Cathepsin-facilitated invasion of BMI1-high hepatocellular carcinoma cells drives bile duct tumor thrombi formation

Bile duct tumor thrombosis (BDTT) is a complication mostly observed in patients with advanced hepatocellular carcinoma (HCC), causing jaundice and associated with poor clinical outcome. However, its underlying molecular mechanism is unclear. Here, we develop spontaneous preclinical HCC animal models with BDTT to identify the role of BMI1 expressing tumor initiating cells (BMI1high TICs) in inducing BDTT. BMI1 overexpression transforms liver progenitor cells into BMI1high TICs, which possess strong tumorigenicity and increased trans-intrahepatic biliary epithelial migration ability by secreting lysosomal cathepsin B (CTSB). Orthotopic liver implantation of BMI1high TICs into mice generates tumors and triggers CTSB mediated bile duct invasion to form tumor thrombus, while CTSB inhibitor treatment prohibits BDTT and extends mouse survival. Clinically, the elevated serum CTSB level determines BDTT incidence in HCC patients. Mechanistically, BMI1 epigenetically up-regulates CTSB secretion in TICs by repressing miR-218-1-3p expression. These findings identify a potential diagnostic and therapeutic target for HCC patients with BDTT.

Chemoresistant fibroblasts dictate neoadjuvant chemotherapeutic response of head and neck cancer via TGFα-EGFR paracrine signaling

Conventional chemotherapy targets malignant cells without evaluating counter protection from the tumor microenvironment that often causes treatment failure. Herein, we establish chemoresistant fibroblasts (rCAFs) as regulators of neoadjuvant chemotherapeutic (NACT) response in head and neck squamous cell carcinoma (HNSCC). Clinically, high expression of CAF-related gene signature correlates with worse prognosis and chemotherapeutic response in multiple cancers, while the population of CAFs in the residual tumors of chemoresistant HNSCC patients remains unchanged after NACT treatment, compared to chemosensitive patients. Using a murine cancer model or patient-derived organoid, and primary CAFs isolated from chemo-sensitive (sCAFs) or -resistant patients, we show that rCAFs, but not sCAFs, are resistant to chemotherapy-induced apoptosis while reducing HNSCC cell chemosensitivity via paracrine signals. Combined multi-omics and biochemical analyses indicate an elevated PI3K/AKT/p65 driven cell survival and cytokine production in rCAFs, while rCAF-secreted TGFα promotes cancer cell chemoresistance by activating EGFR/Src/STAT3 survival signaling axis. Treatment with anti-EGFR cetuximab restores the chemosensitivity of tumors derived from co-injection of cancer cells and rCAFs in vivo, while the serum level of TGFα determines NACT response in HNSCC patients. Overall, our findings uncover a novel insight whereby the crosstalk between tumor cell and rCAF determines chemotherapeutic response and prognosis in cancer patients.

Immunization with a multi-antigen targeted DNA vaccine eliminates chemoresistant pancreatic cancer by disrupting tumor-stromal cell crosstalk

BACKGROUND

Pancreatic ductal adenocarcinoma (PDAC) is characterised by limited responses to chemoimmunotherapy attributed to highly desmoplastic tumor microenvironment. Disrupting the tumor-stromal cell crosstalk is considered as an improved PDAC treatment strategy, whereas little progress has been made due to poor understanding of its underlying mechanism. Here, we examined the cellular role of melanoma associated antigen A isoforms (MAGEA) in regulating tumor-stromal crosstalk mediated chemoresistance.

METHODS

We used clinical samples to explore the correlation between MAGEA expression and patient prognosis in multiple cancers. We utilized cancer cell lines, patient derived organoids and orthotopic PDAC model to examine the function of MAGEA in chemoresistance. We performed biochemical, proteome profiler array and transcriptional analysis to uncover a mechanism that governs tumor-stromal crosstalk. We developed a multi-MAGEA antigen targeted DNA vaccine and tested its effect on PDAC tumor growth.

RESULTS

We establish MAGEA as a regulator of the tumor-stromal crosstalk in PDAC. We provide strong clinical evidence indicating that high MAGEA expression, including MAGEA2, MAGEA3 and MAGEA10, correlates with worse chemotherapeutic response and poor prognosis in multiple cancers, while their expression is up-regulated in chemoresistant PDAC patient derived organoids and cancer cell lines. Mechanistically, MAGEA2 prohibits gemcitabine-induced JNK-c-Jun-p53 mediated cancer cell apoptosis, while gemcitabine stimulated pancreatic stellate cells secretes GDF15 to further enhance the gemcitabine resistance of MAGEA2 expressing cells by activating GFRAL-RET mediated Akt and ERK1/2 dependent survival pathway. Strikingly, immunization with a DNA vaccine that targeting multiple MAGEA antigens, including MAGEA2, MAGEA3 and MAGEA10, elicits robust immune responses against the growth of gemcitabine resistant tumors.

CONCLUSIONS

These findings suggest that targeting MAGEA-mediated paracrine regulation of chemoresistance by immunotherapy can be an improved pancreatic cancer treatment strategy.

Identification of a distinct tumor endothelial cell-related gene expression signature associated with patient prognosis and immunotherapy response in multiple cancers

BACKGROUND

Tumor endothelial cells (TECs) play a significant role in regulating the tumor microenvironment, drug response, and immune cell activities in various cancers. However, the association between TEC gene expression signature and patient prognosis or therapeutic response remains poorly understood.

METHODS

We analyzed transcriptomics data of normal and tumor endothelial cells obtained from the GEO database to identify differentially expressed genes (DEGs) associated with TECs. We then compared these DEGs with those commonly found across five different tumor types from the TCGA database to determine their prognostic relevance. Using these genes, we constructed a prognostic risk model integrated with clinical features to develop a nomogram model, which we validated through biological experiments.

RESULTS

We identified 12 TEC-related prognostic genes across multiple tumor types, of which five genes were sufficient to construct a prognostic risk model with an AUC of 0.682. The risk scores effectively predicted patient prognosis and immunotherapeutic response. Our newly developed nomogram model provided more accurate prognostic estimates of cancer patients than the TNM staging method (AUC = 0.735) and was validated using external patient cohorts. Finally, RT-PCR and immunohistochemical analyses indicated that the expression of these 5 TEC-related prognostic genes was up-regulated in both patient-derived tumors and cancer cell lines, while depletion of the hub genes reduced cancer cell growth, migration and invasion, and enhanced their sensitivity to gemcitabine or cytarabine.

CONCLUSIONS

Our study discovered the first TEC-related gene expression signature that can be used to construct a prognostic risk model for guiding treatment options in multiple cancers.

Cancer associated fibroblast derived gene signature determines cancer subtypes and prognostic model construction in head and neck squamous cell carcinomas

BACKGROUND

Head and neck squamous cell carcinomas (HNSCC) are the most common type of head and neck cancer with an unimproved prognosis over the past decades. Although the role of cancer-associated-fibroblast (CAF) has been demonstrated in HNSCC, the correlation between CAF-derived gene expression and patient prognosis remains unknown.

METHODS

A total of 528 patients from TCGA database and 270 patients from GSE65858 database were contained in this study. After extracting 66 CAF-related gene expression data from TCGA database, consensus clustering was performed to identify different HNSCC subtypes. Limma package was used to distinguish the differentially expression genes (DEGs) between these subtypes, followed by Lasso regression analysis to construct a prognostic model. The model was validated by performing Kaplan-Meier survival, ROC and risk curve, univariate and multivariate COX regression analysis. GO, KEGG, GSEA, ESTIMATE and ssGSEA analyses was performed to explort the potential mechanism leading to different prognosis.

RESULTS

Based on the 66 CAF-related gene expression pattern we stratitied HNSCC patients into two previously unreported subtypes with different clinical outcomes. A prognostic model composed of 15 DEGs was constructed and validated. In addition, bioinformatics analysis showed that the prognostic risk of HNSCC patients was also negatively correlated to immune infiltration, implying the role of tumor immune escape in HNSCC prognosis and treatment option.

CONCLUSIONS

The study develops a reliable prognostic prediction tool and provides a theoretical treatment guidance for HNSCC patients.

Targeting Src reactivates pyroptosis to reverse chemoresistance in lung and pancreatic cancer models

Pancreatic and lung cancers frequently develop resistance to chemotherapy-induced cell apoptosis during the treatment, indicating that targeting nonapoptotic-related pathways, such as pyroptosis, can be an alternative cancer treatment strategy. Pyroptosis is a gasdermin-driven lytic programmed cell death triggered by inflammatory caspases when initiated by canonical or noncanonical pathways that has been recently seen as a potential therapeutic target in cancer treatment. However, overcoming chemoresistance in cancers by modulating pyroptosis has not been explored. Here, we demonstrate that β5-integrin represses chemotherapy-induced canonical pyroptosis to confer cancer chemoresistance through ASAH2-driven sphingolipid metabolic reprogramming. Clinically, high β5-integrin expression associates with poor patient prognosis and chemotherapeutic responses in cancers. In addition, chemoresistant cells in vitro fail to undergo chemotherapy-induced pyroptosis, which is controlled by β5-integrin. Mechanistically, proteomic and lipidomic analyses indicate that β5-integrin up-regulates sphingolipid metabolic enzyme ceramidase (ASAH2) expression through Src-signal transducer and activator of transcription 3 (STAT3) signaling, which then reduces the metabolite ceramide concentration and subsequent ROS production to prohibit chemotherapy-induced canonical pyroptosis. Using cancer cell lines, patient-derived tumor organoids, and orthotopic lung and pancreatic animal models, we show that administration of a Src or ceramidase inhibitor rescues the response of chemoresistant pancreatic and lung cancer cells to chemotherapy by reactivating pyroptosis in vitro and in vivo. Overall, our results suggest that pyroptosis-based therapy is a means to improve cancer treatment and warrants further investigation.

Ceramide kinase confers tamoxifen resistance in estrogen receptor-positive breast cancer by altering sphingolipid metabolism

Dysregulated sphingolipid metabolism contributes to ER+ breast cancer progression and therapeutic response, whereas its underlying mechanism and contribution to tamoxifen resistance (TAMR) is unknown. Here, we establish sphingolipid metabolic enzyme CERK as a regulator of TAMR in breast cancer. Multi-omics analysis reveals an elevated CERK driven sphingolipid metabolic reprogramming in TAMR cells, while high CERK expression associates with worse patient prognosis in ER+ breast cancer. CERK overexpression confers tamoxifen resistance and promotes tumorigenicity in ER+ breast cancer cells. Knocking out CERK inhibits the orthotopic breast tumor growth of TAMR cells while rescuing their tamoxifen sensitivity. Mechanistically, the elevated EHF expression transcriptionally up-regulates CERK expression to prohibit tamoxifen-induced sphingolipid ceramide accumulation, which then inhibits tamoxifen-mediated repression on PI3K/AKT dependent cell proliferation and its driven p53/caspase-3 mediated apoptosis in TAMR cells. This work provides insight into the regulation of sphingolipid metabolism in tamoxifen resistance and identifies a potential therapeutic target for this disease.

Suppression of Endothelial Cell FAK Expression Reduces Pancreatic Ductal Adenocarcinoma Metastasis after Gemcitabine Treatment

Despite substantial advances in the treatment of solid cancers, resistance to therapy remains a major obstacle to prolonged progression-free survival. Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive cancers, with a high level of liver metastasis. Primary PDAC is highly hypoxic, and metastases are resistant to first-line treatment, including gemcitabine. Recent studies have indicated that endothelial cell (EC) focal adhesion kinase (FAK) regulates DNA-damaging therapy-induced angiocrine factors and chemosensitivity in primary tumor models. Here, we show that inducible loss of EC-FAK in both orthotopic and spontaneous mouse models of PDAC is not sufficient to affect primary tumor growth but reduces liver and lung metastasis load and improves survival rates in gemcitabine-treated, but not untreated, mice. EC-FAK loss did not affect primary tumor angiogenesis, tumor blood vessel leakage, or early events in metastasis, including the numbers of circulating tumor cells, tumor cell homing, or metastatic seeding. Phosphoproteomics analysis showed a downregulation of the MAPK, RAF, and PAK signaling pathways in gemcitabine-treated FAK-depleted ECs compared with gemcitabine-treated wild-type ECs. Moreover, low levels of EC-FAK correlated with increased survival and reduced relapse in gemcitabine-treated patients with PDAC, supporting the clinical relevance of these findings. Altogether, we have identified a new role of EC-FAK in regulating PDAC metastasis upon gemcitabine treatment that impacts outcome.

SIGNIFICANCE

These findings establish the potential utility of combinatorial endothelial cell FAK targeting together with gemcitabine in future clinical applications to control metastasis in patients with pancreatic ductal adenocarcinoma.

Hexokinase 2-driven glycolysis in pericytes activates their contractility leading to tumor blood vessel abnormalities

Defective pericyte-endothelial cell interaction in tumors leads to a chaotic, poorly organized and dysfunctional vasculature. However, the underlying mechanism behind this is poorly studied. Herein, we develop a method that combines magnetic beads and flow cytometry cell sorting to isolate pericytes from tumors and normal adjacent tissues from patients with non-small cell lung cancer (NSCLC) and hepatocellular carcinoma (HCC). Pericytes from tumors show defective blood vessel supporting functions when comparing to those obtained from normal tissues. Mechanistically, combined proteomics and metabolic flux analysis reveals elevated hexokinase 2(HK2)-driven glycolysis in tumor pericytes, which up-regulates their ROCK2-MLC2 mediated contractility leading to impaired blood vessel supporting function. Clinically, high percentage of HK2 positive pericytes in blood vessels correlates with poor patient overall survival in NSCLC and HCC. Administration of a HK2 inhibitor induces pericyte-MLC2 driven tumor vasculature remodeling leading to enhanced drug delivery and efficacy against tumor growth. Overall, these data suggest that glycolysis in tumor pericytes regulates their blood vessel supporting role.

Pericyte-endothelial cells interaction defines tumor vasculature and has implications in tumorigenesis development and therapy efficacy. Here, the authors show that hexokinase 2- driven glycolysis activates ROCK1-MLC2 mediated contractility in pericytes leading to tumor blood vessel abnormality.

The Emerging Roles of Pericytes in Modulating Tumor Microenvironment

Pericytes (PCs), known as mural cells, play an important blood vessel (BV) supporting role in regulating vascular stabilization, permeability and blood flow in microcirculation as well as blood brain barrier. In carcinogenesis, defective interaction between PCs and endothelial cells (ECs) contributes to the formation of leaky, chaotic and dysfunctional vasculature in tumors. However, recent works from other laboratories and our own demonstrate that the direct interaction between PCs and other stromal cells/cancer cells can modulate tumor microenvironment (TME) to favor cancer growth and progression, independent of its BV supporting role. Furthermore, accumulating evidence suggests that PCs have an immunomodulatory role. In the current review, we focus on recent advancement in understanding PC's regulatory role in the TME by communicating with ECs, immune cells, and tumor cells, and discuss how we can target PC's functions to re-model TME for an improved cancer treatment strategy.

A circular network of coregulated sphingolipids dictates lung cancer growth and progression

Background

Sphingolipid metabolism is among the top dysregulated pathways in non-small cell lung carcinomas (NSCLC). However, the molecular control of sphingolipid metabolic reprogramming in cancer progression remains unclear.

Methods

We first determined the correlation between sphingolipid metabolic gene expression and patient prognosis. We then carried out sphingolipidomics analysis of health individual and NSCLC patient sera as well as B3GNT5 and GAL3ST1 genetically perturbed NSCLC cell lines. We used these cell lines to perform tumorigenesis study to determine the cellular role of B3GNT5 and GAL3ST1 in cancer growth and progression.

Findings

The expression of B3GNT5 and GAL3ST1 among sphingolipid metabolic enzymes is most significantly associated with patient prognosis, whilst sphingolipidomics analysis of healthy individual and NSCLC patient sera identifies their metabolites, lacto/neolacto-series glycosphingolipid and sulfatide species, as potential biomarkers that were more effective than current clinical biomarkers for staging patients. Further network analysis of the sphingolipidomes reveals a circular network of coregulated sphingolipids, indicating that the lacto/neolacto-series glycosphingolipid/sulfatide balance functions as a checkpoint to determine sphingolipid metabolic reprograming during patient progression. Sphingolipidomics analysis of B3GNT5/GAL3ST1 genetically perturbed NSCLC cell lines confirms their key regulatory role in sphingolipid metabolism, while B3GNT5 and GAL3ST1 expression has an opposite role on tumorigenesis.

Interpretation

Our results provide new insights whereby B3GNT5 and GAL3ST1 differentially regulate sphingolipid metabolism in lung cancer growth and progression.

Funding

This work was supported by the Natural Science Foundation of China (81872142, 81920108028); Guangzhou Science and Technology Program (201904020008); Guangdong Science and Technology Department (2020A0505100029, 2019A1515011802, 2020A1515011280, 2020B1212060018, 2020B1212030004); China Postdoctoral Science Foundation (2019M650226, 2019M650227).

Galactosyltransferase B4GALT1 confers chemoresistance in pancreatic ductal adenocarcinomas by upregulating N-linked glycosylation of CDK11p110

Aberrant glycosylation in pancreatic cancer has been linked to cancer development, progression and chemoresistance. However, the role of glycogene, such as galactosyltransferase, in pancreatic cancer remains unknown. Herein, we establish beta-1.4-galactosyltransferase 1 (B4GALT1) as a clinical marker and regulator of chemoresistance. Clinically, high B4GALT1 expression correlates with poor survival, enhanced tumor size, increased lymph node metastasis, elevated cancer progression and enhanced incidence of relapse in PDAC patients. Expression of B4GALT1 is up-regulated in gemcitabine resistant patient derived organoids as well as chemoresistant cancer cell lines, while genetic perturbation of its expression in PDAC cell lines regulates cancer progression and chemoresistance. Mechanistically, we show that elevated p65 activity transcriptionally up-regulates B4GALT1 expression, which then interacts with and stabilizes cyclin dependent kinase 11 isomer CDK11^p110 protein via N-linked glycosylation, in order to promote cancer progression and chemoresistance. Finally, depletion of B4GALT1 rescues the response of chemoresistant cells to gemcitabine in an orthotopic PDAC model. Overall, our data uncovers a mechanism by which p65-B4GALT1-CDK11^p110 signalling axis determines cancer progression and chemoresistance, providing a new therapeutic target for an improved pancreatic cancer treatment.

Cancer Burden Is Controlled by Mural Cell-β3-Integrin Regulated Crosstalk with Tumor Cells

Enhanced blood vessel (BV) formation is thought to drive tumor growth through elevated nutrient delivery. However, this observation has overlooked potential roles for mural cells in directly affecting tumor growth independent of BV function. Here we provide clinical data correlating high percentages of mural-β3-integrin-negative tumor BVs with increased tumor sizes but no effect on BV numbers. Mural-β3-integrin loss also enhances tumor growth in implanted and autochthonous mouse tumor models with no detectable effects on BV numbers or function. At a molecular level, mural-cell β3-integrin loss enhances signaling via FAK-p-HGFR-p-Akt-p-p65, driving CXCL1, CCL2, and TIMP-1 production. In particular, mural-cell-derived CCL2 stimulates tumor cell MEK1-ERK1/2-ROCK2-dependent signaling and enhances tumor cell survival and tumor growth. Overall, our data indicate that mural cells can control tumor growth via paracrine signals regulated by β3-integrin, providing a previously unrecognized mechanism of cancer growth control.

DStruBTarget: Integrating Binding Affinity with Structure Similarity for Ligand-Binding Protein Prediction

Motivation: Identification of ligand-binding proteins is an important issue for drug development. Most of the current computational approach is developed only utilizing ligand structure similarity. However, the ligand structure similarity has failed to reflect the binding quality between the ligand and the target protein, which limited the performance of current methods. Results: The present study integrated two-dimensional (2D) and three-dimensional (3D) ligand structure similarity between query ligand and template with known ligand-protein binding affinity (BA) to identify proteins binding with the query ligand. This method is named as DStruBTarget. The performance of DStruBTarget was evaluated by 10-fold cross-validation in a dataset containing 9197 ligands and 1111 ligand-binding proteins (DBD dataset). This dataset was constructed by excluding the ligands with similar structures and the proteins with high sequence identity. The DStruBTarget achieved a hit rate of 77% in top 1 prediction, which is 4.80 and 3.00% better than the methods only using 2D structure similarity, and the method integrating 2D and 3D structure similarity (2D + 3D), respectively. An independent test of DStruBTarget was performed in a publicly available dataset constructed by SwissTargetPrediction. In this dataset, the top 1 hit rate of DStruBTarget reached 44.02%, which was better than the SwissTargetPrediction, and also outstands other methods, such as 2D, 3D, 2D + 3D, 2D integrating binding affinity (2D + BA), and 3D integrating binding affinity (3D + BA). DStruBTarget was compared to another newly published method HitPickV2 and achieved 52.17% hit rate of the top 1 prediction, which was significantly better than the result of HitpickV2 (30.43%). Finally, DStruBTarget was integrated with protein BLAST to predict the ligand-binding proteins not limited in a certain database. DStruBTarget with BLAST was tested in the DBD dataset. Its top 1 hit rate was 51.15%, which is lower than DStruBTarget without BLAST. Further comparison was on the ligands that bind to multiple numbers of proteins, which illustrated that DStruBTarget with BLAST performed better than without BLAST when the number of binding proteins of the query ligands is larger than six. Meanwhile, the prediction power of the DStruBTarget with BLAST in top 1 prediction was found to be positively correlated with the number of proteins binding with the query ligands, while the top 1 prediction power of DStruBTarget without BLAST was negatively correlated with the number of binding proteins for query ligands. Thus, DStruBTarget with BLAST is a potentially useful approach for predicting novel proteins for ligands that bind to multiple proteins.

Multifunctional sharp pH-responsive nanoparticles for targeted drug delivery and effective breast cancer therapy

The intrinsic limits of conventional cancer therapies prompt the development of a new technology for a more effective and safer cancer treatment. The bioresponsive delivery technique has recently emerged as an innovative strategy to overcome multiple barriers in the systemic delivery of nanoparticle (NP)-based therapeutics. However, some issues especially the tumor penetration-retention balance have not been completely solved, which may induce the suboptimal therapeutic effect. Herein, we developed a new multifunctional sharp pH-responsive NP platform for targeted drug delivery and effective cancer therapy. This NP platform is made of the sharp pH-responsive poly(2-(diisopropylamino)ethylmethacrylate) (PDPA) polymer as the inner core, amphiphilic lipid-poly(ethylene glycol) (lipid-PEG) as the outer shell, and the internalizing RGD (iRGD) peptide encoded on the surface. After anticancer drug loading and then systemic administration, the resulting NP platform shows the following features in one nanostructure: (i) the PEG shell to prolong blood circulation; (ii) the iRGD peptide to enhance tumor targeting and penetration; (iii) a larger particle size (∼80 nm) than that of free drug to ensure long tumor retention; (iv) the sharp endosomal pH response of the PDPA polymer to induce fast intracellular drug release and thus efficient inhibition of tumor growth. Together with facile polymer synthesis and robust NP formulation to enable easy scale-up, the multifunctional NP platform reported herein shows great potential as a new generation nanomedicine for effective cancer treatment.

Exploring Novel Methods for Modulating Tumor Blood Vessels in Cancer Treatment

Several studies have explored the potential of targeting tumor angiogenesis in cancer treatment. Anti-angiogenesis monotherapy, which reduces blood vessel numbers, may still hold some promise in cancer treatment, but thus far it has only provided a modest effect on overall survival benefits. When combined with standard chemotherapies, some significant improvements in cancer therapy have been reported. However, anti-angiogenesis therapies can have undesirable effects, including the induction of tumor hypoxia and reduction of delivery of chemotherapeutic drugs. Interestingly, anti-angiogenic drugs, such as bevacizumab, when used at lower doses, can actually induce vascular normalization (that is, they improve blood vessel function and flow) and potentially enhance co-administrated chemotherapeutic drug delivery. Unfortunately, vascular normalization is a difficult approach to apply in clinical settings. Thus, there is an urgent need to explore new approaches for modulating the tumor vasculature. Here, we explore how vascular promotion strategies (which enhance blood vessel numbers and leakiness) may be optimized for combination therapies as an alternative option for cancer treatment.

Dual-action combination therapy enhances angiogenesis while reducing tumor growth and spread

Increasing chemotherapy delivery to tumors, while enhancing drug uptake and reducing side effects, is a primary goal of cancer research. In mouse and human cancer models in vivo, we show that coadministration of low-dose Cilengitide and Verapamil increases tumor angiogenesis, leakiness, blood flow, and Gemcitabine delivery. This approach reduces tumor growth, metastasis, and minimizes side effects while extending survival. At a molecular level, this strategy alters Gemcitabine transporter and metabolizing enzyme expression levels, enhancing the potency of Gemcitabine within tumor cells in vivo and in vitro. Thus, the dual action of low-dose Cilengitide, in vessels and tumor cells, improves chemotherapy efficacy. Overall, our data demonstrate that vascular promotion therapy is a means to improve cancer treatment.

Endothelial-cell FAK targeting sensitizes tumours to DNA-damaging therapy

Chemoresistance is a serious limitation of cancer treatment. Until recently, almost all the work done to study this limitation has been restricted to tumour cells. Here we identify a novel molecular mechanism by which endothelial cells regulate chemosensitivity. We establish that specific targeting of focal adhesion kinase (FAK; also known as PTK2) in endothelial cells is sufficient to induce tumour-cell sensitization to DNA-damaging therapies and thus inhibit tumour growth in mice. The clinical relevance of this work is supported by our observations that low blood vessel FAK expression is associated with complete remission in human lymphoma. Our study shows that deletion of FAK in endothelial cells has no apparent effect on blood vessel function per se, but induces increased apoptosis and decreased proliferation within perivascular tumour-cell compartments of doxorubicin- and radiotherapy-treated mice. Mechanistically, we demonstrate that endothelial-cell FAK is required for DNA-damage-induced NF-κB activation in vivo and in vitro, and the production of cytokines from endothelial cells. Moreover, loss of endothelial-cell FAK reduces DNA-damage-induced cytokine production, thus enhancing chemosensitization of tumour cells to DNA-damaging therapies in vitro and in vivo. Overall, our data identify endothelial-cell FAK as a regulator of tumour chemosensitivity. Furthermore, we anticipate that this proof-of-principle data will be a starting point for the development of new possible strategies to regulate chemosensitization by targeting endothelial-cell FAK specifically.

Dual association by TFAP2A during activation of the p21cip/CDKN1A promoter

The cyclin-dependent kinase inhibitor p21cip/CDKN1A is induced to promote growth arrest in response to a variety of stimuli in normal cells and loss of correct regulation of this gene is frequently observed in cancer. In particular, the upregulation of CDKN1A by p53 is considered to be a central mechanism of tumour suppression. Other transcription factors with tumour suppressor activity can also regulate CDKN1A, including the developmentally regulated factor, TFAP2A. Here we identify a novel AP-2 binding site within the proximal promoter of the CDKN1A gene and show this is required for optimal, p53-independent expression of p21cip/CDKN1A. We further describe a non-tumourgenic breast epithelial cell line model to study the role of endogenous TFAP2A and p53 in the control of drug-induced p21cip expression using ChIP. Maximal expression of CDKN1A requires TFAP2A which binds to two regions of the promoter: the proximal region where the AP-2 site lies and upstream near the major p53 binding site. The pattern of binding alters with time post-induction, with the proximal, p53-independent site becoming more important at later stages of p21cip induction. This pattern of promoter interaction by TFAP2A is distinct from that seen for the TFAP2C family member which represses CDKN1A expression.

Acetylation of Rb by PCAF is required for nuclear localization and keratinocyte differentiation

Although the retinoblastoma protein (Rb) functions as a checkpoint in the cell cycle, it also regulates differentiation. It has recently been shown that Rb is acetylated during differentiation; however, the role of this modification has not been identified. Depletion of Rb levels with short hairpin RNA resulted in inhibition of human keratinocyte differentiation, delayed cell cycle exit and allowed cell cycle re-entry. Restoration of Rb levels rescued defects in differentiation and cell cycle exit and re-entry; however, re-expression of Rb with the major acetylation sites mutated did not. During keratinocyte differentiation, acetylation of Rb is mediated by PCAF and it is further shown that PCAF acetyltransferase activity is also required for normal differentiation. The major acetylation sites in Rb are located within the nuclear localization sequence and, although mutation did not alter Rb localization in cycling cells, the mutant is mislocalized to the cytoplasm during differentiation. Studies indicate that acetylation is a mechanism for controlling Rb localization in human keratinocytes, with either reduction of the PCAF or exogenous expression of the deacetylase SIRT1, resulting in mislocalization of Rb. These findings identify PCAF-mediated acetylation of Rb as an event required to retain Rb within the nucleus during keratinocyte differentiation.

Characterization of azospirillum isolated from nitrogen-fixing roots of harvested sorghum plants

Root segments of harvested sorghum plants had acetylene reduction activity ranging from 11 to 61 nmol of ethylene formed per h per g (dry weight). Five strains of Azospirillum brasilense sp. nov. were isolated from root segments.

Recognition of leguminous hosts by a promiscuous Rhizobium strain

The lima bean (Phaseolus lunatus L.) and the pole bean (Phaseolus vulgaris L.) are nodulated by rhizobia of two different cross-inoculation groups. Rhizobium sp. 127E15, a cowpea-type Rhizobium, can induce effective nodules on the lima bean and partially effective nodules on the pole bean. Rhizobium phaseoli 127K14 can induce effective nodules on the pole bean but does not reciprocally nodulate the lima bean. Root hairs of the lima bean when inoculated with Rhizobium sp. 127E15 showed tip curling and swelling and infection thread formation as observed by light microscopy and scanning electron microscopy. When lima bean root hairs were inoculated with R. phaseoli 127K14, no host-specific responses were observed. Pole bean root hairs that had been inoculated with R. phaseoli 127K14 or Rhizobium sp. 127E15 also showed tip curling and swelling and infection thread formation. Colonization of lima bean root hairs by Rhizobium sp. 127E15 and pole bean root hairs by R. phaseoli 127K14 or Rhizobium sp. 127E15 appeared to involve the elaboration of microfibrils. This study showed that when Rhizobium sp. 127E15 nodulates a host of a different cross-inoculation group, it elicits the same specific host responses as it does from a host of the same cross-inoculation group.

Nodulation of Pole Bean (Phaseolus vulgaris L.) by Rhizobium Species of Two Cross-Inoculation Groups

Physiology and morphology of pole bean (Phaseolus vulgaris L. cv Kentucky Wonder) root nodules induced by two Rhizobium species of different cross-inoculation groups have been compared. Root nodules induced by Rhizobium sp. 127E15, which is a strain of the cowpea group Rhizobium, were pinkish, had irregular shapes, and were only partially effective. Their peak acetylene reduction activity was 4.36 mumol of C(2)H(4) formed per g of fresh nodules per h at 30 days after inoculation. The effective nodules induced by Rhizobium phaseoli 127K14, which is a strain of the bean group Rhizobium, were dark red, spherical, and showed peak acetylene reduction activity of 15.95 mumol of C(2)H(4) formed per g of fresh nodules per h at 15 days after inoculation. The partial effectiveness of 127E15-induced nodules was associated with fewer infected cells, a delay in the increase of bacteroid population within the host cells, abundance of cytoplasmic vesicles in the host cells, more bacteroids within a membrane envelope (peribacteroid membrane), and the inability of bacteroids to completely fill up the host cytoplasmic space. The 127K14-induced nodules were fully mature, with host cells filled with bacteroids by 12 days after inoculation. In contrast, the 127E15-induced nodules did not reach a similar developmental stage even 30 days after inoculation.

Toll-like receptor 4 mediates innate immunity to Kaposi sarcoma herpesvirus

The involvement of Toll-like receptor 4 (TLR4) in immunity against human herpesviruses has not been previously demonstrated. We show that infection of endothelial cells with Kaposi sarcoma herpesvirus (KSHV), a human oncogenic virus, leads to rapid suppression of TLR4 expression. This is a mechanism of immune escape as TLR4 mediates innate immunity against KSHV. In vitro, cells lacking TLR4 are more susceptible to KSHV infection, whereas activation of TLR4 protects cells from infection. In vivo, HIV-1-infected individuals carrying a mutant TLR4 allele appear more likely to have multicentric Castleman's disease, a lymphoproliferation associated with enhanced KSHV replication. ERK activation by KSHV structural proteins and the KSHV-encoded vGPCR plays a key role in the TLR4 downregulation, whereas the KSHV vIRF1 also contributes to this effect. Our findings reveal a role for TLR4 in innate immunity against herpesviruses and suggest the potential use of TLR4 agonists for the treatment of KSHV-related neoplasms.

Mathematical models of cognitive recovery

Longitudinal psychological test results are used as dependent variables to explore the complex relationship between length of coma, time of testing on the recovery curve, and corresponding cognitive status after traumatic brain injury (TBI). A database containing 319 TBI patients with a broad spectrum of coma duration was used. Statistical analysis of mixed effects modelling was applied to longitudinal WAIS-R (Wechsler Adult Intelligence Scale-Revised) scores to construct two mathematical models (verbal IQ and performance IQ). The models predict the course of recovery (initial cognitive level post-coma, eventual recovery level, and level of cognitive functioning at any point on the recovery curve) when the duration of coma is known. Performance IQ was found to recover at a rate that is almost four times slower than verbal IQ. The results have important clinical rehabilitation implications. This statistical modelling technique also enables the medical researcher to investigate disease progression or recovery using structured assessments, which would normally be part of the routine medical monitoring.

Heavy metal concentrations in marine fishes collected from fish culture sites in Hong Kong

The levels of six heavy metals (Cd, Cr, Cu, Ni, Pb, and Zn) in different tissues of three species of cultured marine fishes (Epinephelus areolatus, Lutjanus russelli, and Sparus sarba) collected from three fish culture sites in Hong Kong were evaluated. Metal pollution problems in the fish culture sites were serious, as reflected by the high metal concentrations recorded in sea water, sediments, and the biomonitor Perna viridis. In general, tissues of all three species contained high concentrations of Zn and Cu, but much lower concentrations of Ni, Pb, Cd, and Cr. Similar pattern of heavy metal concentrations was observed in sea water, sediment, and P. viridis. Metal concentrations in various tissues varied greatly among species and among fish culture sites. Different tissues showed different capacity for accumulating heavy metals. Gonad of all three species contained high concentrations of Zn. On the other hand, liver seemed to be the primary organ for Cu accumulation. Overall, metal concentrations in the tissues of culture marine fishes were much lower than those in P. viridis. Despite high metal levels in sea water and sediments, concentrations of Cd, Cr, and Pb in edible tissues, including muscle and skin, did not exceed permissible levels recommended by the Hong Kong Government for human consumption.

SNAP-23 is located in the basolateral plasma membrane of rat pancreatic acinar cells

The SNARE hypothesis proposes that specificity of exocytosis is regulated by the appropriate interactions between the vesicle (v-) SNARE and the target membrane (t-) SNAREs. We show here that pancreatic acinar cells express the SNAP-25 t-SNARE homolog SNAP-23, and find that this t-SNARE is most highly concentrated on the basolateral plasma membrane while being expressed below detectable levels in endocrine islets within the same tissue. This is the first localization of SNAP-23 within a polarized tissue and suggests that this t-SNAREs may interact with syntaxin-4 to mediate basolateral secretion.

How well does epidemiological evidence hold for the relationship between smoking and adverse obstetric outcomes in New South Wales?

This study examines whether the established epidemiological relationship between cigarette-smoking exposure in pregnancy and adverse obstetric outcomes are confirmed in Australian data from the NSW Midwives Data Collection (MDC). These data were analysed to compare the obstetric complications and pregnancy outcomes between smoking and nonsmoking women confined in 1994. Results showed that smoking mothers had higher rates of antepartum haemorrhage due to placental abruption and placenta praevia. They were also at higher risk of giving birth to low birth-weight babies and preterm delivery. Infants born to smoking mothers were 17% more likely to be admitted to hospital special care nurseries or neonatal intensive care units. Moreover, the risk of reported perinatal death among babies of smoking mothers was 20% higher than babies of nonsmoking mothers. However, smoking during pregnancy was found to confer a protective effect against the development of pregnancy-induced hypertension. These results were compared with existing evidence from the literature. Published research reports on the corresponding smoking effects were identified to assess the consistency of evidence and typical risk ratios. Findings from the literature search showed a near-perfect concordance with the associations in the NSW MDC data. The paper documents the likely complications which might be prevented if smoking in pregnancy were eliminated. There remains a real need for effective programmes to reduce smoking prevalence in pregnancy.

Tissue distribution of SNAP-23 and its subcellular localization in 3T3-L1 cells

The SNARE hypothesis of vesicular traffic proposes that three proteins, VAMP/synaptobrevin, syntaxin, and SNAP-25, constitute a complex that docks the vesicle at the target membrane. VAMP and syntaxin isoforms have been identified outside the nervous system, and a cDNA to a SNAP-25 related protein, SNAP-23, was recently identified in human lymphocytes. Here we report the generation of isoform-specific antibodies to SNAP-23 cloned from human melanoma cells, and their use in detecting the expression and localization of the endogenous SNAP-23 protein in several tissues and cell lines. SNAP-23 was readily detected in liver, lung, kidney, and spleen, to a lesser extent in muscle and heart, and was almost undetectable in brain. The protein was also abundant in fibroblast, muscle, and fat cell lines, but relatively less enriched in neuroendocrine PC12 cells. SNAP-23 abundance did not change during differentiation of 3T3-L1 fibroblasts into adipocytes. In both, SNAP-23 was membrane-bound and below detectable levels in the cytosolic fraction. Subcellular fractionation of 3T3-L1 adipocytes revealed that the majority of the protein was associated with plasma membranes. These findings support the conclusion that a tripartite SNARE complex exists outside of the nervous system, and suggest that SNAP-23 may play a role in vesicle traffic in most cell types.

Exercise increases the plasma membrane content of the Na+ -K+ pump and its mRNA in rat skeletal muscles

Muscle fibers adapt to ionic challenges of exercise by increasing the plasma membrane Na+-K+ pump activity. Chronic exercise training has been shown to increase the total amount of Na+-K+ pumps present in skeletal muscle. However, the mechanism of adaptation of the Na+-K+ pump to an acute bout of exercise has not been determined, and it is not known whether it involves alterations in the content of plasma membrane pump subunits. Here we examine the effect of 1 h of treadmill running (20 m/min, 10% grade) on the subcellular distribution and expression of Na+-K+ pump subunits in rat skeletal muscles. Red type I and IIa (red-I/IIa) and white type IIa and IIb (white-IIa/IIb) hindlimb muscles from resting and exercised female Sprague-Dawley rats were removed for subcellular fractionation. By homogenization and gradient centrifugation, crude membranes and purified plasma membranes were isolated and subjected to gel electrophoresis and immunoblotting by using pump subunit-specific antibodies. Furthermore, mRNA was isolated from specific red type I (red-I) and white type IIb (white-IIb) muscles and subjected to Northern blotting by using subunit-specific probes. In both red-I/IIa and white-IIa/IIb muscles, exercise significantly raised the plasma membrane content of the alpha1-subunit of the pump by 64 +/- 24 and 55 +/- 22%, respectively (P < 0.05), and elevated the alpha2-polypeptide by 43 +/- 22 and 94 +/- 39%, respectively (P < 0.05). No significant effect of exercise could be detected on the amount of these subunits in an internal membrane fraction or in total membranes. In addition, exercise significantly increased the alpha1-subunit mRNA in red-I muscle (by 50 +/- 7%; P < 0.05) and the beta2-subunit mRNA in white-IIb muscles (by 64 +/- 19%; P < 0.01), but the alpha2- and beta1-mRNA levels were unaffected in this time period. We conclude that increased presence of alpha1- and alpha2-polypeptides at the plasma membrane and subsequent elevation of the alpha1- and beta2-subunit mRNAs may be mechanisms by which acute exercise regulates the Na+-K+ pump of skeletal muscle.

Re-examining the concept of severity in traumatic brain injury

This paper re-examines the theoretical concept of severe brain injury focusing on the duration of coma as a precise indicator of the clinical profile. A retrospective hospital chart study of 361 traumatic brain-injured patients was undertaken to determine the homogeneity of the subsample of the severely brain-injured (defined as 2 or more days of coma) with respect to the probability of four types of impairment: ataxia, contractures, paralysis and speech impairment. The current concept of severity assumes homogeneity among the 'severely brain-injured'. However, our results indicate significant differences in impairment within this population. The authors feel strongly that future studies must describe coma duration in finer gradations, and test for homogeneity within samples before inferences are made. Improvements in life-sustaining technologies have resulted in longer coma durations. The need to use coma days as an indicator of impairment rather than a broad category of severity is emphasized.

Clover development during spaceflight: a model system

The development of legume root nodules was studied as a model system for the examination of gravitational effects on plant root development. In order to examine whether rhizobial association with clover roots can be achieved in microgravity, experiments were performed aboard the KC-135 parabolic aircraft and aboard the sounding rocket mission Consort 3. Binding of rhizobia to roots and the initial stages of root nodule development successfully occurred in microgravity. Seedling germination experiments were performed in the sliding block device, the Materials Dispersion Apparatus, aboard STS-37. When significant hydration of the seeds was achieved, normal rates of germination and seedling development were observed.

Statistical profile of traumatic brain injury: a Canadian rehabilitation population

A retrospective clinical hospital chart study was undertaken to prepare a statistical profile of traumatic brain-injured patients in rehabilitation. It included 498 consecutive admissions to the Traumatic Brain Injury Rehabilitation Program of the Queen Elizabeth Hospital (Toronto, Canada) from 1978 to 1991. Descriptive statistics were obtained for age, gender, marital status, educational status, occupational status, history of drug and alcohol use, cause of injury, month of injury and length of coma. Comparisons are made between the studied population and several Canadian centres, as well as international brain injury demographics in the literature. Results are discussed in terms of the gender differences and lifestyle parameters associated with brain injury.

The key to successful program planning

For program planning to be cost-effective, it must combine clear vision and realistic strategy. Reliable demographic information on target populations is essential, and in-house research can contribute substantially to the accuracy of information that health care administrators use in such planning. This article describes research into the traumatic brain-injured population at Toronto's Queen Elizabeth Hospital and discusses how this information can be used by health care administrators.

Antipeptide antibodies that can distinguish specific subunit polypeptides of glutamine synthetase from bean (Phaseolus vulgaris L.)

The amino acid sequences of the beta and gamma subunit polypeptides of glutamine synthetase from bean (Phaseolus vulgaris L.) root nodules are very similar. However, there are small regions within the sequences that are significantly different between the two polypeptides. The sequences between amino acids 2 and 9 and between 264 and 274 are examples. Three peptides (gamma 2-9, gamma 264-274, and beta 264-274) corresponding to these sequences were synthesized. Antibodies against these peptides were raised in rabbits and purified with corresponding peptide-Sepharose affinity chromatography. Western blot analysis of polyacrylamide gel electrophoresis of bean nodule proteins demonstrated that the anti-beta 264-274 antibodies reacted specifically with the beta polypeptide and the anti-gamma 264-274 and anti-gamma 2-9 antibodies reacted specifically with the gamma polypeptide of the native and denatured glutamine synthetase. These results showed the feasibility of using synthetic peptides in developing antibodies that are capable of distinguishing proteins with similar primary structures.

Late consolidative radiation therapy in the treatment of limited-stage small cell lung cancer

Two hundred twenty-three patients were enrolled on this randomized Phase III trial testing the value of late consolidative involved-field radiation therapy in the treatment of limited-stage small cell lung cancer (SCLC). Patients were treated with induction chemotherapy consisting of alternating cycles of procarbazine, vincristine, lomustine, and cyclophosphamide (POCC) and etoposide, doxorubicin, and methotrexate (VAM) for 6 to 9 months. Responding patients were then randomized at 6 or 9 months to chemotherapy alone or to involved-field radiation therapy. All partial and complete responders received prophylactic cranial irradiation. Of the 180 eligible and evaluable patients, 80 (44%) achieved a complete response and 39 (22%) achieved a partial response (overall rate of response, 66%). Actuarial median survival time was 11.6 months, with 16% of patients surviving 2 years and 11% surviving 5 years. Forty-eight patients were randomized to chemotherapy alone (24 patients) versus chemotherapy plus involved-field radiation therapy (24 patients). There were no significant differences in time to progression or survival between those patients receiving or not receiving involved-field radiation therapy. The thorax was the site of first relapse in 58% of patients randomized to chemotherapy alone versus 29% in patients randomized to chemotherapy plus involved-field radiation therapy (P equals 0.042). The major acute toxicity was reversible myelosuppression, and the major late toxicity was chronic central nervous system dysfunction. The authors conclude that the addition of late consolidative radiation therapy to induction chemotherapy in the treatment of limited-stage SCLC is well tolerated and improves local control, but does not improve time to progression or rates of survival.

Immunocytochemical Localization of Glutamine Synthetase in Organs of Phaseolus vulgaris L

Glutamine synthetase was localized in nodules, roots, stems, and leaves of red kidney bean (Phaseolus vulgaris L.) by immunocytochemistry. Affinity purified antibodies reactive with glutamine synthetase were prepared using purified nodule-enhanced glutamine synthetase. Immunogold labeling was observed in the cell cytoplasm in each plant organ. In nodules, the labeling was more intense in the infected cells than in the uninfected cells. No labeling was observed in nodule bacteroids, peribacteroid spaces, or in peribacteroid membranes, while previous reports of glutamine synthetase immunolabeling of legume nodules showed labeling in the bacteroid fraction. Significant labeling was observed in nodule proplastids which contained starch granules. Substantial labeling was also observed in leaf chloroplasts. No labeling was observed in other organelles including mitochondria, peroxisomes, and endoplasmic reticulum. Preimmune IgGs did not bind to any structure in the tissues examined.

Binding of isolated plant lectin by rhizobia during episodes of reduced gravity obtained by parabolic flight

Development of a legume root nodule is a complex process culminating in a plant/bacterial symbiosis possessing the capacity for biological dinitrogen fixation. Formation of root nodules is initiated by the binding and stabilization of rhizobia to plant root hairs, mediated in part by a receptor/ligand recognition system composed of lectins on the plant root surface and lectin-binding sites on the rhizobial cell surface. The dinitrogen fixation activity of these root nodules may be an important feature of enclosed, space-based life support systems, and may provide an ecological method to recycle nitrogen for amino acid production. However, the effects on nodule development of varied gravitational fields, or of root nutrient delivery hardware, remain unknown. We have investigated the effects of microgravity on root nodule formation, with preliminary experiments focused upon the receptor/ligand component. Microgravity, obtained during parabolic flight aboard NASA 930, has no apparent effect on the binding of purified lectin to rhizobia, a result that will facilitate forthcoming experiments using intact root tissues.

Subunit Composition of Glutamine Synthetase Isozymes from Root Nodules of Bean (Phaseolus vulgaris L.)

Glutamine synthetase from bean nodules can be separated into two isoforms, GS(n1) and GS(n2). A purification protocol has been developed. It included protamine sulfate precipitation, ammonium sulfate fractionation, anthranilate-affinity chromatography, Dye-Matrex (Orange A) chromatography, and diethylaminoethyl-cellulose ion-exchange chromatography. GS(n1) and GS(n2) have been purified to homogeneity. Subunit structure analysis using two-dimensional polyacrylamide gel electrophoresis revealed that GS(n1) was composed of two different types of subunit polypeptides. They differed in isoelectric points (6.0 and 6.3) but had the same molecular weights (46,000 Daltons). GS(n2) was composed of only one type of subunit polypeptide. It had an isoelectric point of 6.0 and a molecular weight of 46,000 Daltons. It was apparently identical to one of the polypeptides found in GS(n1). Glutamine synthetase holoenzyme consisted of eight subunits. In the nodule there are two different types of glutamine synthetase subunit polypeptides. Random combinations of the polypeptides should generate nine different isozymes. Our electrophoretic analysis revealed that GS(n2) was but one of the isozymes, and GS(n1) was a composite of the other eight. Hence, nodule glutamine synthetase isozymes were homo-octameric as well as hetero-octameric.

Gabaculine Inhibition of Chlorophyll Biosynthesis and Nodulation in Phaseolus lunatus L

Gabaculine (3-amino-2,3-dihydrobenzoic acid) was an inhibitor of in vivo chlorophyll biosynthesis in lima bean (Phaseolus lunatus L. cv Henderson). When applied to roots of 9-day-old plants, 10 micromolar gabaculine was sufficient to terminate biosynthesis of new chlorophyll. The trifoliolate leaves which emerged after gabaculine treatment were yellow. Gabaculine-treated plants had slightly lower dry weights; yet, overall plant size showed very little change. Chlorophyll fluorescence induction kinetics and CO(2) exchange measurements were used to monitor both immediate and long-term effects of gabaculine on photosynthesis. A lowered rate of the decline from the maximum level of fluorescence was observed after 10 hours for nitrate-supplemented plants, and all treated plants showed a slightly increased level of original fluorescence after 6 days. No change was observed in the rate of photosynthesis by unifoliolate leaves. The trifoliolate leaves, though not able to photosynthesize, were able to continue respiration. This suggested that heme biosynthesis for mitochondrial cytochromes was not abolished. In untreated lima bean, root nodules were induced by Rhizobium sp. 127E15. Following gabaculine treatment, root nodules formed, but were largely ineffective in nitrogen fixation. Nodule dry weight, nitrogen fixation activity, and leghemoglobin content were decreased by gabaculine.

Isozymes of Glutamine Synthetase in Phaseolus vulgaris L. and Phaseolus lunatus L. Root Nodules

The glutamine synthetase (GS) isozymes in the plant fraction of nodule extracts from 62 cultivars of Phaseolus vulgaris L. and one cultivar of Phaseolus lunatus L. were analyzed by polyacrylamide gel electrophoresis. All P. vulgaris nodule extracts displayed two GS activity bands: a nodule-specific band (GS(n1)) and a band (GS(n2)) similar to the single band (GS(r)) present in root extracts. In nodule extracts of P. lunatus, the GS(n1) band was detected, but the GS(n2) band was barely detectable. In contrast to P. vulgaris, the GS(n2) band and the GS(r) band of P. lunatus appeared to be different. The electrophoretic mobility of the GS(n1) band in P. vulgaris was governed by both the plant cultivar and the development stage of the nodule. In nodule extracts of P. vulgaris and P. lunatus, the zone of GS(n1) activity coincided with six to nine distinct protein bands as revealed after treatment of gels, which had previously been stained for GS activity, with Coomassie blue. All these protein bands were shown to consist of polypeptides of identical molecular weight (approximately 47,000 daltons) by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Our results indicate that P. vulgaris continuously generates isozymes of GS(n1) of increasing electrophoretic mobility during the course of nodule development.

Nitrate and Carbohydrate Effects on Nodulation and Nitrogen Fixation (Acetylene Reduction) Activity of Lentil (Lens esculenta Moench)

Lentils (Lens esculenta Moench, cv. Tekoas) grown in a nutrient solution containing 15 millimolar nitrate had 84% fewer nodules than lentils grown in nitrate-free nutrient solution. Nodules from the nitrate-grown plants weighed 71% less than nodules from the nitrate-free plants. Nitrate-grown plants also fixed much less nitrogen (measured by acetylene reduction) than the nitrate-free plants. When lentils were grown in a solution containing 15 millimolar nitrate and 75 millimolar fructose, glucose, or sucrose, however, the nitrogen fixation activity of their nodules was similar to that of nodules from nitrate-free plants. Leaves of lentils grown in the nitrate-sugar solutions had only about 7% as much nitrate reductase activity and accumulated only 10% as much nitrate as leaves from lentils grown in the nitrate solution alone. Roots of lentils grown in the nitrate-sugar solutions had similar nitrate reductase activity but accumulated only 17 to 25% as much nitrate as roots from lentils grown in the nitrate solution. The results indicate that the added sugars alleviated the inhibitory effects of nitrate on symbiotic nitrogen fixation not only by increasing the carbohydrate supply so lentils could support both nitrogen fixation and nitrate reduction but also by inhibiting the accumulation of nitrate and, hence, lowering nitrate reductase activity in the leaves.

Interactions between Rhizobia and Lectins of Lentil, Pea, Broad Bean, and Jackbean

A quantitative method was developed to measure the binding of fluorescent-labeled lentil (Lens esculenta Moench), pea (Pisum sativum L.), broad bean (Vicia faba L.), and jackbean (Canavalia ensiformis L., DC.) lectins to various Rhizobium strains. Lentil lectin bound to three of the five Rhizobium leguminosarum strains tested. The number of lentil lectin molecules bound per R. leguminosarum 128C53 cell was 2.1 x 10(4). Lentil lectin also bound to R. japonicum 61A133. Pea and broad bean lectins bound to only two of the five strains of R. leguminosarum, whereas concanavalin A (jackbean lectin) bound to all strains of R. leguminosarum, R. phaseoli, R. japonicum, and R. sp. tested. Since these four lectins have similar sugarbinding properties but different physical properties, the variation in bindings of these lectins to various Rhizobium strains indicates that binding of lectin to Rhizobium is determined not only by the sugar specificity of the lectin but also by its physical characteristics.The binding of lentil lectin and concanavalin A to R. leguminosarum 128C53 could be inhibited by glucose, fructose, and mannose. However, even at 150 millimolar glucose, about 15% of the binding remained. The binding of lentil lectin to R. japonicum 61A133 could be inhibited by glucose but not by galactose. It is concluded that the binding site of lentil lectin to R. japonicum is different from the binding site of soybean lectin to R. japonicum.

Nitrate Effect on Nitrogen Fixation (Acetylene Reduction): ACTIVITIES OF LEGUME ROOT NODULES INDUCED BY RHIZOBIA WITH VARIED NITRATE REDUCTASE ACTIVITIES

The effect of nitrate on symbiotic nitrogen fixation by root nodules of cowpea (Vigna unguiculata L., Walp., cv. California Blackeye) and lupine (Lupinus augustifolius L., cv. Frost) plants inoculated with nitrate reductase-expressing and nitrate reductase-nonexpressing Rhizobium strains were examined. Nitrate reductase of Rhizobium bacteroids in the nodules of cowpea and lupine reduced nitrate to nitrite. Both cowpea and lupine nodules accumulated nitrite when grown in the presence of 15 millimolar nitrate and induced by Rhizobium strains which express nitrate reductase activity (Rhizobium sp. 32H1 and 127E15). The nitrogen fixation (acetylene reduction) activities of cowpea and lupine nodules were inhibited by nitrate whether the nodules were induced by Rhizobium strains that express (Rhizobium sp. 32H1 and 127E15) or do not express (Rhizobium sp. 127E14 and R. lupini ATCC 10318) nitrate reductase activity. These findings indicate that nitrite, the product of bacteroid nitrate reductase, may not play a role in the inhibitory effect of nitrate on nitrogen fixation activities of legume root nodules. However, the degree of inhibition on the fixation activity by nitrate varied in different legume-Rhizobium combinations.

Characterization of a bacterium of the genus Azospirillum from cellulolytic nitrogen-fixing mixed cultures

A bacterium with the taxonomic characteristics of the genus Azospirillum was isolated from celluloytic N2-fixing mixed cultures. Its characteristics fit the descriptions of both Azopirillum lipoferum (Beijerinck) comb. nov. and Azospirillum brasilense sp. nov. It may be a variant strain of A. lipoferum. In mixed cultures with cellulolytic organisms, the bacterium grew and fixed N2 with cellelose as a sole source of energy and carbon. The mixed cultures used cellulose from leaves of wheat (Triticum aestivum L.), corn (Zea mays L.), and big bluestem grass (Andropogon gerardii Vitm). Microaerophilic N2-fixing bacteria of the genus Azospirillum, such as the bacterium we isolated, may be important contributors of fixed N2 in soil with partial anaerobiosis and cellulose decomposition.

Nitrate reductase activities of rhizobia and the correlation between nitrate reduction and nitrogen fixation

All species of Rhizobium except R. lupini had nitrate reductase activity. Only R. lupini was incapable of growth with nitrate as the sole source of nitrogen. However, the conditions necessary for the induction of nitrate reductase varied among species of Rhizobium. Rhizobium japonicum and some Rhizobium species of the cowpea strains expressed nitrate reductase activities both in the root nodules of appropriate leguminous hosts and when grown in the presence of nitrate. Rhizobium trifolii, R. phaseoli, and R. leguminosarum did not express nitrate reductase activities in the root nodules, but they did express them when grown in the presence of nitrate. In bacteroids of R. japonicum and some strains of cowpea Rhizobium, high N2 fixation activities were accompanied by high nitrate reductase activities. In bacteroids of R. trifolii, R. leguminosarum, and R. phaseoli, high N2 fixation activities were not accompanied by high nitrate reductase activities.