The repression of oncoprotein SET by the tumor suppressor p53 reveals a p53-SET-PP2A feedback loop for cancer therapy.
Science China. Life sciences
The oncoprotein SET is frequently overexpressed in many types of tumors and contributes to malignant initiation and progression through multiple mechanisms, including the hijacking of the tumor suppressors p53 and PP2A. Targeting aberrant SET represents a promising strategy for cancer intervention. However, the mechanism by which endogenous SET is regulated in cancer cells remains largely unknown. Here, we identified the tumor suppressor p53 as a key regulator that transcriptionally repressed the expression of SET in both normal and cancer cells. In addition, p53 stimulated PP2A phosphatase activity via p53-mediated transcriptional repression of SET, whereby SET-mediated inhibition of PP2A was alleviated. Moreover, targeting the interaction between SET and PP2A catalytic subunit (PP2Ac) with FTY720 enhanced stress-induced p53 activation via PP2A-mediated dephosphorylation of p53 on threonine 55 (Thr55). Therefore, our findings uncovered a previously unknown p53-SET-PP2A regulatory feedback loop. To functionally potentiate this feedback loop, we designed a combined therapeutic strategy by simultaneously administrating a p53 activator and SET antagonist in cancer cells and observed a dramatic synergistic effect on tumor suppression. Our study reveals mechanistic insight into the regulation of the oncoprotein SET and raises a potential strategy for cancer therapy by stimulating the p53-SET-PP2A feedback loop.
10.1007/s11427-021-2123-8
Ser9 phosphorylation causes cytoplasmic detention of I2PP2A/SET in Alzheimer disease.
Yu Guang,Yan Tonghai,Feng Ye,Liu Xinghua,Xia Yiyuan,Luo Hongbin,Wang Jian-Zhi,Wang Xiaochuan
Neurobiology of aging
The nuclear protein I2(PP2A)/SET, an endogenous inhibitor of protein phosphatase-2A (PP2A), is increased and translocated to the cytoplasm in the neurons of Alzheimer's disease (AD) brains, and PP2A activity in cytoplasm is compromised. However, it is not fully understood how SET is retained in the cytoplasm. By generating a phosphorylation site-specific antibody, we found in the present study that SET is phosphorylated at Ser9, by which it is accumulated in the cytoplasm of the AD brains. Further studies demonstrate that both the phosphor-mimic and casein kinase (CK)II-mediated phosphorylation at Ser9 interferes with the formation of the SET/importin-α/importin-β complex, and thus inhibits SET nuclear import and induces the cytoplasmic detention of SET. Interestingly, Ser9 is nested in the center of the sequence (6)AKVSKK(11) of SET, which is consistent with a classical nuclear localization signal (NLS). To test whether (6)AKVSKK(11) is a new NLS of SET, we mutated SET lysine 7, lysine 10, and lysine 11 to alanine acid (K7A, K10A, K11A) respectively, and expressed these mutants in HEK293/tau cells. We found that expression of SET (K11A) led to a nuclear import defect of SET, and application of a synthesized peptide Tat-AAKVSKKE that can competitively bind to importin α/β resulted in cytoplasmic detention of SET. Finally, phosphorylation of SET aggravates PP2A inhibition and leads to tau hyperphosphorylation. In conclusion, the current study has identified a novel mechanism that causes cytoplasmic detention of SET with a new NLS-dependent CKII-associated phosphorylation of Ser9, suggesting that inhibition of CKII arrests cytoplasmic accumulation of SET and thus preserves PP2A activity in AD brains.
10.1016/j.neurobiolaging.2012.12.025
Neuroprotective actions of PIKE-L by inhibition of SET proteolytic degradation by asparagine endopeptidase.
Liu Zhixue,Jang Sung-Wuk,Liu Xia,Cheng Dongmei,Peng Junmin,Yepes Manuel,Li Xiao-jiang,Matthews Steve,Watts Colin,Asano Masahide,Hara-Nishimura Ikuko,Luo Hongbo R,Ye Keqiang
Molecular cell
Ischemia and seizure cause excessive neuronal excitation that is associated with brain acidosis and neuronal cell death. However, the molecular mechanism of acidification-triggered neuronal injury is incompletely understood. Here, we show that asparagine endopeptidase (AEP) is activated under acidic condition, cuts SET, an inhibitor of DNase, and triggers DNA damage in brain, which is inhibited by PIKE-L. SET, a substrate of caspases, was cleaved by acidic cytosolic extract independent of caspase activation. Fractionation of the acidic cellular extract yielded AEP that is required for SET cleavage. We found that kainate provoked AEP activation and SET cleavage at N175, triggering DNA nicking in wild-type, but not AEP null, mice. PIKE-L strongly bound SET and prevented its degradation by AEP, leading to resistance of neuronal cell death. Moreover, AEP also mediated stroke-provoked SET cleavage and cell death in brain. Thus, AEP might be one of the proteinases activated by acidosis triggering neuronal injury during neuroexcitotoxicity or ischemia.
10.1016/j.molcel.2008.02.017
Asparagine residue 368 is involved in Alzheimer's disease tau strain-specific aggregation.
Shimonaka Shotaro,Matsumoto Shin-Ei,Elahi Montasir,Ishiguro Koichi,Hasegawa Masato,Hattori Nobutaka,Motoi Yumiko
The Journal of biological chemistry
In tauopathies, tau forms pathogenic fibrils with distinct conformations (termed "tau strains") and acts as an aggregation "seed" templating the conversion of normal tau into isomorphic fibrils. Previous research showed that the aggregation core of tau fibril covers the C-terminal region (243-406 amino acids (aa)) and differs among the diseases. However, the mechanisms by which distinct fibrous structures are formed and inherited via templated aggregation are still unknown. Here, we sought to identify the key sequences of seed-dependent aggregation. To identify sequences for which deletion reduces tau aggregation, SH-SY5Y cells expressing a series of 10 partial deletion (Del 1-10, covering 244-400 aa) mutants of tau-CTF24 (243-441 aa) were treated with tau seeds prepared from a different tauopathy patient's brain (Alzheimer's disease, progressive supranuclear palsy, and corticobasal degeneration) or recombinant tau, and then seed-dependent tau aggregation was assessed biochemically. We found that the Del 8 mutant lacking 353-368 aa showed significantly decreased aggregation in both cellular and models. Furthermore, to identify the minimum sequence responsible for tau aggregation, we systematically repeated cellular tau aggregation assays for the delineation of shorter deletion sites and revealed that Asn-368 mutation suppressed tau aggregation triggered by an AD tau seed, but not using other tauopathy seeds. Our study suggested that 353-368 aa is a novel aggregation-responsible sequence other than PHF6 and PHF6*, and within this sequence, the Asn-368 residue plays a role in strain-specific tau aggregation in different tauopathies.
10.1074/jbc.RA120.013271
Asparaginyl endopeptidases: enzymology, applications and limitations.
Organic & biomolecular chemistry
Asparaginyl endopeptidases (AEP) are cysteine proteases found in mammalian and plant cells. Several AEP isoforms from plant species were found to exhibit transpeptidase activity which is integral for the key head-to-tail cyclisation reaction during the biosynthesis of cyclotides. Since many plant AEPs exhibit excellent enzyme kinetics for peptide ligation via a relatively short substrate recognition sequence, they have become appealing tools for peptide and protein modification. In this review, research focused on the enzymology of AEPs and their applications in polypeptide cyclisation and labelling will be presented. Importantly, the limitations of using AEPs and opportunities for future research and innovation will also be discussed.
10.1039/d1ob00608h
The Asparaginyl Endopeptidase Legumain: An Emerging Therapeutic Target and Potential Biomarker for Alzheimer's Disease.
International journal of molecular sciences
Alzheimer's disease (AD) is incurable dementia closely associated with aging. Most cases of AD are sporadic, and very few are inherited; the pathogenesis of sporadic AD is complex and remains to be elucidated. The asparaginyl endopeptidase (AEP) or legumain is the only recognized cysteine protease that specifically hydrolyzes peptide bonds after asparagine residues in mammals. The expression level of AEPs in healthy brains is far lower than that of peripheral organs. Recently, growing evidence has indicated that aging may upregulate and overactivate brain AEPs. The overactivation of AEPs drives the onset of AD through cleaving tau and amyloid precursor proteins (APP), and SET, an inhibitor of protein phosphatase 2A (PP2A). The AEP-mediated cleavage of these peptides enhances amyloidosis, promotes tau hyperphosphorylation, and ultimately induces neurodegeneration and cognitive impairment. Upregulated AEPs and related deleterious reactions constitute upstream events of amyloid/tau toxicity in the brain, and represent early pathological changes in AD. Thus, upregulated AEPs are an emerging drug target for disease modification and a potential biomarker for predicting preclinical AD. However, the presence of the blood-brain barrier greatly hinders establishing body-fluid-based methods to measure brain AEPs. Research on AEP-activity-based imaging probes and our recent work suggest that the live brain imaging of AEPs could be used to evaluate its predictive efficacy as an AD biomarker. To advance translational research in this area, AEP imaging probes applicable to human brain and AEP inhibitors with good druggability are urgently needed.
10.3390/ijms231810223
Cell Biology and Pathophysiology of α-Synuclein.
Cold Spring Harbor perspectives in medicine
α-Synuclein is an abundant neuronal protein that is highly enriched in presynaptic nerve terminals. Genetics and neuropathology studies link α-synuclein to Parkinson's disease (PD) and other neurodegenerative disorders. Accumulation of misfolded oligomers and larger aggregates of α-synuclein defines multiple neurodegenerative diseases called synucleinopathies, but the mechanisms by which α-synuclein acts in neurodegeneration are unknown. Moreover, the normal cellular function of α-synuclein remains debated. In this perspective, we review the structural characteristics of α-synuclein, its developmental expression pattern, its cellular and subcellular localization, and its function in neurons. We also discuss recent progress on secretion of α-synuclein, which may contribute to its interneuronal spread in a prion-like fashion, and describe the neurotoxic effects of α-synuclein that are thought to be responsible for its role in neurodegeneration.
10.1101/cshperspect.a024091
Relationship Between Tau, β Amyloid and α-Synuclein Pathologies.
Walker Lauren,Attems Johannes
Advances in experimental medicine and biology
It is becoming increasing clear that multiple pathological lesions co-exist in the brains of the demented and non-demented elderly, and with putative interactions revealed at the molecular level in addition to the cumulative effects on brain damage, mounting evidence suggests manifestation of multiple protein aggregates will have implications for the clinical course of many neurodegenerative diseases associated with dementia. In this section we will discuss how the presence of multiple pathological lesions can affect the pathological and clinical phenotype of neurodegenerative disorders.
10.1007/978-981-32-9358-8_14
Molecular biomarkers of Alzheimer's disease: progress and prospects.
Lashley Tammaryn,Schott Jonathan M,Weston Philip,Murray Christina E,Wellington Henny,Keshavan Ashvini,Foti Sandrine C,Foiani Martha,Toombs Jamie,Rohrer Jonathan D,Heslegrave Amanda,Zetterberg Henrik
Disease models & mechanisms
The neurodegenerative disorder Alzheimer's disease is characterised by the formation of β-amyloid plaques and neurofibrillary tangles in the brain parenchyma, which cause synapse and neuronal loss. This leads to clinical symptoms, such as progressive memory deficits. Clinically, these pathological changes can be detected in the cerebrospinal fluid and with brain imaging, although reliable blood tests for plaque and tangle pathologies remain to be developed. Plaques and tangles often co-exist with other brain pathologies, including aggregates of transactive response DNA-binding protein 43 and Lewy bodies, but the extent to which these contribute to the severity of Alzheimer's disease is currently unknown. In this 'At a glance' article and poster, we summarise the molecular biomarkers that are being developed to detect Alzheimer's disease and its related pathologies. We also highlight the biomarkers that are currently in clinical use and include a critical appraisal of the challenges associated with applying these biomarkers for diagnostic and prognostic purposes of Alzheimer's disease and related neurodegenerative disorders, also in their prodromal clinical phases.
10.1242/dmm.031781
Synucleinopathies: Where we are and where we need to go.
Brás Inês Caldeira,Dominguez-Meijide Antonio,Gerhardt Ellen,Koss David,Lázaro Diana F,Santos Patrícia I,Vasili Eftychia,Xylaki Mary,Outeiro Tiago Fleming
Journal of neurochemistry
Synucleinopathies are a group of disorders characterized by the accumulation of inclusions rich in the a-synuclein (aSyn) protein. This group of disorders includes Parkinson's disease, dementia with Lewy bodies (DLB), multiple systems atrophy, and pure autonomic failure (PAF). In addition, genetic alterations (point mutations and multiplications) in the gene encoding for aSyn (SNCA) are associated with familial forms of Parkinson's disease, the most common synucleinopathy. The Synuclein Meetings are a series that has been taking place every 2 years for about 12 years. The Synuclein Meetings bring together leading experts in the field of Synuclein and related human conditions with the goal of discussing and advancing the research. In 2019, the Synuclein meeting took place in Ofir, a city in the outskirts of Porto, Portugal. The meeting, entitled "Synuclein Meeting 2019: Where we are and where we need to go", brought together >300 scientists studying both clinical and molecular aspects of synucleinopathies. The meeting covered a many of the open questions in the field, in a format that prompted open discussions between the participants, and underscored the need for additional research that, hopefully, will lead to future therapies for a group of as of yet incurable disorders. Here, we provide a summary of the topics discussed in each session and highlight what we know, what we do not know, and what progress needs to be made in order to enable the field to continue to advance. We are confident this systematic assessment of where we stand will be useful to steer the field and contribute to filling knowledge gaps that may form the foundations for future therapeutic strategies, which is where we need to go.
10.1111/jnc.14965
Mechanism of Tau Hyperphosphorylation Involving Lysosomal Enzyme Asparagine Endopeptidase in a Mouse Model of Brain Ischemia.
Basurto-Islas Gustavo,Gu Jin-Hua,Tung Yunn Chyn,Liu Fei,Iqbal Khalid
Journal of Alzheimer's disease : JAD
Dementias including Alzheimer's disease (AD) are multifactorial disorders that involve several different etiopathogenic mechanisms. Cerebral ischemia has been suspected in the altered regulation of protein kinases and phosphatases that leads to hyperphosphorylation of tau and further neurofibrillary pathology, a key hallmark of AD and related neurodegenerative diseases. However, the deregulation of these enzymes and their relationship with ischemia and AD remain unclear. Previously, we reported a mechanism by which the lysosomal enzyme asparagine endopeptidase (AEP) is associated with brain acidosis and AD. In this study, we subjected mice to middle cerebral artery occlusion and found that compared with wild type mice, the ischemia-induced brain injury and motor deficit in AEP-knockout mice are reduced, probably because ischemia activates AEP. AEP cleaves inhibitor 2 of protein phosphatase 2A (I2PP2A), which translocates from the neuronal nucleus to the cytoplasm and produces hyperphosphorylation of tau through inhibition of PP2A. These findings suggest a possible mechanism of tau pathology associated with ischemia.
10.3233/JAD-170715