Models, Regulations, and Functions of Microtubule Severing by Katanin

Discovery of Novel Diaryl-Substituted Fused Heterocycles Targeting Katanin and Tubulin with Potent Antitumor and Antimultidrug Resistance Efficacy

Disrupting microtubule dynamics has emerged as a promising strategy for cancer treatment. However, drug resistance remains a challenge hindering the development of microtubule-targeting agents. In this work, a novel class of diaryl substituted fused heterocycles were designed, synthesized, and evaluated, which were demonstrated as effective dual katanin and tubulin regulators with antitumor activity. Following three rounds of stepwise optimization, compound 21b, featuring a 3H-imidazo[4,5-b]pyridine core, displayed excellent targeting capabilities on katanin and tubulin, along with notable antiproliferative and antimetastatic effects. Mechanistic studies revealed that 21b disrupts the microtubule network in tumor cells, leading to G2/M cell cycle arrest and apoptosis induction. Importantly, 21b exhibited significant inhibition of tumor growth in MDA-MB-231 and A549/T xenograft tumor models without evident toxicity and side effects. In conclusion, compound 21b presents a novel mechanism for disrupting microtubule dynamics, warranting further investigation as a dual-targeted antitumor agent with potential antimultidrug resistance properties.

Dual-targeting compounds possessing enhanced anticancer activity via microtubule disruption and histone deacetylase inhibition

Dual-targeting anticancer agents 4-29 are designed by combining the structural features of purine-type microtubule-disrupting compounds and HDAC inhibitors. A library of the conjugate compounds connected by appropriate linkers was synthesized and found to possess HDACs inhibitory activity and render microtubule fragmentation by activating katanin, a microtubule-severing protein. Among various zinc-binding groups, hydroxamic acid shows the highest inhibitory activity of Class I HDACs, which was also reconfirmed by three-dimensional quantitative structure-activity relationship (3D-QSAR) pharmacophore prediction. The purine-hydroxamate conjugates exhibit enhanced cytotoxicity against MDA-MB231 breast cancer cells, H1975 lung cancer cells, and various clinical isolated non-small-cell lung cancer cells with different epidermal growth factor receptor (EGFR) status. Pyridyl substituents could be used to replace the C2 and N9 phenyl moieties in the purine-type scaffold, which can help to improve the solubility under physiological conditions, thus increasing cytotoxicity. In mice treated with the purine-hydroxamate conjugates, the tumor growth rate was significantly reduced without causing toxic effects. Our study demonstrates the potential of the dual-targeting purine-hydroxamate compounds for cancer monotherapy.

The fidgetin family: Shaking things up among the microtubule-severing enzymes

The microtubule cytoskeleton is required for several crucial cellular processes, including chromosome segregation, cell polarity and orientation, and intracellular transport. These functions rely on microtubule stability and dynamics, which are regulated by microtubule-binding proteins (MTBPs). One such type of regulator is the microtubule-severing enzymes (MSEs), which are ATPases Associated with Diverse Cellular Activities (AAA+ ATPases). The most recently identified family are the fidgetins, which contain three members: fidgetin, fidgetin-like 1 (FL1), and fidgetin-like 2 (FL2). Of the three known MSE families, the fidgetins have the most diverse range of functions in the cell, spanning mitosis/meiosis, development, cell migration, DNA repair, and neuronal function. Furthermore, they offer intriguing novel therapeutic targets for cancer, cardiovascular disease, and wound healing. In the two decades since their first report, there has been great progress in our understanding of the fidgetins; however, there is still much left unknown about this unusual family. This review aims to consolidate the present body of knowledge of the fidgetin family of MSEs and to inspire deeper exploration into the fidgetins and the MSEs as a whole.

Emerging role of microtubule-associated proteins on cancer metastasis

The major cause of death in cancer patients is strongly associated with metastasis. While much remains to be understood, microtubule-associated proteins (MAPs) have shed light on metastatic progression’s molecular mechanisms. In this review article, we focus on the role of MAPs in cancer aggressiveness, particularly cancer metastasis activity. Increasing evidence has shown that a growing number of MAP member proteins might be fundamental regulators involved in altering microtubule dynamics, contributing to cancer migration, invasion, and epithelial-to-mesenchymal transition. MAP types have been established according to their microtubule-binding site and function in microtubule-dependent activities. We highlight that altered MAP expression was commonly found in many cancer types and related to cancer progression based on available evidence. Furthermore, we discuss and integrate the relevance of MAPs and related molecular signaling pathways in cancer metastasis. Our review provides a comprehensive understanding of MAP function on microtubules. It elucidates how MAPs regulate cancer progression, preferentially in metastasis, providing substantial scientific information on MAPs as potential therapeutic targets and prognostic markers for cancer management.

SUMOylation of microtubule-cleaving enzyme KATNA1 promotes microtubule severing and neurite outgrowth

Katanin p60 ATPase-containing subunit A1 (KATNA1) is a microtubule-cleaving enzyme that regulates the development of neural protrusions through cytoskeletal rearrangements. However, the mechanism underlying the linkage of the small ubiquitin-like modifier (SUMO) protein to KATNA1 and how this modification regulates the development of neural protrusions is unclear. Here we discovered, using mass spectrometry analysis, that SUMO-conjugating enzyme UBC9, an enzyme necessary for the SUMOylation process, was present in the KATNA1 interactome. Moreover, GST-pull down and co-immunoprecipitation assays confirmed that KATNA1 and SUMO interact. We further demonstrated using immunofluorescence experiments that KATNA1 and the SUMO2 isoform colocalized in hippocampal neurites. We also performed a bioinformatics analysis of KATNA1 protein sequences to identify three potentially conserved SUMOylation sites (K77, K157, and K330) among vertebrates. Mutation of K330, but not K77 or K157, abolished KATNA1-induced microtubule severing and decreased the level of binding observed for KATNA1 and SUMO2. Cotransfection of SUMO2 and wildtype KATNA1 in COS7 cells increased microtubule severing, whereas no effect was observed after cotransfection with the K330R KATNA1 mutant. Furthermore, in cultured hippocampal neurons, overexpression of wildtype KATNA1 significantly promoted neurite outgrowth, whereas the K330R mutant eliminated this effect. Taken together, our results demonstrate that the K330 site in KATNA1 is modified by SUMOylation and SUMOylation of KATNA1 promotes microtubule dynamics and hippocampal neurite outgrowth.

The AAA+ superfamily: a review of the structural and mechanistic principles of these molecular machines

ATPases associated with diverse cellular activities (AAA+ proteins) are a superfamily of proteins found throughout all domains of life. The hallmark of this family is a conserved AAA+ domain responsible for a diverse range of cellular activities. Typically, AAA+ proteins transduce chemical energy from the hydrolysis of ATP into mechanical energy through conformational change, which can drive a variety of biological processes. AAA+ proteins operate in a variety of cellular contexts with diverse functions including disassembly of SNARE proteins, protein quality control, DNA replication, ribosome assembly, and viral replication. This breadth of function illustrates both the importance of AAA+ proteins in health and disease and emphasizes the importance of understanding conserved mechanisms of chemo-mechanical energy transduction. This review is divided into three major portions. First, the core AAA+ fold is presented. Next, the seven different clades of AAA+ proteins and structural details and reclassification pertaining to proteins in each clade are described. Finally, two well-known AAA+ proteins, NSF and its close relative p97, are reviewed in detail.

Wdr47, Camsaps, and Katanin cooperate to generate ciliary central microtubules

The axonemal central pair (CP) are non-centrosomal microtubules critical for planar ciliary beat. How they form, however, is poorly understood. Here, we show that mammalian CP formation requires Wdr47, Camsaps, and microtubule-severing activity of Katanin. Katanin severs peripheral microtubules to produce central microtubule seeds in nascent cilia. Camsaps stabilize minus ends of the seeds to facilitate microtubule outgrowth, whereas Wdr47 concentrates Camsaps into the axonemal central lumen to properly position central microtubules. Wdr47 deficiency in mouse multicilia results in complete loss of CP, rotatory beat, and primary ciliary dyskinesia. Overexpression of Camsaps or their microtubule-binding regions induces central microtubules in Wdr47^-/- ependymal cells but at the expense of low efficiency, abnormal numbers, and wrong location. Katanin levels and activity also impact the central microtubule number. We propose that Wdr47, Camsaps, and Katanin function together for the generation of non-centrosomal microtubule arrays in polarized subcellular compartments.

Biallelic mutations in KATNAL2 cause male infertility due to oligo-astheno-teratozoospermia

Oligo-astheno-teratozoospermia (OAT) is a common cause of male infertility, and most of idiopathic OAT patients are thought to be caused by genetic defects. Here, we recruited 38 primary infertile patients with the OAT phenotype and 40 adult men with proven fertility for genetic analysis and identified biallelic mutations of KATNAL2 by whole-exome sequencing in two cases. F013/II:1, from a consanguineous family, carried the KATNAL2 c.328C > T:p.Arg110X homozygous mutations. The other carried c.55A > G: p.Lys19Glu and c.169C > T: p Arg57Trp biallelic mutations. None of the KATNAL2 variants were found in the 40 adult men with proven fertility. The spermatozoa from patients with KATNAL2 biallelic mutations exhibited conspicuous defects in maturation, head morphology, and the structure of mitochondrial sheaths and flagella. KATNAL2 was mainly expressed in the pericentriolar material and mitochondrial sheath of the spermatozoa from control subjects, but it was undetectable in the spermatozoa from the patients. Furthermore, Katnal2 null male mice were infertile and displayed an OAT phenotype. Our results proved that the biallelic mutations in KATNAL2 cause male infertility and OAT in humans for the first time, to our knowledge, which could enrich the genetic defect spectrum of OAT and be beneficial for its accurate genetic screening and clinical diagnosis.

A nuclear localization signal is required for the nuclear translocation of Fign and its microtubule‑severing function

It is commonly known that the specific function of a given ATPase associated with diverse cellular activities protein (i.e., a member of the AAA superfamily of proteins) depends primarily on its subcellular location. The microtubule-severing protein fidgetin (Fign) possesses a nuclear localization signal (NLS) that facilitates its translocation to the nucleus, where its assembly is finalized; here, Fign contributes to the regulation of microtubule configuration by cutting and trimming microtubule polymers. In the present study, Fign was found to be a nuclear protein, whose N-terminal sequence (SSLKRKAFYM; residues 314–323) acts as an NLS. Following substitution (KR to NN; 317–318) or deletion (NT; 314–323) mutations within the NLS, Fign, which is predominantly expressed in the nucleus, was found to reside in the cytoplasm of transfected cells. Furthermore, Fign was found to have an essential role in microtubule severing by preferentially targeting highly-tyrosinated microtubules (tyr-MTs). Mutation of the Fign NLS did not affect its microtubule-severing function or the cleavage of tyr-MTs, but did affect the cellular distribution of the Fign protein itself. Taken altogether, an NLS for Fign was identified, and it was demonstrated that the basic amino acids K317 and R318 are necessary for regulating its entry into the nucleus, whereas an increase in Fign in the cytosol due to mutations of the NLS did not affect its cleavage function.

Comprehensive analysis of the cardiac proteome in a rat model of myocardial ischemia-reperfusion using a TMT-based quantitative proteomic strategy

Background

Traditional studies of the cardiac proteome have mainly investigated in an animal model by two-dimensional gel electrophoresis (2-DE). However, the results have not been of satisfactory quality for an understanding of the underlying mechanism. Recent quantitative proteomic methods have been improved to overcome these limitations. To comprehensively study the cardiac proteome in a rat model of ischemia-reperfusion (IR), we developed a tandem mass tag (TMT)-based quantitative proteomic strategy. Furthermore, using this strategy, we examined the molecular mechanisms underlying the prevention of myocardial infarction by the intake of Triticum aestivum L. extract (TALE), a representative dietary fiber grain.

Methods

Cardiac proteomes were analyzed by 2-DE as a gel-based approach, and TMT labeling coupled with two-dimensional liquid chromatography (2D-LC) and tandem mass spectrometry (MS/MS) as a non-gel-based quantitative approach. Additionally, gene ontology annotation was conducted by PANTHER database. Several proteins of interest were verified by a Western blot analysis.

Results

Total 641 proteins were identified commonly from two independent MS datasets using 2D-LC MS/MS. Among these, we identified 151 IR-related proteins that were differentially expressed between the sham-operation group and IR group, comprising 62 up-regulated proteins and 89 down-regulated proteins. Most of the reduced proteins were involved in metabolic processes. In addition, 57 of the IR-related proteins were affected by TALE intake, representing 25 up-regulated proteins and 32 down-regulated proteins. In particular, TALE intake leads to a switch in metabolism to reduce the loss of high-energy phosphates and the accumulation of harmful catabolites (especially reactive oxygen species (ROS)) and to maintain cytoskeleton balance, leading to a reduction in cardiac IR injury.

Conclusions

Our study provides a comprehensive proteome map of IR-related proteins and potential target proteins and identifies mechanisms implicated in the prevention of myocardial infarction by TALE intake in a rat IR model.

The Microtubule Severing Protein Katanin Regulates Proliferation of Neuronal Progenitors in Embryonic and Adult Neurogenesis

Microtubule severing regulates cytoskeletal rearrangement underlying various cellular functions. Katanin, a heterodimer, consisting of catalytic (p60) and regulatory (p80) subunits severs dynamic microtubules to modulate several stages of cell division. The role of p60 katanin in the mammalian brain with respect to embryonic and adult neurogenesis is poorly understood. Here, we generated a Katna1 knockout mouse and found that consistent with a critical role of katanin in mitosis, constitutive homozygous Katna1 depletion is lethal. Katanin p60 haploinsufficiency induced an accumulation of neuronal progenitors in the subventricular zone during corticogenesis, and impaired their proliferation in the adult hippocampus dentate gyrus (DG) subgranular zone. This did not compromise DG plasticity or spatial and contextual learning and memory tasks employed in our study, consistent with the interpretation that adult neurogenesis may be associated with selective forms of hippocampal-dependent cognitive processes. Our data identify a critical role for the microtubule-severing protein katanin p60 in regulating neuronal progenitor proliferation in vivo during embryonic development and adult neurogenesis.

Klebsiella pneumoniae Redistributes Katanin Severing Proteins and Alters Astral Microtubules during Mitosis

Klebsiella pneumoniae has become a growing concern within hospitals due to multidrug resistant strains and increasing mortality rates. Recently, we showed that at the subcellular level, K. pneumoniae compromises the integrity of the epithelia by disassembling the microtubule networks of cells through the actions of katanin microtubule severing proteins. In this study, we report on the observation that mitotic cells are targeted by K. pneumoniae and that during infections, the katanin proteins are excluded from the microtubule organizing centers of dividing cells, resulting in the alteration of the microtubule cytoskeleton. Anat Rec, 2019. © 2019 American Association for Anatomy Anat Rec, 303:1859-1864, 2020. © 2019 American Association for Anatomy.

Klebsiella pneumoniae disassembles host microtubules in lung epithelial cells

Klebsiella pneumoniae raises significant concerns to the health care industry as these microbes are the source of widespread contamination of medical equipment, cause pneumonia as well as other multiorgan metastatic infections and have gained multidrug resistance. Despite soaring mortality rates, the host cell alterations occurring during these infections remain poorly understood. Here, we show that during in vitro and in vivo K. pneumoniae infections of lung epithelia, microtubules are severed and then eliminated. This destruction does not require direct association of K. pneumoniae with the host cells, as microtubules are disassembled in cells that are distant from the infecting bacteria. This microtubule dismantling is dependent on the K. pneumoniae (Kp) gene ytfL as non-pathogenic Escherichia coli expressing Kp ytfL disassemble microtubules in the absence of K. pneumoniae itself. Our data points to the host katanin catalytic subunit A like 1 protein (KATNAL1) and the katanin regulatory subunit B1 protein (KATNB1) as the gatekeepers to the microtubule severing event as both proteins localise specifically to microtubule cut sites. Infected cells that had either of these proteins knocked out maintained intact microtubules. Taken together, we have identified a novel mechanism that a bacterial pathogen has exploited to cause microtubule destruction within the host epithelia.

Primary Cilia Reconsidered in the Context of Ciliopathies: Extraciliary and Ciliary Functions of Cilia Proteins Converge on a Polarity theme?

Once dismissed as vestigial organelles, primary cilia have garnered the interest of scientists, given their importance in development/signaling, and for their implication in a new disease category known as ciliopathies. However, many, if not all, "cilia" proteins also have locations/functions outside of the primary cilium. These extraciliary functions can complicate the interpretation of a particular ciliopathy phenotype: it may be a result of defects at the cilium and/or at extraciliary locations, and it could be broadly related to a unifying cellular process for these proteins, such as polarity. Assembly of a cilium has many similarities to the development of other polarized structures. This evolutionarily preserved process for the assembly of polarized cell structures offers a perspective on how the cilium may have evolved. We hypothesize that cilia proteins are critical for cell polarity, and that core polarity proteins may have been specialized to form various cellular protrusions, including primary cilia.

Modeling the effects of lattice defects on microtubule breaking and healing

Microtubule reorganization often results from the loss of polymer induced through breakage or active destruction by energy-using enzymes. Pre-existing defects in the microtubule lattice likely lower structural integrity and aid filament destruction. Using large-scale molecular simulations, we model diverse microtubule fragments under forces generated at specific positions to locally crush the filament. We show that lattices with 2% defects are crushed and severed by forces three times smaller than defect-free ones. We validate our results with direct comparisons of microtubule kinking angles during severing. We find a high statistical correlation between the angle distributions from experiments and simulations indicating that they sample the same population of structures. Our simulations also indicate that the mechanical environment of the filament affects breaking: local mechanical support inhibits healing after severing, especially in the case of filaments with defects. These results recall reports of microtubule healing after flow-induced bending and corroborate prior experimental studies that show severing is more likely at locations where microtubules crossover in networks. Our results shed new light on mechanisms underlying the ability of microtubules to be destroyed and healed in the cell, either by external forces or by severing enzymes wedging dimers apart. © 2016 Wiley Periodicals, Inc.

Katanin: A Sword Cutting Microtubules for Cellular, Developmental, and Physiological Purposes

KATANIN is a well-studied microtubule severing protein affecting microtubule organization and dynamic properties in higher plants. By regulating mitotic and cytokinetic and cortical microtubule arrays it is involved in the progression of cell division and cell division plane orientation. KATANIN is also involved in cell elongation and morphogenesis during plant growth. In this way KATANIN plays critical roles in diverse plant developmental processes including the development of pollen, embryo, seed, meristem, root, hypocotyl, cotyledon, leaf, shoot, and silique. KATANIN-dependent microtubule regulation seems to be under the control of plant hormones. This minireview provides an overview on available KATANIN mutants and discusses advances in our understanding of KATANIN biological roles in plants.

Detecting the exposure to Cd and PCBs by means of a non-invasive transcriptomic approach in laboratory and wild contaminated European eels (Anguilla anguilla)

Detecting and separating specific effects of contaminants in a multi-stress field context remain a major challenge in ecotoxicology. In this context, the aim of this study was to assess the usefulness of a non-invasive transcriptomic method, by means of a complementary DNA (cDNA) microarray comprising 1000 candidate genes, on caudal fin clips. Fin gene transcription patterns of European eels (Anguilla anguilla) exposed in the laboratory to cadmium (Cd) or a polychloro-biphenyl (PCBs) mixture but also of wild eels from three sampling sites with differing contamination levels were compared to test whether fin clips may be used to detect and discriminate the exposure to these contaminants. Also, transcriptomic profiles from the liver and caudal fin of eels experimentally exposed to Cd were compared to assess the detection sensitivity of the fin transcriptomic response. A similar number of genes were differentially transcribed in the fin and liver in response to Cd exposure, highlighting the detection sensitivity of fin clips. Moreover, distinct fin transcription profiles were observed in response to Cd or PCB exposure. Finally, the transcription profiles of eels from the most contaminated site clustered with those from laboratory-exposed fish. This study thus highlights the applicability and usefulness of performing gene transcription assays on non-invasive tissue sampling in order to detect the in situ exposure to Cd and PCBs in fish.

The cytoskeleton and neurite initiation

Neurons begin their life as simple spheres, but can ultimately assume an elaborate morphology with numerous, highly arborized dendrites, and long axons. This is achieved via an astounding developmental progression which is dependent upon regulated assembly and dynamics of the cellular cytoskeleton. As neurites emerge out of the soma, neurons break their spherical symmetry and begin to acquire the morphological features that define their structure and function. Neurons regulate their cytoskeleton to achieve changes in cell shape, velocity, and direction as they migrate, extend neurites, and polarize. Of particular importance, the organization and dynamics of actin and microtubules directs the migration and morphogenesis of neurons. This review focuses on the regulation of intrinsic properties of the actin and microtubule cytoskeletons and how specific cytoskeletal structures and dynamics are associated with the earliest phase of neuronal morphogenesis—neuritogenesis.

Mutations in KATNB1 cause complex cerebral malformations by disrupting asymmetrically dividing neural progenitors

Exome sequencing analysis of over 2,000 children with complex malformations of cortical development identified five independent (four homozygous and one compound heterozygous) deleterious mutations in KATNB1, encoding the regulatory subunit of the microtubule-severing enzyme Katanin. Mitotic spindle formation is defective in patient-derived fibroblasts, a consequence of disrupted interactions of mutant KATNB1 with KATNA1, the catalytic subunit of Katanin, and other microtubule-associated proteins. Loss of KATNB1 orthologs in zebrafish (katnb1) and flies (kat80) results in microcephaly, recapitulating the human phenotype. In the developing Drosophila optic lobe, kat80 loss specifically affects the asymmetrically dividing neuroblasts, which display supernumerary centrosomes and spindle abnormalities during mitosis, leading to cell cycle progression delays and reduced cell numbers. Furthermore, kat80 depletion results in dendritic arborization defects in sensory and motor neurons, affecting neural architecture. Taken together, we provide insight into the mechanisms by which KATNB1 mutations cause human cerebral cortical malformations, demonstrating its fundamental role during brain development.