Therapeutic intervention based on protein prenylation and associated modifications

Treatment of a mutant KRAS lung cancer cell line with polyisoprenylated cysteinyl amide inhibitors activates the MAPK pathway, inhibits cell migration and induces apoptosis

KRAS mutations are the most common oncogenic mutations in lung adenocarcinoma in Black Americans. Polyisoprenylated Cysteinyl amide Inhibitors (PCAIs) constitute a group of potential cancer therapy agents that we designed to specifically disrupt and suppress hyperactive G-protein signaling, such as that caused by mutated RAS proteins. Here we determine the effects of PCAIs on the viability, G-protein levels, downstream mediators, and apoptosis-related proteins on the KRAS-mutated, Black American-derived lung adenocarcinoma cell line, NCI-H23. Of the 17 PCAIs tested, compounds NSL-YHJ-2-27 and NSL-YHJ-2-46 showed the most potency with EC50 values of 2.7 and 3.3 μM, respectively. Western blotting was used to determine the effect of the PCAIs on the phosphorylation levels of MAPK pathway enzymes. After 48 h exposure to 5 μM of the PCAIs, NSL-YHJ-2-46, the MAPK proteins BRAF, MEK1/2, ERK1/2, and p90RSK were activated through phosphorylation by 90, 190, 150 and 120%, respectively. However, CRAF/RAF1 phosphorylation decreased by 40%, suggesting significant changes in the KRAS/MAPK signaling patterns. Furthermore, 5 μM of NSL-YHJ-2-27 depleted the singly polyisoprenylated monomeric G-proteins RAC 1/2/3 and CDC42 by 77 and 76%, respectively. The depletion of these key cytoskeletal proteins may account for the observed inhibition of cell migration and invasion, and spheroid invasion observed on exposure to NSL-YHJ-2-27 and NSL-YHJ-2-46. Treatment with 5 μM of NSL-YHJ-2-27 suppressed full-length inactive caspase 3 and 7 levels by 72 and 91%, respectively. An analysis of cells treated with the fluorescently labeled active caspase 3/7 irreversible inhibitor, CaspaTagTM Caspase-3/7 in situ reagent revealed a 124% increase in active caspase at 3 μM over controls. These findings clearly show the direct effects of the PCAIs on the RAS signaling pathway. Given the profound increases observed in RPS6KA1/p90RSK phosphorylation, future work will involve a determination whether the proapoptotic isoforms of RPS6KA1/p90RSK are phosphorylated due to the PCAIs treatments. These results support the potential use of the PCAIs as targeted therapies against cancers with KRAS mutations.

Targeting the RAS upstream and downstream signaling pathway for cancer treatment

Cancer often involves the overactivation of RAS/RAF/MEK/ERK (MAPK) and PI3K-Akt-mTOR pathways due to mutations in genes like RAS, RAF, PTEN, and PIK3CA. Various strategies are employed to address the overactivation of these pathways, among which targeted therapy emerges as a promising approach. Directly targeting specific proteins, leads to encouraging results in cancer treatment. For instance, RTK inhibitors such as imatinib and afatinib selectively target these receptors, hindering ligand binding and reducing signaling initiation. These inhibitors have shown potent efficacy against Non-Small Cell Lung Cancer. Other inhibitors, like lonafarnib targeting Farnesyltransferase and GGTI 2418 targeting geranylgeranyl Transferase, disrupt post-translational modifications of proteins. Additionally, inhibition of proteins like SOS, SH2 domain, and Ras demonstrate promising anti-tumor activity both in vivo and in vitro. Targeting downstream components with RAF inhibitors such as vemurafenib, dabrafenib, and sorafenib, along with MEK inhibitors like trametinib and binimetinib, has shown promising outcomes in treating cancers with BRAF-V600E mutations, including myeloma, colorectal, and thyroid cancers. Furthermore, inhibitors of PI3K (e.g., apitolisib, copanlisib), AKT (e.g., ipatasertib, perifosine), and mTOR (e.g., sirolimus, temsirolimus) exhibit promising efficacy against various cancers such as Invasive Breast Cancer, Lymphoma, Neoplasms, and Hematological malignancies. This review offers an overview of small molecule inhibitors targeting specific proteins within the RAS upstream and downstream signaling pathways in cancer.

De Novo Discovery of Pseudo-Natural Prenylated Macrocyclic Peptide Ligands

Prenylation of peptides is widely observed in the secondary metabolites of diverse organisms, granting peptides unique chemical properties distinct from proteinogenic amino acids. Discovery of prenylated peptide agents has largely relied on isolation or genome mining of naturally occurring molecules. To devise a platform technology for de novo discovery of artificial prenylated peptides targeting a protein of choice, here we have integrated the thioether-macrocyclic peptide (teMP) library construction/selection technology, so-called RaPID (Random nonstandard Peptides Integrated Discovery) system, with a Trp-C3-prenyltransferase KgpF involved in the biosynthesis of a prenylated natural product. This unique enzyme exhibited remarkably broad substrate tolerance, capable of modifying various Trp-containing teMPs to install a prenylated residue with tricyclic constrained structure. We constructed a vast library of prenylated teMPs and subjected it to in vitro selection against a phosphoglycerate mutase. This selection platform has led to the identification of a pseudo-natural prenylated teMP inhibiting the target enzyme with an IC50 of 30 nM. Importantly, the prenylation was essential for the inhibitory activity, enhanced serum stability, and cellular uptake of the peptide, highlighting the benefits of peptide prenylation. This work showcases the de novo discovery platform for pseudo-natural prenylated peptides, which is readily applicable to other drug targets.

Discovery of YAP1/TAZ pathway inhibitors through phenotypic screening with potent anti-tumor activity via blockade of Rho-GTPase signaling

This study describes the identification and target deconvolution of small molecule inhibitors of oncogenic Yes-associated protein (YAP1)/TAZ activity with potent anti-tumor activity in vivo. A high-throughput screen (HTS) of 3.8 million compounds was conducted using a cellular YAP1/TAZ reporter assay. Target deconvolution studies identified the geranylgeranyltransferase-I (GGTase-I) complex as the direct target of YAP1/TAZ pathway inhibitors. The small molecule inhibitors block the activation of Rho-GTPases, leading to subsequent inactivation of YAP1/TAZ and inhibition of cancer cell proliferation in vitro. Multi-parameter optimization resulted in BAY-593, an in vivo probe with favorable PK properties, which demonstrated anti-tumor activity and blockade of YAP1/TAZ signaling in vivo.

Protein lipidation in health and disease: molecular basis, physiological function and pathological implication

Posttranslational modifications increase the complexity and functional diversity of proteins in response to complex external stimuli and internal changes. Among these, protein lipidations which refer to lipid attachment to proteins are prominent, which primarily encompassing five types including S-palmitoylation, N-myristoylation, S-prenylation, glycosylphosphatidylinositol (GPI) anchor and cholesterylation. Lipid attachment to proteins plays an essential role in the regulation of protein trafficking, localisation, stability, conformation, interactions and signal transduction by enhancing hydrophobicity. Accumulating evidence from genetic, structural, and biomedical studies has consistently shown that protein lipidation is pivotal in the regulation of broad physiological functions and is inextricably linked to a variety of diseases. Decades of dedicated research have driven the development of a wide range of drugs targeting protein lipidation, and several agents have been developed and tested in preclinical and clinical studies, some of which, such as asciminib and lonafarnib are FDA-approved for therapeutic use, indicating that targeting protein lipidations represents a promising therapeutic strategy. Here, we comprehensively review the known regulatory enzymes and catalytic mechanisms of various protein lipidation types, outline the impact of protein lipidations on physiology and disease, and highlight potential therapeutic targets and clinical research progress, aiming to provide a comprehensive reference for future protein lipidation research.

An updated review of chemical compounds with anti-Toxoplasma gondii activity

The opportunistic apicomplexan parasite Toxoplasma gondii is the etiologic agent for toxoplasmosis, which can infect a widespread range of hosts, particularly humans and warm-blooded animals. The present chemotherapy to treat or prevent toxoplasmosis is deficient and is based on diverse drugs such as atovaquone, trimethoprim, spiramycine, which are effective in acute toxoplasmosis. Therefore, a safe chemotherapy is required for toxoplasmosis considering that its responsible agent, T. gondii, provokes severe illness and death in pregnant women and immunodeficient patients. A certain disadvantage of the available treatments is the lack of effectiveness against the tissue cyst of the parasite. A safe chemotherapy to combat toxoplasmosis should be based on the metabolic differences between the parasite and the mammalian host. This article covers different relevant molecular targets to combat this disease including the isoprenoid pathway (farnesyl diphosphate synthase, squalene synthase), dihydrofolate reductase, calcium-dependent protein kinases, histone deacetylase, mitochondrial electron transport chain, etc.

CaaX-motif-adjacent residues influence G protein gamma (Gγ) prenylation under suboptimal conditions

Prenylation is an irreversible post-translational modification that supports membrane interactions of proteins involved in various cellular processes, including migration, proliferation, and survival. Dysregulation of prenylation contributes to multiple disorders, including cancers and vascular and neurodegenerative diseases. Prenyltransferases tether isoprenoid lipids to proteins via a thioether linkage during prenylation. Pharmacological inhibition of the lipid synthesis pathway by statins is a therapeutic approach to control hyperlipidemia. Building on our previous finding that statins inhibit membrane association of G protein γ (Gγ) in a subtype-dependent manner, we investigated the molecular reasoning for this differential inhibition. We examined the prenylation of carboxy-terminus (Ct) mutated Gγ in cells exposed to Fluvastatin and prenyl transferase inhibitors and monitored the subcellular localization of fluorescently tagged Gγ subunits and their mutants using live-cell confocal imaging. Reversible optogenetic unmasking-masking of Ct residues was used to probe their contribution to prenylation and membrane interactions of the prenylated proteins. Our findings suggest that specific Ct residues regulate membrane interactions of the Gγ polypeptide, statin sensitivity, and extent of prenylation. Our results also show a few hydrophobic and charged residues at the Ct are crucial determinants of a protein's prenylation ability, especially under suboptimal conditions. Given the cell and tissue-specific expression of different Gγ subtypes, our findings indicate a plausible mechanism allowing for statins to differentially perturb heterotrimeric G protein signaling in cells depending on their Gγ-subtype composition. Our results may also provide molecular reasoning for repurposing statins as Ras oncogene inhibitors and the failure of using prenyltransferase inhibitors in cancer treatment.

CaaX-motif adjacent residues control G protein prenylation under suboptimal conditions

Prenylation is a universal and irreversible post-translational modification that supports membrane interactions of proteins involved in various cellular processes, including migration, proliferation, and survival. Thus, dysregulation of prenylation contributes to multiple disorders, including cancers, vascular diseases, and neurodegenerative diseases. During prenylation, prenyltransferase enzymes tether metabolically produced isoprenoid lipids to proteins via a thioether linkage. Pharmacological inhibition of the lipid synthesis pathway by statins has long been a therapeutic approach to control hyperlipidemia. Building on our previous finding that statins inhibit membrane association of G protein γ (Gγ) in a subtype-dependent manner, we investigated the molecular reasoning for this differential. We examined the prenylation efficacy of carboxy terminus (Ct) mutated Gγ in cells exposed to Fluvastatin and prenyl transferase inhibitors and monitored the subcellular localization of fluorescently tagged Gγ subunits and their mutants using live-cell confocal imaging. Reversible optogenetic unmasking-masking of Ct residues was used to probe their contribution to the prenylation process and membrane interactions of the prenylated proteins. Our findings suggest that specific Ct residues regulate membrane interactions of the Gγ polypeptide statin sensitivity, and prenylation efficacy. Our results also show that a few hydrophobic and charged residues at the Ct are crucial determinants of a protein's prenylation ability, especially under suboptimal conditions. Given the cell and tissue-specific expression of different Gγ subtypes, our findings explain how and why statins differentially perturb heterotrimeric G protein signaling in specific cells and tissues. Our results may provide molecular reasoning for repurposing statins as Ras oncogene inhibitors and the failure of using prenyltransferase inhibitors in cancer treatment.

Polyisoprenylated cysteinyl amide inhibitors deplete singly polyisoprenylated monomeric G-proteins in lung and breast cancer cell lines

Finding effective therapies against cancers driven by mutant and/or overexpressed hyperactive G-proteins remains an area of active research. Polyisoprenylated cysteinyl amide inhibitors (PCAIs) are agents that mimic the essential posttranslational modifications of G-proteins. It is hypothesized that PCAIs work as anticancer agents by disrupting polyisoprenylation-dependent functional interactions of the G-Proteins. This study tested this hypothesis by determining the effect of the PCAIs on the levels of RAS and related monomeric G-proteins. Following 48 h exposure, we found significant decreases in the levels of KRAS, RHOA, RAC1, and CDC42 ranging within 20-66% after NSL-YHJ-2-27 (5 μM) treatment in all four cell lines tested, A549, NCI-H1299, MDA-MB-231, and MDA-MB-468. However, no significant difference was observed on the G-protein, RAB5A. Interestingly, 38 and 44% decreases in the levels of the farnesylated and acylated NRAS were observed in the two breast cancer cell lines, MDA-MB-231, and MDA-MB-468, respectively, while HRAS levels showed a 36% decrease only in MDA-MB-468 cells. Moreover, after PCAIs treatment, migration, and invasion of A549 cells were inhibited by 72 and 70%, respectively while the levels of vinculin and fascin dropped by 33 and 43%, respectively. These findings implicate the potential role of PCAIs as anticancer agents through their direct interaction with monomeric G-proteins.

Analyzing the postulated inhibitory effect of Manumycin A on farnesyltransferase

Manumycin A is postulated to be a specific inhibitor against the farnesyltransferase (FTase) since this effect has been shown in 1993 for yeast FTase. Since then, plenty of studies investigated Manumycin A in human cells as well as in model organisms like Caenorhabditis elegans. Some studies pointed to additional targets and pathways involved in Manumycin A effects like apoptosis. Therefore, these studies created doubt whether the main mechanism of action of Manumycin A is FTase inhibition. For some of these alternative targets half maximal inhibitory concentrations (IC₅₀) of Manumycin A are available, but not for human and C. elegans FTase. So, we aimed to 1) characterize missing C. elegans FTase kinetics, 2) elucidate the IC₅₀ and K_i values of Manumycin A on purified human and C. elegans FTase 3) investigate Manumycin A dependent expression of FTase and apoptosis genes in C. elegans. C. elegans FTase has its temperature optimum at 40°C with K_M of 1.3 µM (farnesylpyrophosphate) and 1.7 µM (protein derivate). Whilst other targets are inhibitable by Manumycin A at the nanomolar level, we found that Manumycin A inhibits cell-free FTase in micromolar concentrations (K_{i human} 4.15 μM; K_{i C. elegans} 3.16 μM). Furthermore, our gene expression results correlate with other studies indicating that thioredoxin reductase 1 is the main target of Manumycin A. According to our results, the ability of Manumycin A to inhibit the FTase at the micromolar level is rather neglectable for its cellular effects, so we postulate that the classification as a specific FTase inhibitor is no longer valid.

Photoswitchable Isoprenoid Lipids Enable Optical Control of Peptide Lipidation

Photoswitchable lipids have emerged as attractive tools for the optical control of lipid bioactivity, metabolism, and biophysical properties. Their design is typically based on the incorporation of an azobenzene photoswitch into the hydrophobic lipid tail, which can be switched between its trans- and cis-form using two different wavelengths of light. While glycero- and sphingolipids have been successfully designed to be photoswitchable, isoprenoid lipids have not yet been investigated. Herein, we describe the development of photoswitchable analogs of an isoprenoid lipid and systematically assess their potential for the optical control of various steps in the isoprenylation processing pathway of CaaX proteins in Saccharomyces cerevisiae. One photoswitchable analog of farnesyl diphosphate (AzoFPP-1) allowed effective optical control of substrate prenylation by farnesyltransferase. The subsequent steps of isoprenylation processing (proteolysis by either Ste24 or Rce1 and carboxyl methylation by Ste14) were less affected by photoisomerization of the group introduced into the lipid moiety of the substrate a-factor, a mating pheromone from yeast. We assessed both proteolysis and methylation of the a-factor analogs in vitro and the bioactivity of a fully processed a-factor analog containing the photoswitch, exogenously added to cognate yeast cells. Combined, these data describe the first successful conversion of an isoprenoid lipid into a photolipid and suggest the utility of this approach for the optical control of protein prenylation.

Combining Isoprenoid Probes with Antibody Markers for Mass Cytometric Analysis of Prenylation in Single Cells

Protein prenylation is an essential post-translational modification that plays a key role in facilitating protein localization. Aberrations in protein prenylation have been indicated in multiple disease pathologies including progeria, some forms of cancer, and Alzheimer's disease. While there are single-cell methods to study prenylation, these methods cannot simultaneously assess prenylation and other cellular changes in the complex cell environment. Here, we report a novel method to monitor, at the single-cell level, prenylation and expression of autophagy markers. An isoprenoid analogue containing a terminal alkyne, substrate of prenylation enzymes, was metabolically incorporated into cells in culture. Treatment with a terbium reporter containing an azide functional group, followed by copper-catalyzed azide-alkyne cycloaddition, covalently attached terbium ions to prenylated proteins within cells. In addition, simultaneous treatment with a holmium-containing analogue of the reporter, without an azide functional group, was used to correct for non-specific retention at the single-cell level. This procedure was compatible with other mass cytometric sample preparation steps that use metal-tagged antibodies. We demonstrate that this method reports changes in levels of prenylation in competitive and inhibitor assays, while tracking autophagy molecular markers with metal-tagged antibodies. The method reported here makes it possible to track prenylation along with other molecular pathways in single cells of complex systems, which is essential to elucidate the role of this post-translational modification in disease, cell response to pharmacological treatments, and aging.

Overcoming chemoresistance in glioblastoma by fluvastatin via prenylation-dependent inhibition of Ras signaling

The resistance of glioblastoma to chemotherapy remains a significant clinical problem. Targeting alternative pathways such as protein prenylation is known to be effective against many cancers. Fluvastatin is a potent competitive inhibitor of 3-hydroxy-3-methylglutaryl- CoA (HMG-CoA) reductase, thereby inhibits prenylation. We demonstrate that fluvastatin alone effectively inhibits proliferation and induces apoptosis in multiple human glioblastoma cell lines. The combination index analysis shows that fluvastatin acts synergistically with common chemotherapy drugs for glioblastoma: temozolomide and irinotecan. We further show that fluvastatin acts on glioblastoma through inhibiting prenylation-dependent Ras activation. The combination of fluvastatin and low dose temozolomide resulted in remarkable inhibition of glioblastoma tumor in mice throughout the whole treatment duration without causing toxicity. Such combinatorial effects provide the basis for utilizing these FDA-approved drugs as a potential clinical approach in overcoming resistance and improving glioblastoma treatment.

Dual-Stage Neutral Loss Tandem Mass Spectrometric Strategy for Confident Identification of Protein Prenylation

Protein prenylation is an important post-translational modification that regulates protein interactions, localizations, and signaling pathways in normal functioning of eukaryotic cells. It is also a critical step in the oncogenic developments of various cancers. Direct identification of native protein prenylation by mass spectrometry (MS) has been challenging due to high hydrophobicity and the lack of an efficient enrichment technique. Prior MS studies of prenylation revealed that prenyl peptides readily generate high-intensity fragments after neutral loss of the prenyl group (R group), and more recent investigation of oxidized prenyl peptides discovered more consistent neutral loss of the oxidized prenyl group (RSOH group). Here, a dual-stage neutral loss MS³ (DS-NLMS3)-based strategy is therefore developed by combining both gas-phase cleavable properties of the prenyl thioether bond and mono-oxidized thioether to improve the large-scale identification of prenylation. Both neutral losses can individually and distinctively confirm the prenylation type in MS² and the sequence of the prenyl peptide upon targeted MS³ fragmentation. This dual-faceted NLMS3 strategy significantly improves the confidence in the identification of protein prenylation from large-scale samples, which enables the unambiguous identification of prenylated sites of the spiked low-abundance farnesyl peptide and native prenyl proteins from mouse macrophage cells, even without prior enrichment during sample preparation. The ease of incorporating this strategy into the prenylation study workflow and minimum disruption to the biological lipidome are advantageous for unraveling unknown native protein prenylation and further developments in profiling and quantifying prenylome.

Tyrosine phosphorylation of lamin A by Src promotes disassembly of nuclear lamina in interphase

Lamins form the nuclear lamina, which is important for nuclear structure and activity. Although posttranslational modifications, in particular serine phosphorylation, have been shown to be important for structural properties and functions of lamins, little is known about the role of tyrosine phosphorylation in this regard. In this study, we found that the constitutively active Src Y527F mutant caused the disassembly of lamin A/C. We demonstrate that Src directly phosphorylates lamin A mainly at Tyr45 both in vitro and in intact cells. The phosphomimetic Y45D mutant was diffusively distributed in the nucleoplasm and failed to assemble into the nuclear lamina. Depletion of lamin A/C in HeLa cells induced nuclear dysmorphia and genomic instability as well as increased nuclear plasticity for cell migration, all of which were partially restored by re-expression of lamin A, but further promoted by the Y45D mutant. Together, our results reveal a novel mechanism for regulating the assembly of nuclear lamina through Src and suggest that aberrant phosphorylation of lamin A by Src may contribute to nuclear dysmorphia, genomic instability, and nuclear plasticity.

Post-Translational Modification and Subcellular Compartmentalization: Emerging Concepts on the Regulation and Physiopathological Relevance of RhoGTPases

Cells and tissues are continuously exposed to both chemical and physical stimuli and dynamically adapt and respond to this variety of external cues to ensure cellular homeostasis, regulated development and tissue-specific differentiation. Alterations of these pathways promote disease progression-a prominent example being cancer. Rho GTPases are key regulators of the remodeling of cytoskeleton and cell membranes and their coordination and integration with different biological processes, including cell polarization and motility, as well as other signaling networks such as growth signaling and proliferation. Apart from the control of GTP-GDP cycling, Rho GTPase activity is spatially and temporally regulated by post-translation modifications (PTMs) and their assembly onto specific protein complexes, which determine their controlled activity at distinct cellular compartments. Although Rho GTPases were traditionally conceived as targeted from the cytosol to the plasma membrane to exert their activity, recent research demonstrates that active pools of different Rho GTPases also localize to endomembranes and the nucleus. In this review, we discuss how PTM-driven modulation of Rho GTPases provides a versatile mechanism for their compartmentalization and functional regulation. Understanding how the subcellular sorting of active small GTPase pools occurs and what its functional significance is could reveal novel therapeutic opportunities.

Protein farnesylation negatively regulates brassinosteroid signaling via reducing BES1 stability in Arabidopsis thaliana

Brassinosteroids (BRs) are a group of steroidal phytohormones, playing critical roles in almost all physiological aspects during the life span of a plant. In Arabidopsis, BRs are perceived at the cell surface, triggering a reversible phosphorylation-based signaling cascade that leads to the activation and nuclear accumulation of a family of transcription factors, represented by BES1 and BZR1. Protein farnesylation is a type of post-translational modification, functioning in many important cellular processes. Previous studies demonstrated a role of farnesylation in BR biosynthesis via regulating the endoplasmic reticulum localization of a key bassinolide (BL) biosynthetic enzyme BR6ox2. Whether such a process is also involved in BR signaling is not understood. Here, we demonstrate that protein farnesylation is involved in mediating BR signaling in Arabidopsis. A loss-of-function mutant of ENHANCED RESPONSE TO ABA 1 (ERA1), encoding a β subunit of the protein farnesyl transferase holoenzyme, can alter the BL sensitivity of bak1-4 from a reduced to a hypersensitive level. era1 can partially rescue the BR defective phenotype of a heterozygous mutant of bin2-1, a gain-of-function mutant of BIN2 which encodes a negative regulator in the BR signaling. Our genetic and biochemical analyses revealed that ERA1 plays a significant role in regulating the protein stability of BES1.

Subtype-dependent regulation of Gβγ signalling

G protein-coupled receptors (GPCRs) transmit information to the cell interior by transducing external signals to heterotrimeric G protein subunits, Gα and Gβγ subunits, localized on the inner leaflet of the plasma membrane. Though the initial focus was mainly on Gα-mediated events, Gβγ subunits were later identified as major contributors to GPCR-G protein signalling. A broad functional array of Gβγ signalling has recently been attributed to Gβ and Gγ subtype diversity, comprising 5 Gβ and 12 Gγ subtypes, respectively. In addition to displaying selectivity towards each other to form the Gβγ dimer, numerous studies have identified preferences of distinct Gβγ combinations for specific GPCRs, Gα subtypes and effector molecules. Importantly, Gβ and Gγ subtype-dependent regulation of downstream effectors, representing a diverse range of signalling pathways and physiological functions have been found. Here, we review the literature on the repercussions of Gβ and Gγ subtype diversity on direct and indirect regulation of GPCR/G protein signalling events and their physiological outcomes. Our discussion additionally provides perspective in understanding the intricacies underlying molecular regulation of subtype-specific roles of Gβγ signalling and associated diseases.

Deconvoluting the biology and druggability of protein lipidation using chemical proteomics

Lipids are indispensable cellular building blocks, and their post-translational attachment to proteins makes them important regulators of many biological processes. Dysfunction of protein lipidation is also implicated in many pathological states, yet its systematic analysis presents significant challenges. Thanks to innovations in chemical proteomics, lipidation can now be readily studied by metabolic tagging using functionalized lipid analogs, enabling global profiling of lipidated substrates using mass spectrometry. This has spearheaded the first deconvolution of their full scope in a range of contexts, from cells to pathogens and multicellular organisms. Protein N-myristoylation, S-acylation, and S-prenylation are the most well-studied lipid post-translational modifications because of their extensive contribution to the regulation of diverse cellular processes. In this review, we focus on recent advances in the study of these post-translational modifications, with an emphasis on how novel mass spectrometry methods have elucidated their roles in fundamental biological processes.

Regulation of FKBP51 and FKBP52 functions by post-translational modifications

FKBP51 and FKBP52 are two iconic members of the family of peptidyl-prolyl-(cis/trans)-isomerases (EC: 5.2.1.8), which comprises proteins that catalyze the cis/trans isomerization of peptidyl-prolyl peptide bonds in unfolded and partially folded polypeptide chains and native state proteins. Originally, both proteins have been studied as molecular chaperones belonging to the steroid receptor heterocomplex, where they were first discovered. In addition to their expected role in receptor folding and chaperoning, FKBP51 and FKBP52 are also involved in many biological processes, such as signal transduction, transcriptional regulation, protein transport, cancer development, and cell differentiation, just to mention a few examples. Recent studies have revealed that both proteins are subject of post-translational modifications such as phosphorylation, SUMOlyation, and acetylation. In this work, we summarize recent advances in the study of these immunophilins portraying them as scaffolding proteins capable to organize protein heterocomplexes, describing some of their antagonistic properties in the physiology of the cell, and the putative regulation of their properties by those post-translational modifications.

Diffuse or hitch a ride: how photoreceptor lipidated proteins get from here to there

Photoreceptors are polarized neurons, with specific subcellular compartmentalization and unique requirements for protein expression and trafficking. Each photoreceptor contains an outer segment (OS) where vision begins, an inner segment (IS) where protein synthesis occurs and a synaptic terminal for signal transmission to second-order neurons. The OS is a large, modified primary cilium attached to the IS by a slender connecting cilium (CC), the equivalent of the transition zone (TZ). Daily renewal of ~10% of the OS requires massive protein biosynthesis in the IS with reliable transport and targeting pathways. Transport of lipidated (‘sticky’) proteins depends on solubilization factors, phosphodiesterase δ (PDEδ) and uncoordinated protein-119 (UNC119), and the cargo dispensation factor (CDF), Arf-like protein 3-guanosine triphosphate (ARL3-GTP). As PDE6 and transducin still reside prominently in the OS of PDEδ and UNC119 germline knockout mice, respectively, we propose the existence of an alternate trafficking pathway, whereby lipidated proteins migrate in rhodopsin-containing vesicles of the secretory pathway.

Emerging Role of Migration and Invasion Enhancer 1 (MIEN1) in Cancer Progression and Metastasis

Tumor metastasis is a sequential event accounting for numerous cancer-related fatalities worldwide. The process of metastasis serially involves invasion, intravasation, extravasation, and tumor growth at the secondary site. Migration and invasion enhancer 1 (MIEN1) is a membrane associated protein overexpressed in various human cancers. Biological activity of MIEN1 is driven by geranylgeranyltransferase-I mediated prenylation at CAAX motif and methylation of the prenylated protein that anchors MIEN1 into the cellular membrane. Post-translationally modified MIEN1 interacts with Syk kinase and Annexin A2 protein; polymerizes G-actin and stabilizes F-actin filament; induces focal adhesion kinase phosphorylation and decrease cofilin phosphorylation implicated in both invasion and metastasis of different cancer types. In the present review, we discuss the structure, function, and involvement of MIEN1 in cancer progression. We also highlight the future prospects of MIEN1 as an emerging molecule and novel target in cancer cell invasion and metastasis.

The chaperone SmgGDS-607 has a dual role, both activating and inhibiting farnesylation of small GTPases

Ras family small GTPases undergo prenylation (such as farnesylation) for proper localization to the plasma membrane, where they can initiate oncogenic signaling pathways. Small GTP-binding protein GDP-dissociation stimulator (SmgGDS) proteins are chaperones that bind and traffic small GTPases, although their exact cellular function is unknown. Initially, SmgGDS proteins were classified as guanine nucleotide exchange factors, but recent findings suggest that SmgGDS proteins also regulate prenylation of small GTPases in vivo in a substrate-selective manner. SmgGDS-607 recognizes the polybasic region and the CAAX box of several small GTPases and inhibits prenylation by impeding their entry into the geranylgeranylation pathway. Here, using recombinant and purified enzymes for prenylation and protein-binding assays, we demonstrate that SmgGDS-607 differentially regulates farnesylation of several small GTPases. SmgGDS-607 inhibited farnesylation of some proteins, such as DiRas1, by sequestering the protein and limiting modification catalyzed by protein farnesyltransferase (FTase). We found that the competitive binding affinities of the small GTPase for SmgGDS-607 and FTase dictate the extent of this inhibition. Additionally, we discovered that SmgGDS-607 increases the rate of farnesylation of HRas by enhancing product release from FTase. Our work indicates that SmgGDS-607 binds to a broad range of small GTPases and does not require a PBR for recognition. Together, these results provide mechanistic insight into SmgGDS-607-mediated regulation of farnesylation of small GTPases and suggest that SmgGDS-607 has multiple modes of substrate recognition.

Isoprenoids and protein prenylation: implications in the pathogenesis and therapeutic intervention of Alzheimer's disease

The mevalonate-isoprenoid-cholesterol biosynthesis pathway plays a key role in human health and disease. The importance of this pathway is underscored by the discovery that two major isoprenoids, farnesyl and geranylgeranyl pyrophosphate, are required to modify an array of proteins through a process known as protein prenylation, catalyzed by prenyltransferases. The lipophilic prenyl group facilitates the anchoring of proteins in cell membranes, mediating protein-protein interactions and signal transduction. Numerous essential intracellular proteins undergo prenylation, including most members of the small GTPase superfamily as well as heterotrimeric G proteins and nuclear lamins, and are involved in regulating a plethora of cellular processes and functions. Dysregulation of isoprenoids and protein prenylation is implicated in various disorders, including cardiovascular and cerebrovascular diseases, cancers, bone diseases, infectious diseases, progeria, and neurodegenerative diseases including Alzheimer's disease (AD). Therefore, isoprenoids and/or prenyltransferases have emerged as attractive targets for developing therapeutic agents. Here, we provide a general overview of isoprenoid synthesis, the process of protein prenylation and the complexity of prenylated proteins, and pharmacological agents that regulate isoprenoids and protein prenylation. Recent findings that connect isoprenoids/protein prenylation with AD are summarized and potential applications of new prenylomic technologies for uncovering the role of prenylated proteins in the pathogenesis of AD are discussed.

Ligand-Phospholipid Conjugation: A Versatile Strategy for Developing Long-Acting Ligands That Bind to Membrane Proteins by Restricting the Subcellular Localization of the Ligand

We hypothesized that if drug localization can be restricted to a particular subcellular domain where their target proteins reside, the drugs could bind to their target proteins without being metabolized and/or excreted, which would significantly extend the half-life of the corresponding drug-target complex. Thus, we designed ligand-phospholipid conjugates in which the ligand is conjugated with a phospholipid through a polyethylene glycol linker to restrict the subcellular localization of the ligand in the vicinity of the lipid bilayer. Here, we present the design, synthesis, pharmacological activity, and binding mode analysis of ligand-phospholipid conjugates with muscarinic acetylcholine receptors as the target proteins. These results demonstrate that ligand-phospholipid conjugation can be a versatile strategy for developing long-acting ligands that bind to membrane proteins in drug discovery.

Spatial modeling of the membrane-cytosolic interface in protein kinase signal transduction

The spatial architecture of signaling pathways and the interaction with cell size and morphology are complex, but little understood. With the advances of single cell imaging and single cell biology, it becomes crucial to understand intracellular processes in time and space. Activation of cell surface receptors often triggers a signaling cascade including the activation of membrane-attached and cytosolic signaling components, which eventually transmit the signal to the cell nucleus. Signaling proteins can form steep gradients in the cytosol, which cause strong cell size dependence. We show that the kinetics at the membrane-cytosolic interface and the ratio of cell membrane area to the enclosed cytosolic volume change the behavior of signaling cascades significantly. We suggest an estimate of average concentration for arbitrary cell shapes depending on the cell volume and cell surface area. The normalized variance, known from image analysis, is suggested as an alternative measure to quantify the deviation from the average concentration. A mathematical analysis of signal transduction in time and space is presented, providing analytical solutions for different spatial arrangements of linear signaling cascades. Quantification of signaling time scales reveals that signal propagation is faster at the membrane than at the nucleus, while this time difference decreases with the number of signaling components in the cytosol. Our investigations are complemented by numerical simulations of non-linear cascades with feedback and asymmetric cell shapes. We conclude that intracellular signal propagation is highly dependent on cell geometry and, thereby, conveys information on cell size and shape to the nucleus.

Discovery of Novel KRAS-PDEδ Inhibitors by Fragment-Based Drug Design

Targeting KRAS-PDEδ protein-protein interactions with small molecules represents a promising opportunity for developing novel antitumor agents. However, current KRAS-PDEδ inhibitors are limited by poor cellular antitumor potency and the druggability of the target remains to be validated by new inhibitors. To tackle these challenges, herein, novel, highly potent KRAS-PDEδ inhibitors were identified by fragment-based drug design, providing promising lead compounds or chemical probes for investigating the biological functions and druggability of KRAS-PDEδ interaction.

Rce1: mechanism and inhibition

Ras converting enzyme 1 (Rce1) is an integral membrane endoprotease localized to the endoplasmic reticulum that mediates the cleavage of the carboxyl-terminal three amino acids from CaaX proteins, whose members play important roles in cell signaling processes. Examples include the Ras family of small GTPases, the γ-subunit of heterotrimeric GTPases, nuclear lamins, and protein kinases and phosphatases. CaaX proteins, especially Ras, have been implicated in cancer, and understanding the post-translational modifications of CaaX proteins would provide insight into their biological function and regulation. Many proteolytic mechanisms have been proposed for Rce1, but sequence alignment, mutational studies, topology, and recent crystallographic data point to a novel mechanism involving a glutamate-activated water and an oxyanion hole. Studies using in vivo and in vitro reporters of Rce1 activity have revealed that the enzyme cleaves only prenylated substrates and the identity of the a₂ amino residue in the Ca₁a₂X sequence is most critical for recognition, preferring Ile, Leu, or Val. Substrate mimetics can be somewhat effective inhibitors of Rce1 in vitro. Small-molecule inhibitor discovery is currently limited by the lack of structural information on a eukaryotic enzyme, but a set of 8-hydroxyquinoline derivatives has demonstrated an ability to mislocalize all three mammalian Ras isoforms, giving optimism that potent, selective inhibitors might be developed. Much remains to be discovered regarding cleavage specificity, the impact of chemical inhibition, and the potential of Rce1 as a therapeutic target, not only for cancer, but also for other diseases.

Small change, big effect: Taking RAS by the tail through suppression of post-prenylation carboxylmethylation

Mutant RAS isoforms are the most common oncogenes affecting human cancers. After decades of effort in developing drugs targeting oncogenic RAS-driven cancers, we are still charting an unclear path. Despite recent developments exemplified by KRAS (G12C) inhibitors, direct targeting of mutant RAS remains a difficult endeavor. Inhibiting RAS function by targeting its post-translational prenylation processing has remained an important approach, especially with recent progress on the study of isoprenylcysteine carboxylmethyltransferase (ICMT), the unique enzyme for the last step of prenylation processing of RAS isoforms and other substrates. Inhibition of ICMT has shown efficacy both in vitro and in vivo in RAS-mutant cancer models. We will discuss the roles of RAS family of proteins in human cancers and the impact of post-prenylation carboxylmethylation on RAS driven tumorigenesis. In addition, we will review what is known of the molecular and cellular impact of ICMT inhibition on cancer cells that underlie its anti-proliferative and pro-apoptosis efficacy.

Aspirin inhibits the proliferation of human uterine leiomyoma cells by downregulation of K‑Ras‑p110α interaction

Aspirin has been confirmed as an effective antitumor drug in various cancers. However, the relationship between aspirin and uterine leiomyoma is still underexplored. Here, we explored the effects of aspirin on human uterine leiomyoma cells and provide insights into the underlying mechanisms. Cell Counting Kit-8 (CCK-8) and flow cytometry analysis showed that aspirin treatment inhibited cell proliferation and promoted cell cycle arrest at G0/G1 phase in a dose- and time‑dependent manner of human uterine leiomyoma cells. Further studies revealed that aspirin blocked the interaction between K-Ras and p110α by co-immunoprecipitation and immunofluorescence. Western blotting demonstrated K‑Ras‑p110α interaction was required for the effects of aspirin‑induced inhibition on cell growth and cell cycle transition via cell cycle regulators, including cyclin D1 and cyclin-dependent kinase 2 (CDK2). PI3K/Akt/caspase signaling pathway was involved in human uterine leiomyoma cell growth under aspirin treatment. Taken together, these results suggest that aspirin inhibited human uterine leiomyoma cell growth by regulating K‑Ras‑p110α interaction. Aspirin which targeting on interaction between K-Ras and p110α may serve as a new therapeutic drug for uterine leiomyoma treatment.

Structure-based development of PDEδ inhibitors

The prenyl binding protein PDEδ enhances the diffusion of farnesylated Ras proteins in the cytosol, ultimately affecting their correct localization and signaling. This has turned PDEδ into a promising target to prevent oncogenic KRas signaling. In this review we summarize and describe the structure-guided-development of the three different PDEδ inhibitor chemotypes that have been documented so far. We also compare both their potency for binding to the PDEδ pocket and their in vivo efficiency in suppressing oncogenic KRas signaling, as a result of the inhibition of the PDEδ/KRas interaction.

Polyisoprenylated cysteinyl amide inhibitors induce caspase 3/7- and 8-mediated apoptosis and inhibit migration and invasion of metastatic prostate cancer cells

Metastatic castration-resistant prostate cancer (mCRPC) is the most aggressive and deadly form of prostate cancer. It is characterized by the overexpression of epidermal growth factor receptors whose signals are mediated by small monomeric G proteins of the Ras superfamily. These require polyisoprenylation for functional activity. Polyisoprenylated cysteinyl amide inhibitors (PCAIs) of polyisoprenylated methylated protein methyl esterase (PMPMEase) were developed as potential targeted therapies to mitigate excessive growth signaling in mCRPC either by inhibiting PMPMEase and/or perturbing the polyisoprenylation-dependent functional interactions. We investigated the effects of PCAIs on the viability of prostate cancer PC 3, DU 145, MDA PCa 2b, LNCaP and 22Rv1 cells, determined the effect of the PCAIs on PC 3 cell proliferation, survival and caspase-mediated apoptotic cell death. Metastatic PC 3 and DU 145 cell migration and invasion in the presence of NSL-BA-040 were determined using the scratch and matrigel invasion assays. We further investigated the effect of NSL-BA-040 on F-actin organization in TagRFP F-actin marker-transfected metastatic PC 3 cells. The PCAIs suppress mCRPC cell viability with EC₅₀ values ranging from 1.3 to 4.0 µM for the most potent of the PCAIs against PC 3, DU 145, MDA PCa 2b, LNCaP and 22Rv cells. PCAIs induced apoptotic cell death in PC 3 and DU 145 cells as determined by annexin V/propidium iodide flow cytometry analysis through the activation of caspases 3 and 8 while also inhibiting migration and invasion through the disruption of F-actin organization. Taken together, our studies show the anti-cancer effects on mCRPC cells through induction of caspase-mediated apoptosis and F-actin-mediated inhibition of cell motility and invasion thereby indicating the anti-tumor and anti-metastatic potential of the PCAIs.

Atorvastatin augments temozolomide's efficacy in glioblastoma via prenylation-dependent inhibition of Ras signaling

Ras signaling is often dysregulated and plays essential roles for the maintenance of glioblastoma. The proper function of Ras depends largely on the appropriate post-translational modification termed prenylation. Targeting protein prenylation therefore represents an alternative therapeutic strategy in glioblastoma. In this study, we demonstrate that prenylation inhibition by atorvastatin is active against glioblastoma. Atorvastatin alone dose-dependently inhibits growth and survival of multiple glioblastoma cell lines. Its combination with temozolomide significantly enhances temozolomide's efficacy in in vitro cultured cell system as well as in vivo xenograft glioblastoma tumor model. We further show that this is achieved by the inhibition of Ras prenylation, leading to decreased activation of Ras and its downstream signaling pathways, including Erk, rS6 and eIF4E. Our findings suggest that inhibition of Ras activity by atorvastatin effectively targets the MEK and other signaling pathways. Our study provides a fundamental evidence to repurpose atorvastatin for a potential treatment of glioblastoma.

Inhibiting HDAC1 Enhances the Anti-Cancer Effects of Statins through Downregulation of GGTase-Iβ Expression

Hydroxy-methyl-glutaryl-coenzyme A (HMG-CoA) reductase inhibitors, namely statins, are potential anti-tumor agents. Previously, we showed that a pan-histone deacetylase (HDAC) inhibitor enhances the anti-tumor effects of the HMG-CoA inhibitor. However, the underlying mechanisms were not fully understood. Cancer cell lines (CAL-27 and SACC-83) were exposed to pan-HDAC inhibitor, or HDAC1 inhibitor, or geranylgeranyl transferase type I (GGTase-I) inhibitor alone or in combination with statin. Cell viability, apoptosis, migration, and invasion were assessed by Cell Count Kit-8, 4′,6-diamidino-2-phenylindole staining, and transwell assay, respectively. A xenograft model was used for assessing tumor growth in vivo. Western blot and real-time PCR were used to assess the expression of genes. We observed that inhibiting HDAC1 could enhance the anti-tumor effects of statins both in vitro and in vivo. Inhibiting HDAC1 blocked the statin-induced upregulation of geranylgeranyl transferase type Iβ subunit (GGTase-Iβ), resulting in an enhancement of the anti-cancer effects of statin. Overexpression of GGTase-Iβ or constitutively active RhoA abolished the enhancement by inhibiting HDAC1 on anti-tumor effects of statins. The HDAC1 inhibitor failed to enhance cytotoxicity in non-tumor primary cells treated with statin. Inhibiting HDAC1 enhanced the anti-cancer effects of statins through downregulation of GGTase-Iβ expression, and thus further inactivation of RhoA. A combination of statin with HDAC1 or GGTase-I inhibitor would be a new strategy for cancer chemotherapy.

Development of Pyridazinone Chemotypes Targeting the PDEδ Prenyl Binding Site

The K-Ras GTPase is a major target in anticancer drug discovery. However, direct interference with signaling by K-Ras has not led to clinically useful drugs yet. Correct localization and signaling by farnesylated K-Ras is regulated by the prenyl binding protein PDEδ. Interfering with binding of PDEδ to K-Ras by means of small molecules provides a novel opportunity to suppress oncogenic signaling. Here we describe the identification and structure-guided development of novel K-Ras-PDEδ inhibitor chemotypes based on pyrrolopyridazinones and pyrazolopyridazinones that bind to the farnesyl binding pocket of PDEδ with low nanomolar affinity. We delineate the structure-property relationship and in vivo pharmacokinetic (PK) and toxicokinetic (Tox) studies for pyrazolopyridazinone-based K-Ras-PDEδ inhibitors. These findings may inspire novel drug discovery efforts aimed at the development of drugs targeting oncogenic Ras.

Lipoprotein insertion into membranes of various complexity: lipid sorting, interfacial adsorption and protein clustering

In a combined chemical-biological and biophysical approach we explored the membrane partitioning of the lipidated signaling proteins N-Ras and K-Ras4B into membrane systems of different complexity, ranging from one-component lipid bilayers and anionic binary and ternary heterogeneous membrane systems even up to partitioning studies on protein-free and protein-containing giant plasma membrane vesicles (GPMVs). To yield a pictorial view of the localization process, imaging using confocal laser scanning and atomic force microscopy was performed. The results reveal pronounced isoform-specific differences regarding the lateral distribution and formation of protein-rich membrane domains. Line tension is one of the key parameters controlling not only the size and dynamic properties of segregated lipid domains but also the partitioning process of N-Ras that acts as a lineactant. The formation of N-Ras protein clusters is even recorded for almost vanishing hydrophobic mismatch. Conversely, for K-Ras4B, selective localization and clustering are electrostatically mediated by its polybasic farnesylated C-terminus. The formation of K-Ras4B clusters is also observed for the multi-component GPMV membrane, i.e., it seems to be a general phenomenon, largely independent of the details of the membrane composition, including the anionic charge density of lipid headgroups. Our data indicate that unspecific and entropy-driven membrane-mediated interactions play a major role in the partitioning behavior, thus relaxing the need for a multitude of fine-tuned interactions. Such a scenario seems also to be reasonable recalling the high dynamic nature of cellular membranes. Finally, we note that even relatively simple models of heterogeneous membranes are able to reproduce many of the properties of much more complex biological membranes.

Selective Gas-Phase Oxidation and Localization of Alkylated Cysteine Residues in Polypeptide Ions via Ion/Ion Chemistry

The thiol group in cysteine residues is susceptible to several post-translational modifications (PTMs), including prenylation, nitrosylation, palmitoylation, and the formation of disulfide bonds. Additionally, cysteine residues involved in disulfide bonds are commonly reduced and alkylated prior to mass spectrometric analysis. Several of these cysteine modifications, specifically S-alkyl modifications, are susceptible to gas-phase oxidation via selective ion/ion reactions with periodate anions. Multiply protonated peptides containing modified cysteine residues undergo complex formation upon ion/ion reaction with periodate anions. Activation of the ion/ion complexes results in oxygen transfer from the reagent to the modified sulfur residue to create a sulfoxide functionality. Further activation of the sulfoxide derivative yields abundant losses of the modification with the oxidized sulfur as a sulfenic acid (namely, XSOH) to generate a dehydroalanine residue. This loss immediately indicates the presence of an S-alkyl cysteine residue, and the mass of the loss can be used to easily deduce the type of modification. An additional step of activation can be used to localize the modification to a specific residue within the peptide. Selective cleavage to create c- and z-ions N-terminal to the dehydroalanine residue is often noted. As these types of ions are not typically observed upon collision-induced dissociation (CID), they can be used to immediately indicate where in the peptide the PTM was originally located.

Aβ-Induced Insulin Resistance and the Effects of Insulin on the Cholesterol Synthesis Pathway and Aβ Secretion in Neural Cells

Alzheimer's disease (AD) is characterized by amyloid-β (Aβ) toxicity, tau pathology, insulin resistance, neuroinflammation, and dysregulation of cholesterol homeostasis, all of which play roles in neurodegeneration. Insulin has polytrophic effects on neurons and may be at the center of these pathophysiological changes. In this study, we investigated possible relationships among insulin signaling and cholesterol biosynthesis, along with the effects of Aβ42 on these pathways in vitro. We found that neuroblastoma 2a (N2a) cells transfected with the human gene encoding amyloid-β protein precursor (AβPP) (N2a-AβPP) produced Aβ and exhibited insulin resistance by reduced p-Akt and a suppressed cholesterol-synthesis pathway following insulin treatment, and by increased phosphorylation of insulin receptor subunit-1 at serine 612 (p-IRS-S612) as compared to parental N2a cells. Treatment of human neuroblastoma SH-SY5Y cells with Aβ42 also increased p-IRS-S612, suggesting that Aβ42 is responsible for insulin resistance. The insulin resistance was alleviated when N2a-AβPP cells were treated with higher insulin concentrations. Insulin increased Aβ release from N2a-AβPP cells, by which it may promote Aβ clearance. Insulin increased cholesterol-synthesis gene expression in SH-SY5Y and N2a cells, including 24-dehydrocholesterol reductase (DHCR24) and 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMGCR) through sterol-regulatory element-binding protein-2 (SREBP2). While Aβ42-treated SH-SY5Y cells exhibited increased HMGCR expression and c-Jun phosphorylation as pro-inflammatory responses, they also showed down-regulation of neuro-protective/anti-inflammatory DHCR24. These results suggest that Aβ42 may cause insulin resistance, activate JNK for c-Jun phosphorylation, and lead to dysregulation of cholesterol homeostasis, and that enhancing insulin signaling may relieve the insulin-resistant phenotype and the dysregulated cholesterol-synthesis pathway to promote Aβ release for clearance from neural cells.

Methylene blue alleviates nuclear and mitochondrial abnormalities in progeria

Hutchinson–Gilford progeria syndrome (HGPS), a fatal premature aging disease, is caused by a single‐nucleotide mutation in the LMNA gene. Previous reports have focused on nuclear phenotypes in HGPS cells, yet the potential contribution of the mitochondria, a key player in normal aging, remains unclear. Using high‐resolution microscopy analysis, we demonstrated a significantly increased fraction of swollen and fragmented mitochondria and a marked reduction in mitochondrial mobility in HGPS fibroblast cells. Notably, the expression of PGC‐1α, a central regulator of mitochondrial biogenesis, was inhibited by progerin. To rescue mitochondrial defects, we treated HGPS cells with a mitochondrial‐targeting antioxidant methylene blue (MB). Our analysis indicated that MB treatment not only alleviated the mitochondrial defects but also rescued the hallmark nuclear abnormalities in HGPS cells. Additional analysis suggested that MB treatment released progerin from the nuclear membrane, rescued perinuclear heterochromatin loss and corrected misregulated gene expression in HGPS cells. Together, these results demonstrate a role of mitochondrial dysfunction in developing the premature aging phenotypes in HGPS cells and suggest MB as a promising therapeutic approach for HGPS.

Relative Contributions of Prenylation and Postprenylation Processing in Cryptococcus neoformans Pathogenesis

Cryptococcus neoformans is an important human fungal pathogen that causes disease and death in immunocompromised individuals. The growth and morphogenesis of this fungus are controlled by conserved Ras-like GTPases, which are also important for its pathogenicity. Many of these proteins require proper subcellular localization for full function, and they are directed to cellular membranes through a posttranslational modification process known as prenylation. These studies investigate the roles of one of the prenylation enzymes, farnesyltransferase, as well as the postprenylation processing enzymes in C. neoformans. We demonstrate that the postprenylation processing steps are dispensable for the localization of certain substrate proteins. However, both protein farnesylation and the subsequent postprenylation processing steps are required for full pathogenesis of this fungus.

Prenyltransferase enzymes promote the membrane localization of their target proteins by directing the attachment of a hydrophobic lipid group at a conserved C-terminal CAAX motif. Subsequently, the prenylated protein is further modified by postprenylation processing enzymes that cleave the terminal 3 amino acids and carboxymethylate the prenylated cysteine residue. Many prenylated proteins, including Ras1 and Ras-like proteins, require this multistep membrane localization process in order to function properly. In the human fungal pathogen Cryptococcus neoformans, previous studies have demonstrated that two distinct forms of protein prenylation, farnesylation and geranylgeranylation, are both required for cellular adaptation to stress, as well as full virulence in animal infection models. Here, we establish that the C. neoformans RAM1 gene encoding the farnesyltransferase β-subunit, though not strictly essential for growth under permissive in vitro conditions, is absolutely required for cryptococcal pathogenesis. We also identify and characterize postprenylation protease and carboxyl methyltransferase enzymes in C. neoformans. In contrast to the prenyltransferases, deletion of the genes encoding the Rce1 protease and Ste14 carboxyl methyltransferase results in subtle defects in stress response and only partial reductions in virulence. These postprenylation modifications, as well as the prenylation events themselves, do play important roles in mating and hyphal transitions, likely due to their regulation of peptide pheromones and other proteins involved in development.

IMPORTANCECryptococcus neoformans is an important human fungal pathogen that causes disease and death in immunocompromised individuals. The growth and morphogenesis of this fungus are controlled by conserved Ras-like GTPases, which are also important for its pathogenicity. Many of these proteins require proper subcellular localization for full function, and they are directed to cellular membranes through a posttranslational modification process known as prenylation. These studies investigate the roles of one of the prenylation enzymes, farnesyltransferase, as well as the postprenylation processing enzymes in C. neoformans. We demonstrate that the postprenylation processing steps are dispensable for the localization of certain substrate proteins. However, both protein farnesylation and the subsequent postprenylation processing steps are required for full pathogenesis of this fungus.

Synthesis of structural analogues of GGT1-DU40, a potent GGTase-1 inhibitor

A series of new substituted pyrazoles 2–12 have been synthesized. The synthesized compounds are structural analogues of GGT1-DU40 1, a highly potent and selective inhibitor of protein geranylgeranyltransferase I (GGTase-I) both in vitro and in vivo. The implications of GGTase-I in oncogenesis have highlighted its potential as a cancer therapeutic target. Accordingly, the development of GGTase-I inhibitors has been a subject of much interest. The synthesis of 2–12 stemmed from the acetylation or acylation of N-function of amino acids to produce suitably modified amino acids. Meanwhile, the substituted pyrazole subunit originated from the reaction of ethyl nicotinate with γ-butyrolactone followed by condensation of the resultant β-keto lactone with (3,4-dichlorophenyl)hydrazine. The operations of O-alkylation and thioetherification on the resultant intermediate eventually produced the substituted pyrazole fragment. The amidation of the latter with amino acid derivatives finally rendered 2–12 in good to excellent yields.

Synthetic isoprenoid analogues for the study of prenylated proteins: Fluorescent imaging and proteomic applications

Protein prenylation is a posttranslational modification catalyzed by prenyltransferases involving the attachment of farnesyl or geranylgeranyl groups to residues near the C-termini of proteins. This irreversible covalent modification is important for membrane localization and proper signal transduction. Here, the use of isoprenoid analogues for studying prenylated proteins is reviewed. First, experiments with analogues containing small fluorophores that are alternative substrates for prenyltransferases are described. Those analogues have been useful for quantifying binding affinity and for the production of fluorescently labeled proteins. Next, the use of analogues that incorporate biotin, bioorthogonal groups or antigenic moieties is described. Such probes have been particularly useful for identifying proteins that are naturally prenylated within mammalian cells. Overall, the use of isoprenoid analogues has contributed significantly to the understanding of protein prenlation.

Nanoformulation of Geranylgeranyltransferase-I Inhibitors for Cancer Therapy: Liposomal Encapsulation and pH-Dependent Delivery to Cancer Cells

Small molecule inhibitors against protein geranylgeranyltransferase-I such as P61A6 have been shown to inhibit proliferation of a variety of human cancer cells and exhibit antitumor activity in mouse models. Development of these inhibitors could be dramatically accelerated by conferring tumor targeting and controlled release capability. As a first step towards this goal, we have encapsulated P61A6 into a new type of liposomes that open and release cargos only under low pH condition. These low pH-release type liposomes were prepared by adjusting the ratio of two types of phospholipid derivatives. Loading of geranylgeranyltransferase-I inhibitor (GGTI) generated liposomes with average diameter of 50–100 nm. GGTI release in solution was sharply dependent on pH values, only showing release at pH lower than 6. Release of cargos in a pH-dependent manner inside the cell was demonstrated by the use of a proton pump inhibitor Bafilomycin A1 that Increased lysosomal pH and inhibited the release of a dye carried in the pH-liposome. Delivery of GGTI to human pancreatic cancer cells was demonstrated by the inhibition of protein geranylgeranylation inside the cell and this effect was blocked by Bafilomycin A1. In addition, GGTI delivered by pH-liposomes induced proliferation inhibition, G1 cell cycle arrest that is associated with the expression of cell cycle regulator p21^CIP1/WAF1. Proliferation inhibition was also observed with various lung cancer cell lines. Availability of nanoformulated GGTI opens up the possibility to combine with other types of inhibitors. To demonstrate this point, we combined the liposomal-GGTI with farnesyltransferase inhibitor (FTI) to inhibit K-Ras signaling in pancreatic cancer cells. Our results show that the activated K-Ras signaling in these cells can be effectively inhibited and that synergistic effect of the two drugs is observed. Our results suggest a new direction in the use of GGTI for cancer therapy.

Curcumin loaded pH-sensitive hybrid lipid/block copolymer nanosized drug delivery systems

Curcumin is a perspective drug candidate with pleiotropic antineoplastic activity, whose exceptionally low aqueous solubility and poor pharmacokinetic properties have hampered its development beyond the preclinical level. A possible approach to overcome these limitations is the encapsulation of curcumin into nano-carriers, incl. liposomes. The present contribution is focused on feasibility of using hybrid pH-sensitive liposomes, whereby curcumin is entrapped as a free drug and as a water soluble inclusion complex with PEGylated tert-butylcalix[4]arene, which allows the drug to occupy both the phospholipid membranes and the aqueous core of liposomes. The inclusion complexes were encapsulated in dipalmithoylphosphathydilcholine:cholesterol liposomes, whose membranes were grafted with a poly(isoprene-b-acrylic acid) diblock copolymer to confer pH-sensitivity. The liposomes were characterized by DLS, ζ-potential measurements, cryo-TEM, curcumin encapsulation efficacy, loading capacity, and in vitro release as a function of pH. Free and formulated curcumin were further investigated for cytotoxicity, apoptosis-induction and caspase-8, and 9 activation in chemosensitive HL-60 and its resistant sublines HL-60/Dox and HL-60/CDDP. Formulated curcumin was superior cytotoxic and apoptogenic agent vs. the free drug. The mechanistic assay demonstrated that the potent proapoptotic effects of pH-sensitive liposomal curcumin presumably mediated via recruitment of both extrinsic and intrinsic apoptotic pathways in both HL-60 and HL-60/CDDP cells.