Showing papers in "Cellular and Molecular Life Sciences in 2005"

Hsp70 chaperones: cellular functions and molecular mechanism.

Abstract: Hsp70 proteins are central components of the cellular network of molecular chaperones and folding catalysts. They assist a large variety of protein folding processes in the cell by transient association of their substrate binding domain with short hydrophobic peptide segments within their substrate proteins. The substrate binding and release cycle is driven by the switching of Hsp70 between the low-affinity ATP bound state and the high-affinity ADP bound state. Thus, ATP binding and hydrolysis are essential in vitro and in vivo for the chaperone activity of Hsp70 proteins. This ATPase cycle is controlled by co-chaperones of the family of J-domain proteins, which target Hsp70s to their substrates, and by nucleotide exchange factors, which determine the lifetime of the Hsp70-substrate complex. Additional co-chaperones fine-tune this chaperone cycle. For specific tasks the Hsp70 cycle is coupled to the action of other chaperones, such as Hsp90 and Hsp100.

Tyrosinase inhibitors from natural and synthetic sources: structure, inhibition mechanism and perspective for the future.

Abstract: Tyrosinase is known to be a key enzyme in melanin biosynthesis, involved in determining the color of mammalian skin and hair. Various dermatological disorders, such as melasma, age spots and sites of actinic damage, arise from the accumulation of an excessive level of epidermal pigmentation. In addition, unfavorable enzymatic browning of plant-derived foods by tyrosinase causes a decrease in nutritional quality and economic loss of food products. The inadequacy of current conventional techniques to prevent tyrosinase action encourages us to seek new potent tyrosinase inhibitors. This article overviews the various inhibitors obtained from natural and synthetic sources with their industrial importance.

Surface exposure of phosphatidylserine in pathological cells.

Abstract: The asymmetric phospholipid distribution in plasma membranes is normally maintained by energy-dependent lipid transporters that translocate different phospholipids from one monolayer to the other against their respective concentration gradients. When cells are activated, or enter apoptosis, lipid asymmetry can be perturbed by other lipid transporters (scramblases) that shuttle phospholipids non-specifically between the two monolayers. This exposes phosphatidylserine (PS) at the cells' outer surface. Since PS promotes blood coagulation, defective scramblase activity upon platelet stimulation causes a bleeding disorder (Scott syndrome). PS exposure also plays a pivotal role in the recognition and removal of apoptotic cells via a PS-recognizing receptor on phagocytic cells. Furthermore, expression of PS at the cell surface can occur in a wide variety of disorders. This review aims at highlighting how PS expression in different cells may complicate a variety of pathological conditions, including those that promote thromboembolic complications or produce aberrations in apoptotic cell removal.

Cell-penetrating peptides: tools for intracellular delivery of therapeutics.

Abstract: The main problem of therapeutic efficiency lies in the crossing of cellular membranes. Therefore, significant effort is being made to develop agents which can cross these barriers and deliver therapeutic agents into cellular compartments. In recent years, a large amount of data on the use of peptides as delivery agents has accumulated. Several groups have published the first positive results using peptides for the delivery of therapeutic agents in relevant animal models. These peptides, called cell-penetrating peptides (CPPs), are short peptides (fewer than 30 residues) with a net positive charge and acting in a receptor- and energy-independent manner. Here, we give an extensive review of peptide-mediated delivery systems and discuss their applications, with particular focus on the mechanisms leading to cellular internalization.

Small heat shock proteins: molecular structure and chaperone function

Abstract: Small heat shock proteins (sHSPs) associate with nuclei, cytoskeleton and membranes, and as molecular chaperones they bind partially denatured proteins, thereby preventing irreversible protein aggregation during stress. sHSP monomers consist of a conserved alpha-crystallin domain of approximately 90 amino acid residues, bordered by variable amino- and carboxy-terminal extensions. The sHSPs undergo dynamic assembly into mono- and poly-disperse oligomers where the rate of disassembly affects chaperoning. The alpha-crystallin domain contains several beta-strands organized into two beta-sheets responsible for dimer formation, the basic building block of most sHSPS. The amino-terminal extension modulates oligomerization, subunit dynamics and substrate binding, whereas the flexible carboxy-terminal extension promotes solubility, chaperoning and oligomerization, the latter by inter-subunit linkage. Crystallization studies have revealed sHSP structure and function. Additionally, site-directed mutagenesis, biophysical investigations, functional studies and the discovery of relationships between mutated sHSPs and diseases have illuminated the role of sHSP within cells.

G-protein signaling: back to the future

Abstract: Heterotrimeric G-proteins are intracellular partners of G-protein-coupled receptors (GPCRs). GPCRs act on inactive Gα·GDP/Gβγ heterotrimers to promote GDP release and GTP binding, resulting in liberation of Gα from Gβγ. Gα·GTP and Gβγ target effectors including adenylyl cyclases, phospholipases and ion channels. Signaling is terminated by intrinsic GTPase activity of Gα and heterotrimer reformation — a cycle accelerated by ‘regulators of G-protein signaling’ (RGS proteins). Recent studies have identified several unconventional G-protein signaling pathways that diverge from this standard model. Whereas phospholipase C (PLC) β is activated by Gαq and Gβγ, novel PLC isoforms are regulated by both heterotrimeric and Ras-superfamily G-proteins. An Arabidopsis protein has been discovered containing both GPCR and RGS domains within the same protein. Most surprisingly, a receptor-independent Gα nucleotide cycle that regulates cell division has been delineated in both Caenorhabditis elegans and Drosophila melanogaster. Here, we revisit classical heterotrimeric G-protein signaling and explore these new, non-canonical G-protein signaling pathways.

Type II restriction endonucleases: structure and mechanism.

Abstract: Type II restriction endonucleases are components of restriction modification systems that protect bacteria and archaea against invading foreign DNA. Most are homodimeric or tetrameric enzymes that cleave DNA at defined sites of 4-8 bp in length and require Mg2+ ions for catalysis. They differ in the details of the recognition process and the mode of cleavage, indicators that these enzymes are more diverse than originally thought. Still, most of them have a similar structural core and seem to share a common mechanism of DNA cleavage, suggesting that they evolved from a common ancestor. Only a few restriction endonucleases discovered thus far do not belong to the PD...D/ExK family of enzymes, but rather have active sites typical of other endonuclease families. The present review deals with new developments in the field of Type II restriction endonucleases. One of the more interesting aspects is the increasing awareness of the diversity of Type II restriction enzymes. Nevertheless, structural studies summarized herein deal with the more common subtypes. A major emphasis of this review will be on target site location and the mechanism of catalysis, two problems currently being addressed in the literature.

Host defense peptides as new weapons in cancer treatment.

Abstract: In the last decade intensive research has been conducted to determine the role of innate immunity host defense peptides (also termed antimicrobial peptides) in the killing of prokaryotic and eukaryotic cells. Many antimicrobial peptides damage the cellular membrane as part of their killing mechanism. However, it is not clear what makes cancer cells more susceptible to some of these peptides, and what the molecular mechanisms underlying these activities are. Two general mechanisms were suggested: (i) plasma membrane disruption via micellization or pore formation, and (ii) induction of apoptosis via mitochondrial membrane disruption. To be clinically used, these peptides need to combine high and specific anticancer activity with stability in serum. Although so far very limited, new studies have paved the way for promising anticancer host defense peptides with a new mode of action and with a broad spectrum of anticancer activity.

Phospholipase D: a lipid centric review.

Abstract: Phospholipase D (PLD) hydrolyzes the phosphodiester bond of the glycerolipid phosphatidylcholine, resulting in the production of phosphatidic acid and free choline. Phosphatidic acid is widely considered to be the intracellular lipid mediator of many of the biological functions attributed to PLD. However, phosphatidic acid is a tightly regulated lipid in cells and can be converted to other potentially bioactive lipids, including diacylglycerol and lysophosphatidic acid. PLD activities have been described in multiple organisms, including plants, mammals, bacteria and yeast. In mammalian systems, PLD activity regulates the actin cytoskeleton, vesicle trafficking for secretion and endocytosis, and receptor signaling. PLD is in turn regulated by phosphatidylinositol-4,5-bisphosphate, protein kinase C and ADP Ribosylation Factor and Rho family GTPases. This review focuses on the lipid precursors and products of mammalian PLD metabolism, especially phosphatidic acid and the roles this lipid performs in the mediation of the functions of PLD.

Lactoferricin: a lactoferrin-derived peptide with antimicrobial, antiviral, antitumor and immunological properties.

Abstract: The peptide lactoferricin (Lfcin) can be released from the multifunctional protein lactoferrin (LF) through proteolysis by pepsin under acidic conditions, a reaction that occurs naturally in the stomach. Lfcin encompasses a large portion of the functional domain of the intact protein, and in many cases it not only retains the activities of LF but is more active. Lfcin possesses strong antimicrobial and weak antiviral activities, and it also has potent antitumor and immunological properties. This review covers the current state of research in this field, focusing on the many beneficial activities of this peptide. Throughout we will discuss the breadth of Lfcin activity as well as the mechanism of action. Many recent studies have drawn attention to the fact that the main site of action for the peptide may be intracellular. In addition the results of structural and dynamic studies of Lfcin are presented, and the relationship between structure and activity is explored.

Lactoferrin: an important host defence against microbial and viral attack.

Abstract: The first function attributed to lactoferrin (Lf), an iron binding protein belonging to the non-immune natural defences, was antimicrobial activity that depended on its capacity to sequester iron. Iron-independent microbicidal activities, requiring direct interaction between this cationic protein and microbial surface components, were later demonstrated. Many other anti-microbial and anti-viral functions have since been ascribed to Lf. In mucosal secretions, iron and Lf modulate the motility and aggregation of pathogenic bacteria. Lf inhibits bacterial adhesion on abiotic surfaces through ionic binding to biomaterials, or specific binding to bacterial structures or both. Lf inhibition of bacterial adhesion to host cells requires Lf binding to bacteria and/or host cells. Lf hinders microbial internalization by binding to both glycosaminoglycans and bacterial proteins which can be degraded by Lf-mediated proteolysis. Moreover, Lf internalisation and localisation to the host cell nuclei could modulate bacterial entry into cells through gene regulation. Finally, the capability of Lf to exert antiviral activity, through its binding to host cells and/or viral particles, strengthens the idea that it is an important brick in the mucosal wall, effective against both microbial and viral attacks.

Acetyl-coenzyme A carboxylase: crucial metabolic enzyme and attractive target for drug discovery.

Abstract: Acetyl-coenzyme A carboxylases (ACCs) have crucial roles in fatty acid metabolism in most living organisms. Mice deficient in ACC2 have continuous fatty acid oxidation and reduced body fat and body weight, validating this enzyme as a target for drug development against obesity, diabetes and other symptoms of the metabolic syndrome. ACC is a biotin-dependent enzyme and catalyzes the carboxylation of acetyl-CoA to produce malonyl-CoA through its two catalytic activities, biotin carboxylase (BC) and carboxyltransferase (CT). ACC is a multi-subunit enzyme in most prokaryotes, whereas it is a large, multi-domain enzyme in most eukaryotes. The activity of the enzyme can be controlled at the transcriptional level as well as by small molecule modulators and covalent modification. This review will summarize the structural information that is now available for both the BC and CT enzymes, as well as the molecular mechanism of action of potent ACC inhibitors. The current intense research on these enzymes could lead to the development of novel therapies against metabolic syndrome and other diseases.

Multifunctional roles of lactoferrin: a critical overview.

Abstract: Lactoferrin (LF) is a member of the transferrin family that is expressed and secreted by glandular epithelial cells and is found in the secondary granules of neutrophils. Originally viewed as an iron-binding protein in milk, with bacteriostatic properties, it is becoming increasingly evident that LF is a multifunctional protein to which several physiological roles have been attributed. These include regulation of iron homeostasis, host defense against a broad range of microbial infections, anti-inflammatory activity, regulation of cellular growth and differentiation and protection against cancer development and metastasis. While iron binding is likely central to some of the biological roles of LF, other activities, including specific interactions with mammalian receptors and microbial components, also contribute to the pleoitropic functional nature of this protein. In this article, recent advances in the understanding of these functions at the cellular and molecular level are discussed.

Lateral gene transfer in eukaryotes

Abstract: Lateral gene transfer – the transfer of genetic material between species – has been acknowledged as a major mechanism in prokaryotic genome evolution for some time. Recently accumulating data indicate that the process also occurs in the evolution of eukaryotic genomes. However, there are large rate variations between groups of eukaryotes; animals and fungi seem to be largely unaffected, with a few exceptions, while lateral gene transfer frequently occurs in protists with phagotrophic lifestyles, possibly with rates comparable to prokaryotic organisms. Gene transfers often facilitate the acquisition of functions encoded in prokaryotic genomes by eukaryotic organisms, which may enable them to colonize new environments. Transfers between eukaryotes also occur, mainly into larger phagotrophic eukaryotes that ingest eukaryotic cells, but also between plant lineages. These findings have implications for eukaryotic genomic research in general, and studies of the origin and phylogeny of eukaryotes in particular.

The catalytic triad of serine peptidases

Abstract: The catalytic action of serine peptidases depends on the interplay of a nucleophile, a general base and an acid. In the classic trypsin and subtilisin families this catalytic triad is composed of serine, histidine and aspartic acid residues and exhibits similar spatial arrangements, but the order of the residues in the amino acid sequence is different. By now several new families have been discovered, in which the nucleophile-base-acid pattern is generally conserved, but the individual components can vary. The variations illustrate how different groups and different protein structures achieve the same reaction.

Lactoferrin: a modulator of immune and inflammatory responses.

Abstract: Lactoferrin is an iron-binding glycoprotein of the transferrin family. Abundant expression and secretion of lactoferrin, in particular in milk and fluids of the digestive tract, are related to its implication in the first line of host defense. Lactoferrin is also a prominent component of the secondary granules of neutrophils (PMNs) and is released in infected tissues and blood during the inflammatory process. In addition to its direct antimicrobial properties, the abilities of lactoferrin to regulate the immune response and to protect against infection and septic shock have been described in numerous in vitro and in vivo studies. Although the cellular and molecular mechanisms that account for the modulation of the inflammatory and immune responses by lactoferrin are not yet totally elucidated, many are now established. At the cellular level, lactoferrin modulates the migration, maturation and function of immune cells. At the molecular level and in addition to iron binding, interactions of lactoferrin with a plethora of compounds, either soluble or membrane molecules, account for its modulatory properties. This paper reviews our current understanding of the cellular and molecular mechanisms that explain the regulatory properties of lactoferrin in host defence.

Molecular structure, binding properties and dynamics of lactoferrin.

Abstract: Lactoferrin (Lf), a prominent protein in milk, many other secretory fluids and white blood cells, is a monomeric, 80-kDa glycoprotein, with a single polypeptide chain of about 690 amino acid residues. Amino acid sequence relationships place it in the wider transferrin family. Crystallographic analyses of human Lf, and of the Lfs from cow, horse, buffalo and camel, reveal a highly conserved three-dimensional structure, but with differences in detail between species. The molecule is folded into homologous N- and C-terminal lobes, each comprising two domains that enclose a conserved iron binding site. Iron binding and release is accompanied by domain movements that close or open the sites, and is influenced by cooperative interactions between the lobes. Patches of high positive charge on the surface contribute to other binding properties, but the attached glycan chains appear to have little impact on structure and function.

Mammalian lactoferrin receptors: structure and function.

Abstract: Mammalian lactoferrin (Lf) receptors are suggested to have pivotal roles for mediating multiple functions of Lf. In this review, we focus on current knowledge of the structure and function of mammalian Lf receptors, mainly the first cloned Lf receptor that has been shown to be expressed in the infant small intestine at high levels but also in virtually all other tissues. The small intestinal Lf receptor takes up iron from Lf into cells and presumably exerts other physiological functions. Other Lf receptors in various tissues have also been reported to mediate some functions of Lf, such as modulating immune function, inhibiting platelet aggregation and enhancing collagen gel contractile strength. The detailed mechanisms behind the receptor-Lf interactions still need to be elucidated.

Characterization of the rdar morphotype, a multicellular behaviour in Enterobacteriaceae.

Abstract: The rdar morphotype, a multicellular behaviour of Salmonella enterica and Escherichia coli is characterized by the expression of the adhesive extracellular matrix components cellulose and curli fimbriae. The response regulator CsgD, which transcriptionally activates the biosynthesis of the exopolysaccharide cellulose and curli, also transforms cell physiology to the multicellular state. However, the only role of CsgD in cellulose biosynthesis is the activation of AdrA, a GGDEF domain protein that mediates production of the allosteric activator cyclic-di-(3'-5')guanylic acid (c-di-GMP). In S. enterica serovar Typhimurium a regulatory network consisting of 19 GGDEF/EAL domain-containing proteins tightly controls the concentration of c-di-GMP. c-di-GMP not only regulates the expression of cellulose, but also stimulates expression of adhesive curli and represses various modes of motility. Functions of characterized GGDEF and EAL domain proteins, as well as database searches, point to a global role for c-di-GMP as a novel secondary messenger that regulates a variety of cellular functions in response to diverse environmental stimuli already in the deepest roots of the prokaryotes.

Modeling the MHC class I pathway by combining predictions of proteasomal cleavage, TAP transport and MHC class I binding.

Abstract: Epitopes presented by major histocompatibility complex (MHC) class I molecules are selected by a multi-step process. Here we present the first computational prediction of this process based on in vitro experiments characterizing proteasomal cleavage, transport by the transporter associated with antigen processing (TAP) and MHC class I binding. Our novel prediction method for proteasomal cleavages outperforms existing methods when tested on in vitro cleavage data. The analysis of our predictions for a new dataset consisting of 390 endogenously processed MHC class I ligands from cells with known proteasome composition shows that the immunological advantage of switching from constitutive to immunoproteasomes is mainly to suppress the creation of peptides in the cytosol that TAP cannot transport. Furthermore, we show that proteasomes are unlikely to generate MHC class I ligands with a C-terminal lysine residue, suggesting processing of these ligands by a different protease that may be tripeptidyl-peptidase II (TPPII).

Understanding microtubule dynamics for improved cancer therapy

Abstract: Microtubules (MTs), key components of the cytoskeleton, are dynamic polymers of tubulin that form a well-organized network of polarized tube filaments. MT dynamics are highly regulated both spacially and temporally by several MT-related proteins, themselves regulated by several kinases and phosphatases via signaling cascades, and also by coordinated interactions with actin cytoskeleton and adhesion sites. Regulation of MT dynamics is crucial for mitosis, cell migration, cell signaling and trafficking. MT-targeted drugs (MTDs), which constitute a major anticancer drug family with antimitotic and antiangiogenic properties, inhibit tumor progression mainly by altering MT dynamics in both cancer and endothelial cells. Identification of proteins regulating the MT network will lead to a better understanding of tumor progression regulators and will be helpful in improving cancer therapy.

Scaffolding microdomains and beyond: the function of reggie/flotillin proteins.

Abstract: Reggie/flotillin proteins are considered to be components of lipid rafts and are commonly used as marker proteins for lipid microdomains. Yet almost a decade after their discovery, the function of reggies/ flotillins is still enigmatic. In this review we summarize the present state of knowledge on reggie/flotillin structure, localization and function, and discuss the role of the proteins in development and disease. Based on insights into reggie/flotillin function and by comparison with related proteins of the so-called SPFH (Stomatin/Prohibitin/Flotillin/HflK/C) protein family, including stomatin, podocin and prohibitin, we propose the existence of specific types of protein-defined microdomains which are sculpt by the clustering of individual SPFH proteins. As 'specialized rafts' similar to caveolae, these membrane domains provide platforms for the recruitment of multiprotein complexes. Since, under certain circumstances, reggie-2/flotillin-1 translocates to the nucleus, reggie/ flotillin microdomains are not only stable scaffolds but also dynamic units with their own regulatory functions.

Aluminium in Alzheimer's disease: are we still at a crossroad?

Abstract: Aluminium, an environmentally abundant non-redox trivalent cation has long been implicated in the pathogenesis of Alzheimer's disease (AD). However, the definite mechanism of aluminium toxicity in AD is not known. Evidence suggests that trace metal homeostasis plays a crucial role in the normal functioning of the brain, and any disturbance in it can exacerbate events associated with AD. The present paper reviews the scientific literature linking aluminium with AD. The focus is on aluminium levels in brain, region-specific and subcellular distribution, its relation to neurofibrillary tangles, amyloid beta, and other metals. A detailed mechanism of the role of aluminium in oxidative stress and cell death is highlighted. The importance of complex speciation chemistry of aluminium in relation to biology has been emphasized. The debatable role of aluminium in AD and the cross-talk between aluminium and genetic susceptibility are also discussed. Finally, it is concluded based on extensive literature that the neurotoxic effects of aluminium are beyond any doubt, and aluminium as a factor in AD cannot be discarded. However, whether aluminium is a sole factor in AD and whether it is a factor in all AD cases still needs to be understood.

The plant thioredoxin system.

Abstract: Thioredoxins are small proteins catalyzing thiol-disulfide interchange and are involved in the regulation of the redox environment of the cell. In plants, the thioredoxin system is particularly complex since at least 20 thioredoxin isoforms are found in the plant model Arabidopsis thaliana. Based upon primary sequence analysis and subcellular localization, thioredoxins can be classified into different groups and subgroups. Different pathways allowing thioredoxin reduction also coexist in the plant involving ferredoxin-thioredoxin reductase, thioredoxin reductases and the glutathione/glutaredoxin system. This review discusses the literature of plant thioredoxins with emphasis on recent findings in the field.

Regulation and termination of NADPH oxidase activity.

Abstract: NADPH oxidase of phagocytes plays a crucial role in host defense by producing reactive oxygen species (ROS) that are intended to kill invading microbes. Many other cells produce ROS for signaling purposes. The respiratory burst oxidase in human neutrophils is the main but not exclusive subject of this review, because it is archetypical and has been studied most extensively. The activity of this enzyme must be controlled in phagocytes to prevent collateral damage, and in non-phagocytic cells to perform its signaling role. With many stimuli, NADPH oxidase activity is transient. Various forms of evidence indicate that sustained NADPH oxidase activity requires continuous renewal of the enzyme complex, without which rapid deactivation occurs. This review considers mechanisms that have been proposed to terminate the phagocyte respiratory burst. Changes in the phosphorylation state of p47phox and in the species of nucleotide bound to Rac seem to be the dominant factors in deactivation.

Leptin receptor action and mechanisms of leptin resistance.

Abstract: The adipose tissue-derived hormone leptin regulates energy balance and neuroendocrine function. Resistance to the appetite-suppressing effects of leptin is associated with common forms of obesity. Here, we review the mechanisms by which leptin activates intracellular signals and the roles that these signals play in leptin action in vivo. Furthermore, we discuss potential mechanisms of leptin resistance, specifically focusing on data regarding the neuroanatomical locus of leptin resistance and potential mechanisms by which expression of the suppressor of cytokine signaling-3 may impair leptin action.

Function and molecular evolution of multicopper blue proteins

Abstract: Multicopper blue proteins (MCBPs) are multidomain proteins that utilize the distinctive redox ability of copper ions. There are a variety of MCBPs that have been roughly classified into three different groups, based on their domain organization and functions: (i) nitrite reductase-type with two domains, (ii) laccase-type with three domains, and (iii) ceruloplasmin-type with six domains. Together, the second and third group are often commonly called multicopper oxidases (MCOs). The rapid accumulation of genome sequence information in recent years has revealed several new types of proteins containing MCBP domains, mainly from bacteria. In this review, the recent research on the functions and structures of MCBPs is summarized, mainly focusing on the new types. The latter half of this review focusses on the twodomain MCBPs, which we propose as the evolutionary intermediate of the MCBP family.

Human selenoproteins at a glance

Abstract: The public perception of selenium has changed significantly over the last decades. Originally mainly known for its high toxicity, it was later recognized as an essential trace element and is now (despite its narrow therapeutic window) almost being marketed as a lifestyle drug. Indeed, some clinical and preclinical studies suggest that selenium supplementation may be beneficial in a large number of clinical conditions. However, its mode of action is unresolved in most of these cases. Selenocysteine – identified as the 21st amino acid used in ribosome-mediated protein synthesis – is incorporated in at least 25 specific, genetically determined human selenoproteins, many of which have only recently been discovered. Restoration of normal selenoprotein levels may be – apart from direct supranutritional effects – one possible explanation for the effects of selenium supplements. In this review we provide a brief but up-to-date overview of what is currently known about these 25 acknowledged human selenoproteins and their synthesis.

Antitumor effect of β-elemene in non-small-cell lung cancer cells is mediated via induction of cell cycle arrest and apoptotic cell death

Abstract: β-Elemene is a novel anticancer drug, which was extracted from the ginger plant. However, the mechanism of action of β-elemene in non-small-cell lung cancer (NSCLC) remains unknown. Here we show that β-elemene had differential inhibitory effects on cell growth between NSCLC cell lines and lung fibroblast and bronchial epithelial cell lines. In addition, β-elemene was found to arrest NSCLC cells at G2-M phase, the arrest being accompanied by decreases in the levels of cyclin B1 and phospho-Cdc2 (Thr-161) and increases in the levels of p27kip1 and phospho-Cdc2 (Tyr-15). Moreover, β-elemene reduced the expression of Cdc25C, which dephosphorylates/activates Cdc2, but enhanced the expression of the checkpoint kinase, Chk2, which phosphorylates/ inactivates Cdc25C. These findings suggest that the effect of β-elemene on G2-M arrest in NSCLC cells is mediated partly by a Chk2-dependent mechanism. We also demonstrate that β-elemene triggered apoptosis in NSCLC cells. Our results clearly show that β-elemene induced caspase-3, −7 and −9 activities, decreased Bcl-2 expression, caused cytochrome c release and increased the levels of cleaved caspase-9 and poly(ADP-ribose) polymerase in NSCLC cells. These data indicate that the effect of β-elemene on lung cancer cell death may be through a mitochondrial release of the cytochrome c-mediated apoptotic pathway.

Phosphodiesterase: overview of protein structures, potential therapeutic applications and recent progress in drug development.

Abstract: Phosphodiesterases (PDEs) are essential regulators of cyclic nucleotide signaling with diverse physiological functions. Because of their great market potential and therapeutic importance, PDE inhibitors became recognized as important therapeutic agents in the treatment of various diseases. Currently, there are seven PDE inhibitors on the market, and the pharmacological and safety evaluations of many drug candidates are in progress. Three-dimensional (3D) structures of catalytic domains of PDE 1, -3, -4, -5 and -9 in the presence of their inhibitors are now available, and can be utilized for rational drug design. Recent advances in molecular pharmacology of PDE isoenzymes resulted in identification of new potential applications of PDE inhibitors in various therapeutic areas, including dementia, depression and schizophrenia. This review will describe the latest advances in PDE research on 3D structural studies, the potential of therapeutic applications and the development of drug candidates.