Regulatory Role of Free Fatty Acids (FFAs)—Palmitoylation and Myristoylation

Multicellular organisms use chemical messengers to transmit signals among organelles and to other cells. Relatively small hydrophobic molecules such as lipids are excellent candidates for this signaling purpose. In most proteins, palmitic acid and other saturated and some unsaturated fatty acids are esterified to the free thiol of cysteines and to the N-amide terminal. This palmitoylation process enhances the surface hydrophobicity and membrane affinity of protein substrates and plays important roles in modulating proteins’ trafficking, stability, and sorting etc. Protein palmitoylation has been involved in numerous cellular processes, including signaling, apoptosis, and neuronal transmission. The palmitoylation process is involved in multiple diseases such as Huntington’s disease, various cardiovascular and T-cell mediated immune disorders, as well as cancer. Protein palmitoylation through the thioester (S-acylation) is unique in that it is the only reversible lipid modification. Our study on lipopolysaccharide (LPS) and deoxynivalenol (DON) treatment to rats provides some insights to the complex role of protein palmitoylation in chemical and microbial toxicity. In contrast, myrisoylated proteins contain the 14-carbon fatty acid myristate attached via amide linkage to the N-terminal glycine residue of protein, and occur cotranslationally. The bacterial outer membrane enzyme lipid A palmitoyltransferase (PagP) confers resistance to host immune defenses by transferring a palmitate chain from a phospholipid to the lipid A component of LPS. PagP is sensitive to cationic antimicrobial peptides (CAMP) which are included among the products of the Toll-like receptor 4 (TLR4) signal transduction pathway. This modification of lipid A with a palmitate appears to both and protects the pathogenic bacteria from host immune defenses and attenuates the activation of those same defenses through the TLR4 signal transduction pathway.

Nucieocytoplasmic Shuttling of Geminivirus C4 Protein Mediated by Phosphorylation and Myristoylation Is Critical for Viral Pathogenicity

Many geminivirus C4 proteins induce severe developmental abnormalities in plants.We previously demon- strated that Tomato leaf curl Yunnan virus (TLCYnV)C4 induces plant developmental abnormalities at least partically by decreasing the accumulation of NbSKη,an ortholog of Arabidopsis BIN2 kinase involved in the brassinosteroid signaling pathway,in the nucleus through directing it to the plasma membrane.However, the molecular mechanism by which the membrane-associated C4 modifies the localization of NbSKη in the host cell remains unclear.Here,we show that TLCYnV C4 is a nucleocytoplasmic shuttle protein,and that C4 shuttling is accompanied by nuclear export of NbSKTI.TLCYnV C4 is phosphorylated by NbSKη in the nucleus,which promotes myristoylation of the viral protein.Myristoylation of phosphorylated C4 favors its interaction with exportin-α(XPO I);which in turn facilitates nuclear export of the C4/NbSKTI complex. Supporting this model,chemical inhibition of N-myristoyltransferases or exportin-α enhanced nuclear retention of C4,and mutations of the putative phosphorylation or myristoylation sites in C4 resulted in increased nuclear retention ofrC4 and thus decreased severity of C4-induced developmental abnormalities. The impact of C4 on development is also lessened when a nuclear localization signal or a nuclear export signal is added to its C-terminus,restricting it to a specific cellular niche and therefore impairing nucleocytoplasmic shuttling.Taken together,our results suggest that nucleocytoplasmic shuttling of TLCYnV C4,enabled by phosphorylation by NbSKη,myristoylation,and interaction with exportin-α is critical for its function as a pathogenicity factor.

Protein N-myristoylation:functions and mechanisms in control of innate immunity

Protein N-myristoylation is an important fatty acylation catalyzed by N-myristoyltransferases(NMTs),which are ubiquitous enzymes in eukaryotes.Specifically,attachment of a myristoyl group is vital for proteins participating in various biological functions,including signal transduction,cellular localization,and oncogenesis.Recent studies have revealed unexpected mechanisms indicating that protein N-myristoylation is involved in host defense against microbial and viral infections.In this review,we describe the current understanding of protein N-myristoylation(mainly focusing on myristoyl switches)and summarize its crucial roles in regulating innate immune responses,including TLR4-dependent inflammatory responses and demyristoylation-induced innate immunosuppression during Shigella flexneri infection.Furthermore,we examine the role of myristoylation in viral assembly,intracellular host interactions,and viral spread during human immunodeficiency virus-1(HIV-1)infection.Deeper insight into the relationship between protein N-myristoylation and innate immunity might enable us to clarify the pathogenesis of certain infectious diseases and better harness protein N-myristoylation for new therapeutics.

Myristoylation of EV71 VP4 is Essential for Infectivity and Interaction with Membrane Structure

The Enterovirus 71(EV71)VP4 is co-translationally linked to myristic acid at its amino-terminal glycine residue.However,the role of this myristoylation in the EV71 life cycle remains largely unknown.To investigate this issue,we developed a myristoylation-deficient virus and reporter(luciferase)pseudovirus with a Gly-to-Ala mutation(G2A)on EV71 VP4.When transfecting the EV71-G2 A genome encoding plasmid in cells,the loss of myristoylation on VP4 did not affect the expression of viral proteins and the virus morphology,however,it did significantly influence viral infectivity.Further,in myristoylation-deficient reporter pseudovirus-infected cells,the luciferase activity and viral genome RNA decreased significantly as compared to that of wild type virus;however,cytopathic effect and viral capsid proteins were not detected in myristoylation-deficient virus-infected cells.Also,although myristoylation-deficient viral RNA and proteins were detected in the second blind passage of infection,they were much fewer in number compared to that of the wild type virus.The replication of genomic RNA and negative-strand viral RNA were both blocked in myristoylation-deficient viruses,suggesting that myristoylation affects viral genome RNA release from capsid to cytoplasm.Besides,loss of myristoylation on VP4 altered the distribution of VP4-green fluorescent protein protein,which disappeared from the membrane structure fraction.Finally,a liposome leakage assay showed that EV71 myristoylation mediates the permeability of the model membrane.Hence,the amino-terminal myristoylation of VP4 is pivotal to EV71 infection and capsidmembrane structure interaction.This study provides novel molecular mechanisms regarding EV71 infection and potential molecular targets for antiviral drug design.

LINC01268 promotes epithelial-mesenchymal transition,invasion and metastasis of gastric cancer via the PI3K/Akt signaling pathway and targeting MARCKS

BACKGROUND Long non-coding RNAs(lncRNAs)with differential expression characteristics have been found to be closely related to the tumorigenesis and development of gastric cancer(GC),but their specific mechanisms and roles still need to be further elucidated.AIM To investigate the expression of LINC01268 in GC and its mechanism of affecting GC progression.METHODS Real-time quantitative polymerase chain reaction was used to detect the expression of LINC01268 in GC tissues,cell lines and plasma.The Kaplan-Meier method was used to evaluate the value of LINC01268 in the prognostication of GC patients.An receiver operating characteristic curve was constructed to evaluate the value of LINC01268 in the diagnosis of GC.Transwell migration and invasion assays and wound healing assays were used to confirm the effect of LINC01268 on the invasion and migration of GC cells.The regulatory relationship between LINC01268 and myristoylated alanine rich protein kinase C substrate(MARCKS),the PI3K/Akt signaling pathway,and the epithelial-mesenchymal transition(EMT)process in GC was demonstrated by western blot analysis.RESULTS The expression of LINC01268 was increased in GC tissues and cell lines.The expression level of LINC01268 was significantly correlated with lymph node metastasis,TNM stage,and tumor differentiation in patients with GC.Over-expression of LINC01268 indicated a poor prognosis for patients with GC,and it had a certain auxiliary diagnostic value for GC.In vitro functional experiments proved that the abnormal expression of LINC01268 further activated the PI3K/Akt signaling pathway and promoted EMT by targeting and regulating MARCKS and ultimately promoted the invasion and metastasis of GC.CONCLUSION This study elucidates that LINC01268 in GC may be an oncogene that further activates the PI3K/Akt signaling pathway and EMT by targeting and regulating MARCKS,and ultimately promotes the invasion and metastasis of GC.LINC01268 may be a potential effective target for the treatment of GC.

Role of Free Fatty Acids in Physiological Conditions and Mitochondrial Dysfunction

The role of free fatty acids (FFAs) as a source of energy and their functions in energy transport within the body are well established. Equally important is a role that FFAs play in oxidative stress following cell membrane depolarization. FFAs are physiologically active, not only as nutritional components, but also as molecules involved in cell signaling and stabilization of membranes via palmitoylation and myristoylation. Protein palmitoylation is involved in numerous cellular processes, including apoptosis, and neuronal transmission. Besides nuclear peroxisome proliferator-activated receptors that mediate the biological effects of FFAs, G protein-coupled receptors (GPCRs) that are activated by FFA, have been recently identified. Those multiple FFA receptors (FFARs), which function on the cell surface as activated FFAs, play significant roles in the regulation of energy metabolism and mediate a wide range of important metabolic processes. FFARs have been targeted in drug development for the treatment of type 2 diabetes and metabolic syndrome. FFAs upregulate transcription of uncoupling proteins, increasing their expression in brain, cardiac, and skeletal muscle that may be protective or cytotoxic, depending on the cellular energy state. Recently, FFA effects on the endothelial function and dysfunction are being recognized. FFAs play a key role in endothelium-dependent nitric oxide production. A disturbance of endothelial function, due to an imbalance in production and release of relaxing and constricting factors, has implications in the development of cardiovascular problems, such as hypertension, as well as neurotoxicity following loss of blood-brain barrier integrity. This review presents information on broad range of FFAs actions of prime importance for physiological processes. Understanding of FFA functions in the body is crucial for developing new therapeutic strategies against several metabolic disorders.

Reciprocal regulation between lunapark and atlastin facilitates ER three-way junction formation

Three-way junctions are characteristic structures of the tubular endoplasmic reticulum (ER) network. Junctions are formed through atlastin (ATL)-mediated membrane fusion and stabilized by lunapark (Lnp). However, how Lnp is preferentially enriched at three-way junctions remains elusiveHere, we showed that Lnp loses its junction localization when ATLs are deleted. Reintroduction of ATL1 R77A and ATL3, which have been shown to cluster at the junctions, but not wild-type ATL1, relocates Lnp to the junctions. Mutations in the Nmyristoylation site or hydrophobic residues in the coiled coil (CC1) of Lnp N-terminus (NT) cause mis-targeting of LnpConversely, deletion of the lunapark motif in the C-terminal zinc fin ger domain, which affects the homooligomerization of Lnp, does not alter its localizationPurified Lnp-NT attaches to the membrane in a myristoylation- dependent manner. The mutation of hydrophobic residues in CC1 does not affect membrane association, but compromises ATL interactionsIn addition, Lnp-NT inhibits ATL-mediated vesicle fusion in vitro. These results suggest that CC1 in Lnp-NT contacts junction-enriched ATLs for proper localization;subsequently, further ATL activity is limited by Lnp after the junction is formed. The proposed mechanism ensures coordinated actions of ATL and Lnp in generating and maintaining three-way junctions.