REVIEW: Pin1 in Alzheimer's disease

An update on clinical proteomics in Alzheimer's research

Alzheimer's disease (AD) is a pathologically complex and aetiologically multifactorial dementing disorder affecting millions of people worldwide. The pathological brain changes are assumed to occur decades prior to the onset of clinical symptoms. The diagnosis of early AD remains problematic and is mainly based on clinical and neuropsychological findings after the onset of symptoms. Currently available drugs are able to delay the symptom progression of the disease but not to attenuate the progression of pathological brain changes. Many studies exploring AD proteomes have been conducted as the middle of 1990s as a consequence of recent advances in the development of both gel-based and gel-free proteomics approaches. It is hoped that proteomics can contribute to improving the understanding, diagnosis, and follow-up of the progression of AD. In this review, we summarise the present status of proteome alterations, with emphasis on quantitative approaches, in AD brain, CSF and blood, and their relevance to dementia research.

Redox characterization of human cyclophilin D: identification of a new mammalian mitochondrial redox sensor?

Mitochondria are metabolically highly active cell organelles that are also implicated in reactive oxygen species production and in cell death regulation. Cyclophilin D, the only human mitochondrial isoform of cyclophilins, plays an essential role in the formation of the mitochondrial permeability transition pore leading to cell necrosis. Recently, it has been shown that redox environment modifies structural and functional properties of some plant cyclophilins. Here, it is shown that oxidation of human cyclophilin D influences the conformation of the enzyme but also its activity. Site-directed mutagenized variants of cyclophilin D allowed the identification of cysteine 203 as an important redox-sensitive residue. Moreover, the redox modulation of cyclophilin D was confirmed in human neuroblastoma SH-SY5Y cells exposed to oxidative stress. Altogether, our results suggest that cyclophilin D may play a role as a redox sensor in mitochondria of mammalian cells transmitting information on the redox environment to target proteins.

The peptidyl-prolyl isomerase, Pin1, facilitates NF-kappaB binding in hepatocytes and protects against hepatic ischemia/reperfusion injury

BACKGROUND/AIMS

Our previous work suggested an important role for the peptidyl-prolyl isomerase, Pin1, in hepatic NF-kappaB activation and liver injury during ischemia/reperfusion (I/R). In this study, we sought to determine the function of Pin1 in the injury response to hepatic I/R.

METHODS

Wild-type and Pin1(-/-) mice were subjected to partial hepatic I/R. In addition, hepatocytes and Kupffer cells were isolated from these mice.

RESULTS

Pin1(-/-) mice had reduced hepatic NF-kappaB activation and more liver injury after I/R than wild-type mice. The increased injury was not a result of enhanced inflammation as Pin1(-/-) mice had the same level of proinflammatory cytokine production and less neutrophil accumulation in the liver. The reduced NF-kappaB activation was not a result of a defect in nuclear translocation of NF-kappaB. In fact, hepatic nuclear p65 protein expression was higher in Pin1(-/-) mice than wild-type mice. This suggests that Pin1 is important for NF-kappaB-DNA binding. This effect was specific to hepatocytes as isolated Kupffer cells from wild-type and Pin1(-/-) mice were identical in their activation of NF-kappaB and production of cytokines after stimulation. In contrast, hepatocytes stimulated with TNFalpha had greatly reduced NF-kappaB activation, reduced production of the CXC chemokine, MIP-2, and increased cell death.

CONCLUSIONS

These data suggest that Pin1 is a critical regulator of NF-kappaB activation in hepatocytes and its role in these cells appears to confer direct protective effects.

Oxidatively modified proteins in Alzheimer's disease (AD), mild cognitive impairment and animal models of AD: role of Abeta in pathogenesis

Oxidative stress has been implicated in the pathogenesis of a number of diseases including Alzheimer's disease (AD). The oxidative stress hypothesis of AD pathogenesis, in part, is based on beta-amyloid peptide (Abeta)-induced oxidative stress in both in vitro and in vivo studies. Oxidative modification of the protein may induce structural changes in a protein that might lead to its functional impairment. A number of oxidatively modified brain proteins were identified using redox proteomics in AD, mild cognitive impairment (MCI) and Abeta models of AD, which support a role of Abeta in the alteration of a number of biochemical and cellular processes such as energy metabolism, protein degradation, synaptic function, neuritic growth, neurotransmission, cellular defense system, long term potentiation involved in formation of memory, etc. All the redox proteomics-identified brain proteins fit well with the appearance of the three histopathological hallmarks of AD, i.e., synapse loss, amyloid plaque formation and neurofibrillary tangle formation and suggest a direct or indirect association of the identified proteins with the pathological and/or biochemical alterations in AD. Further, Abeta models of AD strongly support the notion that oxidative stress induced by Abeta may be a driving force in AD pathogenesis. Studies conducted on arguably the earliest stage of AD, MCI, may elucidate the mechanism(s) leading to AD pathogenesis by identifying early markers of the disease, and to develop therapeutic strategies to slow or prevent the progression of AD. In this review, we summarized our findings of redox proteomics identified oxidatively modified proteins in AD, MCI and AD models.

Protein aggregation as a paradigm of aging

The process of physiological decline leading to death of the individual is driven by the deteriorating capacity to withstand extrinsic and intrinsic hazards, resulting in damage accumulation with age. The dynamic changes with time of the network governing the outcome of misfolded proteins, exemplifying as intrinsic hazards, is considered here as a paradigm of aging. The main features of the network, namely, the non-linear increase of damage and the presence of amplifying feedback loops within the system are presented through a survey of the different components of the network and related cellular processes in aging and disease.

Neurobiology of Alzheimer's disease

Alzheimer's disease (AD) is a devastating neurodegenerative disease, the most common among the dementing illnesses. The neuropathological hallmarks of AD include extracellular beta-amyloid (amyloid precursor protein (APP) deposits, intracellular neurofibrillary tangles (NFT)), dystrophic neuritis and amyloid angiopathy. The mismetabolism of APP and the defective clearance of beta amyloid generate a cascade of events including hyperphosphorylated tau (tau) mediated breakdown of microtubular assembly and resultant synaptic failure which results in AD. The exact aetiopathogenesis of AD is still obscure. The preeminent hypotheses of AD include amyloid cascade hypothesis and tau hyperphosphorylation. The amyloid hypothesis states that extracellular amyloid plaques formed by aggregates of Abeta peptide generated by the proteolytic cleavages of APP are central to AD pathology. Intracellular assembly states of the oligomeric and protofibrillar species may facilitate tau hyperphosphorylation, disruption of proteasome and mitochondria function, dysregulation of calcium homeostasis, synaptic failure, and cognitive dysfunction. The tau hypothesis states that excessive or abnormal phosphorylation of tau results in the transformation of normal adult tau into PHF-tau (paired helical filament) and NFTs. Vascular hypothesis is also proposed for AD and it concludes that advancing age and the presence of vascular risk factors create a Critically Attained Threshold of Cerebral Hypoperfusion (CATCH) which leads to cellular and subcellular pathology involving protein synthesis, development of plaques, inflammatory response, and synaptic damage leading to the manifestations of AD. Multiple other aetiological and pathogenetic hypotheses have been put forward including genetics, oxidative stress, dysfunctional calcium homeostasis, hormonal, inflammatory-immunologic, and cell cycle dysregulation with the resultant neurotransmitter dysfunctions and cognitive decline. The available therapeutic agents target only the neurotransmitter dysfunction in AD and agents specifically targeting the pathogenetic mechanisms like amyloid deposition and tau hyperphosphorylation might provide a definite therapeutic edge.

The dual histidine motif in the active site of Pin1 has a structural rather than catalytic role

The catalytic domain of the peptidyl-prolyl cis/ trans isomerase Pin1 is a member of the FKBP superfold family. Within its active site are two highly conserved histidine residues, H59 and H157. Despite their sequence conservation in parvulin PPIase domains, the role of these histidine residues remains unclear. Our previous work (Behrsin et al. (2007) J. Mol. Biol. 365, 1143- 1162.) was consistent with a model where one or both histidines had critical roles in a hydrogen bonding network in the active site. Here, we test this model by looking at the effect of mutations to H59 and H157 on Pin1 function, activity, and protein stability. Using a yeast complementation assay, we show that both H59 and H157 can be mutated to non-hydrogen bonding residues and still support viability. Surprisingly, a nonfunctional H59L mutation can be rescued by a mutation of H157, to leucine. This double mutation (H59L/H157L) also had about 5-fold greater isomerase activity than the H59L mutation with a phosphorylated substrate. Structural analyses suggest that rescue of function and activity results from partial rescue of protein stability. Our findings indicate that H59 and H157 are not required for hydrogen bonding within the active site, and in contrast to the active site C113, they do not participate directly in catalysis. Instead, we suggest these histidines play a key role in domain structure or stability.

Swedish amyloid precursor protein mutation increases cell cycle-related proteins in vitro and in vivo

Reactivation of the cell cycle, including DNA replication, might play a major role in Alzheimer's disease. In this study, we report that the expressions of Swedish double mutation of amyloid precursor protein (Swe-APP) or of the APP intracellular domain (AICD) into nerve growth factor (NGF)-differentiated PC12 cells or rat primary cortical neurons increased mRNA and protein levels of cyclin D1 and cyclin B1. Treatment with lithium chloride (a glycogen synthase kinase-3beta inhibitor) down-regulated cyclin B1 induced by Swe-APP expression but up-regulated cyclin D1 expression induced by Swe-APP, suggesting that glycogen synthase kinase-3beta activity is involved in these expression changes of cyclins D1 and B1. Swe-APP, which is a prevailing cause of familial Alzheimer's disease, is well known to increase amyloid beta peptide production both in vitro and in vivo, but the underlying molecular means whereby it leads to the pathogenesis of AD remains unknown. The finding that cyclin D1 and B1 expressions were up-regulated by Swe-APP in in vitro cultured cells was substantiated in the brain tissues of Tg2576 mice, which harbor the Swe-APP mutation. These results suggest that some disturbances in cell cycle regulation may be involved in Swe-APP or AICD-induced neurodegeneration and that these contribute to the pathogenesis of AD.

Proteomic identification of proteins in the human brain: Towards a more comprehensive understanding of neurodegenerative disease

Proteomics has revealed itself as a powerful tool in the identification and determination of proteins and their biological significance. More recently, several groups have taken advantage of the high-throughput nature of proteomics in order to gain a more in-depth understanding of the human brain. In turn, this information has provided researchers with invaluable insight into the potential pathways and mechanisms involved in the pathogenesis of several neurodegenerative disorders, e.g., Alzheimer and Parkinson disease. Furthermore, these findings likely will improve methods to diagnose disease and monitor disease progression as well as generate novel targets for therapeutic intervention. Despite these advances, comprehensive understanding of the human brain proteome remains challenging, and requires development of improved sample enrichment, better instrumentation, and innovative analytic techniques. In this review, we will focus on the most recent progress related to identification of proteins in the human brain under normal as well as pathological conditions, mainly Alzheimer and Parkinson disease, their potential application in biomarker discovery, and discuss current advances in protein identification aimed at providing a more comprehensive understanding of the brain.

Peptides and proteins in plasma and cerebrospinal fluid as biomarkers for the prediction, diagnosis, and monitoring of therapeutic efficacy of Alzheimer's disease

Alzheimer's disease (AD) affects millions of persons worldwide. Earlier detection and/or diagnosis of AD would permit earlier intervention, which conceivably could delay progression of this dementing disorder. In order to accomplish this goal, reliable and specific biomarkers are needed. Biomarkers are multidimensional and have the potential to aid in various facets of AD such as diagnostic prediction, assessment of disease stage, discrimination from normally cognitive controls as well as other forms of dementia, and therapeutic efficacy of AD drugs. To date, biomarker research has focused on plasma and cerebrospinal fluid (CSF), two bodily fluids believed to contain the richest source of biomarkers for AD. CSF is the fluid surrounding the central nervous system (CNS), and is the most indicative obtainable fluid of brain pathology. Blood plasma contains proteins that affect brain processes from the periphery, as well as proteins/peptides exported from the brain; this fluid would be ideal for biomarker discovery due to the ease and non-invasive process of sample collection. However, it seems reasonable that biomarker discovery will result in combinations of CSF, plasma, and other fluids such as urine, to serve the aforementioned purposes. This review focuses on proteins and peptides identified from CSF, plasma, and urine that may serve as biomarkers in AD.

Pin1 has opposite effects on wild-type and P301L tau stability and tauopathy

Tau pathology is a hallmark of many neurodegenerative diseases including Alzheimer disease (AD) and frontotemporal dementia with Parkinsonism linked to chromosome 17 (FTDP-17). Genetic tau mutations can cause FTDP-17, and mice overexpressing tau mutants such as P301L tau are used as AD models. However, since no tau mutations are found in AD, it remains unclear how appropriate tau mutant mice are as an AD model. The prolyl isomerase Pin1 binds and isomerizes tau and has been implicated in protecting against neurodegeneration, but whether such Pin1 regulation is affected by tau mutations is unknown. Consistent with earlier findings that Pin1 KO induces tauopathy, here we demonstrate that Pin1 knockdown or KO increased WT tau protein stability in vitro and in mice and that Pin1 overexpression suppressed the tauopathy phenotype in WT tau transgenic mice. Unexpectedly, Pin1 knockdown or KO decreased P301L tau protein stability and abolished its robust tauopathy phenotype in mice. In contrast, Pin1 overexpression exacerbated the tauopathy phenotype in P301L tau mice. Thus, Pin1 has opposite effects on the tauopathy phenotype depending on whether the tau is WT or a P301L mutant, indicating the need for disease-specific therapies for tauopathies.

Redox proteomics studies of in vivo amyloid beta-peptide animal models of Alzheimer's disease: Insight into the role of oxidative stress

Alzheimer's disease (AD) is an age-related neurodegenerative disease. AD is characterized by the presence of senile plaques, neurofibrillary tangles, and synaptic loss. Amyloid β-peptide (Aβ), a component of senile plaques, has been proposed to play an important role in oxidative stress in AD brain and could be one of the key factors in the pathogenesis of AD. In the present review, we discuss some of the AD animal models that express Aβ, and compare the proteomics-identified oxidatively modified proteins between AD brain and those of Aβ models. Such a comparison would allow better understanding of the role of Aβ in AD pathogenesis thereby helping in developing potential therapeutics to treat or delay AD.

Small family with key contacts: par14 and par17 parvulin proteins, relatives of pin1, now emerge in biomedical research

The parvulin-type peptidyl-prolyl cis/trans isomerase Pin1 is subject of intense biochemical and clinical research as it seems to be involved in the pathogenesis of certain cancers and protein folding illnesses like Alzheimer's and Parkinson's disease. In addition to Pin1, the human genome only contains a single other parvulin locus encoding two protein species-Par14 and Par17. Much less is known about these enzymes although their sequences are highly conserved in all metazoans. Parvulin has been proposed to function as Pin1 complementing enzyme in cell cycle regulation and in chromatin remodelling. Pharmaceutical modulation of Par14 might therefore have benefits for certain types of cancer. Moreover, the Par17 protein that has been shown to be confined to anthropoid primate species only might provide a deeper understanding for human-specific brain development. This review aims at stimulating further research on Par14 and Par17 that are overlooked drug targets in the shadow of an overwhelming plethora of Pin1 literature by summarising all current knowledge on these parvulin proteins.

Novel procedure to investigate the effect of phosphorylation on protein complex formation in vitro and in cells

The identification of phosphorylation state-dependent interacting proteins provides clues as to the function of the phosphorylation. Techniques such as yeast two hybrid and co-immunoprecipitation do not employ a single species of fully phosphorylated proteins. This is a particular problem for substrates of glycogen synthase kinase-3 (GSK3), where multiple Ser/Thr residues can be targeted, almost always subsequent to a priming phosphorylation by an alternative kinase. We previously identified the brain enriched collapsin response mediator proteins (CRMP2 and CRMP4) as physiological substrates of GSK3. Cdk5 phosphorylates CRMP2 at Ser522, priming for subsequent phosphorylation at three residues by GSK3 in vitro and in vivo. It is clear that phosphorylation of CRMP2 influences axonal growth; however, the molecular processes underlying this action are not fully established. In addition, the role of phosphorylation in other actions of CRMPs has not been elucidated. We developed a novel procedure to isolate CRMP2 and CRMP4 fully phosphorylated at four sites, namely, Ser522 (by CDK5), Ser518, Thr514, and Thr509 (by GSK3). These phosphoproteins were then used to identify binding partners in rat brain lysates in direct comparison with the non-phosphorylated isoforms. We validated the approach by confirming that a previously reported interaction with tubulin-beta is regulated by phosphorylation. We also show that CRMPs (CRMP1, CRMP2, and CRMP4) form heteromers and found that these complexes may also be regulated by phosphorylation. We identified DYRK and Pin1 as novel CRMP4 binding proteins with DYRK interacting preferentially with dephospho-CRMP4 and Pin1 with phospho-CRMP4. Finally, we used this approach to identify the mitochondrial protein ANT as a novel CRMP2 and CRMP4 binding protein. We believe that this approach could be applied generally to the study of phosphorylation-dependent interactions.

Binding of phosphatase inhibitor-2 to prolyl isomerase Pin1 modifies specificity for mitotic phosphoproteins

Inhibitor-2 (I-2) is the most ancient protein that selectively recognizes type-1 protein phosphatase and is phosphorylated by CDK1-cyclinB during mitosis at Thr72 in a conserved PXTP site. Pin1 is a peptide prolyl cis/trans isomerase conserved among eukaryotes that specifically reacts with proteins phosphorylated at Ser/Thr-Pro sites. We tested phospho-T72-I-2 as a substrate for Pin1 and discovered that unphosphorylated I-2 bound Pin1 with micromolar affinity and phosphorylation of the PXTP site or truncation of I-2 reduced binding 10-fold. Ectopic Pin1 coprecipitated endogenous I-2 and ectopic I-2 coprecipitated endogenous Pin1, but only in the absence of detergents, which may account for the interaction not being detected previously. Endogenous I-2 and Pin1 colocalized in HeLa cells and showed nuclear-cytoplasmic redistribution in response to cell density, suggestive of their association in living cells. Recombinant Pin1 binding to different phosphoproteins in mitotic cell extracts was modulated by I-2, and binding to individual mitotic phosphoproteins was increased, decreased or unaffected by I-2, showing that I-2 allosterically modifies Pin1 specificity. This was confirmed by mutation of Ser16 to Ala in the Pin1 WW domain that eliminated I-2 binding and abrogated I-2 effects on Pin1 binding to different phosphoproteins. A S16E mutation to mimic Pin1 phosphorylation restored binding to both I-2 and phospho-T72-I-2, indicating that phosphorylation of both proteins governs their interaction. The results reveal a novel function for I-2, and suggest phosphorylation-dependent regulation of Pin1 specificity during entry and exit of mitosis, in other phases of the cell cycle, and in multiple cell signaling processes.

Prolyl cis-trans isomerization as a molecular timer

Proline is unique in the realm of amino acids in its ability to adopt completely distinct cis and trans conformations, which allows it to act as a backbone switch that is controlled by prolyl cis-trans isomerization. This intrinsically slow interconversion can be catalyzed by the evolutionarily conserved group of peptidyl prolyl cis-trans isomerase enzymes. These enzymes include cyclophilins and FK506-binding proteins, which are well known for their isomerization-independent role as cellular targets for immunosuppressive drugs. The significance of enzyme-catalyzed prolyl cis-trans isomerization as an important regulatory mechanism in human physiology and pathology was not recognized until the discovery of the phosphorylation-specific prolyl isomerase Pin1. Recent studies indicate that both phosphorylation-dependent and phosphorylation-independent prolyl cis-trans isomerization can act as a novel molecular timer to help control the amplitude and duration of a cellular process, and prolyl cis-trans isomerization might be a new target for therapeutic interventions.

The prolyl isomerase PIN1: a pivotal new twist in phosphorylation signalling and disease

Protein phosphorylation regulates many cellular processes by causing changes in protein conformation. The prolyl isomerase PIN1 has been identified as a regulator of phosphorylation signalling that catalyses the conversion of specific phosphorylated motifs between the two completely distinct conformations in a subset of proteins. PIN1 regulates diverse cellular processes, including growth-signal responses, cell-cycle progression, cellular stress responses, neuronal function and immune responses. In line with the diverse physiological roles of PIN1, it has also been linked to several diseases that include cancer, Alzheimer's disease and asthma, and thus it might represent a novel therapeutic target.

Molecular mechanisms of the phospho-dependent prolyl cis/trans isomerase Pin1

Since its discovery 10 years ago, Pin1, a prolyl cis/trans isomerase essential for cell cycle progression, has been implicated in a large number of molecular processes related to human diseases, including cancer and Alzheimer's disease. Pin1 is made up of a WW interaction domain and a C-terminal catalytic subunit, and several high-resolution structures are available that have helped define its function. The enzymatic activity of Pin1 towards short peptides containing the pSer/Thr-Pro motif has been well documented, and we discuss the available evidence for the molecular mechanisms of its isomerase activity. We further focus on those studies that examine its cis/trans isomerase function using full-length protein substrates. The interpretation of this research has been further complicated by the observation that many of its pSer/Thr-Pro substrate motifs are located in natively unstructured regions of polypeptides, and are characterized by minor populations of the cis conformer. Finally, we review the data on the possibility of alternative modes of substrate binding and the complex role that Pin1 plays in the degradation of its substrates. After considering the available work, it seems that further analysis is required to determine whether binding or catalysis is the primary mechanism through which Pin1 affects cell cycle progression.

Roles of amyloid beta-peptide-associated oxidative stress and brain protein modifications in the pathogenesis of Alzheimer's disease and mild cognitive impairment

Oxidative stress has been implicated to play a crucial role in the pathogenesis of a number of diseases, including neurodegenerative disorders, cancer, and ischemia, just to name a few. Alzheimer disease (AD) is an age-related neurodegenerative disorder that is recognized as the most common form of dementia. AD is histopathologically characterized by the presence of extracellular amyloid plaques, intracellular neurofibrillary tangles, the presence of oligomers of amyloid beta-peptide (Abeta), and synapse loss. In this review we discuss the role of Abeta in the pathogenesis of AD and also the use of redox proteomics to identify oxidatively modified brain proteins in AD and mild cognitive impairment. In addition, redox proteomics studies in in vivo models of AD centered around human Abeta(1-42) are discussed.

Alzheimer’s disease, oxidative stress and B-vitamin depletion

There is an association between cognitive function and vitamin B12 and folate status. Both vitamins participate in recycling the potentially toxic amino acid homocysteine to methionine and, ultimately, to the methyl donor S-adenosylmethionine (SAM). Consequently, B12 and folate indirectly influence glutathione synthesis – a major intracellular antioxidant. Neuroinflammation and oxidative stress are early features of Alzheimer’s disease (AD). Such stress impairs homocysteine recycling, degrades folate and decreases its cellular retention, resulting in limited SAM availability and increased homocysteine levels. Oxidized homocysteine derivatives, such as homocysteic acid, can initiate a vicious cycle by promoting free-radical formation. Decreased SAM also fosters development of characteristic AD neuropathologies – neurofibrillary tangles and amyloid plaques. The latter generate additional free radicals in a further feed-forward cascade. Future therapies should simultaneously halt neuroinflammation, restore redox homeostasis and replace depleted intracellular B vitamins. Developing early markers for these harmful processes will allow targeting of such therapy before irreversible cellular damage ensues.

Inhibition of Pin1 reduces glutamate-induced perikaryal accumulation of phosphorylated neurofilament-H in neurons

Under normal conditions, the proline-directed serine/threonine residues of neurofilament tail-domain repeats are exclusively phosphorylated in axons. In pathological conditions such as amyotrophic lateral sclerosis (ALS), motor neurons contain abnormal perikaryal accumulations of phosphorylated neurofilament proteins. The precise mechanisms for this compartment-specific phosphorylation of neurofilaments are not completely understood. Although localization of kinases and phosphatases is certainly implicated, another possibility involves Pin1 modulation of phosphorylation of the proline-directed serine/threonine residues. Pin1, a prolyl isomerase, selectively binds to phosphorylated proline-directed serine/threonine residues in target proteins and isomerizes cis isomers to more stable trans configurations. In this study we show that Pin1 associates with phosphorylated neurofilament-H (p-NF-H) in neurons and is colocalized in ALS-affected spinal cord neuronal inclusions. To mimic the pathology of neurodegeneration, we studied glutamate-stressed neurons that displayed increased p-NF-H in perikaryal accumulations that colocalized with Pin1 and led to cell death. Both effects were reduced upon inhibition of Pin1 activity by the use of an inhibitor juglone and down-regulating Pin1 levels through the use of Pin1 small interfering RNA. Thus, isomerization of lys-ser-pro repeat residues that are abundant in NF-H tail domains by Pin1 can regulate NF-H phosphorylation, which suggests that Pin1 inhibition may be an attractive therapeutic target to reduce pathological accumulations of p-NF-H.

The commonality of protein interaction networks determined in neurodegenerative disorders (NDDs)

MOTIVATION

Neurodegenerative disorders (NDDs) are progressive and fatal disorders, which are commonly characterized by the intracellular or extracellular presence of abnormal protein aggregates. The identification and verification of proteins interacting with causative gene products are effective ways to understand their physiological and pathological functions. The objective of this research is to better understand common molecular pathogenic mechanisms in NDDs by employing protein-protein interaction networks, the domain characteristics commonly identified in NDDs and correlation among NDDs based on domain information.

RESULTS

By reviewing published literatures in PubMed, we created pathway maps in Kyoto Encyclopedia of Genes and Genomes (KEGG) for the protein-protein interactions in six NDDs: Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), Huntington's disease (HD), dentatorubral-pallidoluysian atrophy (DRPLA) and prion disease (PRION). We also collected data on 201 interacting proteins and 13 compounds with 282 interactions from the literature. We found 19 proteins common to these six NDDs. These common proteins were mainly involved in the apoptosis and MAPK signaling pathways. We expanded the interaction network by adding protein interaction data from the Human Protein Reference Database and gene expression data from the Human Gene Expression Index Database. We then carried out domain analysis on the extended network and found the characteristic domains, such as 14-3-3 protein, phosphotyrosine interaction domain and caspase domain, for the common proteins. Moreover, we found a relatively high correlation between AD, PD, HD and PRION, but not ALS or DRPLA, in terms of the protein domain distributions.

AVAILABILITY

http://www.genome.jp/kegg/pathway/hsa/hsa01510.html (KEGG pathway maps for NDDs).

WW domain-containing oxidoreductase: a candidate tumor suppressor

Common fragile site gene WWOX encodes a candidate tumor suppressor WW domain-containing oxidoreductase. Alteration of this gene, along with dramatic downregulation of WWOX protein, is shown in the majority of invasive cancer cells. Ectopic WWOX exhibits proapoptotic and tumor inhibitory functions in vitro and in vivo, probably interacting with growth regulatory proteins p53, p73 and others. Hyaluronidases regulate WWOX expression, increase cancer invasiveness and seem to be involved in the development of hormone-independent growth of invasive cancer cells. Estrogen and androgen stimulate phosphorylation and nuclear translocation of WWOX, although binding of WWOX to these sex hormones is unknown. We propose that suppression of WWOX expression by overexpressed hyaluronidases might contribute in part to the development of hormone independence in invasive cancer.

Regional expression of key cell cycle proteins in brain from subjects with amnestic mild cognitive impairment

Mild cognitive impairment (MCI) is regarded as a transition stage between the cognitive changes of normal aging and the more serious problems caused by Alzheimer's disease (AD). Previous studies had demonstrated increased expression of cell cycle proteins in AD brain. In the present study, we have analyzed the expression of the cell cycle proteins, CDK2, CDK5 and cyclin G1 in hippocampus and inferior parietal lobule (IPL) in subjects with amnestic mild cognitive impairment and control using Western blot analysis. The expression of CDK2, CDK5 and cyclin G1 were found to be significantly increased in MCI hippocampus as well as in IPL compared to control brain. These results suggest that some cells may have re-entered the cell cycle. However, the expression of CDK2 and CDK5 is greater in MCI hippocampus compared to those of MCI IPL, and hippocampus is a region that is severely affected by AD pathology. Since these proteins are involved directly or indirectly in microtubule destabilization and hyperphosphorylation of tau, and also in APP processing we hypothesize that cell cycle disturbance may be important contributor in the pathogenesis of AD.