids and saccharolipids, glycerophospholipids accounted for the largest proportion in the two groups. Also, this study found that glycerophospholipid metabolism pathway was the most relevant pathway for these lipid metabolisms. The identified lipids may enhance the disease prediction and provide a new tool to monitor the progression of T2D-associated hyperlipidemia.

Zebrafish as a Model for the Study of Lipid-Lowering Drug-Induced Myopathies

Drug-induced myopathies are classified as acquired myopathies caused by exogenous factors. These pathological conditions develop in patients without muscle disease and are triggered by a variety of medicaments, including lipid-lowering drugs (LLDs) such as statins, fibrates, and ezetimibe. Here we summarise the current knowledge gained via studies conducted using various models, such as cell lines and mammalian models, and compare them with the results obtained in zebrafish (Danio rerio) studies. Zebrafish have proven to be an excellent research tool for studying dyslipidaemias as a model of these pathological conditions. This system enables in-vivo characterization of drug and gene candidates to further the understanding of disease aetiology and develop new therapeutic strategies. Our review also considers important environmental issues arising from the indiscriminate use of LLDs worldwide. The widespread use and importance of drugs such as statins and fibrates justify the need for the meticulous study of their mechanism of action and the side effects they cause.

Site-Specific Lipidation Enhances IFITM3 Membrane Interactions and Antiviral Activity

Interferon-induced transmembrane proteins (IFITMs) are S-palmitoylated proteins in vertebrates that restrict a diverse range of viruses. S-palmitoylated IFITM3 in particular engages incoming virus particles, prevents their cytoplasmic entry, and accelerates their lysosomal clearance by host cells. However, how S-palmitoylation modulates the structure and biophysical characteristics of IFITM3 to promote its antiviral activity remains unclear. To investigate how site-specific S-palmitoylation controls IFITM3 antiviral activity, we employed computational, chemical, and biophysical approaches to demonstrate that site-specific lipidation of cysteine 72 enhances the antiviral activity of IFITM3 by modulating its conformation and interaction with lipid membranes. Collectively, our results demonstrate that site-specific S-palmitoylation of IFITM3 directly alters its biophysical properties and activity in cells to prevent virus infection.

Rationale for the use of metformin and exercise to counteract statin-associated side effects

INTRODUCTION

Statins are the most widely prescribed drugs for lowering low-density lipoprotein cholesterol (LDL-C) and reducing cardiovascular morbidity and mortality. They are usually well-tolerated, but have two main safety concerns: statin-associated muscle symptoms (SAMS) and new-onset type 2 diabetes (NOD).

METHODS

A PubMed search was carried out using the following key words were used: statins, statin-associated muscle symptoms, statin myalgia, statin-associated diabetes, metformin and statins, exercise and statins.

RESULTS

Mitochondrial damage and muscle atrophy are likely the central mechanisms producing SAMS, whereas decreased glucose transport, fatty acid oxidation and insulin secretion are likely involved in the development of NOD. Metformin and exercise training share many pathways that could potentially contrast SAMS and NOD. Clinical evidence also supports the combination of statins with metformin and exercise.

CONCLUSION

This combination appears attractive both from a clinical and an economical viewpoint, since all three therapies are highly cost-effective and their combination could result in diabetes and cardiovascular disease prevention.

Selective axonal translation of the mRNA isoform encoding prenylated Cdc42 supports axon growth

The small Rho-family GTPase Cdc42 has long been known to have a role in cell motility and axon growth. The eukaryotic Ccd42 gene is alternatively spliced to generate mRNAs with two different 3' untranslated regions (UTRs) that encode proteins with distinct C-termini. The C-termini of these Cdc42 proteins include CaaX and CCaX motifs for post-translational prenylation and palmitoylation, respectively. Palmitoyl-Cdc42 protein was previously shown to contribute to dendrite maturation, while the prenyl-Cdc42 protein contributes to axon specification and its mRNA was detected in neurites. Here, we show that the mRNA encoding prenyl-Cdc42 isoform preferentially localizes into PNS axons and this localization selectively increases in vivo during peripheral nervous system (PNS) axon regeneration. Functional studies indicate that prenyl-Cdc42 increases axon length in a manner that requires axonal targeting of its mRNA, which, in turn, needs an intact C-terminal CaaX motif that can drive prenylation of the encoded protein. In contrast, palmitoyl-Cdc42 has no effect on axon growth but selectively increases dendrite length. Together, these data show that alternative splicing of the Cdc42 gene product generates an axon growth promoting, locally synthesized prenyl-Cdc42 protein. This article has an associated First Person interview with one of the co-first authors of the paper.

The Cys Sense: Thiol Redox Switches Mediate Life Cycles of Cellular Proteins

Protein homeostasis is an essential component of proper cellular function; however, sustaining protein health is a challenging task, especially during the aerobic lifestyle. Natural cellular oxidants may be involved in cell signaling and antibacterial defense; however, imbalanced levels can lead to protein misfolding, cell damage, and death. This merges together the processes of protein homeostasis and redox regulation. At the heart of this process are redox-regulated proteins or thiol-based switches, which carefully mediate various steps of protein homeostasis across folding, localization, quality control, and degradation pathways. In this review, we discuss the "redox code" of the proteostasis network, which shapes protein health during cell growth and aging. We describe the sources and types of thiol modifications and elaborate on diverse strategies of evolving antioxidant proteins in proteostasis networks during oxidative stress conditions. We also highlight the involvement of cysteines in protein degradation across varying levels, showcasing the importance of cysteine thiols in proteostasis at large. The individual examples and mechanisms raised open the door for extensive future research exploring the interplay between the redox and protein homeostasis systems. Understanding this interplay will enable us to re-write the redox code of cells and use it for biotechnological and therapeutic purposes.

Genome-Wide Identification and Characterization of Calcium-Dependent Protein Kinase (CDPK) and CDPK-Related Kinase (CRK) Gene Families in Medicago truncatula

Calcium-dependent protein kinase (CDPK or CPK) and CDPK-related kinase (CRK) play an important role in plant growth, development, and adaptation to environmental stresses. However, their gene families had been yet inadequately investigated in Medicago truncatula. In this study, six MtCRK genes were computationally identified, they were classified into five groups with MtCDPKs based on phylogenetic relationships. Six pairs of segmental duplications were observed in MtCDPK and MtCRK genes and the Ka/Ks ratio, an indicator of selection pressure, was below 0.310, indicating that these gene pairs underwent strong purifying selection. Cis-acting elements of morphogenesis, multiple hormone responses, and abiotic stresses were predicted in the promoter region. The spatial expression of MtCDPKs and MtCRKs displays diversity. The expression of MtCDPKs and MtCRKs could be regulated by various stresses. MtCDPK4, 14, 16, 22, and MtCRK6 harbor both N-myristoylation site and palmitoylation site and were anchored on plasma membrane, while MtCDPK7, 9, and 15 contain no or only one N-acylation site and were distributed in cytosol and nucleus, suggesting that the N-terminal acylation sites play a key role in subcellular localization of MtCDPKs and MtCRKs. In summary, comprehensive characterization of MtCDPKs and MtCRKs provide a subset of candidate genes for further functional analysis and genetic improvement against drought, cold, salt and biotic stress.

Fast Diffusion Sustains Plasma Membrane Accumulation of Phosphatase of Regenerating Liver-1

It has been proposed that the accumulation of farnesylated phosphatase of regenerating liver-1 (PRL-1) at the plasma membrane is mediated by static electrostatic interactions of a polybasic region with acidic membrane lipids and assisted by oligomerization. Nonetheless, localization at early and recycling endosomes suggests that the recycling compartment might also contribute to its plasma membrane accumulation. Here, we investigated in live cells the dynamics of PRL-1 fused to the green fluorescent protein (GFP-PRL-1). Blocking the secretory pathway and photobleaching techniques suggested that plasma membrane accumulation of PRL-1 was not sustained by recycling endosomes but by a dynamic exchange of diffusible protein pools. Consistent with this idea, fluorescence correlation spectroscopy in cells overexpressing wild type or monomeric mutants of GFP-PRL-1 measured cytosolic and membrane-diffusing pools of protein that were not dependent on oligomerization. Endogenous expression of GFP-PRL-1 by CRISPR/Cas9 genome edition confirmed the existence of fast diffusing cytosolic and membrane pools of protein. We propose that plasma membrane PRL-1 replenishment is independent of the recycling compartment and the oligomerization state and mainly driven by fast diffusion of the cytosolic pool.

Regional similarities and differences in mature human milk fatty acids in Chinese population: A systematic review

Maternal factors such as the diet can impact human milk fatty acid profiles. We hypothesized that mature human milk fatty acid profiles differ among regions of China. To test our hypothesis, we conducted a systematic review to calculate regional average contents of fatty acids and the statistical significance of regional differences in fatty acids. We searched both Chinese and English literature databases and selected 21 articles, including 11 in Chinese and 10 in English. We categorized regions of China by 3 ways: 1) north vs. south; 2) inland vs. coastal; 3) socioeconomic development levels. The ratios of ΣSFAs:ΣMUFAs:ΣPUFAs were similar between regions and the average was 1:1:0.7. Contents of palmitic, oleic, and linoleic acids were also similar between regions and together they accounted for more than 70% of all fatty acids in mature human milk. Conversely, concentrations of ALA and DHA differed more than palmitic, oleic, and linoleic acids. We also found that it might be necessary to reduce maternal dietary contents of potentially harmful fatty acids such as erucic acid to minimize detrimental effects on infant health. To our knowledge, this study represents the first systematic review that quantitatively investigated the regional similarities and differences in mature human milk fatty acid contents and is therefore significant for academia and policy makers.

The emerging roles of ZDHHCs-mediated protein palmitoylation in the antiviral innate immune responses

Post-translational modifications (PTMs) play a pivotal role in expanding functional protein diversity. During viral infection, pathogen-associated molecular patterns derived from viruses are recognized by pattern recognition receptors present in the membrane surface and the cytoplasm of infected cells, which subsequently induces the antiviral innate immunity to protect the host from the invading viruses. Fatty acylation modification is identified as a post-translation lipid modification process. Mounting evidence is presented that lipid modification functions as a novel regulatory mechanism of antiviral innate immunity. In mammalian cells, DHHC (Asp-His-His-Cys) domain is indispensable for most of the palmitoylation modification, which belongs to fatty acylation. ZDHHC family proteins are composed of 23 members in human cells. In this review, we will summarize the recent findings of the regulatory mechanism of the palmitoylation in the process of host antiviral innate immunity against viruses.

TFG-maintaining stability of overlooked FANCD2 confers early DNA-damage response

Emerging Fanconi Anemia (FA) signaling in the field of cancer research annotates the extreme importance of its center player, Fanconi Anemia complementation group D2 (FANCD2) in protecting human cells from going awry. However, a previously-unrecognized form of FANCD2, namely FANCD2-V2, is understudied. We report TRK-Fused Gene (TFG) is critical for roles played by FANCD2-V2 in early responses to DNA damage, but not for FANCD2-V1, the long-known form of FANCD2. FANCD2-V2 forms nuclear foci upon DNA damage, and both its focus appearance and disappearance are earlier than FANCD2-V1. The amino acid/aa 5-100 of TFG and the aa1437-1442 of FANCD2-V2 were identified to contribute to their interaction, which maintains the steady-state level of FANCD2-V2 protein. TFGΔaa5-100 or FANCD2-V2Δaa1437-1442-carrying cells could not show timely focus formation of FANCD2-V2 upon DNA damage and gained carcinogenicity over time. This study provides a previously-unknown key to unlock in-depth insights into maintaining genome stability, fostering translational studies on preventing, diagnosing and/or treating related diseases.

The Roles of Histone Deacetylases and Their Inhibitors in Cancer Therapy

Genetic mutations and abnormal gene regulation are key mechanisms underlying tumorigenesis. Nucleosomes, which consist of DNA wrapped around histone cores, represent the basic units of chromatin. The fifth amino group (Nε) of histone lysine residues is a common site for post-translational modifications (PTMs), and of these, acetylation is the second most common. Histone acetylation is modulated by histone acetyltransferases (HATs) and histone deacetylases (HDACs), and is involved in the regulation of gene expression. Over the past two decades, numerous studies characterizing HDACs and HDAC inhibitors (HDACi) have provided novel and exciting insights concerning their underlying biological mechanisms and potential anti-cancer treatments. In this review, we detail the diverse structures of HDACs and their underlying biological functions, including transcriptional regulation, metabolism, angiogenesis, DNA damage response, cell cycle, apoptosis, protein degradation, immunity and other several physiological processes. We also highlight potential avenues to use HDACi as novel, precision cancer treatments.

CD36 facilitates fatty acid uptake by dynamic palmitoylation-regulated endocytosis

Fatty acids (FAs) are essential nutrients, but how they are transported into cells remains unclear. Here, we show that FAs trigger caveolae-dependent CD36 internalization, which in turn delivers FAs into adipocytes. During the process, binding of FAs to CD36 activates its downstream kinase LYN, which phosphorylates DHHC5, the palmitoyl acyltransferase of CD36, at Tyr91 and inactivates it. CD36 then gets depalmitoylated by APT1 and recruits another tyrosine kinase SYK to phosphorylate JNK and VAVs to initiate endocytic uptake of FAs. Blocking CD36 internalization by inhibiting APT1, LYN or SYK abolishes CD36-dependent FA uptake. Restricting CD36 at either palmitoylated or depalmitoylated state eliminates its FA uptake activity, indicating an essential role of dynamic palmitoylation of CD36. Furthermore, blocking endocytosis by targeting LYN or SYK inhibits CD36-dependent lipid droplet growth in adipocytes and high-fat-diet induced weight gain in mice. Our study has uncovered a dynamic palmitoylation-regulated endocytic pathway to take up FAs.