Wnt signaling regulates chemokine production and cell migration of circulating human monocytes

The β-catenin dependent canonical Wnt signaling pathway plays a crucial role in maintaining normal homeostasis. However, when dysregulated, Wnt signaling is closely associated with various pathological conditions, including inflammation and different types of cancer.Here, we show a new connection between the leukocyte inflammatory response and the Wnt signaling pathway. Specifically, we demonstrate that circulating human primary monocytes express distinct Wnt signaling components and are susceptible to stimulation by the classical Wnt ligand-Wnt-3a. Although this stimulation increased the levels of β-catenin protein, the expression of the classical Wnt-target genes was not affected. Intriguingly, treating circulating human monocytes with Wnt-3a induces the secretion of cytokines and chemokines, enhancing monocyte migration. Mechanistically, the enhanced monocyte migration in response to Wnt stimuli is mediated through CCL2, a strong monocyte-chemoattractant.To further explore the physiological relevance of these findings, we conducted ex-vivo experiments using blood samples of patients with rheumatic joint diseases (RJD) - conditions where monocytes are known to be dysfunctional. Wnt-3a generated a unique cytokine expression profile, which was significantly distinct from that observed in monocytes obtained from healthy donors.Thus, our results provide the first evidence that Wnt-3a may serve as a potent stimulator of monocyte-driven immune processes. These findings contribute to our understanding of inflammatory diseases and, more importantly, shed light on the role of a core signaling pathway in the circulation.

Correction: Nonsense mutation suppression is enhanced by targeting different stages of the protein synthesis process

[This corrects the article DOI: 10.1371/journal.pbio.3002355.].

Nonsense mutation suppression is enhanced by targeting different stages of the protein synthesis process

The introduction of premature termination codons (PTCs), as a result of splicing defects, insertions, deletions, or point mutations (also termed nonsense mutations), lead to numerous genetic diseases, ranging from rare neuro-metabolic disorders to relatively common inheritable cancer syndromes and muscular dystrophies. Over the years, a large number of studies have demonstrated that certain antibiotics and other synthetic molecules can act as PTC suppressors by inducing readthrough of nonsense mutations, thereby restoring the expression of full-length proteins. Unfortunately, most PTC readthrough-inducing agents are toxic, have limited effects, and cannot be used for therapeutic purposes. Thus, further efforts are required to improve the clinical outcome of nonsense mutation suppressors. Here, by focusing on enhancing readthrough of pathogenic nonsense mutations in the adenomatous polyposis coli (APC) tumor suppressor gene, we show that disturbing the protein translation initiation complex, as well as targeting other stages of the protein translation machinery, enhances both antibiotic and non-antibiotic-mediated readthrough of nonsense mutations. These findings strongly increase our understanding of the mechanisms involved in nonsense mutation readthrough and facilitate the development of novel therapeutic targets for nonsense suppression to restore protein expression from a large variety of disease-causing mutated transcripts.

Title: The C-terminal amphipathic helix of Carboxypeptidase E mediates export from the ER and secretion via lysosomes

Carboxypeptidase E (CPE), an essential enzyme in the biosynthetic production line of most peptide hormones and neuropeptides, is predominantly expressed in endocrine tissues and in the nervous system. CPE is active in acidic environments where it cleaves the C'-terminal basic residues of peptide precursors to generate their bioactive form. Consequently, this highly conserved enzyme regulates numerous fundamental biological processes. Here, we combined live-cell microscopy and molecular analysis to examine the intracellular distribution and secretion dynamics of fluorescently tagged CPE. We show that, in non-endocrine cells, tagged-CPE is a soluble luminal protein that is efficiently exported from the ER via the Golgi apparatus to lysosomes. The C'-terminal conserved amphipathic helix serves as a lysosomal and secretory granule targeting and a secretion motif. Following secretion, CPE may be reinternalized into the lysosomes of neighboring cells.

Elevated Serum Amyloid A Levels Contribute to Increased Platelet Adhesion in COVID-19 Patients

Coronavirus disease-19 (COVID-19) patients are prone to thrombotic complications that may increase morbidity and mortality. These complications are thought to be driven by endothelial activation and tissue damage promoted by the systemic hyperinflammation associated with COVID-19. However, the exact mechanisms contributing to these complications are still unknown. To identify additional mechanisms contributing to the aberrant clotting observed in COVID-19 patients, we analyzed platelets from COVID-19 patients compared to those from controls using mass spectrometry. We identified increased serum amyloid A (SAA) levels, an acute-phase protein, on COVID-19 patients' platelets. In addition, using an in vitro adhesion assay, we showed that healthy platelets adhered more strongly to wells coated with COVID-19 patient serum than to wells coated with control serum. Furthermore, inhibitors of integrin aIIbβ3 receptors, a mediator of platelet-SAA binding, reduced platelet adhesion to recombinant SAA and to wells coated with COVID-19 patient serum. Our results suggest that SAA may contribute to the increased platelet adhesion observed in serum from COVID-19 patients. Thus, reducing SAA levels by decreasing inflammation or inhibiting SAA platelet-binding activity might be a valid approach to abrogate COVID-19-associated thrombotic complications.

Circulating Wnt Ligands Activate the Wnt Signaling Pathway in Mature Erythrocytes

[Figure: see text].

Therapeutic targeting of the oncogenic Wnt signaling pathway for treating colorectal cancer and other colonic disorders

The canonical Wnt pathway is one of the key cellular signaling cascades that regulates, via the transcriptional co-activator β-catenin, numerous embryogenic developmental processes, as well as tissue homeostasis. It is therefore not surprising that misregulation of the Wnt/β-catenin pathway has been implicated in carcinogenesis. Aberrant Wnt signaling has been reported in a variety of malignancies, and its role in both hereditary and sporadic colorectal cancer (CRC), has been the subject of intensive study. Interestingly, the vast majority of colorectal tumors harbor mutations in the tumor suppressor gene adenomatous polyposis coli (APC). The Wnt pathway is complex, and despite decades of research, the mechanisms that underlie its functions are not completely known. Thus, although the Wnt cascade is an attractive target for therapeutic intervention against CRC, one of the malignancies with the highest morbidity and mortality rates, achieving efficacy and safety is yet extremely challenging. Here, we review the current knowledge of the Wnt different epistatic signaling components and the mechanism/s by which the signal is transduced in both health and disease, focusing on CRC. We address some of the important questions in the field and describe various therapeutic strategies designed to combat unregulated Wnt signaling, the development of targeted therapy approaches and the emerging challenges that are associated with these advanced methods.

Striatin Is Required for Hearing and Affects Inner Hair Cells and Ribbon Synapses

Striatin, a subunit of the serine/threonine phosphatase PP2A, is a core member of the conserved striatin-interacting phosphatase and kinase (STRIPAK) complexes. The protein is expressed in the cell junctions between epithelial cells, which play a role in maintaining cell-cell adhesion. Since the cell junctions are crucial for the function of the mammalian inner ear, we examined the localization and function of striatin in the mouse cochlea. Our results show that in neonatal mice, striatin is specifically expressed in the cell-cell junctions of the inner hair cells, the receptor cells in the mammalian cochlea. Auditory brainstem response measurements of striatin-deficient mice indicated a progressive, high-frequency hearing loss, suggesting that striatin is essential for normal hearing. Moreover, scanning electron micrographs of the organ of Corti revealed a moderate degeneration of the outer hair cells in the middle and basal regions, concordant with the high-frequency hearing loss. Additionally, striatin-deficient mice show aberrant ribbon synapse maturation. Loss of the outer hair cells, combined with the aberrant ribbon synapse distribution, may lead to the observed auditory impairment. Together, these results suggest a novel function for striatin in the mammalian auditory system.

Resorting the function of the colorectal cancer gatekeeper adenomatous polyposis coli

As a large number of cancers are caused by nonsense mutations in key genes, read-through of these mutations to restore full-length protein expression is a potential therapeutic strategy. Mutations in the adenomatous polyposis coli (APC) gene initiate the majority of both sporadic and hereditary colorectal cancers (CRC) and around 30% of these mutations are nonsense mutations. Our goal was to test the feasibility and effectiveness of APC nonsense mutation read-through as a potential chemo-preventive therapy in Familial Adenomatous Polyposis (FAP), an inherited CRC syndrome patients. Ten FAP patients harboring APC nonsense mutations were treated with the read-through inducing antibiotic erythromycin for 4 months. Endoscopic assessment of the adenomas was performed at baseline, after 4 and after 12 months. Adenoma burden was documented in terms of adenoma number, maximal polyp size and cumulative polyp size per procedure. Tissue samples were collected and subjected to molecular and genetic analyses. Our results show that in the majority of patients the treatment led to a decrease in cumulative adenoma burden, median reduction in cumulative adenoma size and median reduction in adenoma number. Molecular and genetic analyses of the adenomas revealed that the treatment led to a reduced number of somatic APC mutations, reduced cellular proliferation and restoration of APC tumor-suppressing activity. Together, our findings show that induced read-through of APC nonsense mutations leads to promising clinical results and should be further investigated to establish its therapeutic potential in FAP and sporadic CRCs harboring nonsense APC mutations.

5-Hydroxymethylcytosine as a clinical biomarker: Fluorescence-based assay for high-throughput epigenetic quantification in human tissues

Epigenetic transformations may provide early indicators for cancer and other disease. Specifically, the amount of genomic 5-hydroxymethylcytosine (5-hmC) was shown to be globally reduced in a wide range of cancers. The integration of this global biomarker into diagnostic workflows is hampered by the limitations of current 5-hmC quantification methods. Here we present and validate a fluorescence-based platform for high-throughput and cost-effective quantification of global genomic 5-hmC levels. We utilized the assay to characterize cancerous tissues based on their 5-hmC content, and observed a pronounced reduction in 5-hmC level in various cancer types. We present data for glioblastoma, colorectal cancer, multiple myeloma, chronic lymphocytic leukemia and pancreatic cancer, compared to corresponding controls. Potentially, the technique could also be used to follow response to treatment for personalized treatment selection. We present initial proof-of-concept data for treatment of familial adenomatous polyposis.

Striatin is a novel modulator of cell adhesion

The adherens junctions (AJs) and tight junctions (TJs) provide critical adhesive contacts between neighboring epithelial cells and are crucial for epithelial adhesion, integrity, and barrier functions in a wide variety of tissues and organisms. The striatin protein family, which are part of the striatin interaction phosphatases and kinases complex, are multidomain scaffolding proteins that play important biologic roles. We have previously shown that striatin colocalizes with the tumor suppressor protein adenomatous polyposis coli in the TJs of epithelial cells. Here we show that striatin affects junction integrity and cell migration, probably through a mechanism that involves the adhesion molecule E-cadherin. Cells engaged in cell-cell adhesion expressed a high MW-modified form of striatin that forms stable associations with detergent-insoluble, membrane-bound cellular fractions. In addition, striatin has recently been suggested to be a target of the poly (ADP-ribose) polymerases Tankyrase 1, and we have found that striatin interacts with Tankyrase 1 and is subsequently poly-ADP-ribosylated. Taken together, our results suggest that striatin is a novel cell-cell junctional protein that functions to maintain correct cell adhesion and may have a role in establishing the relationship between AJs and TJs that is fundamental for epithelial cell-cell adhesion.-Lahav-Ariel, L., Caspi, M., Nadar-Ponniah, P. T., Zelikson, N., Hofmann, I., Hanson, K. K., Franke, W. W., Sklan, E. H., Avraham, K. B., Rosin-Arbesfeld, R. Striatin is a novel modulator of cell adhesion.

High-Temperature Requirement A1 (Htra1) - A Novel Regulator of Canonical Wnt Signaling

Different cancer types as well as many other diseases are caused by aberrant activation of the canonical Wnt signal transduction pathway, and it is especially implicated in the development and progression of colorectal cancer (CRC). The main effector protein of the canonical Wnt signaling cascade is β-catenin, which binds to the T- cell factor/lymphoid enhancer factor (TCF/LEF) and triggers the activation of Wnt target genes. Here, we identify the serine protease High-Temperature Requirement A1 (HTRA1) as a novel component of the canonical Wnt pathway. We show that the HTRA1 protein inhibits the Wnt/β-catenin signaling, in both paracrine and autocrine manners, and affects the expression of several Wnt target genes. Moreover, HTRA1 forms a complex with β-catenin and reduces the proliferation rates of cells. Taken together, our findings indicate that HTRA1 functions as a novel suppressor of the canonical Wnt signaling pathway.

The effect of a germline mutation in the APC gene on β-catenin in human embryonic stem cells

Background

Most cases of colorectal cancer (CRC) are initiated by inactivation mutations in the APC gene, which is a negative regulator of the Wnt-β-catenin pathway. Patients with familial adenomatous polyposis (FAP) inherit a germline mutation in one APC allele, and loss of the second allele leads to the development of polyps that will turn malignant if not removed. It is not fully understood which molecular mechanisms are activated by APC loss and when the loss of the second APC allele occurs.

Methods

Two FAP human embryonic stem cell (hESCs) lines were derived from APC mutated embryos following pre-implantation genetic diagnosis (PGD) for FAP. These FAP-hESCs were cultured in vitro and following extended culture: 1) β-catenin expression was analyzed by Western blot analysis; 2) Wnt-β-catenin/TCF-mediated transcription luciferase assay was performed; 3) cellular localization of β-catenin was evaluated by immunoflorecence confocal microscopy; and 4) DNA sequencing of the APC gene was performed.

Results

We have established a novel human in-vitro model for studying malignant transformation, using hESCs that carry a germline mutation in the APC gene following PGD for FAP. Extended culturing of FAP1 hESCs led to activation of the Wnt signaling pathway, as demonstrated by enhanced β-catenin/TCF-mediated activity. Additionally, β-catenin showed a distinct perinuclear distribution in most (91 %) of the FAP1 hESCs high passage colonies. DNA sequencing of the whole gene detected several polymorphisms in FAP1 hESCs, however, no somatic mutations were discovered in the APC gene. On the other hand, no changes in β-catenin were detected in the FAP2 hESCs, demonstrating the natural diversity of the human FAP population.

Conclusions

Our results describe the establishment of novel hESC lines from FAP patients with a predisposition for cancer mutation. These cells can be maintained in culture for long periods of time and may serve as a platform for studying the initial molecular and cellular changes that occur during early stages of malignant transformation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2809-9) contains supplementary material, which is available to authorized users.

A flow cytometry-based reporter assay identifies macrolide antibiotics as nonsense mutation read-through agents

A large number of human diseases are caused by nonsense mutations. These mutations result in premature protein termination and the expression of truncated, usually nonfunctional products. A promising therapeutic strategy for patients suffering from premature termination codon (PTC)-mediated disorders is to suppress the nonsense mutation and restore the expression of the affected protein. Such a suppression approach using specific antibiotics and other read-through promoting agents has been shown to suppress PTCs and restore the production of several important proteins. Here, we report the establishment of a novel, rapid, and very efficient method for screening stop-codon read-through agents. We also show that, in both mammalian cells and in a transgenic mouse model, distinct members of the macrolide antibiotic family can induce read-through of disease-causing stop codons leading to re-expression of several key proteins and to reduced disease phenotypes. Taken together, our results may help in the identification and characterization of well-needed customized pharmaceutical PTC suppression agents.

KEY MESSAGES

Establishment of a flow cytometry-based reporter assay to identify nonsense mutation read-through agents. Macrolide antibiotics can induce read-through of disease-causing stop codons. Macrolide-induced protein restoration can alleviate disease-like phenotypes.

Aldolase positively regulates of the canonical Wnt signaling pathway

The Wnt signaling pathway is an evolutionary conserved system, having pivotal roles during animal development. When over-activated, this signaling pathway is involved in cancer initiation and progression. The canonical Wnt pathway regulates the stability of β-catenin primarily by a destruction complex containing a number of different proteins, including Glycogen synthase kinase 3β (GSK-3β) and Axin, that promote proteasomal degradation of β-catenin. As this signaling cascade is modified by various proteins, novel screens aimed at identifying new Wnt signaling regulators were conducted in our laboratory. One of the different genes that were identified as Wnt signaling activators was Aldolase C (ALDOC). Here we report that ALDOC, Aldolase A (ALDOA) and Aldolase B (ALDOB) activate Wnt signaling in a GSK-3β-dependent mechanism, by disrupting the GSK-3β-Axin interaction and targeting Axin to the dishevelled (Dvl)-induced signalosomes that positively regulate the Wnt pathway thus placing the Aldolase proteins as novel Wnt signaling regulators.

14-3-3 and β-catenin are secreted on extracellular vesicles to activate the oncogenic Wnt pathway

Aberrant activation of the canonical Wnt signal transduction pathway is involved in a large number of human diseases. β-catenin, the key effector protein of the canonical Wnt pathway, functions in the nucleus with T-cell factor/lymphoid enhancer factor (TCF/LEF) to activate expression of Wnt target genes. Here we show that members of the 14-3-3 protein family bind disheveled-2 (Dvl-2) and glycogen synthase-3β (GSK-3β) to attenuate the interaction between GSK-3β and β-catenin. Importantly, 14-3-3 and β-catenin form "bleb-like" structures and are secreted via extracellular vesicles to induce Wnt signaling activity in target cells. Our data suggest a novel way of transducing the oncogenic Wnt signal in which β-catenin is regulated by 14-3-3ζ through the formation of "oncosomes" that contain both the 14-3-3 and β-catenin proteins.

The EDD E3 ubiquitin ligase ubiquitinates and up-regulates beta-catenin

The effector protein of the canonical Wnt pathway is β-catenin, which is regulated by the ubiquitin system. This study shows that the E3 ubiquitin ligase EDD ubiquitinates β-catenin, leading to up-regulation of β-catenin's expression levels and activity. Thus the results demonstrate a role for the ubiquitin system in up-regulation of the Wnt pathway.

Wnt/β-catenin signaling plays a central role in development and is also involved in a diverse array of diseases. β-Catenin activity is tightly regulated via a multiprotein complex that includes the kinase glycogen synthase kinase-3β (GSK-3β). GSK-3β phosphorylates β-catenin, marking it for ubiquitination and degradation via the proteasome. Thus in regulation of the Wnt pathway, the ubiquitin system is known to be involved mostly in mediating the turnover of β-catenin, resulting in reduced Wnt signaling levels. Here we report that an arm of the ubiquitin system increases β-catenin protein levels. We show that GSK-3β directly interacts with the E3 ubiquitin ligase identified by differential display (EDD) that also binds β-catenin. Expression of EDD leads to enhanced nuclear accumulation of both GSK-3β and β-catenin and results in up-regulation of β-catenin expression levels and activity. Importantly, EDD ubiquitinates β-catenin through Lys29- or Lys11-linked ubiquitin chains, leading to enhanced stability of β-catenin. Our results demonstrate a role for the ubiquitin system in up-regulation of the Wnt signaling pathway, suggesting that EDD could function as a colorectal oncogene.

The armadillo repeat domain of the APC tumor suppressor protein interacts with Striatin family members

Adenomatous polyposis coli (APC) is a multifunctional tumor suppressor protein that negatively regulates the Wnt signaling pathway. The APC gene is ubiquitously expressed in various tissues, especially throughout the large intestine and central nervous system. Mutations in the gene encoding APC have been found in most colorectal cancers and in other types of cancer. The APC gene product is a large multidomain protein that interacts with a variety of proteins, many of which bind to the well conserved armadillo repeat domain of APC. Through its binding partners, APC affects a large number of important cellular processes, including cell-cell adhesion, cell migration, organization of the actin and microtubule cytoskeletons, spindle formation and chromosome segregation. The molecular mechanisms that control these diverse APC functions are only partly understood. Here we describe the identification of an additional APC armadillo repeat binding partner - the Striatin protein. The Striatin family members are multidomain molecules that are mainly neuronal and are thought to function as scaffolds. We have found that Striatin is expressed in epithelial cells and co-localizes with APC in the epithelial tight junction compartment and in neurite tips of PC12 cells. The junctional localization of APC and Striatin is actin-dependent. Depletion of APC or Striatin affected the localization of the tight junction protein ZO-1 and altered the organization of F-actin. These results raise the possibility that the contribution of APC to cell-cell adhesion may be through interaction with Striatin in the tight junction compartment of epithelial cells.

Nuclear GSK-3beta inhibits the canonical Wnt signalling pathway in a beta-catenin phosphorylation-independent manner

Beta-catenin is the central signalling molecule of the canonical Wnt pathway, where it activates target genes in a complex with lymphoid enhancer factor/T-cell factor transcription factors in the nucleus. The regulation of beta-catenin activity is thought to occur via a cytoplasmatic multiprotein complex that includes the serine/threonine kinase glycogen synthase kinase-3beta (GSK-3beta) that phosphorylates beta-catenin, marking it for degradation by the proteasome. Here, we provide evidence showing that GSK-3beta has a nuclear function in downregulating the activity of beta-catenin. Using colorectal cell lines that express a mutant form of beta-catenin, which cannot be phosphorylated by GSK-3beta and ectopically expressed mutant beta-catenin protein, we show that nuclear GSK-3beta functions in a mechanism that does not involve beta-catenin phosphorylation to reduce the levels of Wnt signalling. We show that GSK-3beta enters the nucleus, forms a complex with beta-catenin and lowers the levels of beta-catenin/TCF-dependent transcription in a mechanism that involves GSK-3beta-Axin binding.

LIS1 missense mutations: variable phenotypes result from unpredictable alterations in biochemical and cellular properties

Mutations in one allele of the human LIS1 gene cause a severe brain malformation, lissencephaly. Although most LIS1 mutations involve deletions, several point mutations with a single amino acid alteration were described. Patients carrying these mutations reveal variable phenotypic manifestations. We have analyzed the functional importance of these point mutations by examining protein stability, folding, intracellular localization, and protein-protein interactions. Our data suggest that the mutated proteins were affected at different levels, and no single assay could be used to predict the lissencephaly phenotype. Most interesting are those mutant proteins that retain partial folding and interactions. In the case of LIS1 mutated in F31S, the cellular phenotype may be modified by overexpression of specific interacting proteins. Overexpression of the PAF-AH alpha1 subunit dissolved aggregates induced by this mutant protein and increased its half-life. Overexpression of NudE or NudEL localized this mutant protein to spindle poles and kinetochores but had no effect on protein stability. Our results implicate that there are probably different biochemical and cellular mechanisms obstructed in each patient yielding the varied lissencephaly phenotypes.

LIS1, CLIP-170's key to the dynein/dynactin pathway

CLIP-170 is a plus-end tracking protein which may act as an anticatastrophe factor. It has been proposed to mediate the association of dynein/dynactin to microtubule (MT) plus ends, and it also binds to kinetochores in a dynein/dynactin-dependent fashion, both via its C-terminal domain. This domain contains two zinc finger motifs (proximal and distal), which are hypothesized to mediate protein-protein interactions. LIS1, a protein implicated in brain development, acts in several processes mediated by the dynein/dynactin pathway by interacting with dynein and other proteins. Here we demonstrate colocalization and direct interaction between CLIP-170 and LIS1. In mammalian cells, LIS1 recruitment to kinetochores is dynein/dynactin dependent, and recruitment there of CLIP-170 is dependent on its site of binding to LIS1, located in the distal zinc finger motif. Overexpression of CLIP-170 results in a zinc finger-dependent localization of a phospho-LIS1 isoform and dynactin to MT bundles, raising the possibility that CLIP-170 and LIS1 regulate dynein/dynactin binding to MTs. This work suggests that LIS1 is a regulated adapter between CLIP-170 and cytoplasmic dynein at sites involved in cargo-MT loading, and/or in the control of MT dynamics.

ngl9: a third MADS box gene expressed in alfalfa root nodules

Expression of MADS box genes has previously been localized to the infected cells of alfalfa (Medicago sativa) root nodules. These genes represent the first putative transcription factors to be identified in nodules and are hypothesized to be involved in a signal transduction pathway initiated by the intracellular bacterium. The eventual activation of specific target genes defines pertinent characteristics of this nitrogen-fixing differentiated cell. In this study, we identify a third nodule MADS box gene, ngl9, and demonstrate that the DNA-binding activity of its protein product is dependent on the presence of a second MADS box protein, NMH7. Despite previous results to the contrary, both genes are expressed in the early stages of flower development, further strengthening the premise that nodule developmental programming may capitalize upon existing developmental cascades.

Interaction between LIS1 and doublecortin, two lissencephaly gene products

Mutations in either LIS1 or DCX are the most common cause for type I lissencephaly. Here we report that LIS1 and DCX interact physically both in vitro and in vivo. Epitope-tagged DCX transiently expressed in COS cells can be co-immunoprecipitated with endogenous LIS1. Furthermore, endogenous DCX could be co-immunoprecipitated with endogenous LIS1 in embryonic brain extracts, demonstrating an in vivo association. The two protein products also co-localize in transfected cells and in primary neuronal cells. In addition, we demonstrate homodimerization of DCX in vitro. Using fragments of both LIS1 and DCX, the domains of interaction were mapped. LIS1 and DCX interact with tubulin and microtubules. Our results suggest that addition of DCX and LIS1 to tubulin enhances polymerization in an additive fashion. In in vitro competition assays, when LIS1 is added first, DCX competes with LIS1 in its binding to microtubules, but when DCX is added prior to the addition of LIS1 it enhances the binding of LIS1 to microtubules. We conclude that LIS1 and DCX cross-talk is important to microtubule function in the developing cerebral cortex.

Homologs of the alpha- and beta-subunits of mammalian brain platelet-activating factor acetylhydrolase Ib in the Drosophila melanogaster genome

The mammalian intracellular brain platelet-activating factor acetylhydrolase, implicated in the development of cerebral cortex, is a member of the phospholipase A2 superfamily. It is made up of a homodimer of the 45 kDa LIS1 protein (a product of the causative gene for type I lissencephaly) and a pair of homologous 26-kDa alpha-subunits which account for all the catalytic activity. LIS1 is hypothesized to regulate nuclear movement in migrating neurons through interactions with the cytoskeleton, while the alpha-subunits, whose structure is known, contain a trypsin-like triad within the framework of a unique tertiary fold. The physiological significance of the association of the two types of subunits is not known. In an effort to better understand the function of the complex we turned to genomic data mining in search of related proteins in lower eukaryotes. We found that the Drosophila melanogaster genome contains homologs of both alpha- and beta-subunits, and we cloned both genes. The alpha-subunit homolog has been overexpressed, purified and crystallized. It lacks two of the three active-site residues and, consequently, is catalytically inactive against PAF-AH (Ib) substrates. Our study shows that the beta-subunit homolog is highly conserved from Drosophila to mammals and is able to interact with the mammalian alpha-subunits but is unable to interact with the Drosophila alpha-subunit. Proteins 2000;39:1-8.

Doublecortin mutations cluster in evolutionarily conserved functional domains

Mutations in the X-linked gene doublecortin ( DCX ) result in lissencephaly in males or subcortical laminar heterotopia ('double cortex') in females. Various types of mutation were identified and the sequence differences included nonsense, splice site and missense mutations throughout the gene. Recently, we and others have demonstrated that DCX interacts and stabilizes microtubules. Here, we performed a detailed sequence analysis of DCX and DCX-like proteins from various organisms and defined an evolutionarily conserved Doublecortin (DC) domain. The domain typically appears in the N-terminus of proteins and consists of two tandemly repeated 80 amino acid regions. In the large majority of patients, missense mutations in DCX fall within the conserved regions. We hypothesized that these repeats may be important for microtubule binding. We expressed DCX or DCLK (KIAA0369) repeats in vitro and in vivo. Our results suggest that the first repeat binds tubulin but not microtubules and enhances microtubule polymerization. To study the functional consequences of DCX mutations, we overexpressed seven of the reported mutations in COS7 cells and examined their effect on the microtubule cytoskeleton. The results demonstrate that some of the mutations disrupt microtubules. The most severe effect was observed with a tyrosine to histidine mutation at amino acid 125 (Y125H). Produced as a recombinant protein, this mutation disrupts microtubules in vitro at high molar concentration. The positions of the different mutations are discussed according to the evolutionarily defined DC-repeat motif. The results from this study emphasize the importance of DCX-microtubule interaction during normal and abnormal brain development.

Doublecortin, a stabilizer of microtubules

X-linked lissencephaly is a severe brain malformation affecting males. Recently it has been demonstrated that the doublecortin gene is implicated in this disorder. In order to study the function of Doublecortin, we analyzed the protein upon transfection of COS cells. Doublecortin was found to bind to the microtubule cytoskeleton. In vitro assays (using biochemical methods, DIC microscopy and electron microscopy) demonstrate that Doublecortin binds microtubules directly, stabilizes them and causes bundling. In vivo assays also show that Doublecortin stabilizes microtubules and causes bundling. Doublecortin is a basic protein with an iso-electric point of 10, typical of microtubule-binding proteins. However, its sequence contains no known microtubule-binding domain(s). The results obtained in this study with Doublecortin and our previous work on another lissencephaly gene ( LIS1 ) emphasize the central role of regulation of microtubule dynamics and stability during neuronal morphogenesis.

Evolutionary diversity of symbiotically induced nodule MADS box genes: characterization of nmhC5, a member of a novel subfamily

Unique organs called nodules form on legume roots in response to intracellular infection by soil bacteria in the genus Rhizobium. This study describes a new MADS box gene, nmhC5, which along with nmh7 (J. Heard and K. Dunn, Proc. Natl. Acad. Sci. USA 92:5273-5277, 1995), is expressed in alfalfa (Medicago sativa) root nodules. Together, these genes represent the first putative transcription factors identified in nodules. Expression in a root-derived structure supports the growing sentiment that MADS box proteins have diverse roles in plant development. Comparison of the putative translation product of nmhC5 with those of other reported members of the MADS box family suggests that the overall structure of nmhC5 is conserved. Evolutionary analysis among the MADS box family showed that nmhC5 is orthologous to a root-expressed clone in Arabidopsis thaliana, agl17, and that nmh7 is similar to the floral subfamily with AP3 (DefA)/PI (Glo). Consistent with a prediction of homodimer formation, NMHC5 was shown to bind a CArG consensus sequence in vitro. In contrast, NMH7, which shows structural similarity to MADS box proteins that form heterodimers, did not bind the CArG element in an in vitro DNA-binding assay, suggesting the existence of an unknown dimer partner. The root-derived MADS box genes constitute a novel subfamily of vegetatively expressed MADS box genes. The evolutionary diversity between nmh7 and nmhC5 could represent an overall mechanistic conservation between plant developmental processes or could mean that nmh7 and nmhC5 make fundamentally different contributions to the development of the nodule.

[Thrombolysis for evolving myocardial infarction in a rural primary care clinic]

Early thrombolytic therapy gives maximum benefit in acute myocardial infarction. In remote rural areas with no mobile intensive care service there is a significant delay between onset of symptoms and administration of thrombolytic therapy which has a critical impact on revascularization. Thrombolytic therapy with streptokinase 1,500,000 U was given in a primary care rural clinic to 2 patients with evolving myocardial infarction 45-50 minutes from onset of symptoms. In both patients, who were transported to hospital after the therapy, there were clinical signs of reperfusion. There were no complications during treatment or transportation. We conclude that thrombolytic therapy given for evolving myocardial infarction in a rural primary care clinic is possible and safe.

Effect of a pharmacist's and a nurse's interventions on cost of drug therapy in a medical intensive-care unit

The effect of interventions by a pharmacist and a nurse on the cost of drug therapy in a medical intensive-care unit (ICU) was determined. A pharmacist taught cost-avoidance concepts related to medication use to a senior member of the nursing staff. The pharmacist and the nurse documented during a 91-day period all interventions that resulted in a discontinuation or change in drug therapy or involved nonformulary drug requests or serum drug concentration determinations. Costs that were avoided or added as a result of these interventions were determined using drug acquisition costs and (for interventions involving i.v. therapy) the cost of related supplies. Costs were calculated for both the initial 24-hour period after each intervention and the expected duration of therapy. The 345 interventions of the pharmacist and the nurse represented $6,383 in 24-hour cost avoidance and $23,993 in total cost avoidance. The majority of interventions resulted in discontinuation of medications or changes in drug dosage; most of those interventions involved antimicrobial agents. Other frequent interventions involved changes in route of administration and the interchange of therapeutic alternates. A pharmacist and a nurse had a positive impact on the cost of drug therapy in a medical ICU.