Redox priming promotes Aurora A activation during mitosis

A chloroplast sulphate transporter modulates glutathione-mediated redox cycling to regulate cell division

Glutathione redox cycling is important for cell cycle regulation, but its mechanisms are not well understood. We previously identified a small-sized mutant, suppressor of mat3 15-1 (smt15-1) that has elevated cellular glutathione. Here, we demonstrated that SMT15 is a chloroplast sulphate transporter. Reducing expression of γ-GLUTAMYLCYSTEINE SYNTHETASE, encoding the rate-limiting enzyme required for glutathione biosynthesis, corrected the size defect of smt15-1 cells. Overexpressing GLUTATHIONE SYNTHETASE (GSH2) recapitulated the small-size phenotype of smt15-1 mutant, confirming the role of glutathione in cell division. Hence, SMT15 may regulate chloroplast sulphate concentration to modulate cellular glutathione levels. In wild-type cells, glutathione and/or thiol-containing molecules (GSH/thiol) accumulated in the cytosol at the G1 phase and decreased as cells entered the S/M phase. While the cytosolic GSH/thiol levels in the small-sized mutants, smt15-1 and GSH2 overexpressors, mirrored those of wild-type cells (accumulating during G1 and declining at early S/M phase), GSH/thiol was specifically accumulated in the basal bodies at early S/M phase in the small-sized mutants. Therefore, we propose that GSH/thiol-mediated redox signalling in the basal bodies may regulate mitotic division number in Chlamydomonas reinhardtii. Our findings suggest a new mechanism by which glutathione regulates the multiple fission cell cycle in C. reinhardtii.

Oxidative stress-mediated protein sulfenylation in human diseases: Past, present, and future

Reactive Oxygen Species (ROS) refer to a variety of derivatives of molecular oxygen that play crucial roles in regulating a wide range of physiological and pathological processes. Excessive ROS levels can cause oxidative stress, leading to cellular damage and even cell demise. However, moderately elevated levels of ROS can mediate the oxidative post-translational modifications (oxPTMs) of redox-sensitive proteins, thereby affecting protein functions and regulating various cellular signaling pathways. Among the oxPTMs, ROS-induced reversible protein sulfenylation represents the initial form of cysteine oxidation for sensing redox signaling. In this review, we will summarize the discovery, chemical formation, and detection approaches of protein sulfenylation. In addition, we will highlight recent findings for the roles of protein sulfenylation in various diseases, including thrombotic disorders, diabetes, cardiovascular diseases, neurodegenerative diseases, and cancer.

The significant others of aurora kinase a in cancer: combination is the key

AURKA is predominantly famous as an essential mitotic kinase. Recent findings have also established its critical role in a plethora of other biological processes including ciliogenesis, mitochondrial dynamics, neuronal outgrowth, DNA replication and cell cycle progression. AURKA overexpression in numerous cancers is strongly associated with poor prognosis and survival. Still no AURKA-targeted drug has been approved yet, partially because of the associated collateral toxicity and partly due to its limited efficacy as a single agent in a wide range of tumors. Mechanistically, AURKA overexpression allows it to phosphorylate numerous pathological substrates promoting highly aggressive oncogenic phenotypes. Our review examines the most recent advances in AURKA regulation and focuses on 33 such direct cancer-specific targets of AURKA and their associated oncogenic signaling cascades. One of the common themes that emerge is that AURKA is often involved in a feedback loop with its substrates, which could be the decisive factor causing its sustained upregulation and hyperactivation in cancer cells, an Achilles heel not exploited before. This dynamic interplay between AURKA and its substrates offers potential opportunities for targeted therapeutic interventions. By targeting these substrates, it may be possible to disrupt this feedback loop to effectively reverse AURKA levels, thereby providing a promising avenue for developing safer AURKA-targeted therapeutics. Additionally, exploring the synergistic effects of AURKA inhibition with its other oncogenic and/or tumor-suppressor targets could provide further opportunities for developing effective combination therapies against AURKA-driven cancers, thereby maximizing its potential as a critical drug target.

Coenzyme A biosynthesis: mechanisms of regulation, function and disease

The tricarboxylic acid cycle, nutrient oxidation, histone acetylation and synthesis of lipids, glycans and haem all require the cofactor coenzyme A (CoA). Although the sources and regulation of the acyl groups carried by CoA for these processes are heavily studied, a key underlying question is less often considered: how is production of CoA itself controlled? Here, we discuss the many cellular roles of CoA and the regulatory mechanisms that govern its biosynthesis from cysteine, ATP and the essential nutrient pantothenate (vitamin B5), or from salvaged precursors in mammals. Metabolite feedback and signalling mechanisms involving acetyl-CoA, other acyl-CoAs, acyl-carnitines, MYC, p53, PPARα, PINK1 and insulin- and growth factor-stimulated PI3K-AKT signalling regulate the vitamin B5 transporter SLC5A6/SMVT and CoA biosynthesis enzymes PANK1, PANK2, PANK3, PANK4 and COASY. We also discuss methods for measuring CoA-related metabolites, compounds that target CoA biosynthesis and diseases caused by mutations in pathway enzymes including types of cataracts, cardiomyopathy and neurodegeneration (PKAN and COPAN).

The bidirectional relationship between metabolism and cell cycle control

The relationship between metabolism and cell cycle progression is complex and bidirectional. Cells must rewire metabolism to meet changing biosynthetic demands across cell cycle phases. In turn, metabolism can influence cell cycle progression through direct regulation of cell cycle proteins, through nutrient-sensing signaling pathways, and through its impact on cell growth, which is linked to cell division. Furthermore, metabolism is a key player in mediating quiescence-proliferation transitions in physiologically important cell types, such as stem cells. How metabolism impacts cell cycle progression, exit, and re-entry, as well as how these processes impact metabolism, is not fully understood. Recent advances uncovering mechanistic links between cell cycle regulators and metabolic processes demonstrate a complex relationship between metabolism and cell cycle control, with many questions remaining.

1-Amino-1-deoxy-d-fructose ("fructosamine") and its derivatives: An update

1-Amino-1-deoxy-d-fructose (fructosamine, FN) derivatives are omnipresent in all living organisms, as a result of non-enzymatic condensation and Amadori rearrangement reactions between free glucose and biogenic amines such as amino acids, polypeptides, or aminophospholipids. Over decades, steady interest in fructosamine was largely sustained by its role as a key intermediate structure in the Maillard reaction that is responsible for the organoleptic and nutritional value of thermally processed foods, and for pathophysiological effects of hyperglycemia in diabetes. New trends in fructosamine research include the discovery and engineering of FN-processing enzymes, development of advanced tools for hyperglycemia monitoring, and evaluation of the therapeutic potential of both fructosamines and FN-recognizing proteins. This article covers developments in the field of fructosamine and its derivatives since 2010 and attempts to ascertain challenges in future research.

Alexander disease: the road ahead

Alexander disease is a rare neurodegenerative disorder caused by mutations in the glial fibrillary acidic protein, a type III intermediate filament protein expressed in astrocytes. Both early (infantile or juvenile) and adult onsets of the disease are known and, in both cases, astrocytes present characteristic aggregates, named Rosenthal fibers. Mutations are spread along the glial fibrillary acidic protein sequence disrupting the typical filament network in a dominant manner. Although the presence of aggregates suggests a proteostasis problem of the mutant forms, this behavior is also observed when the expression of wild-type glial fibrillary acidic protein is increased. Additionally, several isoforms of glial fibrillary acidic protein have been described to date, while the impact of the mutations on their expression and proportion has not been exhaustively studied. Moreover, the posttranslational modification patterns and/or the protein-protein interaction networks of the glial fibrillary acidic protein mutants may be altered, leading to functional changes that may modify the morphology, positioning, and/or the function of several organelles, in turn, impairing astrocyte normal function and subsequently affecting neurons. In particular, mitochondrial function, redox balance and susceptibility to oxidative stress may contribute to the derangement of glial fibrillary acidic protein mutant-expressing astrocytes. To study the disease and to develop putative therapeutic strategies, several experimental models have been developed, a collection that is in constant growth. The fact that most cases of Alexander disease can be related to glial fibrillary acidic protein mutations, together with the availability of new and more relevant experimental models, holds promise for the design and assay of novel therapeutic strategies.

A critical evaluation of protein kinase regulation by activation loop autophosphorylation

Phosphorylation of proteins is a ubiquitous mechanism of regulating their function, localization, or activity. Protein kinases, enzymes that use ATP to phosphorylate protein substrates are, therefore, powerful signal transducers in eukaryotic cells. The mechanism of phosphoryl-transfer is universally conserved among protein kinases, which necessitates the tight regulation of kinase activity for the orchestration of cellular processes with high spatial and temporal fidelity. In response to a stimulus, many kinases enhance their own activity by autophosphorylating a conserved amino acid in their activation loop, but precisely how this reaction is performed is controversial. Classically, kinases that autophosphorylate their activation loop are thought to perform the reaction in trans, mediated by transient dimerization of their kinase domains. However, motivated by the recently discovered regulation mechanism of activation loop cis-autophosphorylation by a kinase that is autoinhibited in trans, we here review the various mechanisms of autoregulation that have been proposed. We provide a framework for critically evaluating biochemical, kinetic, and structural evidence for protein kinase dimerization and autophosphorylation, and share some thoughts on the implications of these mechanisms within physiological signaling networks.

A mitotic NADPH upsurge promotes chromosome segregation and tumour progression in aneuploid cancer cells

Redox metabolites have been observed to fluctuate through the cell cycle in cancer cells, but the functional impacts of such metabolic oscillations remain unknown. Here, we uncover a mitosis-specific nicotinamide adenine dinucleotide phosphate (NADPH) upsurge that is essential for tumour progression. Specifically, NADPH is produced by glucose 6-phosphate dehydrogenase (G6PD) upon mitotic entry, which neutralizes elevated reactive oxygen species (ROS) and prevents ROS-mediated inactivation of mitotic kinases and chromosome missegregation. Mitotic activation of G6PD depends on the phosphorylation of its co-chaperone protein BAG3 at threonine 285, which results in dissociation of inhibitory BAG3. Blocking BAG3T285 phosphorylation induces tumour suppression. A mitotic NADPH upsurge is present in aneuploid cancer cells with high levels of ROS, while nearly unobservable in near-diploid cancer cells. High BAG3T285 phosphorylation is associated with worse prognosis in a cohort of patients with microsatellite-stable colorectal cancer. Our study reveals that aneuploid cancer cells with high levels of ROS depend on a G6PD-mediated NADPH upsurge in mitosis to protect them from ROS-induced chromosome missegregation.

Structural basis for CEP192-mediated regulation of centrosomal AURKA

Aurora kinase A (AURKA) performs critical functions in mitosis. Thus, the activity and subcellular localization of AURKA are tightly regulated and depend on diverse factors including interactions with the multiple binding cofactors. How these different cofactors regulate AURKA to elicit different levels of activity at distinct subcellular locations and times is poorly understood. Here, we identified a conserved region of CEP192, the major cofactor of AURKA, that mediates the interaction with AURKA. Quantitative binding studies were performed to map the interactions of a conserved helix (Helix-1) within CEP192. The crystal structure of Helix-1 bound to AURKA revealed a distinct binding site that is different from other cofactor proteins such as TPX2. Inhibiting the interaction between Helix-1 and AURKA in cells led to the mitotic defects, demonstrating the importance of the interaction. Collectively, we revealed a structural basis for the CEP192-mediated AURKA regulation at the centrosome, which is distinct from TPX2-mediated regulation on the spindle microtubule.

Emerging roles of Aurora-A kinase in cancer therapy resistance

Aurora kinase A (Aurora-A), a serine/threonine kinase, plays a pivotal role in various cellular processes, including mitotic entry, centrosome maturation and spindle formation. Overexpression or gene-amplification/mutation of Aurora-A kinase occurs in different types of cancer, including lung cancer, colorectal cancer, and breast cancer. Alteration of Aurora-A impacts multiple cancer hallmarks, especially, immortalization, energy metabolism, immune escape and cell death resistance which are involved in cancer progression and resistance. This review highlights the most recent advances in the oncogenic roles and related multiple cancer hallmarks of Aurora-A kinase-driving cancer therapy resistance, including chemoresistance (taxanes, cisplatin, cyclophosphamide), targeted therapy resistance (osimertinib, imatinib, sorafenib, etc.), endocrine therapy resistance (tamoxifen, fulvestrant) and radioresistance. Specifically, the mechanisms of Aurora-A kinase promote acquired resistance through modulating DNA damage repair, feedback activation bypass pathways, resistance to apoptosis, necroptosis and autophagy, metastasis, and stemness. Noticeably, our review also summarizes the promising synthetic lethality strategy for Aurora-A inhibitors in RB1, ARID1A and MYC gene mutation tumors, and potential synergistic strategy for mTOR, PAK1, MDM2, MEK inhibitors or PD-L1 antibodies combined with targeting Aurora-A kinase. In addition, we discuss the design and development of the novel class of Aurora-A inhibitors in precision medicine for cancer treatment.

Aurora Kinase A Regulation by Cysteine Oxidative Modification

Aurora kinase A (AURKA), which is a member of serine/threonine kinase family, plays a critical role in regulating mitosis. AURKA has drawn much attention as its dysregulation is critically associated with various cancers, leading to the development of AURKA inhibitors, a new class of anticancer drugs. As the spatiotemporal activity of AURKA critically depends on diverse intra- and inter-molecular factors, including its interaction with various protein cofactors and post-translational modifications, each of these pathways should be exploited for the development of a novel class of AURKA inhibitors other than ATP-competitive inhibitors. Several lines of evidence have recently shown that redox-active molecules can modify the cysteine residues located on the kinase domain of AURKA, thereby regulating its activity. In this review, we present the current understanding of how oxidative modifications of cysteine residues of AURKA, induced by redox-active molecules, structurally and functionally regulate AURKA and discuss their implications in the discovery of novel AURKA inhibitors.

BCAT1 redox function maintains mitotic fidelity

The metabolic enzyme branched-chain amino acid transaminase 1 (BCAT1) drives cell proliferation in aggressive cancers such as glioblastoma. Here, we show that BCAT1 localizes to mitotic structures and has a non-metabolic function as a mitotic regulator. Furthermore, BCAT1 is required for chromosome segregation in cancer and induced pluripotent stem cells and tumor growth in human cerebral organoid and mouse syngraft models. Applying gene knockout and rescue strategies, we show that the BCAT1 CXXC redox motif is crucial for controlling cysteine sulfenylation specifically in mitotic cells, promoting Aurora kinase B localization to centromeres, and securing accurate chromosome segregation. These findings offer an explanation for the well-established role of BCAT1 in promoting cancer cell proliferation. In summary, our data establish BCAT1 as a component of the mitotic apparatus that safeguards mitotic fidelity through a moonlighting redox functionality.

Effects of aneuploidy on cell behaviour and function

Aneuploidy, a genomic alternation characterized by deviations in the copy number of chromosomes, affects organisms from early development through to aging. Although it is a main cause of human pregnancy loss and a hallmark of cancer, how aneuploidy affects cellular function has been elusive. The last two decades have seen rapid advances in the understanding of the causes and consequences of aneuploidy at the molecular and cellular levels. These studies have uncovered effects of aneuploidy that can be beneficial or detrimental to cells and organisms in an environmental context-dependent and karyotype-dependent manner. Aneuploidy also imposes general stress on cells that stems from an imbalanced genome and, consequently, also an imbalanced proteome. These insights provide the fundamental framework for understanding the impact of aneuploidy in genome evolution, human pathogenesis and drug resistance.

Aurora A kinase activation: Different means to different ends

Aurora A is a serine/threonine kinase essential for mitotic entry and spindle assembly. Recent molecular studies have revealed the existence of multiple, distinct mechanisms of Aurora A activation, each occurring at specific subcellular locations, optimized for cellular context, and primed by signaling events including phosphorylation and oxidation.

APC/C CDH1 ubiquitinates IDH2 contributing to ROS increase in mitosis

NADPH is a cofactor used by reactive oxygen species (ROS) scavenging enzymes to block ROS produced in cells. Recently, it was shown that in cancer cells, ROS progressively increases in tune to cell cycle leading to a peak in mitosis. Loss of IDH2 is known to cause severe oxidative stress in cell and mouse models as ROS increases in mitochondria. Therefore, we hypothesized that IDH2, a major NADPH-producing enzyme in mitochondria is ubiquitinated for ROS to increase in mitosis. To test this hypothesis, in cancer cells we examined IDH2 ubiquitination in mitosis and measured the ROS produced. We found that IDH2 is ubiquitinated in mitosis and on inhibiting anaphase-promoting complex/Cyclosome (APC/C) IDH2 was stabilized. Further, we observed that overexpressing APC/C coactivator CDH1 decreased IDH2, whereas depleting CDH1 decreased IDH2 ubiquitination. To understand the link between IDH2 ubiquitination and ROS produced in mitosis, we show that overexpressing mitochondria-targeted-IDH1 decreased ROS by increasing NADPH in IDH2 ubiquitinated cells. We conclude that APC/C CDH1 ubiquitinates IDH2, a major NADPH-producing enzyme in mitochondria contributing to ROS increase in mitosis. Based on our results, we suggest that mitosis can be a therapeutic window in mutant IDH2-linked pathologies.

Structural insights into redox-active cysteine residues of the Src family kinases

The Src Family Kinases (SFKs) are pivotal regulators of cellular signal transduction and highly sought-after targets in drug discovery. Their actions within cells are controlled by alterations in protein phosphorylation that switch the SFKs from autoinhibited to active states. The SFKs are also well recognized to contain redox-active cysteine residues where oxidation of certain residues directly contribute to kinase function. To more completely understand the factors that influence cysteine oxidation within the SFKs, a review is presented of the local structural environments surrounding SFK cysteine residues compared to their quantified oxidation in vivo from the Oximouse database. Generally, cysteine local structure and degree of redox sensitivity vary with respect to sequence conservation. Cysteine residues found in conserved positions are more mildly redox-active as they are found in hydrophobic environments and not fully exposed to solvent. Non-conserved redox-active cysteines are generally the most reactive with direct solvent access and/or in hydrophilic environments. Results from this analysis motivate future efforts to conduct comprehensive proteome-wide analysis of redox-sensitivity, conservation, and local structural environments of proteins containing reactive cysteine residues.

Are redox changes a critical switch for mitotic progression?

Cell-cycle dependent redox changes result in increased protein oxidation in mitotic cells. We show that oxidative modifications of a conserved cysteine residue within Aurora A kinase (AURKA) can promote its activation during mitosis. Targeting redox-sensitive cysteine residues within AURKA may lead to the development of novel anti-cancer agents with improved clinical efficacy.

New connections: Redox regulation of kinases

Several studies glean insight into how kinases are structurally regulated by reversible oxidation.