Identification of new components of the basal pole of Toxoplasma gondii provides novel insights into its molecular organization and functions

The Toxoplasma gondii tachyzoite is a singled-cell obligate intracellular parasite responsible for the acute phase of toxoplasmosis. This polarized cell exhibits an apical complex, a hallmark of the phylum Apicomplexa, essential for motility, invasion, and egress from the host cell. Located on the opposite end of the cell is the basal complex, an elaborated cytoskeletal structure that also plays critical roles in the lytic cycle of the parasite, being involved in motility, cell division, constriction and cytokinesis, as well as intravacuolar cell-cell communication. Nevertheless, only a few proteins of this structure have been described and functionally assessed. In this study, we used spatial proteomics to identify new basal complex components (BCC), and in situ imaging, including ultrastructure expansion microscopy, to position them. We thus confirmed the localization of nine BCCs out of the 12 selected candidates and assigned them to different sub-compartments of the basal complex, including two new domains located above the basal ring and below the posterior cup. Their functional investigation revealed that none of these BCCs are essential for parasite growth in vitro. However, one BCC is critical for constricting of the basal complex, likely through direct interaction with the class VI myosin heavy chain J (MyoJ), and for gliding motility. Four other BCCs, including a phosphatase and a guanylate-binding protein, are involved in the formation and/or maintenance of the intravacuolar parasite connection, which is required for the rosette organization and synchronicity of cell division.

TFK1, a basal body transition fibre protein that is essential for cytokinesis in Trypanosoma brucei

In Trypanosoma brucei, transition fibres (TF) form a nine-bladed pattern-like structure connecting the base of the flagellum to the flagellar pocket membrane. Despite the characterization of two TF proteins, CEP164C and TbRP2, little is known about the organization of these fibres. Here, we report the identification and characterization of the first kinetoplastid-specific TF protein named TFK1 (Tb927.6.1180). Bioinformatics and functional domain analysis identified three TFK1 distinct domains: an N-terminal domain of an unpredicted function, a coiled-coil domain involved in TFK1-TFK1 interaction and a C-terminal intrinsically disordered region potentially involved in protein interaction. Cellular immuno-localization showed that TFK1 is a newly identified basal body maturation marker. Further, using ultrastructure expansion and immuno-electron microscopies we localized CEP164C and TbRP2 at the TF and TFK1 on the distal appendage matrix of the TF. Importantly, RNAi knockdown of TFK1 in bloodstream form cells induced misplacement of basal bodies, a defect in the furrow or fold generation and eventually cell death. We hypothesize that TFK1 is a basal body positioning specific actor and a key regulator of cytokinesis in the bloodstream form Trypanosoma brucei.

TbKINX1B: a novel BILBO1 partner and an essential protein in bloodstream form Trypanosoma brucei

The flagellar pocket (FP) of the pathogen Trypanosoma brucei is an important single copy structure that is formed by the invagination of the pellicular membrane. It is the unique site of endo- and exocytosis and is required for parasite pathogenicity. The FP consists of distinct structural sub-domains with the least explored being the flagellar pocket collar (FPC). TbBILBO1 is the first-described FPC protein of Trypanosoma brucei. It is essential for parasite survival, FP and FPC biogenesis. In this work, we characterize TbKINX1B, a novel TbBILBO1 partner. We demonstrate that TbKINX1B is located on the basal bodies, the microtubule quartet (a set of four microtubules) and the FPC in T. brucei. Down-regulation of TbKINX1B by RNA interference in bloodstream forms is lethal, inducing an overall disturbance in the endomembrane network. In procyclic forms, the RNAi knockdown of TbKINX1B leads to a minor phenotype with a small number of cells displaying epimastigote-like morphologies, with a misplaced kinetoplast. Our results characterize TbKINX1B as the first putative kinesin to be localized both at the basal bodies and the FPC with a potential role in transporting cargo along with the microtubule quartet.

Bhalin, an Essential Cytoskeleton-Associated Protein of Trypanosoma brucei Linking TbBILBO1 of the Flagellar Pocket Collar with the Hook Complex

Background: In most trypanosomes, endo and exocytosis only occur at a unique organelle called the flagellar pocket (FP) and the flagellum exits the cell via the FP. Investigations of essential cytoskeleton-associated structures located at this site have revealed a number of essential proteins. The protein TbBILBO1 is located at the neck of the FP in a structure called the flagellar pocket collar (FPC) and is essential for biogenesis of the FPC and parasite survival. TbMORN1 is a protein that is present on a closely linked structure called the hook complex (HC) and is located anterior to and overlapping the collar. TbMORN1 is essential in the bloodstream form of T. brucei. We now describe the location and function of BHALIN, an essential, new FPC-HC protein. Methodology/Principal Findings: Here, we show that a newly characterised protein, BHALIN (BILBO1 Hook Associated LINker protein), is localised to both the FPC and HC and has a TbBILBO1 binding domain, which was confirmed in vitro. Knockdown of BHALIN by RNAi in the bloodstream form parasites led to cell death, indicating an essential role in cell viability. Conclusions/Significance: Our results demonstrate the essential role of a newly characterised hook complex protein, BHALIN, that influences flagellar pocket organisation and function in bloodstream form T. brucei parasites.

The kinesin of the flagellum attachment zone in Leishmania is required for cell morphogenesis, cell division and virulence in the mammalian host

Leishmania parasites possess a unique and complex cytoskeletal structure termed flagellum attachment zone (FAZ) connecting the base of the flagellum to one side of the flagellar pocket (FP), an invagination of the cell body membrane and the sole site for endocytosis and exocytosis. This structure is involved in FP architecture and cell morphogenesis, but its precise role and molecular composition remain enigmatic. Here, we characterized Leishmania FAZ7, the only known FAZ protein containing a kinesin motor domain, and part of a clade of trypanosomatid-specific kinesins with unknown functions. The two paralogs of FAZ7, FAZ7A and FAZ7B, display different localizations and functions. FAZ7A localizes at the basal body, while FAZ7B localizes at the distal part of the FP, where the FAZ structure is present in Leishmania. While null mutants of FAZ7A displayed normal growth rates, the deletion of FAZ7B impaired cell growth in both promastigotes and amastigotes of Leishmania. The kinesin activity is crucial for its function. Deletion of FAZ7B resulted in altered cell division, cell morphogenesis (including flagellum length), and FP structure and function. Furthermore, knocking out FAZ7B induced a mis-localization of two of the FAZ proteins, and disrupted the molecular organization of the FP collar, affecting the localization of its components. Loss of the kinesin FAZ7B has important consequences in the insect vector and mammalian host by reducing proliferation in the sand fly and pathogenicity in mice. Our findings reveal the pivotal role of the only FAZ kinesin as part of the factors important for a successful life cycle of Leishmania.

Leishmania are flagellated trypanosomatid parasites causing worldwide human and animal diseases. As ’divergent eukaryotes’, their biology presents unique features and structures, of which the specific functions constitute potential drug targets. Among others, they possess a unique cytoskeletal structure termed the flagellum attachment zone (FAZ) attaching the base of their flagellum to one side of the flagellar pocket (FP), which is the sole site for endocytosis and exocytosis. The FP together with other unique flagellum-associated structures are crucial for parasite survival, but the functioning of this whole remains largely enigmatic. Leishmania also possess an expanded repertoire of kinesins (>55), including two trypanosomatid-specific families. Here, we show that the deletion of the sole kinesin among FAZ proteins disrupts cell morphogenesis, FP organisation and cell division. Furthermore, the ability to proliferate in the insect vector and mammalian host is reduced in parasites lacking the kinesin FAZ7B. This study helps elucidate the factors contributing to the successful lifecycle and pathogenicity of the parasite. It also highlights the functional diversification of motor proteins during evolution.

Structural studies of the shortest extended synaptotagmin with only two C2 domains from Trypanosoma brucei

Extended synaptotagmins (E-Syts) localize at membrane contact sites between the endoplasmic reticulum (ER) and the plasma membrane to mediate inter-membrane lipid transfer and control plasma membrane lipid homeostasis. All known E-Syts contain an N-terminal transmembrane (TM) hairpin, a central synaptotagmin-like mitochondrial lipid-binding protein (SMP) domain, and three or five C2 domains at their C termini. Here we report an uncharacterized E-Syt from the protist parasite Trypanosoma brucei, namely, TbE-Syt. TbE-Syt contains only two C2 domains (C2A and C2B), making it the shortest E-Syt known by now. We determined a 1.5-Å-resolution crystal structure of TbE-Syt-C2B and revealed that it binds lipids via both Ca²⁺- and PI(4,5)P₂-dependent means. In contrast, TbE-Syt-C2A lacks the Ca²⁺-binding site but may still interact with lipids via a basic surface patch. Our studies suggest a mechanism for how TbE-Syt tethers the ER membrane tightly to the plasma membrane to transfer lipids between the two organelles.

•

We identified a new type of extended synaptotagmin (E-Syt) in Trypanosoma brucei

•

TbE-Syt is the shortest known E-Syt with only two C2 domains, C2A and C2B

•

TbE-Syt-C2B binds lipids via both Ca²⁺- and PI(4,5)P₂-dependent means

•

Unlike all other known E-Syts, TbE-Syt-C2A and C2B are connected by a flexible loop

Biallelic variants in MAATS1 encoding CFAP91, a calmodulin-associated and spoke-associated complex protein, cause severe astheno-teratozoospermia and male infertility

BACKGROUND

Multiple morphological abnormalities of the flagella (MMAF) consistently lead to male infertility due to a reduced or absent sperm motility defined as asthenozoospermia. Despite numerous genes recently described to be recurrently associated with MMAF, more than half of the cases analysed remain unresolved, suggesting that many yet uncharacterised gene defects account for this phenotype METHODS: Exome sequencing was performed on 167 infertile men with an MMAF phenotype. Immunostaining and transmission electron microscopy (TEM) in sperm cells from affected individuals were performed to characterise the ultrastructural sperm defects. Gene inactivation using RNA interference (RNAi) was subsequently performed in Trypanosoma.

RESULTS

We identified six unrelated affected patients carrying a homozygous deleterious variants in MAATS1, a gene encoding CFAP91, a calmodulin-associated and spoke-associated complex (CSC) protein. TEM and immunostaining experiments in sperm cells showed severe central pair complex (CPC) and radial spokes defects. Moreover, we confirmed that the WDR66 protein is a physical and functional partner of CFAP91 into the CSC. Study of Trypanosoma MAATS1's orthologue (TbCFAP91) highlighted high sequence and structural analogies with the human protein and confirmed the axonemal localisation of the protein. Knockdown of TbCFAP91 using RNAi impaired flagellar movement led to CPC defects in Trypanosoma as observed in humans.

CONCLUSIONS

We showed that CFAP91 is essential for normal sperm flagellum structure and function in human and Trypanosoma and that biallelic variants in this gene lead to severe flagellum malformations resulting in astheno-teratozoospermia and primary male infertility.

Crystal structure of the N-terminal domain of the trypanosome flagellar protein BILBO1 reveals a ubiquitin fold with a long structured loop for protein binding

Trypanosoma brucei is a protist parasite causing sleeping sickness and nagana in sub-Saharan Africa. T. brucei has a single flagellum whose base contains a bulblike invagination of the plasma membrane called the flagellar pocket (FP). Around the neck of the FP on its cytoplasmic face is a structure called the flagellar pocket collar (FPC), which is essential for FP biogenesis. BILBO1 was the first characterized component of the FPC in trypanosomes. BILBO1's N-terminal domain (NTD) plays an essential role in T. brucei FPC biogenesis and is thus vital for the parasite's survival. Here, we report a 1.6-Å resolution crystal structure of TbBILBO1-NTD, which revealed a conserved horseshoe-like hydrophobic pocket formed by an unusually long loop. Results from mutagenesis experiments suggested that another FPC protein, FPC4, interacts with TbBILBO1 by mainly contacting its three conserved aromatic residues Trp-71, Tyr-87, and Phe-89 at the center of this pocket. Our findings disclose the binding site of TbFPC4 on TbBILBO1-NTD, which may provide a basis for rational drug design targeting BILBO1 to combat T. brucei infections.

Mutations in TTC29, Encoding an Evolutionarily Conserved Axonemal Protein, Result in Asthenozoospermia and Male Infertility

In humans, structural or functional defects of the sperm flagellum induce asthenozoospermia, which accounts for the main sperm defect encountered in infertile men. Herein we focused on morphological abnormalities of the sperm flagellum (MMAF), a phenotype also termed "short tails," which constitutes one of the most severe sperm morphological defects resulting in asthenozoospermia. In previous work based on whole-exome sequencing of a cohort of 167 MMAF-affected individuals, we identified bi-allelic loss-of-function mutations in more than 30% of the tested subjects. In this study, we further analyzed this cohort and identified five individuals with homozygous truncating variants in TTC29, a gene preferentially and highly expressed in the testis, and encoding a tetratricopeptide repeat-containing protein related to the intraflagellar transport (IFT). One individual carried a frameshift variant, another one carried a homozygous stop-gain variant, and three carried the same splicing variant affecting a consensus donor site. The deleterious effect of this last variant was confirmed on the corresponding transcript and protein product. In addition, we produced and analyzed TTC29 loss-of-function models in the flagellated protist T. brucei and in M. musculus. Both models confirmed the importance of TTC29 for flagellar beating. We showed that in T. brucei the TPR structural motifs, highly conserved between the studied orthologs, are critical for TTC29 axonemal localization and flagellar beating. Overall our work demonstrates that TTC29 is a conserved axonemal protein required for flagellar structure and beating and that TTC29 mutations are a cause of male sterility due to MMAF.

Trypanosoma brucei gambiense excreted/secreted factors impair lipopolysaccharide-induced maturation and activation of human monocyte-derived dendritic cells

Trypanosoma brucei gambiense, an extracellular eukaryotic flagellate parasite, is the main etiological agent of human African trypanosomiasis (HAT) or sleeping sickness. Dendritic cells (DCs) play a pivotal role at the interface between innate and adaptive immune response and are implicated during HAT. In this study, we investigated the effects of T gambiense and its excreted/secreted factors (ESF) on the phenotype of human monocyte-derived DCs (Mo-DCs). Mo-DCs were cultured with trypanosomes, lipopolysaccharide (LPS), ESF derived from T gambiense bloodstream strain Biyamina (MHOM/SD/82), or both ESF and LPS. Importantly, ESF reduced the expression of the maturation markers HLA-DR and CD83, as well as the secretion of IL-12, TNF-alpha and IL-10, in LPS-stimulated Mo-DCs. During mixed-leucocyte reactions, LPS- plus ESF-exposed DCs induced a non-significant decrease in the IFN-gamma/IL-10 ratio of CD4 + T-cell cytokines. Based on the results presented here, we raise the hypothesis that T gambiense has developed an immune escape strategy through the secretion of paracrine mediators in order to limit maturation and activation of human DCs. The identification of the factor(s) in the T gambiense ESF and of the DCs signalling pathway(s) involved may be important in the development of new therapeutic targets.

(De)glutamylation and cell death in Leishmania parasites

Trypanosomatids are flagellated protozoan parasites that are very unusual in terms of cytoskeleton organization but also in terms of cell death. Most of the Trypanosomatid cytoskeleton consists of microtubules, forming different substructures including a subpellicular corset. Oddly, the actin network appears structurally and functionally different from other eukaryotic actins. And Trypanosomatids have an apoptotic phenotype under cell death conditions, but the pathways involved are devoid of key mammal proteins such as caspases or death receptors, and the triggers involved in apoptotic induction remain unknown. In this article, we have studied the role of the post-translational modifications, deglutamylation and polyglutamylation, in Leishmania. We have shown that Leishmania apoptosis was linked to polyglutamylation and hypothesized that the cell survival process autophagy was linked to deglutamylation. A balance seems to be established between polyglutamylation and deglutamylation, with imbalance inducing microtubule or other protein modifications characterizing either cell death if polyglutamylation was prioritized, or the cell survival process of autophagy if deglutamylation was prioritized. This emphasizes the role of post-translational modifications in cell biology, inducing cell death or cell survival of infectious agents.

Leishmania are unique unicellular organisms in terms of cytoskeleton organization and mechanisms of cell death. For example, the major cytoskeletal components of these parasites are microtubules, which form a subpellicular corset. In terms of cell death, an apoptotic phenotype has been characterized in Leishmania but the pathways remain unknown, being devoid of key mammal cell death proteins. In a previous article, we demonstrated that the cytoskeleton of this parasite is extensively glutamylated but, paradoxically, overexpression or inhibition of polyglutamylase expression have limited visible cellular consequences. In this manuscript, we have highlighted the link between polyglutamylation and Leishmania cell death, suggesting the importance of the polyglutamylation/deglutamylation balance in this parasite. Further, we have identified, for the first time in Leishmania, deglutamylases, among which one that, in an original manner, deglutamylates glutamates at branching points but also long glutamate side chains. This work emphasizes the role of post-translational modifications as essential regulators of protein function, not only of mammal cells such as neurons or ciliated/flagellated cells, but also of infectious agents. This work suggests an important and discernible “live or die”—“cell death or autophagy” balance pathway and the conceptual mechanism that is involved in cellular decision making.

Purification of Extracellular Trypanosomes, Including African, from Blood by Anion-Exchangers (Diethylaminoethyl-cellulose Columns)

This method allows the separation of trypanosomes, parasites responsible for animal and human African trypanosomiasis (HAT), from infected blood. This is the best method for diagnosis of first stage HAT and furthermore this parasite purification method permits serological and research investigations. HAT is caused by Tsetse fly transmitted Trypanosoma brucei gambiense and T. b. rhodesiense. Related trypanosomes are the causative agents of animal trypanosomiasis. Trypanosome detection is essential for HAT diagnosis, treatment and follow-up. The technique described here is the most sensitive parasite detection technique, adapted to field conditions for the diagnosis of T. b. gambiense HAT and can be completed within one hour. Blood is layered onto an anion-exchanger column (DEAE cellulose) previously adjusted to pH 8, and elution buffer is added. Highly negatively charged blood cells are adsorbed onto the column whereas the less negatively charged trypanosomes pass through. Collected trypanosomes are pelleted by centrifugation and observed by microscopy. Moreover, parasites are prepared without cellular damage whilst maintaining their infectivity. Purified trypanosomes are required for immunological testing; they are used in the trypanolysis assay, the gold standard in HAT serology. Stained parasites are utilized in the card agglutination test (CATT) for field serology. Antigens from purified trypanosomes, such as variant surface glycoprotein, exoantigens, are also used in various immunoassays. The procedure described here is designed for African trypanosomes; consequently, chromatography conditions have to be adapted to each trypanosome strain, and more generally, to the blood of each species of host mammal. These fascinating pathogens are easily purified and available to use in biochemical, molecular and cell biology studies including co-culture with host cells to investigate host-parasite relationships at the level of membrane receptors, signaling, and gene expression; drug testing in vitro; investigation of gene deletion, mutation, or overexpression on metabolic processes, cytoskeletal biogenesis and parasite survival.

Abstract PD9-12: Integrative molecular profiling of breast cancer brain metastasis and patient-derived xenograft organoids from resected breast cancer brain metastases to interrogate and prioritize therapeutic personalized strategies

Background: Breast cancer brain metastasis (BM) is an area of unmet need in metastatic breast cancer patients. Novel therapeutic interventions to help prevent and treat BM are warranted. We conducted integrative molecular profiling of BM and matched primary tumors (PT) using next-generation DNA and RNA sequencing to examine the molecular landscape. In addition, we established patient-derived xenograft/organoid (PDX/PDO) to examine drug sensitivity according to the molecular and clinical features of the BM.

Methods: Archived, formalin fixed paraffin-embedded BM was collected retrospectively. BM were also collected prospectively at the time of clinically indicated surgical resection through the central nervous system tissue banking and the Michigan Oncology Sequencing Center (MI-ONCOSEQ) protocols. Matched archived PT tissues were collected when available. Integrative next-generation sequencing was conducted using the MI-ONCOSEQ platform. The prospectively collected BM were further used to establish PDXs/ PDOs. Successfully established PDXs/PDOs were used for ex vivo drug testing via MiDrugScreen, a novel drug sensitivity testing platform, where testing was performed in a dose-response format with drug selection prioritized by clinical scenario and molecular alterations if known a priori.

Results: 12 matched BM-PT pairs were analyzed: 6 triple negative, 5 HER2 positive, and 1 ER positive HER2 negative. All except one (11/12) had TP53 mutations. When present, TP53 mutations in BM were also found in PT (except for 1 unknwon case in PT due to low coverage). ER+HER2- was the only one without TP53 mutation but had hyper-mutation (APOBEC signature). Driver mutations and unique copy number alterations (CDKN2A loss in 1/12, mutations in PIK3CA in 1/12 and ESR1 in 1/12, CCNE1 amplification in 1/12) were noted in BMs. In 75% of cases, mutational burden was higher in BM vs. PT. 2 PDX/PDO were available for drug testing. PDO-BC9 was noted to have RB1 (splice acceptor) and LOH. As predicted by this alteration, PDO-BC9 was insensitive to CDK4/6 inhibitors (palbociclib, abemaciclib) tested on MiDrugScreen panel. PDX-BC4 was established from PIK3CA and ESR1 mutated BM from an ER+HER2- patient who had previously progressed on endocrine therapy with a CDK4/6 inhibitor. As predicted, the PDX-BC4 was resistant to CDK4/6 inhibitor but interestingly sensitive to PIK3CA, ERK, and MEK inhibitors.

Conclusions: TP53 mutation was highly prevalent and may be a biomarker for increased risk of BM. Further study is warranted to see if specific TP53 mutations are associated with a risk of BM development and can be used in risk stratification for BM specific intervention. Unique molecular alterations in BM compared to matched PT may have a therapeutic implication as a target or resistance biomarker. Conducting drug testing in addition to molecular profiling has the strong potential of being informative in tailoring or prioritizing therapeutic agents in the era of precision medicine. Additional BM PDXs/PDOs from breast and other solid tumors are being examined using this novel therapeutic tailoring approach with the combination of MIONCOSEQ and MiDrugScreen.

Citation Format: Morikawa A, Robinson DR, Soellner M, Wu Y-M, Lonigro R, Gilani R, Cheng X, Lachacz E, Thomas D, McMurray K, Smerage J, Henry NL, Heth J, Chinnaiyan A, Hayes DF, Merajver S. Integrative molecular profiling of breast cancer brain metastasis and patient-derived xenograft organoids from resected breast cancer brain metastases to interrogate and prioritize therapeutic personalized strategies [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr PD9-12.

Abstract P5-04-01: Functional and therapeutic significance of ESR1 fusions in metastatic ER+ breast cancer

Background. Next-generation sequencing methods have identified several ESR1 fusion genes in treatment refractory ER+ breast cancer, however detailed functional studies in experimental models are lacking and how they might be targeted remains poorly understood. We recently reported two transcriptionally active, in-frame ESR1 fusions, ESR1-YAP1 and ESR1-PCDH11X, identified in a small cohort of metastatic ER+ cases, that induce not only pan-endocrine therapy resistance but also metastatic disease progression (Lei et al., Cell Reports, in press). Limited characterization of ESR1-DAB2 and ESR1-GYG1, also identified in metastatic ER+ disease from a recent study, suggests these two ESR1 fusions also drive estrogen-independent gene activation (Hartmaier et al., Annals of Oncology, 2018). Here, we functionally characterize ESR1-DAB2 and ESR1-GYG1 along with additional ESR1 fusions discovered in metastatic ER+ breast tumors to further support a causal role for in-frame ESR1 fusions in driving endocrine therapy resistance and promoting metastasis-associated biology, and explore therapeutic vulnerabilities induced by ESR1 fusion gene formation.

Methods. RNA-seq identified ESR1 fusions from treatment refractory, ER+ metastatic breast tumors. In-frame ESR1 fusions constructs were generated and stably expressed in ER+ breast cancer cell lines: T47D, MCF7, and ZR75-1. Estrogen-independent and fulvestrant-resistant growth was monitored in hormone-deprived stable cell lines. mRNA-qPCR was performed to examine expression of estrogen responsive and epithelial-to-mesenchymal transition (EMT) genes. In vitro sensitivity to CDK4/6 inhibition was tested with palbociclib and abemaciclib.

Results. In addition to previously described ESR1-YAP1, ESR1-PCDH11X, ESR1-DAB2, and ESR1-GYG1, that follow a pattern retaining the first 6 exons of ESR1 (ESR1-e6) fused in-frame to C-terminal sequences provided by the partner gene, additional in-frame ESR1-e6 fusions, ESR1-PCMT1, ESR1-ARNT2, and ESR1-ARID1B, all identified in metastatic ER+ samples, were found to follow the same fusion pattern. ESR1-DAB2 and ESR1-GYG1 produced stable ESR1 fusion proteins in ER+ breast cancer cell lines. In T47D, these two fusions drove estrogen-independent and fulvestrant-resistant growth. In addition, T47D and ZR75-1 models revealed that ESR1-DAB2 drove estrogen-independent expression of estrogen responsive genes and also EMT genes, including SNAI1, suggesting this fusion, like ESR1-YAP1 and ESR1-PCDH11X, could also drive metastasis. Treatment with CDK4/6 inhibitors suppressed growth induced by ESR1-DAB2 and ESR1-GYG1.

Conclusion. The majority of in-frame ESR1 exon 6 fusions found in metastatic ER+ breast are transcriptionally active, drive endocrine therapy resistant proliferation, and induce an EMT-like transcriptional program. The ability to block ESR1 fusion induced growth with a CDK4/6 inhibitor is clinically significant as ESR1 fusion gene formation renders ER insensitive to all endocrine therapies that target the ligand binding domain. Furthermore, clinical diagnosis of an active ESR1 fusion could potentially stratify patients for CDK4/6 inhibitor treatment. This presentation is the most complete description of the role for ESR1 fusions in endocrine therapy resistance and metastasis described to date.

Citation Format: Lei JT, Gou X, Seker S, Haricharan S, Lee AV, Robinson DR, Ellis MJ. Functional and therapeutic significance of ESR1 fusions in metastatic ER+ breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P5-04-01.

Abstract P2-09-26: Frequency and mechanisms of elevated somatic mutation burden in metastatic breast cancer and response to immune checkpoint blockade

Background: Immune checkpoint blockade (ICB) is effective in the treatment of various malignancies. Thus far, however, results in breast cancer have been mixed. Elevated tumor mutational load, and subsequent increased likelihood of forming immunogenic neoantigens, has been correlated with response to ICB. Mutational load observed in breast cancers varies widely. However, most studies have assessed mutational load using primary tumors. Few studies have explored the frequency of high mutational load, molecular mechanisms accounting for this phenomenon, and its potential impact on response to ICB in metastatic breast cancer (MBC).

Methods: From 2011-2016, 124 patients (pts) with MBC of varying subtypes underwent research biopsy of their metastatic disease for whole genome, exome and transcriptome sequencing of tumor and matched normal sample through the Michigan Oncology Sequencing Center (Mi-OncoSeq). Those pts with elevated somatic mutation load were defined as having greater than 10 mutations per megabase of targeted sequencing and mutational signatures accounting for high mutation load were noted. Pts treated subsequently with ICB were followed to assess response.

Results: Twelve MBC pts had high mutation load (10% of cohort). Eight pts had estrogen receptor (ER) positive MBC and 4 pts had metastatic triple negative breast cancer (TNBC). In 5 cases, a clear mutational signature accounting for high mutation load was evident. Two TNBC cases harbored an APOBEC mutational signature in addition to 1 TNBC and 2 ER positive tumors displaying a microsatellite instability signature (MSI-H). Among the tumors with MSI-H signature, 1 case was associated with a pathogenic germline alteration in MLH1. Two pts were subsequently treated with ICB on a clinical trial. One pt came off study after 3 months due to progressive brain metastases and another had partial response to therapy lasting 7 months.

Conclusions: Elevated somatic mutation burden in MBC is observed in approximately 10% of pts, and is detected in both ER positive and TNBC. Since high mutation burden has been associated with increased likelihood of response to ICB, identification of this genomic feature could have important therapeutic implications for MBC pts.

Citation Format: Cobain EF, Robinson DR, Wu Y-M, Lonigro R, Vats P, Rabban E, Kumar-Sinha C, Schott AF, Smerage JB, Morikawa A, Burness ML, Van Poznak CH, Griggs J, Wicha M, Hayes DF, Chinnaiyan AM. Frequency and mechanisms of elevated somatic mutation burden in metastatic breast cancer and response to immune checkpoint blockade [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P2-09-26.

Trypanosoma brucei CYP51: Essentiality and Targeting Therapy in an Experimental Model

Trypanosoma brucei gambiense is the main causative agent of Human African Trypanosomiasis (HAT), also known as sleeping sickness. Because of limited alternatives and treatment toxicities, new therapeutic options are urgently needed for patients with HAT. Sterol 14alpha-demethylase (CYP51) is a potential drug target but its essentiality has not been determined in T. brucei. We used a tetracycline-inducible RNAi system to assess the essentiality of CYP51 in T. brucei bloodstream form (BSF) cells and we evaluated the effect of posaconazole, a well-tolerated triazole drug, within a panel of virulent strains in vitro and in a murine model. Expression of CYP51 in several T. brucei cell lines was demonstrated by western blot and its essentiality was demonstrated by RNA interference (CYP51RNAi) in vitro. Following reduction of TbCYP51 expression by RNAi, cell growth was reduced and eventually stopped compared to WT or non-induced cells, showing the requirement of CYP51 in T. brucei. These phenotypes were rescued by addition of ergosterol. Additionally, CYP51RNAi induction caused morphological defects with multiflagellated cells (p<0.05), suggesting cytokinesis dysfunction. The survival of CYP51RNAi Doxycycline-treated mice (p = 0.053) and of CYP51RNAi 5-day pre-induced Doxycycline-treated mice (p = 0.008) were improved compared to WT showing a CYP51 RNAi effect on trypanosomal virulence in mice. The posaconazole concentrations that inhibited parasite growth by 50% (IC50) were 8.5, 2.7, 1.6 and 0.12 μM for T. b. brucei 427 90-13, T. b. brucei Antat 1.1, T. b. gambiense Feo (Feo/ITMAP/1893) and T. b. gambiense Biyamina (MHOM/SD/82), respectively. During infection with these last three virulent strains, posaconazole-eflornithine and nifurtimox-eflornithine combinations showed similar improvement in mice survival (p≤0.001). Our results provide support for a CYP51 targeting based treatment in HAT. Thus posaconazole used in combination may represent a therapeutic alternative for trypanosomiasis.

Tracking adenovirus genomes identifies morphologically distinct late DNA replication compartments

In adenoviral virions, the genome is organized into a chromatin-like structure by viral basic core proteins. Consequently viral DNAs must be replicated, chromatinized and packed into progeny virions in infected cells. Although viral DNA replication centers can be visualized by virtue of viral and cellular factors, the spatiotemporal regulation of viral genomes during subsequent steps remains to be elucidated. In this study, we used imaging analyses to examine the fate of adenoviral genomes and to track newly replicated viral DNA as well as replication-related factors. We show de novo formation of a subnuclear domain, which we termed Virus-induced Post-Replication (ViPR) body, that emerges concomitantly with or immediately after disintegration of initial replication centers. Using a nucleoside analogue, we show that viral genomes continue being synthesized in morphologically distinct replication compartments at the periphery of ViPR bodies and are then transported inward. In addition, we identified a nucleolar protein Mybbp1a as a molecular marker for ViPR bodies, which specifically associated with viral core protein VII. In conclusion, our work demonstrates the formation of previously uncharacterized viral DNA replication compartments specific for late phases of infection that produce progeny viral genomes accumulating in ViPR bodies.

The Trypanosome Flagellar Pocket Collar and Its Ring Forming Protein-TbBILBO1

Sub-species of Trypanosoma brucei are the causal agents of human African sleeping sickness and Nagana in domesticated livestock. These pathogens have developed an organelle-like compartment called the flagellar pocket (FP). The FP carries out endo- and exocytosis and is the only structure this parasite has evolved to do so. The FP is essential for parasite viability, making it an interesting structure to evaluate as a drug target, especially since it has an indispensible cytoskeleton component called the flagellar pocket collar (FPC). The FPC is located at the neck of the FP where the flagellum exits the cell. The FPC has a complex architecture and division cycle, but little is known concerning its organization. Recent work has focused on understanding how the FP and the FPC are formed and as a result of these studies an important calcium-binding, polymer-forming protein named TbBILBO1 was identified. Cellular biology analysis of TbBILBO1 has demonstrated its uniqueness as a FPC component and until recently, it was unknown what structural role it played in forming the FPC. This review summarizes the recent data on the polymer forming properties of TbBILBO1 and how these are correlated to the FP cytoskeleton.

Abstract P2-02-19: Somatic genetic profiling of circulating tumor cells (CTC) in metastatic breast cancer (MBC) patients

Introduction: Somatic mutations, including those in TP53, PIK3CA, and estrogen receptor alpha (ESR1), are key to the biology of cancer and response to therapy. Recently, somatic cancer-associated mutations have been identified in circulating cell free plasma tumor DNA (ptDNA). Less is known about the mutation profile of DNA extracted from CTC (CTC-DNA). Since CTC-DNA provides mutational information of single cells, we hypothesize CTC-DNA will complement ptDNA to give greater insight into tumor heterogeneity.

Methods: Patients with ER positive MBC who were enrolled in the Mi CTC-ONCOSEQ, a companion trial to Mi-ONCOSEQ (the Michigan Oncology Sequencing Program), and who had ≥5CTC/7.5 ml whole blood were included. CTC were enriched from white blood cells (WBC) with CellSearch© (CXC kit). CTC and WBC were then purified using DEPArrayTM. DNA from individual CTC and WBC was isolated and subjected to whole genomic amplification (Ampli 1TM WGA). Genetic analysis was performed on individual CTC, pooled CTC and pooled WBC DNA by multiplexed PCR based targeted next generation sequencing (NGS) using the Oncomine Comprehensive Panel (targeting ∼130 onco- and tumor suppressor genes) and the Ion Torrent Proton. All patients had exome sequencing performed on research biopsies of metastases using an Illumina HiSeq 2500 platform.

Results: This pilot study was conducted using high quality DNA from two patients assessed to date. Both patients had lobular carcinoma and as expected harbored somatic, deleterious CDH1 (E-cadherin) mutations (frameshift and non-sense) in both research biopsy and CTC-DNA. These data supported our approach. Patient #1 was TP53 wild type in her research biopsy, but multiple CTC harbored somatic TP53 frame-shift mutations (Table). Patient #2 harbored an ESR1 Y537S mutation in her research biopsy. However, only 4 of 7 CTC also harbored this somatic, heterozygous mutation.

Prioritized mutations in CTCPt#Cell Type (CTC vs WBC), numberGeneMutationVariant fraction (expected 1=homozygous; 0.5=heterozygous)Found in research biopsy?1CTC_A2CDH1p.I584fs1YES CTC_A4  1  CTC_A7  0.54  CTC_pool*  0.74  WBC_pool  0  CTC_A2TP53p.152_156del1NO CTC_A4  1  CTC_A7  0.51  CTC_pool*  0.88  WBC_pool  0 2CTC_A9ESR1p.Y537S0.52YES CTC_D1  0.34  CTC_D2  0.46  CTC_D6  0.65  CTC_pool*  0.35  WBC_pool  0  CTC_A12  0  CTC_D3  0  CTC_D7  0  CTC_A12CDH1p.Q641X1YES CTC_A9  1  CTC_D1  1  CTC_D3  1  CTC_D6  1  CTC_pool*  1  WBC_pool  0 * pool of all CTC

Conclusions: We demonstrate the ability to purify CTC, isolate, and amplify DNA of suitable quality for genetic analysis using a comprehensive targeted sequencing panel. Both known and novel alterations were identified in comparison to research biopsy specimens. This approach allows single cell analysis demonstrating heterogeneity of mutational status in different single cells. Studies of CTC-ESR1 and other genetic abnormalities in patients with known tissue mutations who participated in Mi CTC-ONCOSEQ are now underway.

Citation Format: Paoletti C, Cani AK, Aung K, Darga EP, Cannell EM, Hovelson DH, Yazdani M, Blevins AR, Tokudome N, Larios JM, Thomas DG, Brown ME, Gersch C, Schott AF, Robinson DR, Chinnaiyan AM, Bischoff F, Hayes DF, Rae JM, Tomlins SA. Somatic genetic profiling of circulating tumor cells (CTC) in metastatic breast cancer (MBC) patients. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P2-02-19.

Abstract P3-05-01: Molecular analysis of cancer tissue, circulating tumor cells (CTC) and cell-free plasma tumor DNA (ptDNA) suggests variable mechanisms of resistance to endocrine therapy (ET) in estrogen receptor (ER) positive metastatic breast cancer (MBC)

Introduction: Fifty percent of ER positive MBC patients do not benefit from ET. Potential mechanisms of resistance to ET in this patient population include absence of ER expression by deletion or suppression, alteration in ER signaling pathway genes, or upregulation of multiple growth factor receptor pathways. We hypothesized that genotyping and phenotyping of CTC combined with genomic analysis of ptDNA will provide important insights into the multiple mechanisms of ET resistance and that a set of blood tests might serve as a "liquid biopsy" abrogating the need for tissue specimens.

Methods: Twenty-four patients providing informed consent were enrolled into the Mi CTC-ONCOSEQ study, a companion trial to Mi-ONCOSEQ (the Michigan Oncology Sequencing Program). Seven of these patients (5 with ER immunohistochemistry (IHC) positive and 2 with ER negative cancers) who had available archived primary and metastatic cancer tissue, a research metastatic biopsy for genomic analysis, and who had ≥5CTC/7.5 ml whole blood (WB) characterized for ER protein (CTC-ER) are the focus of this report. All the patients were ET refractory. None of them was progressing on fulvestrant at the time of study entry. CTC enumeration and phenotyping was performed with CellSearch©. Circulating ptDNA was analyzed by droplet digital polymerase chain reaction (ddPCR). ER status from archived tissue was obtained from chart review. ER mRNA expression was determined in the research biopsy of metastatic tissue by using quantitative RNA sequencing. Mutational status of ER gene, ESR1, was determined by Next-gen Sequencing using the Illumina HiSeq 2500 platform.

Results: The 2 control patients with triple negative breast cancer had negative CTC-ER. Discordance between CTC-ER and tissue ER by IHC was observed (Table). Two of the 5 ER positive patients retained CTC-ER positivity (39% and 19% of the CTC). One of them (#7) harbored an ESR1 mutation in the research biopsy tissue and in ptDNA, whereas the other (#14) had wild type (WT) ESR1. CTC-ER protein levels in patients #12, 17 and 24 were negative. All had WT ESR1 in the research biopsy tissue. Of note, patient #12 had WT ESR1 in the research biopsy, but an ESR1 mutation was detected in her ptDNA.

Pt#CTC-ER Tissue-ER  ESR1 status in research biopsyESR1 status in ptDNA N[deg]CTC/7.5ml WB% CTC-ER +Primary by IHCMet by IHCMet research biopsy by mRNA  71839%+++Y537SY537S141619%+NA+WTWT12130%+++WTD538G17160%++weakly+WTWT242750%+weakly+weakly+WTWT

Conclusions: These exploratory data suggest heterogeneous mechanisms of resistance to ET in patients with previously determined ER-positive MBC, including ESR1 mutations in ER positive cases (seen in 2 patients) and loss of ER expression (seen in CTC of 3 patients). In contrast, other cancers continue to express WT ESR1, and therefore must have developed alternative mechanisms of resistance. At least 2 of these mechanisms can be detected and monitored with complementary circulating assays: CTC and ptDNA. Further investigations are needed to understand the heterogeneous mechanisms of resistance to ET.

Citation Format: Paoletti C, Aung K, Cannell EM, Darga EP, Chu D, Kidwell KM, Thomas DG, Tokudome N, Brown ME, McNutt LM, Gersch C, Schott AF, Park BH, Robinson DR, Chinnaiyan AM, Rae JM, Hayes DF. Molecular analysis of cancer tissue, circulating tumor cells (CTC) and cell-free plasma tumor DNA (ptDNA) suggests variable mechanisms of resistance to endocrine therapy (ET) in estrogen receptor (ER) positive metastatic breast cancer (MBC). [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P3-05-01.

Predictors of mortality in patients with cardiogenic shock treated with primary percutaneous coronary intervention and intra-aortic balloon counterpulsation

BACKGROUND

Cardiogenic shock remains the most serious complication of patients hospitalized with acute myocardial infarction (AMI). Early revascularization is the cornerstone of invasive therapy, while mechanical support with intra-aortic balloon pump (IABP) is debatable. From our institutional shock registry we sought to determine predictors of in-hospital mortality-including the aspect of IABP timing-and to develop a clinical risk score for shock patients with AMI.

METHODS

From January 2005 till December 2010, 102 patients with cardiogenic shock due to AMI treated with primary percutaneous coronary intervention (PCI) and IABP were analyzed. Univariate and multivariate logistic regression analyses were used to identify independent predictors of in-hospital mortality. Logistic regression analysis and receiver-operating curves were used to generate a mortality risk score.

RESULTS

The mean age of the cohort was 70.1 ± 11.0 years and 70 % were men. One third of patients had a non-ST segment elevation myocardial infarction and 30 % had to be resuscitated before coronary intervention. Mean left ventricular ejection fraction was 25 %. After admission, 23 % of patients developed an acute renal failure and 10 % needed renal dialysis during hospital stay. In 52 % of patients IABP therapy was initiated after primary PCI, while the remaining patients had an IABP-assisted primary PCI. All-cause in-hospital mortality was 40.2 %. Using multivariate analysis, age (odds ratio [OR] 1.08, p = 0.006), resuscitation before PCI (OR 3.46, p = 0.045), vasopressor use (OR 7.88, p = 0.003), acute renal failure (OR 11.18, p = 0.001), and IABP implantation after PCI (OR 4.36, p = 0.011) were independently associated with in-hospital mortality. Based on these predictors, a mortality-risk score was calculated as follows: 1.5 × IABP timing before PCI + 0.1 × age + resuscitation before PCI + 2 × vasopressor use + 2.5 × acute renal failure. Using a cut-off value of 10.4, this score had a specificity of 83 % and a sensitivity of 82 % for prediction of in-hospital death.

CONCLUSIONS

We identified age, vasopressor use, resuscitation before PCI, acute renal failure and IABP implantation after PCI as independent predictors of in-hospital mortality in patients with cardiogenic shock due to AMI. The timing of IABP insertion was the only modifiable factor predicting in-hospital mortality in our cohort. Consequently, balloon pumping should be started before PCI to improve outcome of cardiogenic shock patients.

BILBO1 is a scaffold protein of the flagellar pocket collar in the pathogen Trypanosoma brucei

The flagellar pocket (FP) of the pathogen Trypanosoma brucei is an important single copy structure that is formed by the invagination of the pellicular membrane. It is the unique site of endo- and exocytosis and is required for parasite pathogenicity. The FP consists of distinct structural sub-domains with the least explored being the annulus/horseshoe shaped flagellar pocket collar (FPC). To date the only known component of the FPC is the protein BILBO1, a cytoskeleton protein that has a N-terminus that contains an ubiquitin-like fold, two EF-hand domains, plus a large C-terminal coiled-coil domain. BILBO1 has been shown to bind calcium, but in this work we demonstrate that mutating either or both calcium-binding domains prevents calcium binding. The expression of deletion or mutated forms of BILBO1 in trypanosomes and mammalian cells demonstrate that the coiled-coil domain is necessary and sufficient for the formation of BILBO1 polymers. This is supported by Yeast two-hybrid analysis. Expression of full-length BILBO1 in mammalian cells induces the formation of linear polymers with comma and globular shaped termini, whereas mutation of the canonical calcium-binding domain resulted in the formation of helical polymers and mutation in both EF-hand domains prevented the formation of linear polymers. We also demonstrate that in T. brucei the coiled-coil domain is able to target BILBO1 to the FPC and to form polymers whilst the EF-hand domains influence polymers shape. This data indicates that BILBO1 has intrinsic polymer forming properties and that binding calcium can modulate the form of these polymers. We discuss whether these properties can influence the formation of the FPC.

Trypanosoma brucei avoids destruction by, in part, changing its surface glycoprotein coat, which is trafficked onto the cell surface via an invagination of the cell surface called the flagellar pocket. The pocket is essential for pathogenicity. The distal membrane of the pocket is anchored to a cytoskeleton structure called the flagellar pocket collar (FPC). The FPC is a ring/horseshoe shaped structure, which itself is attached to the single copy flagellum of the parasite. How the “ring” shape of the collar is formed is not understood. Moreover, the only known protein component of the FPC is the protein BILBO1. BILBO1 is modular and has a distinct N-terminal domain, two EF-hand calcium-binding domains and a large C-terminal coiled-coil domain. Here we demonstrate that mutating the EF hand domains prevent calcium binding and that the coiled-coil domain is not only sufficient to target to the collar, but can also form polymers in mammalian cells. Mutating either or both calcium-binding domains of BILBO1 influences polymer formation and type when expressed in mammalian and trypanosome cells. Our premise is that BILBO1 has intrinsic polymer forming properties that are essential for the flagellar pocket collar making the pocket a target for intervention.

Human FAM154A (SAXO1) is a microtubule-stabilizing protein specific to cilia and related structures

Cilia and flagella are microtubule-based organelles present at the surface of most cells, ranging from protozoa to vertebrates, in which these structures are implicated in processes from morphogenesis to cell motility. In vertebrate neurons, microtubule-associated MAP6 proteins stabilize cold-resistant microtubules through their Mn and Mc modules, and play a role in synaptic plasticity. Although centrioles, cilia and flagella have cold-stable microtubules, MAP6 proteins have not been identified in these organelles, suggesting that additional proteins support this role in these structures. Here, we characterize human FAM154A (hereafter referred to as hSAXO1) as the first human member of a widely conserved family of MAP6-related proteins specific to centrioles and cilium microtubules. Our data demonstrate that hSAXO1 binds specifically to centriole and cilium microtubules. We identify, in vivo and in vitro, hSAXO1 Mn modules as responsible for microtubule binding and stabilization as well as being necessary for ciliary localization. Finally, overexpression and knockdown studies show that hSAXO1 modulates axoneme length. Taken together, our findings suggest a fine regulation of hSAXO1 localization and important roles in cilium biogenesis and function.

Extra-glycosomal localisation of Trypanosoma brucei hexokinase 2

The majority of the glycolytic enzymes in the African trypanosome are compartmentalised within peroxisome-like organelles, the glycosomes. Polypeptides harbouring peroxisomal targeting sequences (PTS type 1 or 2) are targeted to these organelles. This targeting is essential to parasite viability, as compartmentalisation of glycolytic enzymes prevents unregulated ATP-dependent phosphorylation of intermediate metabolites. Here, we report the surprising extra-glycosomal localisation of a PTS-2 bearing trypanosomal hexokinase, TbHK2. In bloodstream form parasites, the protein localises to both glycosomes and to the flagellum. Evidence for this includes fractionation and immunofluorescence studies using antisera generated against the authentic protein as well as detection of epitope-tagged recombinant versions of the protein. In the insect stage parasite, distribution is different, with the polypeptide localised to glycosomes and proximal to the basal bodies. The function of the extra-glycosomal protein remains unclear. While its association with the basal body suggests that it may have a role in locomotion in the insect stage parasite, no detectable defect in directional motility or velocity of cell movement were observed for TbHK2-deficient cells, suggesting that the protein may have a different function in the cell.

The Trypanosoma brucei AIR9-like protein is cytoskeleton-associated and is required for nucleus positioning and accurate cleavage furrow placement

AIR9 is a cytoskeleton-associated protein in Arabidopsis thaliana with roles in cytokinesis and cross wall maturation, and reported homologues in land plants and excavate protists, including trypanosomatids. We show that the Trypanosoma brucei AIR9-like protein, TbAIR9, is also cytoskeleton-associated and colocalizes with the subpellicular microtubules. We find it to be expressed in all life cycle stages and show that it is essential for normal proliferation of trypanosomes in vitro. Depletion of TbAIR9 from procyclic trypanosomes resulted in increased cell length due to increased microtubule extension at the cell posterior. Additionally, the nucleus was re-positioned to a location posterior to the kinetoplast, leading to defects in cytokinesis and the generation of aberrant progeny. In contrast, in bloodstream trypanosomes, depletion of TbAIR9 had little effect on nucleus positioning, but resulted in aberrant cleavage furrow placement and the generation of non-equivalent daughter cells following cytokinesis. Our data provide insight into the control of nucleus positioning in this important pathogen and emphasize differences in the cytoskeleton and cell cycle control between two life cycle stages of the T. brucei parasite.

A MAP6-related protein is present in protozoa and is involved in flagellum motility

In vertebrates the microtubule-associated proteins MAP6 and MAP6d1 stabilize cold-resistant microtubules. Cilia and flagella have cold-stable microtubules but MAP6 proteins have not been identified in these organelles. Here, we describe TbSAXO as the first MAP6-related protein to be identified in a protozoan, Trypanosoma brucei. Using a heterologous expression system, we show that TbSAXO is a microtubule stabilizing protein. Furthermore we identify the domains of the protein responsible for microtubule binding and stabilizing and show that they share homologies with the microtubule-stabilizing Mn domains of the MAP6 proteins. We demonstrate, in the flagellated parasite, that TbSAXO is an axonemal protein that plays a role in flagellum motility. Lastly we provide evidence that TbSAXO belongs to a group of MAP6-related proteins (SAXO proteins) present only in ciliated or flagellated organisms ranging from protozoa to mammals. We discuss the potential roles of the SAXO proteins in cilia and flagella function.

A monoclonal antibody marker for the exclusion-zone filaments of Trypanosoma brucei

Background

Trypanosoma brucei is a haemoflagellate pathogen of man, wild animals and domesticated livestock in central and southern Africa. In all life cycle stages this parasite has a single mitochondrion that contains a uniquely organised genome that is condensed into a flat disk-like structure called the kinetoplast. The kinetoplast is essential for insect form procyclic cells and therefore is a potential drug target. The kinetoplast is unique in nature because it consists of novel structural proteins and thousands of circular, interlocking, DNA molecules (kDNA). Secondly, kDNA replication is critically timed to coincide with nuclear S phase and new flagellum biogenesis. Thirdly, the kinetoplast is physically attached to the flagellum basal bodies via a structure called the tripartite attachment complex (TAC). The TAC consists of unilateral filaments (within the mitochondrion matrix), differentiated mitochondrial membranes and exclusion-zone filaments that extend from the distal end of the basal bodies. To date only one protein, p166, has been identified to be a component of the TAC.

Results

In the work presented here we provide data based on a novel EM technique developed to label and characterise cytoskeleton structures in permeabilised cells without extraction of mitochondrion membranes. We use this protocol to provide data on a new monoclonal antibody reagent (Mab 22) and illustrate the precise localisation of basal body-mitochondrial linker proteins. Mab 22 binds to these linker proteins (exclusion-zone filaments) and provides a new tool for the characterisation of cytoskeleton mediated kinetoplast segregation.

Conclusion

The antigen(s) recognised by Mab 22 are cytoskeletal, insensitive to extraction by high concentrations of non-ionic detergent, extend from the proximal region of basal bodies and bind to the outer mitochondrial membrane. This protein(s) is the first component of the TAC exclusion-zone fibres to be identified. Mab 22 will therefore be important in characterising TAC biogenesis.

The leishmania ARL-1 and Golgi traffic

We present here the characterisation of the Leishmania small G protein ADP-Ribosylation Factor-Like protein 1 (ARL-1). The ARL-1 gene is present in one copy per haploid genome and conserved among trypanosomatids. It encodes a protein of 20 kDa, which is equally expressed in the insect promastigote and mammalian amastigote forms of the parasite. ARL-1 localises to the Trans-Golgi Network (TGN); N-terminal myristoylation is essential for TGN localisation. In vivo expression of the LdARL-1/Q74L and LdARL-1/T51N mutants (GTP- and GDP-bound blocked forms respectively) shows that GDP/GTP cycling occurs entirely within the TGN. This is contrary to previous reports in yeast and mammals, where the mutant empty form devoid of nucleotide has been considered as the GDP-blocked form. The dominant-negative empty form mutant LdARL-1/T34N inhibits endocytosis and intracellular trafficking from the TGN to the Lysosome/Multivesicular Tubule and to the acidocalcisomes; these defects are probably related to a mislocalisation of the GRIP domain-containing vesicle tethering factors which cannot be recruited to the TGN by the cytoplasmic LdARL-1/T34N. Thus, besides the functional characterization of a new mutant and a better understanding of ARL-1 GDP/GTP cycling, this work shows that Leishmania ARL-1 is a key component of an essential pathway worth future study.

p166, a link between the trypanosome mitochondrial DNA and flagellum, mediates genome segregation

Kinetoplast DNA (kDNA), the trypanosome mitochondrial genome, is a giant network containing several thousand interlocked DNA rings. Within the mitochondrion, kDNA is condensed into a disk-shaped structure positioned near the flagellar basal body. The disk is linked to the basal body by a remarkable transmembrane filament system named the tripartite attachment complex (TAC). Following kDNA replication, the TAC mediates network segregation, pulling the progeny networks into the daughter cells by their linkage to the basal bodies. So far TAC has been characterized only morphologically with no known protein components. By screening an RNAi library, we discovered p166, a protein localizing between the kDNA and basal body in intact cells and in isolated flagellum-kDNA complexes. RNAi of p166 has only small effects on kDNA replication, but it causes profound defects in network segregation. For example, kDNA replication without segregation causes the networks to grow to enormous size. Thus, p166 is the first reported molecular component of the TAC, and its discovery will facilitate study of kDNA segregation machinery at the molecular level.

Matrix metalloproteinase 3 is present in the cell nucleus and is involved in apoptosis

Matrix metalloproteinase (MMP)-3 is a protease involved in cancer progression and tissue remodeling. Using immunofluorescence and immunoelectron microscopy, we identified nuclear localization of MMP-3 in several cultured cell types and in human liver tissue sections. Western blot analysis of nuclear extracts revealed two immunoreactive forms of MMP-3 at 35 and 45 kd, with the 35-kd form exhibiting caseinolytic activity. By transient transfection, we expressed active MMP-3 fused to the enhanced green fluorescent protein (EGFP/aMMP-3) in Chinese hamster ovary cells. We showed that EGFP/aMMP-3 translocates into the nucleus. A functional nuclear localization signal was demonstrated by the loss of nuclear translocation after site-directed mutagenesis of a putative nuclear localization signal and by the ability of the MMP-3 nuclear localization signal to drive a heterologous protein into the nucleus. Finally, expression by Chinese hamster ovary cells of EGFP/aMMP-3 induced a twofold increase of apoptosis rate, compared with EGFP/pro-MMP-3, which does not translocate to the nucleus. Increased apoptosis was abolished by site-directed mutagenesis of the catalytic site of MMP-3 or by using the MMP inhibitor GM6001. This study elucidates for the first time the mechanisms of nuclear localization of a MMP and shows that nuclear MMP-3 can induce apoptosis via its catalytic activity.

NIMA-related kinase TbNRKC is involved in basal body separation in Trypanosoma brucei

The NIMA-related kinase 2 (NEK 2) has important cell cycle functions related to centriole integrity and splitting. Trypanosoma brucei does not possess centrioles, however, cytokinesis is coupled to basal body separation events. Here we report the first functional characterisation of a T. brucei basal body-cytoskeletal NIMA-related kinase (NRK) protein, TbNRKC. The TbNRKC kinase domain has high amino acid identity with the human NEK1 kinase domain (50%) but also shares 42% identity with human NEK2. TbNRKC is expressed in bloodstream and procyclic cells and functions as a bona fide kinase in vitro. Remarkably, RNAi knockdown of TbNRKC and overexpression of kinase-dead TbNRKC in procyclic forms induces the accumulation of cells with four basal bodies, whereas overexpression of active protein produces supernumary basal bodies and blocks cytokinesis. TbNRKC is located on mature and immature basal bodies and is the first T. brucei NRK to be found associated with the basal body cytokinesis pathway.

Impaired left ventricular systolic function early after heart transplantation is associated with cardiac allograft vasculopathy

Cardiac allograft vasculopathy (CAV) is a major cause of death more than 1 year after heart transplantation. We evaluated the role and possible predictive value of different etiological factors on development of CAV as diagnosed by quantitative coronary angiography (QCA). A total of 121 patients were studied with baseline QCA and 117 had a follow-up study at 1 year to assess the relationship of mean lumen diameter loss (MLDL) in main coronary arteries to immunological and non-immunological factors potentially affecting long-term survival. Out of them, 103 patients were males (85%), 114 (94%) patients were Caucasians and mean age was 48.5 +/- 10 years. Univariate analysis showed that MLDL at 1 year was inversely related to echocardiographic fractional shortening (FS) measured within the first week after transplantation (p = 0.0098) and to intracranial hemorrhage as cause of donor death (p = 0.04) and was directly related to male donors (p = 0.0008), domino transplants (p = 0.037) and donor negative cytomegalovirus (CMV) status (p = 0.022). Multivariate analysis showed that initial FS (p = 0.006) and donor intracranial hemorrhage as a cause of death (p = 0.042) were inversely related to MLDL whereas donor male sex (p = 0.003) and prednisolone treatment throughout the first year (p = 0.012) were directly related. Thus, left ventricular systolic dysfunction early after heart transplantation was associated with subsequent development of CAV.

The extent of akinesis is predictive of the in-hospital mortality from endoaneurysmorrhaphy

Endoaneurysmorrhaphy (EAR) has become an important therapeutic option in the treatment of patients with left ventricular (LV) aneurysm and congestive heart failure. Today, more and more patients are referred for EAR with a dilated akinetic LV rather than a classic dyskinetic LV aneurysm. Little is known about the contribution of the extent of akinesis to perioperative mortality. We reviewed the data of 147 patients with anterior left ventricular aneurysms undergoing EAR. Seventy percent of the patients were male; mean age was 62+/-9 years. Demographic, hemodynamic, angiographic and surgical variables were analyzed using univariate statistic tests in order to determine risk factors for in-hospital mortality.Eighty-two percent of the LV aneurysms had at least some dyskinesia, but 70% were mainly akinetic. 133 patients had additional bypass surgery, one had additional mitral valve replacement. In-hospital mortality was 4.1% (n=6). Risk factors for in-hospital mortality were the total extent of akinetic myocardium (p=0.027) in the 30 degrees RAO view and the duration of cardiopulmonary bypass (CPB, p=0.0068) which was itself dependent on the LV ejection fraction (p=0.001), the number of stenosed coronary arteries (p=0.004), and the extent of akinesis (p=0.023). The extent of dyskinesia was not associated with either perioperative mortality (p=0.36) or CPB duration. EAR can be performed with acceptable perioperative results. Because akinesis increases in many patients with time, and because the duration of ECC was dependent on variables reflecting the severity of the underlying heart disease, our findings underscore the importance of optimal timing for the surgical intervention.

Characterization of the primary spinal afferent innervation of the mouse colon using retrograde labelling

Visceral pain is the most common form of pain produced by disease and is thus of interest in the study of gastrointestinal (GI) complaints such as irritable bowel syndrome, in which sensory signals perceived as GI pain travel in extrinsic afferent neurones with cell bodies in the dorsal root ganglia (DRG). The DRG from which the primary spinal afferent innervation of the mouse descending colon arises are not well defined. This study has combined retrograde labelling and immunohistochemistry to identify and characterize these neurones. Small to medium-sized retrogradely labelled cell bodies were found in the DRG at levels T8-L1 and L6-S1. Calcitonin gene-related peptide (CGRP)- and P2X3-like immunoreactivity (LI) was seen in 81 and 32%, respectively, of retrogradely labelled cells, and 20% bound the Griffonia simplicifolia-derived isolectin IB4. CGRP-LI and IB4 were co-localized in 22% of retrogradely labelled cells, whilst P2X3-LI and IB4 were co-localized in 7% (vs 34% seen in the whole DRG population). Eighty-two per cent of retrogradely labelled cells exhibited vanilloid receptor 1-like immunoreactivity (VR1-LI). These data suggest that mouse colonic spinal primary afferent neurones are mostly peptidergic CGRP-containing, VR1-LI, C fibre afferents. In contrast to the general DRG population, a subset of neurones exist that are P2X3 receptor-LI but do not bind IB4.

A high-order trans-membrane structural linkage is responsible for mitochondrial genome positioning and segregation by flagellar basal bodies in trypanosomes

In trypanosomes, the large mitochondrial genome within the kinetoplast is physically connected to the flagellar basal bodies and is segregated by them during cell growth. The structural linkage enabling these phenomena is unknown. We have developed novel extraction/fixation protocols to characterize the links involved in kinetoplast-flagellum attachment and segregation. We show that three specific components comprise a structure that we have termed the tripartite attachment complex (TAC). The TAC involves a set of filaments linking the basal bodies to a zone of differentiated outer and inner mitochondrial membranes and a further set of intramitochondrial filaments linking the inner face of the differentiated membrane zone to the kinetoplast. The TAC and flagellum-kinetoplast DNA connections are sustained throughout the cell cycle and are replicated and remodeled during the periodic kinetoplast DNA S phase. This understanding of the high-order trans-membrane linkage provides an explanation for the spatial position of the trypanosome mitochondrial genome and its mechanism of segregation. Moreover, the architecture of the TAC suggests that it may also function in providing a structural and vectorial role during replication of this catenated mass of mitochondrial DNA. We suggest that this complex may represent an extreme form of a more generally occurring mitochondrion/cytoskeleton interaction.

Two related subpellicular cytoskeleton-associated proteins in Trypanosoma brucei stabilize microtubules

The subpellicular microtubules of the trypanosome cytoskeleton are cross-linked to each other and the plasma membrane, creating a cage-like structure. We have isolated, from Trypanosoma brucei, two related low-molecular-weight cytoskeleton-associated proteins (15- and 17-kDa), called CAP15 and CAP17, which are differentially expressed during the life cycle. Immunolabeling shows a corset-like colocalization of both CAPs and tubulin. Western blot and electron microscope analyses show CAP15 and CAP17 labeling on detergent-extracted cytoskeletons. However, the localization of both proteins is restricted to the anterior, microtubule minus, and less dynamic half of the corset. CAP15 and CAP17 share properties of microtubule-associated proteins when expressed in heterologous cells (Chinese hamster ovary and HeLa), colocalization with their microtubules, induction of microtubule bundle formation, cold resistance, and insensitivity to nocodazole. When overexpressed in T. brucei, both CAP15 and CAP17 cover the whole subpellicular corset and induce morphological disorders, cell cycle-based abnormalities, and subsequent asymmetric cytokinesis.

A novel CCCH protein which modulates differentiation of Trypanosoma brucei to its procyclic form

Cell differentiation in Trypanosoma brucei involves highly regulated changes in morphology, proliferation and metabolism. However, the controls of these developmental processes are unknown. We have identified two novel proteins from the rare CCCH zinc finger family, each <140 amino acids in length and implicated in life cycle regulation. TbZFP1 is transiently enriched during differentiation from the bloodstream to procyclic form, whereas tbZFP2, when ablated in bloodstream forms by RNA interference, inhibits this developmental step. Moreover, expressing an ectopic copy of tbZFP2 results in a dramatic procyclic stage-specific remodelling of the trypanosome cytoskeleton similar to the morphogenic events of differentiation. This phenotype, we term 'nozzle', involves polar extension of microtubules at the posterior end of the cell and is dependent upon a motif hitherto restricted to E3 ubiquitin ligases. TbZFP1 and tbZFP2 represent the first molecules implicated in the control of trypanosome differentiation to the procyclic form.

Stereotyping among providers and consumers of public mental health services. The role of perceived group variability

The authors examine stigmatization and mental illness, focusing on the role of perceived group variability in stereotype use. Consumers' and providers' in-group and out-group stereotypes were assessed. Although providers had extensive experience, they judged consumers more stereotypically and just as negatively as did the consumers themselves. Consumers' education and involvement in services were weakly predictive of more stereotypic, less variable, and more negative views of providers, whereas providers' education and involvement in services predicted more stereotypic but also more variable views of both groups. Perceived group stereotypicality predicted more stereotypic judgments of individuals, whereas perceived variability predicted less confidence in judgments. Because providers perceived greater variability, they were less confident in applying the stereotype to individuals. We suggest that increasing perceptions of the variability among consumers may lead to more sensitive use of diagnostic criteria, more individualized treatment, and a decrease in the negative effects of stigmatization.

Intramitochondrial localization of universal minicircle sequence-binding protein, a trypanosomatid protein that binds kinetoplast minicircle replication origins

Kinetoplast DNA (kDNA), the mitochondrial DNA of the trypanosomatid Crithidia fasciculata, is a unique structure containing 5,000 DNA minicircles topologically linked into a massive network. In vivo, the network is condensed into a disk-shaped structure. Replication of minicircles initiates at unique origins that are bound by universal minicircle sequence (UMS)-binding protein (UMSBP), a sequence-specific DNA-binding protein. This protein, encoded by a nuclear gene, localizes within the cell's single mitochondrion. Using immunofluorescence, we found that UMSBP localizes exclusively to two neighboring sites adjacent to the face of the kDNA disk nearest the cell's flagellum. This site is distinct from the two antipodal positions at the perimeter of the disk that is occupied by DNA polymerase beta, topoisomerase II, and a structure-specific endonuclease. Although we found constant steady-state levels of UMSBP mRNA and protein and a constant rate of UMSBP synthesis throughout the cell cycle, immunofluorescence indicated that UMSBP localization within the kinetoplast is not static. The intramitochondrial localization of UMSBP and other kDNA replication enzymes significantly clarifies our understanding of the process of kDNA replication.

Marek's disease virus (MDV) encodes an interleukin-8 homolog (vIL-8): characterization of the vIL-8 protein and a vIL-8 deletion mutant MDV

Chemokines induce chemotaxis, cell migration, and inflammatory responses. We report the identification of an interleukin-8 (IL-8) homolog, termed vIL-8, encoded within the genome of Marek's disease virus (MDV). The 134-amino-acid vIL-8 shares closest homology to mammalian and avian IL-8, molecules representing the prototype CXC chemokine. The gene for vIL-8 consists of three exons which map to the BamHI-L fragment within the repeats flanking the unique long region of the MDV genome. A 0.7-kb transcript encoding vIL-8 was detected in an n-butyrate-treated, MDV-transformed T-lymphoblastoid cell line, MSB-1. This induction is essentially abolished by cycloheximide and herpesvirus DNA polymerase inhibitor phosphonoacetate, indicating that vIL-8 is expressed with true late (gamma2) kinetics. Baculovirus-expressed vIL-8 was found to be secreted into the medium and shown to be functional as a chemoattractant for chicken peripheral blood mononuclear cells but not for heterophils. To characterize the function of vIL-8 with respect to MDV infection in vivo, a recombinant MDV was constructed with a deletion of all three exons and a soluble-modified green fluorescent protein (smGFP) expression cassette inserted at the site of deletion. In two in vivo experiments, the vIL-8 deletion mutant (RB1BvIL-8DeltasmGFP) showed a decreased level of lytic infection in comparison to its parent virus, an equal-passage-level parent virus, and to another recombinant MDV containing the insertion of a GFP expression cassette at the nonessential US2 gene. RB1BvIL-8DeltasmGFP retained oncogenicity, albeit at a greatly reduced level. Nonetheless, we have been able to establish a lymphoblastoid cell line from an RB1BvIL-8DeltasmGFP-induced ovarian lymphoma (MDCC-UA20) and verify the presence of a latent MDV genome lacking vIL-8. Taken together, these data describe the identification and characterization of a chemokine homolog encoded within the MDV genome that is dispensable for transformation but may affect the level of MDV in vivo lytic infection.

ANTIVIMENTIN ANTIBODIES ARE AN INDEPENDENT PREDICTOR OF TRANSPLANT-ASSOCIATED CORONARY ARTERY DISEASE AFTER CARDIAC TRANSPLANTATION1

BACKGROUND

Transplant-associated coronary artery disease (TxCAD) is the most serious long-term complication after cardiac transplantation. Anti-endothelial antibodies are associated with disease, and one of the major endothelial antigens recognized in the sera of patients has been shown to be the protein filament vimentin. In this study, we investigated whether antivimentin antibodies are associated with TxCAD and whether their presence can be used to identify patients at high risk of developing angiographically detectable TxCAD.

METHODS

Up to 5 years after transplantation, 880 sequential sera (7.07+/-1.8 samples/patient) were collected retrospectively from 109 patients; the majority were collected in the first 2 years. Sera were assessed for antivimentin antibodies using ELISA. TxCAD was assessed by annual angiography.

RESULTS

Mean titres of antivimentin antibodies, calculated up to 1, 2, and 5 years, were significantly higher in patients who developed TxCAD than those who remained disease free (P<0.0001, P<0.0038, and P<0.0001, respectively). A predictive test based on the first-year mean vimentin titre alone (> or = 120) produced a test with 63% sensitivity and 76% specificity. Inclusion of persistent rejection or high 1-year mean titre (> or = 270) as a risk factor produced a test with 66% sensitivity and 82% specificity. Multivariate analysis of time to occurrence of transplant vasculopathy showed that mean titre at 1 or 2 years was an independent predictor of time until disease in the presence of all other variables.

CONCLUSIONS

Antivimentin antibodies are an independent predictor of TxCAD and can be used to identify some of the patients who are at high risk of developing this complication.

Characterization and disruption of a new Trypanosoma brucei repetitive flagellum protein, using double-stranded RNA inhibition

In Trypanosoma brucei, we have cloned a gene approximately 5 kb downstream of the glucose transporter gene cluster, containing a variable number of 102 bp repeats. This gene encodes a protein with no homologues in the data bases. Antibodies raised against the 34 amino acids repeated motif recognized proteins ranging from 145 to 270 kDa, depending on strains, in both bloodstream and procyclic forms of T. brucei. A correlation was established between the apparent molecular mass of the detected proteins and the number of 34 amino acid repeats which varies from 3 to 40. We have called this protein the flagellum transition zone component (FTZC) due to its localization to the proximal region of the axoneme, within the transition zone. FTZC is the only reported example of a trypanosomal protein present in the transition zone. To determine the role of FTZC we developed a new strategy of gene inactivation based on conditional expression of double-stranded RNA. In the presence of tetracycline, expression of the double-stranded RNA, we observed a complete disappearance of FTZC in the EATRO 1125 and EATRO 427 strains of T. hrucei. Molecular ablation of FTZC does not generate any obvious phenotype such as, lethality, modification of growth rate or cellular shape, in the growth conditions used.

The protein tyrosine kinase family of the human genome

As the sequencing of the human genome is completed by the Human Genome Project, the analysis of this rich source of information will illuminate many areas in medicine and biology. The protein tyrosine kinases are a large multigene family with particular relevance to many human diseases, including cancer. A search of the human genome for tyrosine kinase coding elements identified several novel genes and enabled the creation of a nonredundant catalog of tyrosine kinase genes. Ninety unique kinase genes can be identified in the human genome, along with five pseudogenes. Of the 90 tyrosine kinases, 58 are receptor type, distributed into 20 subfamilies. The 32 nonreceptor tyrosine kinases can be placed in 10 subfamilies. Additionally, mouse orthologs can be identified for nearly all the human tyrosine kinases. The completion of the human tyrosine kinase family tree provides a framework for further advances in biomedical science.

Evidence for novel cell cycle checkpoints in trypanosomes: kinetoplast segregation and cytokinesis in the absence of mitosis

Trypanosoma brucei has a single nucleus and a single kinetoplast (the mitochondrial genome). Each of these organelles has a distinct S phase, which is followed by a segregation period, prior to cell division. The segregation of the two genomes takes place in a specific temporal order by interaction with microtubule-based structures, the spindle for nuclear DNA and the flagellum basal bodies for the kinetoplast DNA. We used rhizoxin, the anti-microtubule agent and polymerisation inhibitor, or the nuclear DNA synthesis inhibitor aphidicolin, to interfere with cell cycle events in order to study how such events are co-ordinated. We show that T. brucei cytokinesis is not dependent upon either mitosis or nuclear DNA synthesis, suggesting that there are novel cell cycle checkpoints in this organism. Moreover, use of monoclonal antibodies to reveal cytoplasmic events such as basal body duplication shows that some aphidicolin treated cells appear to be in G(1) phase (1K1N) but have activated some cytoplasmic events characteristic of G(2) phase (basal body segregation). We discuss a possible dominant role in trypanosomes for kinetoplast/basal body segregation in control of later cell cycle events such as cytokinesis