The insulin degrading enzyme activates ubiquitin and promotes the formation of K48 and K63 diubiquitin

Fraisinib: a calixpyrrole derivative reducing A549 cell-derived NSCLC tumor in vivo acts as a ligand of the glycine-tRNA synthase, a new molecular target in oncology

Background and purpose: Lung cancer is the leading cause of death in both men and women, constituting a major public health problem worldwide. Non-small-cell lung cancer accounts for 85%-90% of all lung cancers. We propose a compound that successfully fights tumor growth in vivo by targeting the enzyme GARS1. Experimental approach: We present an in-depth investigation of the mechanism through which Fraisinib [meso-(p-acetamidophenyl)-calix(4)pyrrole] affects the human lung adenocarcinoma A549 cell line. In a xenografted model of non-small-cell lung cancer, Fraisinib was found to reduce tumor mass volume without affecting the vital parameters or body weight of mice. Through a computational approach, we uncovered that glycyl-tRNA synthetase is its molecular target. Differential proteomics analysis further confirmed that pathways regulated by Fraisinib are consistent with glycyl-tRNA synthetase inhibition. Key results: Fraisinib displays a strong anti-tumoral potential coupled with limited toxicity in mice. Glycyl-tRNA synthetase has been identified and validated as a protein target of this compound. By inhibiting GARS1, Fraisinib modulates different key biological processes involved in tumoral growth, aggressiveness, and invasiveness. Conclusion and implications: The overall results indicate that Fraisinib is a powerful inhibitor of non-small-cell lung cancer growth by exerting its action on the enzyme GARS1 while displaying marginal toxicity in animal models. Together with the proven ability of this compound to cross the blood-brain barrier, we can assess that Fraisinib can kill two birds with one stone: targeting the primary tumor and its metastases "in one shot." Taken together, we suggest that inhibiting GARS1 expression and/or GARS1 enzymatic activity may be innovative molecular targets for cancer treatment.

The Insulin-Degrading Enzyme from Structure to Allosteric Modulation: New Perspectives for Drug Design

The insulin-degrading enzyme (IDE) is a Zn2+ peptidase originally discovered as the main enzyme involved in the degradation of insulin and other amyloidogenic peptides, such as the β-amyloid (Aβ) peptide. Therefore, a role for the IDE in the cure of diabetes and Alzheimer's disease (AD) has been long envisaged. Anyway, its role in degrading amyloidogenic proteins remains not clearly defined and, more recently, novel non-proteolytic functions of the IDE have been proposed. From a structural point of view, the IDE presents an atypical clamshell structure, underscoring unique enigmatic enzymological properties. A better understanding of the structure-function relationship may contribute to solving some existing paradoxes of IDE biology and, in light of its multifunctional activity, might lead to novel therapeutic approaches.

CHCHD2 p.Thr61Ile knock-in mice exhibit motor defects and neuropathological features of Parkinson's disease

The p.Thr61Ile (p.T61I) mutation in coiled-coil-helix-coiled-coil-helix domain containing 2 (CHCHD2) was deemed a causative factor in Parkinson's disease (PD). However, the pathomechanism of the CHCHD2 p.T61I mutation in PD remains unclear. Few existing mouse models of CHCHD2-related PD completely reproduce the features of PD, and no transgenic or knock-in (KI) mouse models of CHCHD2 mutations have been reported. In the present study, we generated a novel CHCHD2 p.T61I KI mouse model, which exhibited accelerated mortality, progressive motor deficits, and dopaminergic (DA) neurons loss with age, accompanied by the accumulation and aggregation of α-synuclein and p-α-synuclein in the brains of the mutant mice. The mitochondria of mouse brains and induced pluripotent stem cells (iPSCs)-derived DA neurons carrying the CHCHD2 p.T61I mutation exhibited aberrant morphology and impaired function. Mechanistically, proteomic and RNA sequencing analysis revealed that p.T61I mutation induced mitochondrial dysfunction in aged mice likely through repressed insulin-degrading enzyme (IDE) expression, resulting in the degeneration of the nervous system. Overall, this CHCHD2 p.T61I KI mouse model recapitulated the crucial clinical and neuropathological aspects of patients with PD and provided a novel tool for understanding the pathogenic mechanism and therapeutic interventions of CHCHD2-related PD.

Polystyrene nanoplastics affect the human ubiquitin structure and ubiquitination in cells: a high-resolution study

Humans are estimated to consume several grams per week of nanoplastics (NPs) through exposure to a variety of contamination sources. Nonetheless, the effects of these polymeric particles on living systems are still mostly unknown. Here, by means of CD, NMR and TEM analyses, we describe at an atomic resolution the interaction of ubiquitin with polystyrene NPs (PS-NPs), showing how a hard protein corona is formed. Moreover, we report that in human HeLa cells exposure to PS-NPs leads to a sensible reduction of ubiquitination. Our study overall indicates that PS-NPs cause significant structural effects on ubiquitin, thereby influencing one of the key metabolic processes at the base of cell viability.

Dipyridamole for tracking amyloidogenic proteins aggregation and enhancing polyubiquitination

Dipyridamole is currently used as a medication that inhibits blood clot formation and it is also investigated in the context of neurodegenerative and other amyloid related diseases. Here, we propose this molecule as a new diagnostic tool to follow the aggregation properties of three different amyloidogenic proteins tested (insulin, amylin and amyloid β peptide 1-40). Results show that dipyridamole is sensitive to early stage amyloid formation undetected by thioflavin T, giving a different response for the aggregation of the three different proteins. In addition, we show that dipyridamole is also able to enhance ubiquitin chain growth, paving the way to its potential application as therapeutic agent in neurodegenerative diseases.

Silybins are stereospecific regulators of the 20S proteasome

A reduced proteasome activity tiles excessive amyloid growth during the progress of protein conformational diseases (PCDs). Hence, the development of safe and effective proteasome enhancers represents an attractive target for the therapeutic treatment of these chronic disorders. Here we analyze two natural diastereoisomers belonging to the family of flavonolignans, Sil A and Sil B, by evaluating their capacity to increase proteasome activity. Enzyme assays carried out on yeast 20S (y20S) proteasome and in parallel on a permanently "open gate" mutant (α3ΔN) evidenced that Sil B is a more efficient 20S activator than Sil A. Conversely, in the case of human 20S proteasome (h20S) a higher affinity and more efficient activation is observed for Sil A. Driven by experimental data, computational studies further demonstrated that the taxifolin group of both diastereoisomers plays a crucial role in their anchoring to the α5/α6 groove of the outer α-ring. However, due to the different stereochemistry at C-7" and C-8" of ring D, only Sil A was able to reproduce the interactions responsible for h20S proteasome activation induced by their cognate regulatory particles. The provided silybins/h20S interaction models allowed us to rationalize their different ability to activate the peptidase activities of h20S and y20S. Our results provide structural details concerning the important role played by stereospecific interactions in driving Sil A and Sil B binding to the 20S proteasome and may support future rational design of proteasome enhancers.

Neuroprotective Effect of Carnosine Is Mediated by Insulin-Degrading Enzyme

l-Carnosine is an endogenous dipeptide that has high potential for therapeutic purposes, being an antioxidant with metal chelating, anti-aggregating, anti-inflammatory, and neuroprotective properties. Despite its potential therapeutic values, the biomolecular mechanisms involved in neuroprotection are not fully understood. Here, we demonstrate, at chemical and biochemical levels, that insulin-degrading enzyme plays a pivotal role in carnosine neuroprotection.

An SPR-based method for Hill coefficient measurements: the case of insulin-degrading enzyme

Insulin-degrading enzyme (IDE) is a highly conserved zinc metallopeptidase and is capable to catalytically cleave several substrates besides insulin, playing a pivotal role in several different biochemical pathways. Although its mechanism of action has been widely investigated, many conundrums still remain, hindering the possibility to rationally design specific modulators which could have important therapeutical applications in several diseases such as diabetes and Alzheimer's disease. In this scenario, we have developed a novel surface plasmon resonance (SPR) method which allows for directly measuring the enzyme cooperativity for the binding of insulin in the presence of different IDE activity modulators: carnosine, ATP, and EDTA. Results indicate that both positive and negative modulations of the IDE activity can be correlated to an increase and a decrease of the measured Hill coefficient, respectively, giving a new insight into the IDE activity mechanism. The use of the IDE R767A mutant for which oligomerization is hindered confirmed that the positive allosteric modulation of IDE by carnosine is due to a change in the enzyme oligomeric state occurring also for the enzyme immobilized on the gold SPR chip.

Insulin-Degrading Enzyme, an Under-Estimated Potential Target to Treat Cancer?

Insulin-degrading enzyme (IDE) is a multifunctional protease due to the variety of its substrates, its various cellular locations, its conservation between species and its many non-proteolytic functions. Numerous studies have successfully demonstrated its implication in two main therapeutic areas: metabolic and neuronal diseases. In recent years, several reports have underlined the overexpression of this enzyme in different cancers. Still, the exact role of IDE in the physiopathology of cancer remains to be elucidated. Known as the main enzyme responsible for the degradation of insulin, an essential growth factor for healthy cells and cancer cells, IDE has also been shown to behave like a chaperone and interact with the proteasome. The pharmacological modulation of IDE (siRNA, chemical compounds, etc.) has demonstrated interesting results in cancer models. All these results point towards IDE as a potential target in cancer. In this review, we will discuss evidence of links between IDE and cancer development or resistance, IDE's functions, catalytic or non-catalytic, in the context of cell proliferation, cancer development and the impact of the pharmacomodulation of IDE via cancer therapeutics.

The insulin-degrading enzyme as a link between insulin and neuropeptides metabolism

We have applied a recently developed HPLC-MS enzymatic assay to investigate the cryptic peptides generated by the action of the insulin-degrading enzyme (IDE) on some neuropeptides (NPs) involved in the development of tolerance and dependence to opioids. Particularly, the tested NPs are generated from the NPFF precursor (pro-NPFF (A)): NPFF (FLFQPQRF) and NPAF (AGEGLSSPFWSLAAPQRF). The results show that IDE is able to cleave NPFF and NPAF, generating specific cryptic peptides. As IDE is also responsible for the processing of many other peptides in the brain (amyloid beta protein among the others), we have also performed competitive degradation assays using mixtures of insulin and the above mentioned NPs. Data show that insulin is able to slow down the degradation of both NPs tested, whereas, surprisingly, NPAF is able to accelerate insulin degradation, hinting IDE as the possible link responsible of the mutual influence between insulin and NPs metabolism.

IL-6 induced enhanced clearance of proANP and ANP by insulin-degrading enzyme in T1DM mice

Cardiovascular disease (CVD) is a prevalent cause of morbidity and mortality in type I diabetes mellitus (T1DM). However, the pathophysiological mechanisms underlying the relationship between CVD, CVD risk factors, and T1DM have not yet been sufficiently explored. Here, we report that insulin-degrading enzyme (IDE) effectively degrades the precursor of atrial natriuretic peptide (proANP) in HEK293T cells. The pro-inflammatory cytokine IL-6 elicited a significant dose-dependent increase in IDE protein expression. Inhibition of the ERK/MAPK signaling pathway with selumetinib abolished the IL-6-stimulated increase in IDE protein levels and decreased ANP secretion in H9C2 cells. Importantly, the T1DM mouse model displayed lower proANP in the heart and ANP in serum, due to increased IDE expression and activity. Our results suggest a novel role of IL-6 in ANP metabolism via IDE and provide possibilities for new potential therapeutic strategies for diabetes-related cardiovascular complications.

Insulin-degrading enzyme: an ally against metabolic and neurodegenerative diseases

Insulin-degrading enzyme (IDE) function goes far beyond its known proteolytic role as a regulator of insulin levels. IDE has a wide substrate promiscuity, degrading several proteins such as amyloid-β peptide, glucagon, islet amyloid polypeptide (IAPP) and insulin-like growth factors, that have diverse physiological and pathophysiological functions. Importantly, IDE plays other non-proteolytical functions such as a chaperone/dead-end chaperone, an E1-ubiquitin activating enzyme, and a proteasome modulator. It also responds as a heat shock protein, regulating cellular proteostasis. Notably, amyloidogenic proteins such as IAPP, amyloid-β and α-synuclein have been reported as substrates for IDE chaperone activity. This is of utmost importance as failure of IDE may result in increased protein aggregation, a key hallmark in the pathogenesis of beta cells in type 2 diabetes mellitus and of neurons in neurodegenerative diseases such as Alzheimer's and Parkinson's disease. In this review, we focus on the biochemical and biophysical properties of IDE and the regulation of its physiological functions. We further raise the hypothesis that IDE plays a central role in the pathological context of dysmetabolic and neurodegenerative diseases and discuss its potential as a therapeutic target. This article is protected by copyright. All rights reserved.

The interplay between lipid and Aβ amyloid homeostasis in Alzheimer's Disease: risk factors and therapeutic opportunities

Alzheimer's Diseases (AD) is characterized by the accumulation of amyloid deposits of Aβ peptide in the brain. Besides genetic background, the presence of other diseases and an unhealthy lifestyle are known risk factors for AD development. Albeit accumulating clinical evidence suggests that an impaired lipid metabolism is related to Aβ deposition, mechanistic insights on the link between amyloid fibril formation/clearance and aberrant lipid interactions are still unavailable. Recently, many studies have described the key role played by membrane bound Aβ assemblies in neurotoxicity. Moreover, it has been suggested that a derangement of the ubiquitin proteasome pathway and autophagy is significantly correlated with toxic Aβ aggregation and dysregulation of lipid levels. Thus, studies focusing on the role played by lipids in Aβ aggregation and proteostasis could represent a promising area of investigation for the design of valuable treatments. In this review we examine current knowledge concerning the effects of lipids in Aβ aggregation and degradation processes, focusing on the therapeutic opportunities that a comprehensive understanding of all biophysical, biochemical, and biological processes involved may disclose.

THE USE OF MASS SPECTROMETRY TO STUDY ZN-METALLOPROTEASE-SUBSTRATE INTERACTIONS

Zinc metalloproteases (ZnMPs) participate in diverse biological reactions, encompassing the synthesis and degradation of all the major metabolites in living organisms. In particular, ZnMPs have been recognized to play a very important role in controlling the concentration level of several peptides and/or proteins whose homeostasis has to be finely regulated for the correct physiology of cells. Dyshomeostasis of aggregation-prone proteins causes pathological conditions and the development of several different diseases. For this reason, in recent years, many analytical approaches have been applied for studying the interaction between ZnMPs and their substrates and how environmental factors can affect enzyme activities. In this scenario, mass spectrometric methods occupy a very important role in elucidating different aspects of ZnMPs-substrates interaction. These range from identification of cleavage sites to quantitation of kinetic parameters. In this work, an overview of all the main achievements regarding the application of mass spectrometric methods to investigating ZnMPs-substrates interactions is presented. A general experimental protocol is also described which may prove useful to the study of similar interactions. © 2020 John Wiley & Sons Ltd. Mass Spec Rev.

Site directed mutagenesis of insulin-degrading enzyme allows singling out the molecular basis of peptidase versus E1-like activity: the role of metal ions

Four specifically designed IDE mutants have been used to unveil the molecular basis of peptidase versus E1-like activity of the enzyme. We have found that physiological concentrations of copper(ii) ions inhibit the proteolytic activity of the enzyme towards small and large substrates but have no effect on the E1-like activity of the enzyme.

IDE Degrades Nociceptin/Orphanin FQ through an Insulin Regulated Mechanism

Insulin-degrading enzyme (IDE) was applied to catalyze hydrolysis of Nociceptin/Orphanin 1-16 (OFQ/N) to show the involvement of the enzyme in degradation of neuropeptides engaged in pain transmission. Moreover, IDE degradative action towards insulin (Ins) was inhibited by the OFQ/N fragments, suggesting a possible regulatory mechanism in the central nervous system. It has been found that OFQ/N and Ins affect each other degradation by IDE, although in a different manner. Indeed, while the digestion of OFQ/N is significantly affected by the presence of Ins, the kinetic profile of the Ins hydrolysis is not affected by the presence of OFQ/N. However, the main hydrolytic fragments of OFQ/N produced by IDE exert inhibitory activity towards the IDE-mediated Ins degradation. Here, we present the results indicating that, besides Ins, IDE cleaves neuropeptides and their released fragments act as inhibitors of IDE activity toward Ins. Having in mind that IDE is present in the brain, which also contains Ins receptors, it cannot be excluded that this enzyme indirectly participates in neural communication of pain signals and that neuropeptides involved in pain transmission may contribute to the regulation of IDE activity. Finally, preliminary results on the metabolism of OFQ/N, carried out in the rat spinal cord homogenate in the presence of various inhibitors specific for different classes of proteases, show that OFQ/N proteolysis in rat spinal cord could be due, besides IDE, also to a cysteine protease not yet identified.

Commentary on Ivancic et al.: Enzyme kinetics from circular dichroism of insulin reveals mechanistic insights into the regulation of insulin-degrading enzyme

Despite the enormous number of therapeutic advances in medicine, nowadays many diseases are still incurable, mainly due to the lack of knowledge of the pathological biochemical pathways triggering those diseases. For this reason, it is compulsory for the scientific community to investigate and unveil the biomolecular mechanisms responsible for the development of those diseases, such as Alzheimer's disease and diabetes, which are widespread all over the world. In this scenario, it is of paramount importance to develop new analytical techniques and experimental procedures that are capable to make the above-mentioned investigations feasible. These new methods should allow easy performable analysis carried out in a label-free environment, in order to give reliable answers to specific biochemical questions. A recent paper published on Bioscience Reports by Ivancic et al. (https://doi.org/10.1042/BSR20181416) proposes a new analytical technique capable to reveal some mechanistic insights into the regulation of insulin-degrading enzyme (IDE), a protein involved in the above-mentioned diseases. IDE is a multifaceted enzyme having different and not well-defined roles in the cell, but it is primarily a proteolytic enzyme capable to degrade several different amyloidogenic substrates involved in different diseases. Moreover, many molecules are responsible for IDE activity modulation so that understanding how IDE activity is regulated represents a very challenging analytical task. The new analytical approach proposed by Ivancic et al. reports on the possibility to study IDE activity in an unbiased and label-free manner, representing a valid alternative assay for the investigation of any proteases degradative activity.

The insulin-degrading enzyme is an allosteric modulator of the 20S proteasome and a potential competitor of the 19S

The interaction of insulin-degrading enzyme (IDE) with the main intracellular proteasome assemblies (i.e, 30S, 26S and 20S) was analyzed by enzymatic activity, mass spectrometry and native gel electrophoresis. IDE was mainly detected in association with assemblies with at least one free 20S end and biochemical investigations suggest that IDE competes with the 19S in vitro. IDE directly binds the 20S and affects its proteolytic activities in a bimodal fashion, very similar in human and yeast 20S, inhibiting at (IDE) ≤ 30 nM and activating at (IDE) ≥ 30 nM. Only an activating effect is observed in a yeast mutant locked in the "open" conformation (i.e., the α-3ΔN 20S), envisaging a possible role of IDE as modulator of the 20S "open"-"closed" allosteric equilibrium. Protein-protein docking in silico proposes that the interaction between IDE and the 20S could involve the C-term helix of the 20S α-3 subunit which regulates the gate opening of the 20S.

E3 Ligase Trim21 Ubiquitylates and Stabilizes Keratin 17 to Induce STAT3 Activation in Psoriasis

Keratin 17 (K17), a marker of keratinocyte hyperproliferation, is a type I intermediate filament that is overexpressed in psoriatic epidermis and plays a critical pathogenic role by stimulating T cells. However, the posttranslational modification of K17, which is reversible and targetable, has not been elucidated. Herein, we reported that K17 could be modified through ubiquitination that controlled its stability and led to the phosphorylation and nuclear translocation of its interactor signal transducers and activators of transcription 3 (STAT3), which is a key regulator of cell proliferation in psoriasis. First, we stimulated human keratinocyte cell line HaCaT cells with psoriasis (pso)-mix, which is a cytokine pool (IL-17, IL-22, tumor necrosis factor-α, and IFN-γ) mimicking the in vitro "psoriasis-like" status and found that the ubiquitination of K17 was essential to stabilize its protein expression in pso-mix-treated HaCaT cells. Subsequently, tripartite motif-containing protein 21 was identified as the E3 ligase of K17, which ubiquitylated K17 via K63 linkage to maintain K17 stabilization. More importantly, we uncovered that K17 was a direct interactor of STAT3, and K17 ubiquitination could promote STAT3 activation in pso-mix-treated HaCaT cells. Our study demonstrated that targeting K17 ubiquitination may be a potential therapeutic approach by attenuating STAT3 signaling in psoriasis.

Engineering a novel protease-based Exendin-4 derivative for type 2 antidiabetic therapeutics

To develop an effective long-acting antidiabetic agent, we designed a novel Exendin-4 derivative (termed LEx4) containing an albumin-binding domain (ABD), a protease-cleavable linker and a native Exendin-4. Here, we present the LEx4 with balanced glucoregulatory activity and prolonged in vivo activity. As a first step, the LEx4 with purity more than 99% was prepared. Microscale thermophoresis (MST) results demonstrated that LEx4 associates with rat and monkey serum albumin with high-affinity (K_a = 1.26 × 10⁶ M^-1 and 1.52 × 10⁶ M^-1, respectively). Then the stability test in vitro showed the enhanced antiproteolytic ability of LEx4 in rat and human plasma compared to native Exendin-4. Oral glucose tolerance test (OGTT) in type 2 diabetic mice showed the glucose-lowering efficacy of LEx4 was clearly dosage-dependent within 25-250 nmol/kg. In addition, the protracted antidiabetic effects of LEx4 were further confirmed by both multiple OGTTs and hypoglycemic efficacies test in type 2 diabetic mice. In Sprague Dawley (SD) rats, LEx4 also showed 3.3-fold longer elimination half-life (t_1/2) than native Exendin-4. Furthermore, once daily injection of LEx4 to db/db mice achieved long-term beneficial effects on body weight, blood biochemical values, glucose tolerance and pancreatic tissue. We believe LEx4 has superior pharmaceutical potential as a therapeutic drug to against type-2 diabetes mellitus (T2DM) based on these results. This strategy of albumin binding is also applicable to other bioactive peptides for development of long-acting therapeutic drugs.

Inhibition of Aβ Amyloid Growth and Toxicity by Silybins: The Crucial Role of Stereochemistry

The self-assembling of the amyloid β (Aβ) peptide into neurotoxic aggregates is considered a central event in the pathogenesis of Alzheimer's disease (AD). Based on the "amyloid hypothesis", many efforts have been devoted to designing molecules able to halt disease progression by inhibiting Aβ self-assembly. Here, we combine biophysical (ThT assays, TEM and AFM imaging), biochemical (WB and ESI-MS), and computational (all-atom molecular dynamics) techniques to investigate the capacity of four optically pure components of the natural product silymarin (silybin A, silybin B, 2,3-dehydrosilybin A, 2,3-dehydrosilybin B) to inhibit Aβ aggregation. Despite TEM analysis demonstrated that all the four investigated flavonoids prevent the formation of mature fibrils, ThT assays, WB and AFM investigations showed that only silybin B was able to halt the growth of small-sized protofibrils thus promoting the formation of large, amorphous aggregates. Molecular dynamics (MD) simulations indicated that silybin B interacts mainly with the C-terminal hydrophobic segment ³⁵MVGGVV⁴⁰ of Aβ40. Consequently to silybin B binding, the peptide conformation remains predominantly unstructured along all the simulations. By contrast, silybin A interacts preferentially with the segments ¹⁷LVFF²⁰ and ²⁷NKGAII³² of Aβ40 which shows a high tendency to form bend, turn, and β-sheet conformation in and around these two domains. Both 2,3-dehydrosilybin enantiomers bind preferentially the segment ¹⁷LVFF²⁰ but lead to the formation of different small-sized, ThT-positive Aβ aggregates. Finally, in vivo studies in a transgenic Caenorhabditis elegans strain expressing human Aβ indicated that silybin B is the most effective of the four compounds in counteracting Aβ proteotoxicity. This study underscores the pivotal role of stereochemistry in determining the neuroprotective potential of silybins and points to silybin B as a promising lead compound for further development in anti-AD therapeutics.

Multiple functions of insulin-degrading enzyme: a metabolic crosslight?

Insulin-degrading enzyme (IDE) is a ubiquitous zinc peptidase of the inverzincin family, which has been initially discovered as the enzyme responsible for insulin catabolism; therefore, its involvement in the onset of diabetes has been largely investigated. However, further studies on IDE unraveled its ability to degrade several other polypeptides, such as β-amyloid, amylin, and glucagon, envisaging the possible implication of IDE dys-regulation in the "aggregopathies" and, in particular, in neurodegenerative diseases. Over the last decade, a novel scenario on IDE biology has emerged, pointing out a multi-functional role of this enzyme in several basic cellular processes. In particular, latest advances indicate that IDE behaves as a heat shock protein and modulates the ubiquitin-proteasome system, suggesting a major implication in proteins turnover and cell homeostasis. In addition, recent observations have highlighted that the regulation of glucose metabolism by IDE is not merely based on its largely proposed role in the degradation of insulin in vivo. There is increasing evidence that improper IDE function, regulation, or trafficking might contribute to the etiology of metabolic diseases. In addition, the enzymatic activity of IDE is affected by metals levels, thus suggesting a role also in the metal homeostasis (metallostasis), which is thought to be tightly linked to the malfunction of the "quality control" machinery of the cell. Focusing on the physiological role of IDE, we will address a comprehensive vision of the very complex scenario in which IDE takes part, outlining its crucial role in interconnecting several relevant cellular processes.

New comprehensive studies of a gold(III) Dithiocarbamate complex with proven anticancer properties: Aqueous dissolution with cyclodextrins, pharmacokinetics and upstream inhibition of the ubiquitin-proteasome pathway

The gold(III)-dithiocarbamate complex AuL12 (dibromo [ethyl-N-(dithiocarboxy-kS,kS')-N-methylglycinate] gold(III)), is endowed with promising in vitro/in vivo antitumor activity and toxicological profile. Here, we report our recent strategies to improve its water solubility and stability under physiological conditions along with our efforts for unravelling its tangled mechanism of action. We used three types of α-cyclodextrins (CDs), namely β-CD, Me-β-CD and HP-β-CD to prepare aqueous solutions of AuL12. The ability of these natural oligosaccharide carriers to enhance water solubility of hydrophobic compounds, allowed drug stability of AuL12 to be investigated. Moreover, pharmacokinetic experiments were first carried out for a gold(III) coordination compound, after i.v. injection of the nanoformulation AuL12/HP-β-CD to female mice. The gold content in the blood samples was detected at scheduled times by AAS (atomic absorption spectrometry) analysis, highlighting a fast biodistribution with a t_β1/2 of few minutes and a slow escretion (t_α1/2 of 14.3 h). The in vitro cytotoxic activity of AuL12 was compared with the AuL12/HP-β-CD mixture against a panel of three human tumor cell lines (i.e., HeLa, KB and MCF7). Concerning the mechanism of action, we previously reported the proteasome-inhibitory activity of some our gold(III)-based compounds. In this work, we moved from the proteasome target to upstream of the important ubiquitin-proteasome pathway, testing the effects of AuL12 on the polyubiquitination reactions involving the Ub-activating (E1) and -conjugating (E2) enzymes.

The Inorganic Side of NGF: Copper(II) and Zinc(II) Affect the NGF Mimicking Signaling of the N-Terminus Peptides Encompassing the Recognition Domain of TrkA Receptor

The nerve growth factor (NGF) N-terminus peptide, NGF(1–14), and its acetylated form, Ac-NGF(1–14), were investigated to scrutinize the ability of this neurotrophin domain to mimic the whole protein. Theoretical calculations demonstrated that non-covalent forces assist the molecular recognition of TrkA receptor by both peptides. Combined parallel tempering/docking simulations discriminated the effect of the N-terminal acetylation on the recognition of NGF(1–14) by the domain 5 of TrkA (TrkA-D5). Experimental findings demonstrated that both NGF(1–14) and Ac-NGF(1–14) activate TrkA signaling pathways essential for neuronal survival. The NGF-induced TrkA internalization was slightly inhibited in the presence of Cu²⁺ and Zn²⁺ ions, whereas the metal ions elicited the NGF(1–14)-induced internalization of TrkA and no significant differences were found in the weak Ac-NGF(1–14)-induced receptor internalization. The crucial role of the metals was confirmed by experiments with the metal-chelator bathocuproine disulfonic acid, which showed different inhibitory effects in the signaling cascade, due to different metal affinity of NGF, NGF(1–14) and Ac-NGF(1–14). The NGF signaling cascade, activated by the two peptides, induced CREB phosphorylation, but the copper addition further stimulated the Akt, ERK and CREB phosphorylation in the presence of NGF and NGF(1–14) only. A dynamic and quick influx of both peptides into PC12 cells was tracked by live cell imaging with confocal microscopy. A significant role of copper ions was found in the modulation of peptide sub-cellular localization, especially at the nuclear level. Furthermore, a strong copper ionophoric ability of NGF(1–14) was measured. The Ac-NGF(1–14) peptide, which binds copper ions with a lower stability constant than NGF(1–14), exhibited a lower nuclear localization with respect to the total cellular uptake. These findings were correlated to the metal-induced increase of CREB and BDNF expression caused by NGF(1–14) stimulation. In summary, we here validated NGF(1–14) and Ac-NGF(1–14) as first examples of monomer and linear peptides able to activate the NGF-TrkA signaling cascade. Metal ions modulated the activity of both NGF protein and the NGF-mimicking peptides. Such findings demonstrated that NGF(1–14) sequence can reproduce the signal transduction of whole protein, therefore representing a very promising drug candidate for further pre-clinical studies.

Multiple allosteric sites are involved in the modulation of insulin-degrading-enzyme activity by somatostatin

Somatostatin is a cyclic peptide, released in the gastrointestinal system and the central nervous system, where it is involved in the regulation of cognitive and sensory functions, motor activity and sleep. It is a substrate of insulin-degrading enzyme (IDE), as well as a modulator of its activity and expression. In the present study, we have investigated the modulatory role of somatostatin on IDE activity at 37 °C and pH 7.3 for various substrates [i.e. insulin, β-amyloid (Aβ)_1-40 and bradykinin], aiming to quantitatively characterize the correlation between the specific features of the substrates and the regulatory mechanism. Functional data indicate that somatostatin, in addition to the catalytic site of IDE (being a substrate), is also able to bind to two additional exosites, which play different roles according to the size of the substrate and its binding mode to the IDE catalytic cleft. In particular, one exosite, which displays high affinity for somatostatin, regulates only the interaction of IDE with larger substrates (such as insulin and Aβ_1-40 ) in a differing fashion according to their various modes of binding to the enzyme. A second exosite, which is involved in the regulation of enzymatic processing by IDE of all substrates investigated (including a 10-25 amino acid long amyloid-like peptide, bradykinin and somatostatin itself, which had been studied previously), probably acts through the alteration of an 'open-closed' equilibrium.