Gillian Higgins

Regioselectivity of glucosylation of caffeic acid by a UDP-glucose:glucosyltransferase is maintained in planta.

Caffeic acid is a phenylpropanoid playing an important role in the pathways leading to lignin synthesis and the production of a wide variety of secondary metabolites. The compound is also an antioxidant and has potential utility as a general protectant against free radicals. Three glucosylated forms of caffeic acid are known to exist: the 3- O - and 4- O -glucosides and the glucose ester. This study describes for the first time a glucosyltransferase [UDP-glucose:glucosyltransferase (UGT)] that is specific for the 3-hydroxyl, and not the 4-hydroxyl, position of caffeic acid. The UGT sequence of Arabidopsis, UGT71C1, has been expressed as a recombinant fusion protein in Escherichia coli, purified and assayed against a range of substrates in vitro. The assay confirmed that caffeic acid as the preferred substrate when compared with other hydroxycinnamates, although UGT71C1 also exhibited substantial activity towards flavonoid substrates, known to have structural features that can be recognized by many different UGTs. The expression of UGT71C1 in transgenic Arabidopsis was driven by the constitutive cauliflower mosaic virus 35 S (CaMV35S) promoter. Nine independent transgenic lines were taken to homozygosity and characterized by Northern-blot analysis, assay of enzyme activity in leaf extracts and HPLC analysis of the glucosides. The level of expression of UGT71C1 was enhanced considerably in several lines, leading to a higher level of the corresponding enzyme activity and a higher level of caffeoyl-3- O -glucoside. The data are discussed in the context of the utility of UGTs for natural product biotransformations.

Overexpression of the UGT73C6 alters brassinosteroid glucoside formation in Arabidopsis thaliana

BackgroundBrassinosteroids (BRs) are signaling molecules that play essential roles in the spatial regulation of plant growth and development. In contrast to other plant hormones BRs act locally, close to the sites of their synthesis, and thus homeostatic mechanisms must operate at the cellular level to equilibrate BR concentrations. Whilst it is recognized that levels of bioactive BRs are likely adjusted by controlling the relative rates of biosynthesis and by catabolism, few factors, which participate in these regulatory events, have as yet been identified. Previously we have shown that the UDP-glycosyltransferase UGT73C5 of Arabidopsis thaliana catalyzes 23-O-glucosylation of BRs and that glucosylation renders BRs inactive. This study identifies the closest homologue of UGT73C5, UGT73C6, as an enzyme that is also able to glucosylate BRs in planta.ResultsIn a candidate gene approach, in which homologues of UGT73C5 were screened for their potential to induce BR deficiency when over-expressed in plants, UGT73C6 was identified as an enzyme that can glucosylate the BRs CS and BL at their 23-O-positions in planta. GUS reporter analysis indicates that UGT73C6 shows over-lapping, but also distinct expression patterns with UGT73C5 and YFP reporter data suggests that at the cellular level, both UGTs localize to the cytoplasm and to the nucleus. A liquid chromatography high-resolution mass spectrometry method for BR metabolite analysis was developed and applied to determine the kinetics of formation and the catabolic fate of BR-23-O-glucosides in wild type and UGT73C5 and UGT73C6 over-expression lines. This approach identified novel BR catabolites, which are considered to be BR-malonylglucosides, and provided first evidence indicating that glucosylation protects BRs from cellular removal. The physiological significance of BR glucosylation, and the possible role of UGT73C6 as a regulatory factor in this process are discussed in light of the results presented.ConclusionThe present study generates essential knowledge and molecular and biochemical tools, that will allow for the verification of a potential physiological role of UGT73C6 in BR glucosylation and will facilitate the investigation of the functional significance of BR glucoside formation in plants.

Variant Ciz1 is a circulating biomarker for early-stage lung cancer

There is an unmet need for circulating biomarkers that can detect early-stage lung cancer. Here we show that a variant form of the nuclear matrix-associated DNA replication factor Ciz1 is present in 34/35 lung tumors but not in adjacent tissue, giving rise to stable protein quantifiable by Western blot in less than a microliter of plasma from lung cancer patients. In two independent sets, with 170 and 160 samples, respectively, variant Ciz1 correctly identified patients who had stage 1 lung cancer with clinically useful accuracy. For set 1, mean variant Ciz1 level in individuals without diagnosed tumors established a threshold that correctly classified 98% of small cell lung cancers (SCLC) and non-SCLC patients [receiver operator characteristic area under the curve (AUC) 0.958]. Within set 2, comparison of patients with stage 1 non-SCLC with asymptomatic age-matched smokers or individuals with benign lung nodules correctly classified 95% of patients (AUCs 0.913 and 0.905), with overall specificity of 76% and 71%, respectively. Moreover, using the mean of controls in set 1, we achieved 95% sensitivity among patients with stage 1 non-SCLC patients in set 2 with 74% specificity, demonstrating the robustness of the classification. RNAi-mediated selective depletion of variant Ciz1 is sufficient to restrain the growth of tumor cells that express it, identifying variant Ciz1 as a functionally relevant driver of cell proliferation in vitro and in vivo. The data show that variant Ciz1 is a strong candidate for a cancer-specific single marker capable of identifying early-stage lung cancer within at-risk groups without resort to invasive procedures.

RAM1 and RAM2 function and expression during Arbuscular Mycorrhizal Symbiosis and Aphanomyces euteiches colonization

The establishment of the symbiotic interaction between plants and arbuscular mycorrhizal (AM) fungi requires a very tight molecular dialogue. Most of the known plant genes necessary for this process are also required for nodulation in legume plants and only very recently genes specifically required for AM symbiosis have been described. Among them we identified RAM (Reduced Arbuscular Mycorrhization)1 and RAM2, a GRAS transcription factor and a GPAT respectively, which are critical for the induction of hyphopodia formation in AM fungi. RAM2 function is also required for appressoria formation by the pathogen Phytophtora palmivora. Here we investigated the activity of RAM1 and RAM2 promoters during mycorrhization and the role of RAM1 and RAM2 during infection by the root pathogen Aphanomyces euteiches. pRAM1 is activated without cell type specificity before hyphopodia formation, while pRAM2 is specifically active in arbusculated cells providing evidence for a potential function of cutin momomers in the regulation of arbuscule formation. Furthermore, consistent with what we observed with Phytophtora, RAM2 but not RAM1 is required during Aphanomyces euteiches infection.

A quantitative immunoassay for lung cancer biomarker CIZ1b in patient plasma.

Objectives Non-invasive tests for early detection of lung cancer are an important unmet clinical need. CIZ1b plasma biomarker can discriminate stage 1 lung cancer from within high-risk groups with clinically useful accuracy, with ROC AUCs in excess of 0.9 for two independent retrospective cohorts, and could therefore meet this need. Our aim was to characterise the native state of the biomarker and develop a quantitative immunoassay. Design and methods Selective denaturation, preparative electrophoresis and mass spectrometry of human plasma were used to characterise the biomarker and interaction partners. A sandwich ELISA was generated, and specificity for CIZ1b biomarker tested on lung cancer patient plasma. Results CIZ1b biomarker is a denaturation-resistant complex between a C-terminal fragment of CIZ1 bearing the CIZ1b epitope specified by alternative splicing of exon14, and fibrinogen alpha chain. Reconstitution of the biomarker epitope with purified fibrinogen and CIZ1b, but not CIZ1a (non-alternatively spliced exon 14) confirmed the specificity of the results. The endogenous complex is highly stable in lung cancer plasma and can be quantified by pairing of a CIZ1b exon-junction specific antibody with detection of fibrinogen. Application of this sandwich ELISA to a prospectively collected development set of plasmas reveals the same level of accuracy as the western blot used to validate the discriminatory capability of the biomarker. Conclusions Unexpected and unusual molecular structure of CIZ1b in native plasma has complicated immunoassay design, and delayed translation of this promising biomarker. However, CIZ1b can now be measured using a high-throughput, hospital-friendly sandwich ELISA format, overcoming an important barrier to further clinical development and application of this blood test for early stage lung cancer.

CIZ1-F, an alternatively spliced variant of the DNA replication protein CIZ1 with distinct expression and localisation, is overrepresented in early stage common solid tumours

ABSTRACT CIZ1 promotes cyclin-dependent DNA replication and resides in sub-nuclear foci that are part of the protein nuclear matrix (NM), and in RNA assemblies that are enriched at the inactive X chromosome (Xi) in female cells. It is subjected to alternative splicing, with specific variants implicated in adult and pediatric cancers. CIZ1-F is characterized by a frame shift that results from splicing exons 8–12 leading to inclusion of a short alternative reading frame (ARF), excluding the previously characterized C-terminal NM anchor domain. Here, we apply a set of novel variant-selective molecular tools targeted to the ARF to profile the expression of CIZ1-F at both transcript and protein levels, with focus on its relationship with the RNA-dependent and -independent fractions of the NM. Unlike full-length CIZ1, CIZ1-F does not accumulate at Xi, though like full-length CIZ1 it does resist extraction with DNase. Notably, CIZ1-F is sensitive to RNase identifying it as part of the RNA-fraction of the NM. In quiescent cells CIZ1-F transcript expression is suppressed and CIZ1-F protein is excluded from the nucleus, with re-expression not observed until the second cell cycle after exit from quiescence. Importantly, CIZ1-F is over-expressed in common solid tumors including colon and breast, pronounced in early stage but not highly-proliferative late stage tumors. Moreover, expression was significantly higher in hormone receptor negative breast tumors than receptor positive tumors. Together these data show that CIZ1-F is expressed in proliferating cells in an unusual cell cycle-dependent manner, and suggest that it may have potential as a tumor biomarker.

Abstract LB-442: The nuclear matrix anchor domain of the DNA replication factor Ciz1 is commonly disrupted in tumours and is a circulating biomarker for lung cancer

The DNA replication protein Ciz1 promotes initiation of mammalian DNA replication in cooperation with cyclin A-dependent kinase, most likely by delivering cyclin A to sites where cyclin E-dependent pre-replication complex assembly has taken place. Normally, Ciz1 is anchored within nuclear matrix-associated foci that co-localize with sites of DNA replication, but in the absence of anchor domain Ciz1 retains the ability to promote initiation of DNA replication in isolated nuclei so attachment to the nuclear matrix is not essential for function. Expression of DNA replication and nuclear matrix anchor domains of Ciz1 are uncoupled and uneven at the transcript level in a wide range of common solid tumours, including breast and lung. In cell-based assays, recombinant anchor domain protein interferes with attachment of endogenous Ciz1 to the nuclear matrix, revealing a dominant negative effect that also impacts on nuclear matrix-recruitment of key components of the pre-replication complex. This suggests that Ciz1 normally plays a role in localizing initiation of DNA replication to the nuclear matrix. These findings implicate spatially unconstrained DNA replication as a source of nuclear disorder in cancer cells. We identified a variant Ciz1 isoform with alterations in the nuclear matrix attachment domain and tumour-restricted expression. RNAi-mediated selective inhibition of variant Ciz1 expression is sufficient to restrain the growth of tumour cells that express it, identifying variant Ciz1 as a functionally relevant driver of cell proliferation. We also present evidence that this form of Ciz1 is expressed in 34/35 lung tumours but not adjacent tissue, giving rise to stable protein quantifiable in less than a microlitre of patient plasma by western blot. Using two independent sets, with 170 and 160 samples, variant Ciz1 correctly identified stage 1 lung cancer patients with clinically useful accuracy. For set 1, mean variant Ciz1 level (+SD) in individuals without diagnosed tumours established a threshold that correctly classified 94% of small cell lung cancers (SCLC) and non-SCLC patients. Within set 2, comparison of stage 1 non-SCLC with asymptomatic age-matched smokers correctly classified 85% of patients, while comparison with individuals with benign lung nodules correctly classified 83% of patients. The data show that this cancer-specific, single marker is capable of indentifying early stage lung cancer within at-risk groups, without resort to invasive procedures. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-442. doi:1538-7445.AM2012-LB-442

Abstract 3022: Disruption of the nuclear matrix attachment domain of the DNA replication factor Ciz1 in common solid tumors and its potential as a biomarker

The DNA replication protein Ciz1 promotes initiation of mammalian DNA replication in cooperation with cyclin A-dependent kinase, most likely by delivery cyclin A to sites where cyclin E-dependent pre-replication complex assembly has taken place. Normally, Ciz1 is anchored within nuclear matrix-associated foci that co-localize with sites of DNA replication, but in the absence of anchor domain Ciz1 retains the ability to promote initiation of DNA replication in isolated nuclei so attachment to the nuclear matrix is not essential for function. Here, we show that expression of DNA replication and nuclear matrix anchor domains of Ciz1 are uncoupled and uneven at the transcript level in a panel of common cancer cell lines, giving rise to excess DNA replication domain protein that is not attached to the nuclear matrix. Moreover Ciz1 domain expression is also uncoupled in a wide range of common solid tumours, including breast and lung, so that anchor domain transcript is elevated over control tissues, and exceeds replication domain in all primary stage I, II and III tumours tested. Notably, more than half of all stage IV tumours tested resemble established cell lines, having more replication domain than anchor domain. In cell based assays, recombinant anchor domain protein interferes with attachment of endogenous Ciz1 to the nuclear matrix, revealing a dominant negative effect that also impacts on nuclear matrix-recruitment of a key component of the pre-replication complex, Cdc6. This shows that Ciz1 normally plays a role in localizing Cdc6 to the nuclear matrix and suggests that cancer-associated uncoupled expression influences recruitment of mammalian pre-replication complexes to the nuclear matrix. These findings implicate spatially unconstrained DNA replication as a source of nuclear disorder in cancer cells. We identified a variant Ciz1 isoform with alterations in nuclear matrix attachment domain and tumour-restricted expression. Variant Ciz1 is elevated at the transcript and protein level with high frequency in small cell lung tumours, and with lower frequency in a range of other tumour types. Selective suppression of variant Ciz1 expression using inducible shRNA restricts proliferation of lung cancer cells that express it in vitro and in vivo, identifying a novel, exploitable therapeutic target with potential application in the treatment of lung cancer. Recent evidence will also be presented on the application of variant Ciz1 as a serum biomarker. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3022. doi:10.1158/1538-7445.AM2011-3022