Regulation of Alzheimer's disease amyloid-beta formation by casein kinase I

Synthesis and biological evaluation of N-aryl-7-methoxybenzo[b]furo[3,2-d]pyrimidin-4-amines and their N-arylbenzo[b]thieno[3,2-d]pyrimidin-4-amine analogues as dual inhibitors of CLK1 and DYRK1A kinases

Novel N-aryl-7-methoxybenzo[b]furo[3,2-d]pyrimidin-4-amines (1) and their N-arylbenzo[b]thieno[3,2-d]pyrimidin-4-amine analogues (2) were designed and prepared for the first time via microwave-accelerated multi-step synthesis. Various anilines were condensed with N'-(2-cyanaryl)-N,N-dimethylformimidamide intermediates obtained by reaction of 3-amino-6-methoxybenzofuran-2-carbonitrile (3) and 3-amino-6-methoxybenzothiophene-2-carbonitrile (4) precursors with dimethylformamide dimethylacetal. The inhibitory potency of the final products against five protein kinases (CDK5/p25, CK1δ/ε, GSK3α/β, DYRK1A and CLK1) was estimated. Compounds (2a-z) turned out to be particularly promising for the development of new pharmacological dual inhibitors of CLK1 and DYRK1A kinases.

Aftins increase amyloid-β42, lower amyloid-β38, and do not alter amyloid-β40 extracellular production in vitro: toward a chemical model of Alzheimer's disease?

Increased production of amyloid-β (Aβ)42 peptide, derived from the amyloid-β protein precursor, and its subsequent aggregation into oligomers and plaques constitutes a hallmark of Alzheimer's disease (AD). We here report on a family of low molecular weight molecules, the Aftins (Amyloid-β Forty-Two Inducers), which, in cultured cells, dramatically affect the production of extracellular/secreted amyloid peptides. Aftins trigger β-secretase inhibitor and γ-secretase inhibitors (GSIs) sensitive, robust upregulation of Aβ42, and parallel down-regulation of Aβ38, while Aβ40 levels remain stable. In contrast, intracellular levels of these amyloids appear to remain stable. In terms of their effects on Aβ38/Aβ40/Aβ42 relative abundance, Aftins act opposite to γ-secretase modulators (GSMs). Aβ42 upregulation induced by Aftin-5 is unlikely to originate from reduced proteolytic degradation or diminished autophagy. Aftin-5 has little effects on mitochondrial functional parameters (swelling, transmembrane potential loss, cytochrome c release, oxygen consumption) but reversibly alters the ultrastructure of mitochondria. Aftins thus alter the Aβ levels in a fashion similar to that described in the brain of AD patients. Aftins therefore constitute new pharmacological tools to investigate this essential aspect of AD, in cell cultures, allowing (1) the detection of inhibitors of Aftin induced action (potential 'anti-AD compounds', including GSIs and GSMs) but also (2) the identification, in the human chemical exposome, of compounds that, like Aftins, might trigger sustained Aβ42 production and Aβ38 down-regulation (potential 'pro-AD compounds').

Tau protein kinases: involvement in Alzheimer's disease

Tau phosphorylation is regulated by a balance between tau kinase and phosphatase activities. Disruption of this equilibrium was suggested to be at the origin of abnormal tau phosphorylation and thereby might contribute to tau aggregation. Thus, understanding the regulation modes of tau phosphorylation is of high interest in determining the possible causes at the origin of the formation of tau aggregates in order to elaborate protection strategies to cope with these lesions in Alzheimer's disease. Among the possible and specific interventions that reverse tau phosphorylation is the inhibition of certain tau kinases. Here, we extensively reviewed tau protein kinases, their physiological roles and regulation, their involvement in tau phosphorylation and their relevance to AD. We also reviewed the most common inhibitory compounds acting on each tau kinase.

Small-molecule inducers of Aβ-42 peptide production share a common mechanism of action

The pathways leading specifically to the toxic Aβ42 peptide production, a key event in Alzheimer's disease (AD), are unknown. While searching for pathways that mediate pathological increases of Aβ42, we identified Aftin-4, a new compound that selectively and potently increases Aβ42 compared to DMSO (N2a cells: 7-fold; primary neurons: 4-fold; brain lysates: 2-fold) with an EC(50) of 30 μM. These results were confirmed by ELISA and IP-WB. Using affinity chromatography and mass spectrometry, we identified 3 proteins (VDAC1, prohibitin, and mitofilin) relevant to AD that interact with Aftin-4, but not with a structurally similar but inactive molecule. Electron microscopy studies demonstrated that Aftin-4 induces a reversible mitochondrial phenotype reminiscent of the one observed in AD brains. Sucrose gradient fractionation showed that Aftin-4 perturbs the subcellular localization of γ-secretase components and could, therefore, modify γ-secretase specificity by locally altering its membrane environment. Remarkably, Aftin-4 shares all these properties with two other "AD accelerator" compounds. In summary, treatment with three Aβ42 raising agents induced similar biochemical alterations that lead to comparable cellular phenotypes in vitro, suggesting a common mechanism of action involving three structural cellular targets.

Synthesis and biological evaluation of N-arylbenzo[b]thieno[3,2-d]pyrimidin-4-amines and their pyrido and pyrazino analogues as Ser/Thr kinase inhibitors

A useful and rapid access to libraries of N-arylbenzo[b]thieno[3,2-d]pyrimidin-4-amines and their pyrido and pyrazino analogues was designed and optimized for the first time via microwave-accelerated condensation and Dimroth rearrangement of the starting anilines with N'-(2-cyanoaryl)-N,N-dimethylformimidamides obtained by reaction of thiophene precursors with dimethylformamide dimethylacetal. The inhibitory potency of the final products against five protein kinases (CDK5/p25, CK1δ/ɛ, GSK3α/β, DYRK1A and CLK1) was estimated. N-arylpyrido[3',2':4,5]thieno[3,2-d]pyrimidin-4-amine series of compounds (4a-j) turned out to be particularly promising for the development of new pharmacological inhibitors of CK1 and CLK1 kinases.

Beneficial effect of antibodies against β- secretase cleavage site of APP on Alzheimer's-like pathology in triple-transgenic mice

The toxicity of amyloid β and tau, the two hallmark proteins in Alzheimer's disease (AD), has been extensively studied individually. Recently new data suggest their possible interactions and synergistic effects in the disease. In this study, we investigate the ability of antibodies against the β secretase cleavage site on APP, named BBS1, to affect tau pathology, besides their well established effect on intracellular Aβ and amyloid load. For this purpose we treated the triple transgenic mice model of AD (3x Tg-AD) with mAb BBS1 intracerebroventricularly, using mini osmotic pumps for one month. The experimental data demonstrated reduction in total and phosphorylated tau levels, explained by significant reduction in GSK3β which phosphorylates tau on sites recognized by antibodies against PHF1 and AT-8. The treatment increased the cognitive capabilities and reduced the brain inflammation levels which accompany AD pathology. The data showing that tau pathology was significantly reduced by BBS1 antibodies suggest a close interaction between tau and Aβ in the development of AD, and may serve as an efficient novel immunotherapy against both hallmarks of this disease.

Enzyme responsive materials: design strategies and future developments

Enzyme responsive materials (ERMs) are a class of stimuli responsive materials with broad application potential in biological settings. This review highlights current and potential future design strategies for ERMs and provides an overview of the present state of the art in the area.

Control of Aβ release from human neurons by differentiation status and RET signaling

Few studies have compared the processing of endogenous human amyloid precursor protein (APP) in younger and older neurons. Here, we characterized LUHMES cells as a human model to study Alzheimer's disease-related processes during neuronal maturation and aging. Differentiated LUHMES expressed and spontaneously processed APP via the secretase pathways, and they secreted amyloid β (Aβ) peptide. This was inhibited by cholesterol depletion or secretase inhibition, but not by block of tau phosphorylation. In vitro aged cells increased Aβ secretion without upregulation of APP or secretases. We identified the medium constituent glial cell line-derived neurotrophic factor (GDNF) as responsible for this effect. GDNF-triggered Aβ release was associated with rapid upregulation of the GDNF coreceptor "rearranged during transfection" (RET). Other direct (neurturin) or indirect (nerve growth factor) RET activators also increased Aβ, whereas different neurotrophins were ineffective. Downstream of RET, we found activation of protein kinase B (AKT) to be involved. Accordingly, inhibitors of the AKT regulator phosphatidylinositol-3-kinase completely blocked GDNF-triggered AKT phosphorylation and Aβ increase. This suggests that RET signaling affects Aβ release from aging neurons.

Casein kinase I delta controls centrosome positioning during T cell activation

CK1delta binds and phosphorylates the microtubule plus-end–binding protein EB1 and promotes centrosome translocation to the immunological synapse in T cells.

Although termed central body, the centrosome is located off-center in many polarized cells. T cell receptor (TCR) engagement by antigens induces a polarity switch in T cells. This leads to the recruitment of the centrosome to the immunological synapse (IS), a specialized cell–cell junction. Despite much recent progress, how TCR signaling triggers centrosome repositioning remains poorly understood. In this paper, we uncover a critical requirement for the centrosomal casein kinase I delta (CKIδ) in centrosome translocation to the IS. CKIδ binds and phosphorylates the microtubule plus-end–binding protein EB1. Moreover, a putative EB1-binding motif at the C terminus of CKIδ is required for centrosome translocation to the IS. We find that depletion of CKIδ in T lymphocytes and inhibition of CKI in epithelial cells reduce microtubule growth. Therefore, we propose that CKIδ–EB1 complexes contribute to the increase in microtubule growth speeds observed in polarized T cells, a mechanism that might serve to generate long-stable microtubules necessary for centrosome translocation.

Monitoring selectivity in kinase-promoted phosphorylation of densely packed peptide monolayers using label-free electrochemical detection

This paper describes remarkably high sensitivities in the label-free detection of kinase-promoted phosphorylation for 14 different peptide substrates on electrode-immobilized monolayers (gold or nitride) using serine/threonine kinases PKA, PKC, and CaMK2. Peptide substrates were preselected using (33)P-labeling in a microarray of 1024 substrates. The three most active peptides (A1-A3, C1-C3, and M1-M3) were investigated using electrochemical impedance spectroscopy (EIS) and ion-sensitive field effect transistors (ISFETs). Some of the peptide substrates, for example, the PKC-specific substrate PPRRSSIRNAH (C1), showed a remarkably high sensitivity in the EIS-based sensor measurements. Our studies revealed that this high sensitivity is primarily due to the monolayer's packing density. Nanoscopic studies demonstrated a distinct disordering of the C1-monolayer upon phosphorylation, while phosphatase-promoted dephosphorylation regenerated the highly ordered peptide monolayer. As a matter of fact, the initial surface packing of the peptide monolayer mainly determined the level of sensitivity, whereas electrostatic repulsion of the redox-active species was found to be much less important.

Recent advances in the multitarget-directed ligands approach for the treatment of Alzheimer's disease

With 27 million cases worldwide documented in 2006, Alzheimer's disease (AD) constitutes an overwhelming health, social, economic, and political problem to nations. Unless a new medicine capable to delay disease progression is found, the number of cases will reach 107 million in 2050. So far, the therapeutic paradigm one-compound-one-target has failed. This could be due to the multiple pathogenic mechanisms involved in AD including amyloid β (Aβ) aggregation to form plaques, τ hyperphosphorylation to disrupt microtubule to form neurofibrillary tangles, calcium imbalance, enhanced oxidative stress, impaired mitochondrial function, apoptotic neuronal death, and deterioration of synaptic transmission, particularly at cholinergic neurons. Approximately 100 compounds are presently been investigated directed to single targets, namely inhibitors of β and γ secretase, vaccines or antibodies that clear Aβ, metal chelators to inhibit Aβ aggregation, blockers of glycogen synthase kinase 3β, enhancers of mitochondrial function, antioxidants, modulators of calcium-permeable channels such as voltage-dependent calcium channels, N-methyl-D-aspartate receptors for glutamate, or enhancers of cholinergic neurotransmission such as inhibitors of acetylcholinesterase or butyrylcholinesterase. In view of this complex pathogenic mechanisms, and the successful treatment of chronic diseases such as HIV or cancer, with multiple drugs having complementary mechanisms of action, the concern is growing that AD could better be treated with a single compound targeting two or more of the pathogenic mechanisms leading to neuronal death. This review summarizes the current therapeutic strategies based on the paradigm one-compound-various targets to treat AD. A treatment that delays disease onset and/or progression by 5 years could halve the number of people requiring institutionalization and/or dying from AD. 

The recent updates of therapeutic approaches against aβ for the treatment of Alzheimer's disease

One of the main neuropathological lesions observed in brain autopsy of Alzheimer's disease (AD) patients is the extracellular senile plaques mainly composed of amyloid-beta (Aβ) peptide. Recently, treatment strategies have focused on modifying the formation, clearance, and accumulation of this potentially neurotoxic peptide. β- and γ-secretase are responsible for the cleavage of amyloid precursor protein (APP) and the generation of Aβ peptide. Treatments targeting these two critical secretases may therefore reduce Aβ peptide levels and positive impact on AD. Vaccination is also an advanced approach against Aβ. This review focuses on recent advances of our understanding of this key peptide, with emphasis on Aβ peptide synthesis, accumulation and neurotoxicity, and current therapies including vaccination and two critical secretase inhibitors. MicroRNAs (miRNAs) are a class of conserved endogenous small noncoding RNAs, known to regulate the expression of complementary messenger RNAs, involved in AD development. We therefore address the relationship of miRNAs in the brain and Aβ generation, as a novel therapeutic approach to the treatment of AD while also providing new insights on the etiology of this neurological disorder.

Dynamic association of tau with neuronal membranes is regulated by phosphorylation

Tau is an abundant cytosolic protein which regulates cytoskeletal stability by associating with microtubules in a phosphorylation-dependent manner. We have found a significant proportion of tau is located in the membrane fraction of rat cortical neurons and is dephosphorylated, at least at Tau-1 (Ser199/Ser202), AT8 (Ser199/Ser202/Thr205) and PHF-1 (Ser396/Ser404) epitopes. Inhibition of tau kinases casein kinase 1 (CK1) or glycogen synthase kinase-3 decreased tau phosphorylation and significantly increased amounts of tau in the membrane fraction. Mutation of serine/threonine residues to glutamate to mimic phosphorylation in the N-terminal, but not C-terminal, region of tau prevented its membrane localization in transfected cells, demonstrating that the phosphorylation state of tau directly impacts its localization. Inhibiting CK1 in neurons lacking the tyrosine kinase fyn also induced tau dephosphorylation but did not affect its membrane association. Furthermore, inhibition of CK1 increased binding of neuronal tau to the fyn-SH3 domain. We conclude that trafficking of tau between the cytosol and the neuronal membrane is dynamically regulated by tau phosphorylation through a mechanism dependent on fyn expression.

Protein kinase C and rho activated coiled coil protein kinase 2 (ROCK2) modulate Alzheimer's APP metabolism and phosphorylation of the Vps10-domain protein, SorL1

Background

Generation of the amyloid β (Aβ) peptide of Alzheimer's disease (AD) is differentially regulated through the intracellular trafficking of the amyloid β precursor protein (APP) within the secretory and endocytic pathways. Protein kinase C (PKC) and rho-activated coiled-coil kinases (ROCKs) are two "third messenger" signaling molecules that control the relative utilization of these two pathways. Several members of the Vps family of receptors (Vps35, SorL1, SorCS1) play important roles in post-trans-Golgi network (TGN) sorting and generation of APP derivatives, including Aβ at the TGN, endosome and the plasma membrane. We now report that Vps10-domain proteins are candidate substrates for PKC and/or ROCK2 and act as phospho-state-sensitive physiological effectors for post-TGN sorting of APP and its derivatives.

Results

Analysis of the SorL1 cytoplasmic tail revealed multiple consensus sites for phosphorylation by protein kinases. SorL1 was subsequently identified as a phosphoprotein, based on sensitivity of its electrophoretic migration pattern to calf intestine alkaline phosphatase and on its reaction with anti-phospho-serine antibodies. Activation of PKC resulted in increased shedding of the ectodomains of both APP and SorL1, and this was paralleled by an apparent increase in the level of the phosphorylated form of SorL1. ROCK2, the neuronal isoform of another protein kinase, was found to form complexes with SorL1, and both ROCK2 inhibition and ROCK2 knockdown enhanced generation of both soluble APP and Aβ.

Conclusion

These results highlight the potential importance of SorL1 in elucidating phospho-state sensitive mechanisms in the regulation of metabolism of APP and Aβ by PKC and ROCK2.

Viable mouse gene ablations that robustly alter brain Aβ levels are rare

BACKGROUND

Accumulation of amyloid-β (Aβ) peptide in the brain is thought to play a key pathological role in Alzheimer's disease. Many pharmacological targets have therefore been proposed based upon the biochemistry of Aβ, but not all are equally tractable for drug discovery.

RESULTS

To search for novel targets that affect brain Aβ without causing toxicity, we screened mouse brain samples from 1930 novel gene knock-out (KO) strains, representing 1926 genes, using Aβ ELISA assays. Although robust Aβ lowering was readily apparent in brains from a BACE1 KO strain, none of the novel strains exhibited robust decreases in brain Aβ, including a GPR3 KO strain, which had previously been proposed as an Aβ target. However, significantly increased Aβ was observed in brain samples from two KO strains, corresponding to genes encoding the glycosylphosphatidylinositol mannosyl transferase PIGZ and quinolinate phosphoribosyltransferase (QPRT).

CONCLUSIONS

Thus, gene ablations that are permissive for mouse survival and that also have a robust effect on Aβ levels in the brain are rare.

Highly sensitive electrogenerated chemiluminescence biosensor in profiling protein kinase activity and inhibition using gold nanoparticle as signal transduction probes

A novel electrogenerated chemiluminescence (ECL) biosensor using gold nanoparticles as signal transduction probes was described for the detection of kinase activity. The gold nanoparticles were specifically conjugated to the thiophosphate group after the phosphorylation process in the presence of adenosine 59-[c-thio] triphosphate (ATP-s) cosubstrate. Due to its good conductivity, large surface area, and excellent electroactivity to luminol oxidization, the gold nanoparticles extremely amplified the ECL signal of luminol, offering a highly sensitive ECL biosensor for kinase activity detection. Protein kinase A (PKA), an important enzyme in regulation of glycogen, sugar, and lipid metabolism in the human body, was used as a model to confirm the proof-of-concept strategy. The as-proposed biosensor presented high sensitivity, low detection limit of 0.07 U mL(-1), wide linear range (from 0.07 to 32 U mL(-1)), and excellent stability. Moreover, this biosensor can also be used for quantitative analysis of kinase inhibition. On the basis of the inhibitor concentration dependent ECL signal, the half-maximal inhibition value IC(50) of ellagic acid, a PKA inhibitor, was estimated, which was in agreement with those characterized with the conventional kinase assay. While nearly no ECL signal change can be observed in the presence of Tyrphostin AG1478, a tyrosine kinase inhibitor, but not PKA inhibitor, shows its excellent performance in kinase inhibitor screening. The simple and sensitive biosensor is promising in developing a high-through assay of in vitro kinase activity and inhibitor screening for clinic diagnostic and drug development.

Probing protein kinase (CK2) and alkaline phosphatase with CdSe/ZnS quantum dots

Semiconductor quantum dots (QDs) are used for the optical analysis of casein kinase (CK2) or the hydrolytic activity of alkaline phosphatase (ALP). Two schemes for the analysis of CK2 by a FRET-based mechanism are described. One approach involves the CK2-catalyzed phosphorylation of a serine-containing peptide (1), linked to CdSe/ZnS QDs, with Atto-590-functionalized ATP. The second analytical method involves the specific association of the Atto-590-functionalized antibody to the phosphorylated product. The hydrolytic activity of ALP is followed by the application of phosphotyrosine (4)-modified CdSe/ZnS QDs in the presence of tyrosinase as a secondary reporter biocatalyst. The hydrolysis of (4) yields the tyrosine units that are oxidized by O(2)/tyrosinase to the respective dopaquinone product. The latter quinone units quench the QDs via an electron transfer route, leading to the optical detection of the ALP activity.

Inhibition of gamma-secretase by the CK1 inhibitor IC261 does not depend on CK1delta

CK1 and gamma-secretase are interesting targets for therapeutic intervention in the treatment of cancer and Alzheimer's disease. The CK1 inhibitor IC261 was reported to inhibit gamma-secretase activity. The question is: Does CK1 inhibition directly influence gamma-secretase activity? Therefore we analyzed the SAR of 15 analogues and their impact on gamma-secretase activity. The most active compounds were investigated on CK1delta activity. These findings exclude a direct influence of CK1delta on gamma-secretase, because any change in the substitution pattern of IC261 diminished CK1 inhibition, whereas gamma-secretase inhibition is still exerted by several analogues.

Forebrain overexpression of CK1delta leads to down-regulation of dopamine receptors and altered locomotor activity reminiscent of ADHD

Dopamine neurotransmission controls motor and perseverative behavior, is mediated by protein phosphorylation, and may be perturbed in disorders of attention and hyperactivity. To assess the role of casein kinase I (CK1) in the regulation of dopamine signaling, we generated a genetically modified mouse line that overexpresses CK1delta (CK1delta OE) specifically in the forebrain. Overexpression was confirmed both at the mRNA and at the protein levels. Under basal conditions, CK1delta OE mice exhibited horizontal and vertical hyperactivity, reduced anxiety, and nesting behavior deficiencies. The CK1delta OE mice also presented paradoxical responses to dopamine receptor stimulation, showing hypoactivity following injection of d-amphetamine or methylphenidate, indicating that CK1 activity has a profound effect on dopamine signaling in vivo. Interestingly, CK1delta overexpression led to significantly reduced D1R and D2R dopamine receptor levels. All together, under basal conditions and in response to drug stimulation, the behavioral phenotype of CK1delta OE mice is reminiscent of the symptoms and drug responses observed in attention-deficit/hyperactivity disorder and therefore the CK1delta OE mice appear to be a model for this disorder.

Mediators of tau phosphorylation in the pathogenesis of Alzheimer's disease

The need for disease-modifying drugs for Alzheimer's disease has become increasingly important owing to escalating disease prevalence and the associated socio-economic burden. Until recently, reducing brain amyloid accumulation has been the main therapeutic focus; however, increasing evidence suggests that targeting abnormal tau phosphorylation could be beneficial. Tau is phosphorylated by several protein kinases and this is balanced by dephosphorylation by protein phosphatases. Phosphorylation at specific sites can influence the physiological functions of tau, including its role in binding to and stabilizing the neuronal cytoskeleton. aberrant phosphorylation of tau could render it susceptible to potentially pathogenic alterations, including conformational changes, proteolytic cleavage and aggregation. While strategies that reduce tau phosphorylation in transgenic models of disease have been promising, our understanding of the mechanisms through which tau becomes abnormally phosphorylated in disease is lacking.

3,4-Diaryl-isoxazoles and -imidazoles as potent dual inhibitors of p38alpha mitogen activated protein kinase and casein kinase 1delta

In this study, we report on the discovery of isoxazole 1 as a potent dual inhibitor of p38alpha (IC(50) = 0.45 microM) and CK1delta (IC(50) = 0.23 microM). Because only a few effective small molecule inhibitors of CK1 have been described so far, we aimed to develop this structural class toward specific agents. Molecular modeling studies comparing p38alpha/CK1delta suggested an optimization strategy leading to design, synthesis, biological characterization, and SAR of highly potent compounds including 9 (IC(50) p38alpha = 0.006 microM; IC(50) CK1delta = 1.6 microM), 13 (IC(50) p38alpha = 2.52 microM; IC(50) CK1delta = 0.033 microM), 17 (IC(50) p38alpha = 0.019 microM; IC(50) CK1delta = 0.004 microM; IC(50) CK1epsilon = 0.073 microM), and 18 (CKP138) (IC(50) p38alpha = 0.041 microM; IC(50) CK1delta = 0.005 microM; IC(50) CK1epsilon = 0.447 microM) possessing differentiated specificity. Selected compounds were profiled over 76 kinases and evaluation of their cellular efficacy showed 18 (CKP138) to be a highly potent and dual-specific inhibitor of CK1delta and p38alpha.

Potential of casein kinase I in digestive cancer screening

Casein kinase I is a group of ubiquitous Serine/Threonine kinases that have been implicated in both normal cellular functions and several pathological conditions including Alzheimer’s disease and cancer. Recent findings in colon and pancreatic cancer have brought tremendous attention to these molecules as potential therapeutic targets in treatment of digestive cancers. In this review, we summarize up to date what is known about this family of kinases and their involvement in carcinogenesis and other pathological conditions. Our emphasis is on their implications in digestive cancers and their potential for cancer screening and therapy.

Aberrant phosphorylation in the pathogenesis of Alzheimer's disease

The modification of proteins by reversible phosphorylation is a key mechanism in the regulation of various physiological functions. Abnormal protein kinase or phosphatase activity can cause disease by altering the phosphorylation of critical proteins in normal cellular and disease processes. Alzheimer's disease (AD), typically occurring in the elderly, is an irreversible, progressive brain disorder characterized by memory loss and cognitive decline. Accumulating evidence suggests that protein kinase and phosphatase activity are altered in the brain tissue of AD patients. Tau is a highly recognized phosphoprotein that undergoes hyperphosphorylation to form neurofibrillary tangles, a neuropathlogical hallmark with amyloid plaques in AD brains. This study is a brief overview of the altered protein phosphorylation pathways found in AD. Understanding the molecular mechanisms by which the activities of protein kinases and phosphatases are altered as well as the phosphorylation events in AD can potentially reveal novel insights into the role aberrant phosphorylation plays in the pathogenesis of AD, providing support for protein phosphorylation as a potential treatment strategy for AD.

BACE and gamma-secretase characterization and their sorting as therapeutic targets to reduce amyloidogenesis

Secretases are named for enzymes processing amyloid precursor protein (APP), a prototypic type-1 membrane protein. This led directly to discovery of novel Aspartyl proteases (beta-secretases or BACE), a tetramer complex gamma-secretase (gamma-SC) containing presenilins, nicastrin, aph-1 and pen-2, and a new role for metalloprotease(s) of the ADAM family as a alpha-secretases. Recent advances in defining pathways that mediate endosomal-lysosomal-autophagic-exosomal trafficking now provide targets for new drugs to attenuate abnormal production of fibril forming products characteristic of AD. A key to success includes not only characterization of relevant secretases but mechanisms for sorting and transport of key metabolites to abnormal vesicles or sites for assembly of fibrils. New developments we highlight include an important role for an 'early recycling endosome' coated in retromer complex containing lipoprotein receptor LRP-II (SorLA) for switching APP to a non-amyloidogenic pathway for alpha-secretases processing, or to shuttle APP to a 'late endosome compartment' to form Abeta or AICD. LRP11 (SorLA) is of particular importance since it decreases in sporadic AD whose etiology otherwise is unknown.

The regulation of p53 by phosphorylation: a model for how distinct signals integrate into the p53 pathway

The tumour suppressor p53 is a transcription factor that has evolved the ability to integrate distinct environmental signals including DNA damage, virus infection, and cytokine signaling into a common biological outcome that maintains normal cellular control. Mutations in p53 switch the cellular transcription program resulting in deregulation of the stress responses that normally maintain cell and tissue integrity. Transgenic studies in mice have indicated that changes in the specific activity of p53 can have profound effects not only on cancer development, but also on organism aging. As the specific activity of p53 is regulated at a post-translational level by sets of enzymes that mediate phosphorylation, acetylation, methylation, and ubiquitin-like modifications, it is likely that physiological modifiers of the aging function of p53 would be enzymes that catalyze such covalent modifications. We demonstrate that distinct stress-activated kinases, including ataxia telangiectasia mutated (ATM), casein kinase 1 (CK1) and AMP-activated protein kinase (AMPK), mediate phosphorylation of a key phospho-acceptor site in the p53 transactivation domain in response to diverse stresses including ionizing radiation, DNA virus infection, and elevation in the intracellular AMP/ATP ratio. As diseases linked to aging can involve activation of p53-dependent changes in cellular protective pathways, the development of specific physiological models might further shed light on the role of p53 kinases in modifying age-related diseases.

Novel role of CXCR2 in regulation of gamma-secretase activity

Alzheimer's disease (AD) is a progressive chronic disorder that leads to cognitive decline. Several studies have associated up-regulation of some of the chemokines and/or their receptors with altered APP processing leading to increased production of beta-amyloid protein (Abeta) and AD pathological changes. However, there is no direct evidence to date to determine whether the altered processing of APP results in up-regulation of these receptors or whether the up-regulation of the chemokine receptors causes modulated processing of APP. In the current study, we demonstrate that treatment of the chemokine receptor CXCR2 with agonists leads to enhancement of Abeta production and treatment with antagonists or immunodepletion of CXCR2's endogenous agonists leads to Abeta inhibition. Further, we found that the inhibitory effect of the antagonist of CXCR2 on Abeta40 and Abeta42 is mediated via gamma-secretase, specifically through reduction in expression of presenilin (PS), one of the gamma-secretase components. Also, in vivo chronic treatment with a CXCR2 antagonist blocked Abeta40 and Abeta42 production. Using small interfering RNAs for CXCR2, we further showed that knockdown of CXCR2 in vitro accumulates gamma-secretase substrates C99 and C83 with reduced production of both Abeta40 and Abeta42. Taken together, these findings strongly suggest for the first time that up-regulation of the CXCR2 receptor can be the driving force in increased production of Abeta. Our findings unravel new mechanisms involving the CXCR2 receptor in the pathogenesis of AD and pose it as a potential target for developing novel therapeutics for intervention in this disease. Also, we propose here a new chemical series of interest that can serve as a prototype for drug development.

Heat shock protein 90: translation from cancer to Alzheimer's disease treatment?

Both malignant transformation and neurodegeneration, as it occurs in Alzheimer's disease, are complex and lengthy multistep processes characterized by abnormal expression, post-translational modification, and processing of certain proteins. To maintain and allow the accumulation of these dysregulated processes, and to facilitate the step-wise evolution of the disease phenotype, cells must co-opt a compensatory regulatory mechanism. In cancer, this role has been attributed to heat shock protein 90 (Hsp90), a molecular chaperone that maintains the functional conformation of multiple proteins involved in cell-specific oncogenic processes. In this sense, at the phenotypic level, Hsp90 appears to serve as a biochemical buffer for the numerous cancer-specific lesions that are characteristic of diverse tumors. The current review proposes a similar role for Hsp90 in neurodegeneration. It will present experimentally demonstrated, but also hypothetical, roles that suggest Hsp90 can act as a regulator of pathogenic changes that lead to the neurodegenerative phenotype in Alzheimer's disease.

Combined kinase inhibition modulates parkin inactivation

Mutations in the parkin gene cause autosomal-recessive, juvenile-onset parkinsonism, and parkin dysfunction may also play a role in the pathogenesis of sporadic Parkinson disease (PD). Although its precise function remains largely unknown, parkin seems to play a neuroprotective role. Several studies indicate that changes in parkin solubility induced by post-translational modifications, such as S-nitrosylation or dopamine modification, comprise one mechanism of parkin inactivation associated with disease. Protein phosphorylation events have recently been linked to the molecular mechanism(s) underlying PD, but the role of this post-translational modification for parkin function has remained unclear. Here we report that compound phosphorylation of parkin by both casein kinase I and cyclin-dependent kinase 5 (cdk5) decreases parkin solubility, leading to its aggregation and inactivation. Combined kinase inhibition partially reverses the aggregative properties of several pathogenic point mutants in cultured cells. Enhanced parkin phosphorylation is detected in distinct brain areas of individuals with sporadic PD and correlates with increases in the levels of p25, the activator of cdk5. These findings indicate that casein kinase I and cdk5 may represent novel combinatorial therapeutic targets for treating PD.

Roscovitine-derived, dual-specificity inhibitors of cyclin-dependent kinases and casein kinases 1

Cyclin-dependent kinases (CDKs) and casein kinases 1 (CK1) are involved in the two key molecular features of Alzheimer's disease, production of amyloid-beta peptides (extracellular plaques) and hyper-phosphorylation of Tau (intracellular neurofibrillary tangles). A series of 2,6,9-trisubstituted purines, structurally related to the CDK inhibitor roscovitine, have been synthesized. They mainly differ by the substituent on the C-6 position. These compounds were screened for kinase inhibitory activities and antiproliferative effects. Several biaryl derivatives displayed potent inhibition of both CDKs and CK1. In particular, derivative 13a was a potent inhibitor of CDK1/cyclin B (IC 50: 220 nM), CDK5/p25 (IC 50: 80 nM), and CK1 (IC 50: 14 nM). Modeling of these molecules into the ATP-binding pocket of CK1delta provided a rationale for the increased selectivity toward this kinase. 13a was able to prevent the CK1-dependent production of amyloid-beta in a cell model. CDK/CK1 dual-specificity inhibitors may have important applications in Alzheimer's disease and cancers.

Following protein kinase acivity by electrochemical means and contact angle measurements

The electrochemical analysis of the protein kinase, casein kinase, is accomplished by the voltammetric response of Ag(+) ions associated with the phosphorylated product; the sensing surface is regenerated by the cleavage of the phosphorylated product with alkaline phosphatase, and the phosphorylation/de-phosphorylation processes are monitored by XPS and contact angle measurements.

Casein Kinase I epsilon positively regulates the Akt pathway in breast cancer cell lines

The Akt pathway is very important in both development and cancer. Here we show that, expression of Casein Kinase I epsilon (CKIepsilon) causes up-regulation of the Akt pathway despite normal protein expression of the pathway inhibitor phosphate and tensin homologue deleted on chromosome ten (PTEN). Conversely, we show that a CKIepsilon/delta-specific inhibitor can inhibit Akt phosphorylation at both Thr308 and Ser473 and drastically reduce phosphorylation of the Akt target Glycogen Synthase Kinase 3beta (GSK3beta). These conclusions were confirmed between MCF7 cells transiently transfected with CKIepsilon and Hs578T cells which already express endogenous CKIepsilon. The results suggest that CKIepsilon is a new positive regulator of the Akt pathway. Here we propose that, rather than inhibiting PTEN function, CKIepsilon positively regulates Akt possibly by inhibiting Protein Phosphatase 2A (PP2A).

Down’s syndrome and Alzheimer’s disease: two sides of the same coin

All Down’s syndrome individuals develop Alzheimer’s disease (AD) neuropathology by the age of 40 years. To unite the two diseases under one hypothesis, we have suggested that classical AD, both of the genetic and late-onset sporadic forms, might be promoted by small numbers of trisomy 21 cells developing during the life of the affected individual. Recent evidence from several laboratories will be presented, which strongly supports the trisomy 21 hypothesis that defects in mitosis, and particularly in chromosome segregation, may be a part of the AD process. Specifically, genetic mutations that cause familial AD disrupt the cell cycle and lead to chromosome aneuploidy, including trisomy 21, in transgenic mice and transfected cells; cells from both familial and sporadic AD patients exhibit chromosome aneuploidy, including trisomy 21. The possibility that many cases of AD are mosaic for trisomy 21 suggests novel approaches to diagnosis and therapy.

Neurosecretases provide strategies to treat sporadic and familial Alzheimer disorders

Recent discoveries on neurosecretases and their trafficking to release fibril-forming neuropeptides or other products, are of interest to pathology, cell signaling and drug discovery. Nomenclature arose from the use of amyloid precursor protein (APP) as a prototypic type-1 substrate leading to the isolation of beta-secretase (BACE), multimeric complexes (gamma-secretase, gamma-SC) for intramembranal cleavage, and attributing a new function to well-characterized metalloproteases of the ADAM family (alpha-secretase) for normal APP turnover. While purified alpha/beta-secretases facilitate drug discovery, gamma-SC presents greater challenges for characterization and mechanisms of catalysis. The review comments on links between mutation or polymorphisms in relation to enzyme mechanisms and disease. The association between lipoprotein receptor LRP11 variants and sporadic Alzheimer's disease (SAD) offers scope to integrate components of pre- and post-Golgi membranes, or brain clathrin-coated vesicles within pathways for trafficking as targets for intervention. The presence of APP and metabolites in brain clathrin-coated vesicles as significant cargo with lipoproteins and adaptors focuses attention as targets for therapeutic intervention. This overview emphasizes the importance to develop new therapies targeting neurosecretases to treat a major neurological disorder that has vast economic and social implications.

Meriolins, a new class of cell death inducing kinase inhibitors with enhanced selectivity for cyclin-dependent kinases

Protein kinases represent promising anticancer drug targets. We describe here the meriolins, a new family of inhibitors of cyclin-dependent kinases (CDK). Meriolins represent a chemical structural hybrid between meridianins and variolins, two families of kinase inhibitors extracted from various marine invertebrates. Variolin B is currently in preclinical evaluation as an antitumor agent. A selectivity study done on 32 kinases showed that, compared with variolin B, meriolins display enhanced specificity toward CDKs, with marked potency on CDK2 and CDK9. The structures of pCDK2/cyclin A/variolin B and pCDK2/cyclin A/meriolin 3 complexes reveal that the two inhibitors bind within the ATP binding site of the kinase, but in different orientations. Meriolins display better antiproliferative and proapoptotic properties in human tumor cell cultures than their parent molecules, meridianins and variolins. Phosphorylation at CDK1, CDK4, and CDK9 sites on, respectively, protein phosphatase 1alpha, retinoblastoma protein, and RNA polymerase II is inhibited in neuroblastoma SH-SY5Y cells exposed to meriolins. Apoptosis triggered by meriolins is accompanied by rapid Mcl-1 down-regulation, cytochrome c release, and activation of caspases. Meriolin 3 potently inhibits tumor growth in two mouse xenograft cancer models, namely, Ewing's sarcoma and LS174T colorectal carcinoma. Meriolins thus constitute a new CDK inhibitory scaffold, with promising antitumor activity, derived from molecules initially isolated from marine organisms.

Novel phosphorylation sites in tau from Alzheimer brain support a role for casein kinase 1 in disease pathogenesis

Tau in Alzheimer disease brain is highly phosphorylated and aggregated into paired helical filaments comprising characteristic neurofibrillary tangles. Here we have analyzed insoluble Tau (PHF-tau) extracted from Alzheimer brain by mass spectrometry and identified 11 novel phosphorylation sites, 10 of which were assigned unambiguously to specific amino acid residues. This brings the number of directly identified sites in PHF-tau to 39, with an additional six sites indicated by reactivity with phosphospecific antibodies to Tau. We also identified five new phosphorylation sites in soluble Tau from control adult human brain, bringing the total number of reported sites to nine. To assess which kinases might be responsible for Tau phosphorylation, we used mass spectrometry to determine which sites were phosphorylated in vitro by several kinases. Casein kinase 1delta and glycogen synthase kinase-3beta were each found to phosphorylate numerous sites, and each kinase phosphorylated at least 15 sites that are also phosphorylated in PHF-tau from Alzheimer brain. A combination of casein kinase 1delta and glycogen synthase kinase-3beta activities could account for over three-quarters of the serine/threonine phosphorylation sites identified in PHF-tau, indicating that casein kinase 1delta may have a role, together with glycogen synthase kinase-3beta, in the pathogenesis of Alzheimer disease.