DSP107 combines inhibition of CD47/SIRPα axis with activation of 4-1BB to trigger anticancer immunity

Background

Treatment of Diffuse Large B Cell Lymphoma (DLBCL) patients with rituximab and the CHOP treatment regimen is associated with frequent intrinsic and acquired resistance. However, treatment with a CD47 monoclonal antibody in combination with rituximab yielded high objective response rates in patients with relapsed/refractory DLBCL in a phase I trial. Here, we report on a new bispecific and fully human fusion protein comprising the extracellular domains of SIRPα and 4-1BBL, termed DSP107, for the treatment of DLBCL. DSP107 blocks the CD47:SIRPα ‘don’t eat me’ signaling axis on phagocytes and promotes innate anticancer immunity. At the same time, CD47-specific binding of DSP107 enables activation of the costimulatory receptor 4-1BB on activated T cells, thereby, augmenting anticancer T cell immunity.

Methods

Using macrophages, polymorphonuclear neutrophils (PMNs), and T cells of healthy donors and DLBCL patients, DSP107-mediated reactivation of immune cells against B cell lymphoma cell lines and primary patient-derived blasts was studied with phagocytosis assays, T cell activation and cytotoxicity assays. DSP107 anticancer activity was further evaluated in a DLBCL xenograft mouse model and safety was evaluated in cynomolgus monkey.

Results

Treatment with DSP107 alone or in combination with rituximab significantly increased macrophage- and PMN-mediated phagocytosis and trogocytosis, respectively, of DLBCL cell lines and primary patient-derived blasts. Further, prolonged treatment of in vitro macrophage/cancer cell co-cultures with DSP107 and rituximab decreased cancer cell number by up to 85%. DSP107 treatment activated 4-1BB-mediated costimulatory signaling by HT1080.4-1BB reporter cells, which was strictly dependent on the SIRPα-mediated binding of DSP107 to CD47. In mixed cultures with CD47-expressing cancer cells, DSP107 augmented T cell cytotoxicity in vitro in an effector-to-target ratio-dependent manner. In mice with established SUDHL6 xenografts, the treatment with human PBMCs and DSP107 strongly reduced tumor size compared to treatment with PBMCs alone and increased the number of tumor-infiltrated T cells. Finally, DSP107 had an excellent safety profile in cynomolgus monkeys.

Conclusions

DSP107 effectively (re)activated innate and adaptive anticancer immune responses and may be of therapeutic use alone and in combination with rituximab for the treatment of DLBCL patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-022-02256-x.

790 DSP502 — A novel approach for targeting TIGIT and PD1 pathways for cancer immunotherapy

Background

TIGIT, an inhibitory immune checkpoint, is a target of interest for immuno-oncology combination therapies. TIGIT is part of a complex molecular network containing four receptors (DNAM1, TIGIT, PVRIG and CD96) and two ligands (PVR and PVRL2). Here we describe Dual Signaling Protein 502 (DSP502), a novel, multi-functional IgG1-Fc-fusion protein targeting this molecular pathway in a unique way. DSP502, comprising the extracellular domains of TIGIT and PD1, is designed to simultaneously bind its two respective ligands, PVR and PD-L1, overexpressed on cancer and myeloid cells in the tumor microenvironment. DSP502 binds PVR preventing inhibitory signaling through TIGIT and CD96 and promoting DNAM1 costimulatory signaling on activated T- and NK-cells. DSP502's PD1 arm binds PD-L1 to unleash effector T-cells through checkpoint inhibition. In parallel, DSP502's IgG1-Fc delivers an immune-activating signal via Fc receptors. The net effect is enhanced anti-tumor immunity (figure 1).

Methods

DSP502 heterodimer was successfully produced in a mammalian expression system. DSP502 was evaluated for binding to its cognate ligands on cells and in ELISA-based assays, with and without competing antibodies. NK and PBMC killing activity were evaluated against human K562 CML cells overexpressing PVR. Simultaneous binding of DSP502 to fluorescently-labeled tumor and NK-cells was evaluated by FACS. In vivo activity of DSP502 was evaluated in a humanized NSG A549 NSCLC xenograft mouse model.

Results

Both DSP502 arms were shown to bind their cognate ligands in ELISA and on cell surface. DSP502 binding was dependent on the presence of both ligands on cells and was abolished by competing antibodies to the respective targets, demonstrating binding specificity and the 'AND-gate' phenomenon. Overexpression of PVR reduced the sensitivity of K562 cells to NK-cell mediated killing, while DSP502 treatment restored it as measured by target cell killing and granzyme-B secretion. Increased, dose-dependent, complexation of NK- and tumor cells was observed following DSP502 treatment and was abolished by both PVR and FcR antibodies. Treatment with DSP502 markedly inhibited tumor growth of A549-NSCLC xenograft in a humanized NSG mouse model, with all mice being tumor-free at the end of the experiment, compared to control PBMC-injected mice.

Conclusions

Here we report the design and function of a novel immunotherapeutic fusion protein, DSP502, that offers multiple functionalities that can coordinately and synergistically drive anti-tumor immunity. Beyond targeting PVR and PDL1, DSP502 has the potential to additionally impact the TIGIT pathway through its effects on CD96 and DNAM1. DSP502 is currently in IND-enabling studies and CMC development.

Ethics Approval

The study was conducted at the Authority of Biological and Preclinical Models, the Hebrew University of Jerusalem, Ein Kerem, Sharet Specific Pathogen-Free (SPF) Unit under the Hebrew university ethic committee board approval (number MD-19-15815-5).

Abstract 790 Figure 1

Decreased expression of heparanase in glioblastoma multiforme

Object. The authors investigated the presence of endoglycosidase heparanase in human glioblastoma multiforme (GBM) and metastatic brain tumors as well as in healthy brain tissue to explore the relationship between the biological characteristics of GBM and the role of heparanase.

Methods. Heparanase messenger (m)RNA was almost undetectable in GBMs in vivo, whereas it was frequently seen in metastatic brain tumors according to results of reverse transcription—polymerase chain reaction (RT-PCR). Immunohistochemical analysis of paraffin-embedded tissue sections showed that neoplastic cells in metastatic brain tumors, especially in cells that invaded blood vessels, exhibit intense heparanase immunoreactivity. Heparanase was present in two highly invasive glioma cell lines, U87MG and U251MG, in vitro. These cell lines did not have metastatic capability, which was tested in an experimental pulmonary metastases model in mice. The activity of heparanase in these cell lines was almost the same as that in the highly metastatic melanoma cell line B16-F1. After nude mice were inoculated with U87MG cells, however, heparanase was no longer detected in subcutaneous or intracerebral experimental glioma in vivo based on results of immunohistochemical analysis. According to results of real-time quantitative PCR, there was a 10-fold increase in heparanase mRNA in U87MG glioma cells in vitro compared with that in experimental U87MG glioma tissue in vivo in nude mice.

Conclusions. These results indicate that the expression of heparanase was downregulated in GBM in vivo, which rarely metastasizes to distant organs outside the central nervous system. Heparanase is not implicated in the invasiveness of GBM to surrounding healthy brain tissue in vivo.

[Clinical significance of heparanase and basic fibroblast growth factor expression in human non-small cell lung cancer]

OBJECTIVE

To assess protein and mRNA expression levels of heparanase and basic fibroblast growth factor (bFGF) genes in human non-small cell lung cancer (NSCLC) and their roles in tumor invasion, metastasis and prognosis.

METHODS

A total of 115 paraffin-embedded and 45 fresh-frozen tissue specimens of NSCLC were studied by immunohistochemistry, Western Blot and in situ hybridization to evaluate the protein and mRNA expression status of heparanase and bFGF genes. The data was analyzed by SPSS statistical software.

RESULTS

Both human heparanase and bFGF were highly expressed in NSCLC cells, in contrast to none or a low expression in normal lung tissue. Expression of heparanase also showed a significantly higher than that in the normal tissue by Western blot (P = 0.041). Immunohistochemistry showed that heparanase expression was both cytoplasmic and membranous. The agreement between heparanase and bFGF was significant. A significant correlation was found between the expression of either protein and TNM stage, vascular invasion, lymphatic metastasis and microvascular density (MVD). Co-expression of the two proteins demonstrated an even higher correlation with the tumor stage and MVD. In addition, expression of bFGF correlated with tumor cell differentiation. Data of a multivariate analysis indicated that tumor cell differentiation, vascular invasion, lymphatic metastasis and expression of bFGF were identified as significant prognostic parameters.

CONCLUSIONS

Both heparanase and bFGF may play important roles in tumor angiogenesis, metastasis, and prognosis of NSCLC.

[Expression of heparanase in human non-small cell lung cancer]

BACKGROUND

To study the relationship between human heparanase expression and biological factors regarding invasion, metastasis and prognosis of human non-small cell lung cancer (NSCLC).

METHODS

The expression of heparanase was assessed in 122 paraffin-embedded specimens and 38 freshly-taken tissues by immunohistochemical staining and Western blot. The relationship between heparanase expression and the clinicopathological factors was analyzed by Chi square test, multivariate analysis and Kaplan-Meier method.

RESULTS

In the immunoreactive cells, staining was mainly located in cytoplasma and membrane. Human heparanase was highly expressed in lung cancer tissues (78.7%, 96/122) while negative in epithelia of normal lung tissues. The level of heparanase was remarkably higher in NSCLC than that in normal tissues ( P = 0.043 ). Expression of heparanase significantly correlated with TNM stage ( P =0.025), lymphatic metastasis ( P =0.002) and vascular invasion ( P =0.000 3). The patients with positive heparanase expression had a significantly shorter survival than those with negative heparanase expression ( P =0.000 6). In multivariate analysis, only p-TNM stage, lymphatic metastasis and vascular invasion could be considered as prognostic factors.

CONCLUSIONS

Heparanase might play an important role in the development, invasion and metastasis of NSCLC. It is indicated that patients with positive heparanase expression would have a greater chance of metastasis and a poorer prognosis. However, heparanase expression is not an independent prognostic factor.

Phenotypic knock out of heparan sulfates in myotubes impairs excitation-induced calcium spiking

Little is known about the physiological functions of heparan sulfates (HSs), which are present in the basal lamina surrounding skeletal muscle fibers. Here, we present a new system in which HS is phenotypically knocked out by endogenous expression of epitope-specific anti-HS antibodies. Single-chain antibodies, containing an immunoglobulin leader peptide, were produced by using various expression systems. Antibodies were detected in the Golgi apparatus, the site of HS biosynthesis. Likewise, the HS-degrading enzyme heparanase was expressed. Endogenous expression of antibodies or heparanase in myoblasts resulted in HS-defective myotubes. Excitability and calcium kinetics of HS-defective myotubes were severely compromised, as determined by analysis of electrically induced calcium spikes via video-speed UV confocal laser scanning microscopy. Phenotypically knocking out of individual HS epitopes resulted in specific effects on excitability and calcium kinetics. These data indicate important roles for HSs in skeletal muscle calcium kinetics.

Activation, processing and trafficking of extracellular heparanase by primary human fibroblasts

Heparanase is a heparan-sulfate-degrading endoglycosidase that has important roles in various biological processes, including angiogenesis, wound healing and metastatsis. Human heparanase is synthesized as a 65 kDa latent precursor, which is proteolytically processed into a highly active 50 kDa form. Extracellular heparanase is found in various tissues and is utilized by both normal cells and metastatic cancer cells to degrade heparan sulfate moieties in basement membranes and extracellular matrices. This study characterizes the processing and trafficking events associated with cellular activation of extracellular heparanase. We show that primary human fibroblasts are capable of binding and converting the 65 kDa heparanase precursor into its highly active 50 kDa form, concomitantly with its cytoplasmic accumulation. Heparanase uptake depends on the actin cytoskeleton integrity, resulting in a prolonged storage of the enzyme, mainly in endosomal structures. Heparanase endocytosis and its proteolytic activation are independent processes,indicating that heparanase cleavage is a cell surface event. Heparin completely inhibits heparanase endocytosis but only partially inhibits its association with the cells, suggesting that cell surface heparan sulfate moieties play a specific role in its endocytosis. Cellular binding and uptake of extracellular heparanase control its activation, clearance rate and storage within the cells.

Heparanase expression in human leukemias is restricted to acute myeloid leukemias

OBJECTIVE

Matrix metalloproteinases and an endo-beta-D-glucuronidase (heparanase) are enzymes that degrade the protein and carbohydrate constituents of basement membranes, thereby facilitating transendothelial migration of blood-borne cells. Heparanase activity was found to correlate with the metastatic potential of solid tumors. We evaluated heparanase expression, at the levels of gene and protein expression and activity in a variety of leukemias, and compared it with normal hematopoietic cells.

MATERIALS AND METHODS

Heparanase expression was evaluated in leukocytes isolated from peripheral blood of 71 patients with myeloid and lymphoid leukemias, or non-Hodgkin's lymphoma. Analysis was performed at two levels: heparanase RNA was determined by reverse transcriptase polymerase chain reaction, and heparanase protein was evaluated by immunocytochemistry and flow cytometry.

RESULTS

In eight peripheral blood samples from normal donors, heparanase RNA was detected, and protein was found within the cytoplasm of granulocytes. In mononuclear cells derived from various leukemias, heparanase RNA was expressed in 14 of 15 acute myeloid leukemia (AML) samples. In contrast, cells derived from all 33 chronic lymphoblastic leukemia, all 7 non-Hodgkin's lymphoma, 7 of 8 chronic myeloid leukemia, and 6 of 8 acute lymphoblastic leukemia patients showed no detectable expression of the heparanase RNA. Heparanase protein was detected primarily within the cytoplasm of AML cells, indicating that the enzyme is produced and stored within the cytoplasm of myeloid cells, with limited expression on the cell surface.

CONCLUSION

We propose that heparanase expression is associated with the myeloid lineage and may serve as an independent marker to support the identification of AMLs.

Expression pattern and secretion of human and chicken heparanase are determined by their signal peptide sequence

Cleavage of heparan sulfate (HS) proteoglycans affects the integrity and function of tissues and thereby fundamental phenomena, involving cell migration and response to changes in the extracellular microenvironment. The role of HS-degrading enzymes, commonly referred to as heparanases, in normal development has not been identified. The present study focuses on cloning, expression, and properties of a chicken heparanase and its distribution in the developing chicken embryo. We have identified a chicken EST, homologous to the recently cloned human heparanase, to clone and express a functional chicken heparanase, 60% homologous to the human enzyme. The full-length chicken heparanase cDNA encodes a 60-kDa proenzyme that is processed at the N terminus into a 45-kDa highly active enzyme. The most prominent difference between the chicken and human enzymes resides in the predicted signal peptide sequence, apparently accounting for the chicken heparanase being readily secreted and localized in close proximity to the cell surface. In contrast, the human enzyme is mostly intracellular, localized in perinuclear granules. Cells transfected with a chimeric construct composed of the chicken signal peptide preceding the human heparanase exhibited cell surface localization and secretion of heparanase, similar to cells transfected with the full-length chicken enzyme. We examined the distribution pattern of the heparanase enzyme in the developing chicken embryo. Both the chicken heparanase mRNA and protein were expressed, as early as 12 h post fertilization, in cells migrating from the epiblast and forming the hypoblast layer. Later on (72 h), the enzyme is preferentially expressed in cells of the developing vascular and nervous systems. Cloning and characterization of heparanase, the first and single functional vertebrate HS-degrading enzyme, may lead to identification of other glycosaminoglycan degrading enzymes, toward elucidation of their significance in normal and pathological processes.

Molecular properties and involvement of heparanase in cancer progression and mammary gland morphogenesis

Tumor spread involves degradation of various components of the extracellular matrix and blood vessel wall. Among these is heparan sulfate proteoglycan, which plays a key role in the self-assembly, insolubility and barrier properties of basement membranes and extracellular matrices. Expression of an endoglycosidase (heparanase) which degrades heparan sulfate correlates with the metastatic potential of tumor cells, and treatment with heparanase inhibitors markedly reduces the incidence of metastasis in experimental animals. Heparin-binding angiogenic proteins are stored as a complex with heparan sulfate in the microenvironment of tumors. These proteins are released and can induce new capillary growth when heparan sulfate is degraded by heparanase. Here, we describe the molecular properties, expression and involvement in tumor progression of a human heparanase. The enzyme is synthesized as a latent approximately 65 kDa protein that is processed at the N-terminus into a highly active approximately 50 kDa form. The heparanase mRNA and protein are preferentially expressed in metastatic human cell lines and in tumor biopsy specimens, including breast carcinoma. Overexpression of the heparanase cDNA in low-metastatic tumor cells conferred a high metastatic potential in experimental animals, resulting in an increased rate of mortality. The heparanase enzyme also released ECM-resident bFGF in vitro, and its overexpression elicited an angiogenic response in vivo. Heparanase may thus facilitate both tumor cell invasion and neovascularization, two critical steps in tumor progression. Mammary glands of transgenic mice overexpressing the heparanase enzyme exhibit precocious branching of ducts and alveolar development, suggesting that the enzyme promotes normal morphogenesis and possibly pre-malignant changes in the mammary gland.

Heparanase expression in primary and metastatic pancreatic cancer

The human endoglycosidase heparanase (hpa) degrades heparan-sulfate proteoglycans, which constitute prominent components of basement membranes and extracellular matrix. Due to the critical function of hpa in cancer cell invasion and metastasis, we have analyzed the expression of hpa in human primary and metastatic pancreatic cancer as well as in the normal pancreas and in chronic pancreatic inflammation. By real-time quantitative PCR, there was a 7.9- and 30.2-fold increase of hpa mRNA in chronic pancreatitis and pancreatic cancer tissue samples, respectively, in comparison with normal pancreatic tissues. There was a significant correlation between enhanced hpa mRNA expression and shorter postoperative patient survival. hpa mRNA and protein localized in the cancer cells of primary and metastatic pancreatic cancer, with a preferentially higher expression at the primary tumor site. Cultured pancreatic cancer cells transfected with a full-length hpa construct displayed enhanced invasiveness in an invasion chamber assay. These results suggest that hpa overexpression in human pancreatic cancers facilitates cancer cell invasion, thereby enhancing the metastatic potential of the tumors.

Expression of heparanase in normal, dysplastic, and neoplastic human colonic mucosa and stroma. Evidence for its role in colonic tumorigenesis

The human heparanase gene, an endo-beta-glucuronidase that cleaves heparan sulfate at specific intrachain sites, has recently been cloned and shown to function in tumor progression and metastatic spread. Antisense digoxigenin-labeled heparanase RNA probe and monoclonal anti-human heparanase antibodies were used to examine the expression of the heparanase gene and protein in normal, dysplastic, and neoplastic human colonic mucosa. To our knowledge, this is the first systematic study of heparanase expression in human colon cancer. Both the heparanase gene and protein were expressed at early stages of neoplasia, already at the stage of adenoma, but were practically not detected in the adjacent normal-looking colon epithelium. Gradually increasing expression of heparanase was evident as the cells progressed from severe dysplasia through well-differentiated to poorly differentiated colon carcinoma. Deeply invading colon carcinoma cells showed the highest levels of the heparanase mRNA and protein associated with expression of both the gene and enzyme by adjacent desmoplastic stromal fibroblasts. A high expression was also found in colon carcinoma metastases to lung, liver, and lymph nodes, as well as in the accompanying stromal fibroblasts. Moreover, extracts derived from tumor tissue expressed much higher levels of the heparanase protein and activity as compared to the normal colon tissue. In all specimens, the heparanase gene and protein exhibited the same pattern of expression. These results suggest a role of heparanase in colon cancer progression and may have both prognostic and therapeutic applications.

Metabolic engineering of astaxanthin production in tobacco flowers

Using metabolic engineering, we have modified the carotenoid biosynthesis pathway in tobacco (Nicotiana tabacum) to produce astaxanthin, a red pigment of considerable economic value. To alter the carotenoid pathway in chromoplasts of higher plants, the cDNA of the gene CrtO from the alga Haematococcus pluvialis, encoding beta-carotene ketolase, was transferred to tobacco under the regulation of the tomato Pds (phytoene desaturase) promoter. The transit peptide of PDS from tomato was used to target the CRTO polypeptide to the plastids. Chromoplasts in the nectary tissue of transgenic plants accumulated (3S,3'S) astaxanthin and other ketocarotenoids, changing the color of the nectary from yellow to red. This accomplishment demonstrates that plants can be used as a source of novel carotenoid pigments such as astaxanthin. The procedures described in this work can serve as a platform technology for future genetic manipulations of pigmentation of fruits and flowers of horticultural and floricultural importance.

Mammalian heparanase as mediator of tumor metastasis and angiogenesis

Expression of heparan sulfate-degrading endoglycosidases, commonly referred to as heparanases, correlates with the metastatic potential of tumor cell lines, and treatment with heparanase inhibitors markedly reduces the incidence of metastasis in experimental animals. We purified a 50 kDa heparanase from human hepatoma and placenta and cloned a cDNA and gene encoding a protein of 543 amino acids. Only one heparanase sequence was identified, suggesting that this enzyme is the dominant endoglucuronidase in mammalian tissues. Expression of the cloned cDNA in insect and mammalian cells yielded 65 kDa and 50 kDa recombinant proteins. The 50 kDa enzyme represents an N-terminal processed enzyme that is at least 200-fold more active than the full-length 65 kDa form. Processing was demonstrated following incubation of the full-length recombinant enzyme with intact tumor cells. The heparanase mRNA and protein are preferentially expressed in metastatic cell lines and in specimens of human melanomas and carcinomas. In the colon, both the heparanase mRNA and protein are expressed already at the stage of tubulovillous adenoma, but not in the adjacent 'normal-looking' colon epithelium. Non-metastatic murine T lymphoma and melanoma cells transfected with the heparanase gene acquired a highly metastatic phenotype in vivo. Apart from its involvement in the egress of cells from the vasculature, heparanase is tightly involved in angiogenesis, both directly--by promoting invasion of endothelial cells (vascular sprouting), and indirectly--by releasing heparan sulfate-bound basic fibroblast growth factor, and generating HS degradation fragments that promote bFGF activity. The angiogenic potential of heparanase was demonstrated in vivo (Matrigel plug assay) by showing a three to fourfold increase in neovascularization induced by Eb T lymphoma cells following their transfection with the heparanase gene. The ability of heparanase to promote both tumor angiogenesis and metastasis makes it a promising target for cancer therapy.

Mammalian heparanase: gene cloning, expression and function in tumor progression and metastasis

Heparan sulfate proteoglycans interact with many extracellular matrix constituents, growth factors and enzymes. Degradation of heparan sulfate by endoglycosidic heparanase cleavage affects a variety of biological processes. We have purified a 50-kDa heparanase from human hepatoma and placenta, and now report cloning of the cDNA and gene encoding this enzyme. Expression of the cloned cDNA in insect and mammalian cells yielded 65-kDa and 50-kDa recombinant heparanase proteins. The 50-kDa enzyme represents an N-terminally processed enzyme, at least 100-fold more active than the 65-kDa form. The heparanase mRNA and protein are preferentially expressed in metastatic cell lines and specimens of human breast, colon and liver carcinomas. Low metastatic murine T-lymphoma and melanoma cells transfected with the heparanase cDNA acquired a highly metastatic phenotype in vivo, reflected by a massive liver and lung colonization. This represents the first cloned mammalian heparanase, to our knowledge, and provides direct evidence for its role in tumor metastasis. Cloning of the heparanase gene enables the development of specific molecular probes for early detection and treatment of cancer metastasis and autoimmune disorders.

Recombinant ATM protein complements the cellular A-T phenotype

Ataxia-telangiectasia (A-T) is an autosomal recessive disorder characterized by neurodegeneration, immunodeficiency, cancer predisposition, genome instability and radiation sensitivity. The cellular phenotype of A-T points to defects in signal transduction pathways involved in activation of cell cycle checkpoints by free radical damage, and other pathways that mediate the transmission of specific mitogenic stimuli. The product of the responsible gene, ATM, belongs to a family of large proteins that contribute to maintaining genome stability and cell cycle progression in various organisms. A recombinant vector that stably expresses a full-length ATM protein is a valuable tool for its functional analysis. We constructed and cloned a recombinant, full-length open reading frame of ATM using a combination of vectors and hosts that overcame an inherent instability of this sequence. Recombinant ATM was stably expressed in insect cells using a baculovirus vector, albeit at a low level, and in human A-T cells using an episomal expression vector. An amino-terminal FLAG epitope added to the protein allowed highly specific detection of the recombinant molecule by immunoblotting, immunoprecipitation and immunostaining, and its isolation using immunoaffinity. Similar to endogenous ATM, the recombinant protein is located mainly in the nucleus, with low levels in the cytoplasm. Ectopic expression of ATM in A-T cells restored normal sensitivity to ionizing radiation and the radiomimetic drug neocarzinostatin, and a normal pattern of post-irradiation DNA synthesis, which represents an S-phase checkpoint. These observations indicate that the recombinant, epitope-tagged protein is functional. Introduction into this molecule of a known A-T missense mutation, Glu2904Gly, resulted in apparent instability of the protein and inability to complement the A-T phenotype. These findings indicate that the physiological defects characteristic of A-T cells result from the absence of the ATM protein, and that this deficiency can be corrected by ectopic expression of this protein.

Identification and chromosomal localization of Atm, the mouse homolog of the ataxia-telangiectasia gene

Atm, the mouse homolog of the human ATM gene defective in ataxia-telangiectasia (A-T), has been identified. The entire coding sequence of the Atm transcript was cloned and found to contain an open reading frame encoding a protein of 3066 amino acids with 84% overall identity and 91% similarity to the human ATM protein. Variable levels of expression of Atm were observed in different tissues. Fluorescence in situ hybridization and linkage analysis located the Atm gene on mouse chromosome 9, band 9C, in a region homologous to the ATM region on human chromosome 11q22-q23.

Cloning and characterization of the cDNA for lycopene beta-cyclase from tomato reveals decrease in its expression during fruit ripening

The cDNA which encodes lycopene cyclase, CrtL, was cloned from tomato (Lycopersicon esculentum cv. VF36) and tobacco (Nicotiana tabacum cv. Samsun NN) and functionally expressed in Escherichia coli. This enzyme converts lycopene to beta-carotene by catalyzing the formation of two beta-rings at each end of the linear carotene. The enzyme interacts with half of the carotenoid molecule and requires a double bond at the C-7,8 (or C-7,8') position. Inhibition in E. coli indicated that lycopene cyclase is the target site for the inhibitor MPTA, 2-(4-methylphenoxy)tri-ethylamine hydrochloride. The primary structure of lycopene cyclase in higher plants is significantly conserved with the enzyme from cyanobacteria but different from that of the non-photosynthetic bacteria Erwinia. mRNA of CrtL and Pds, which encodes phytoene desaturase, was measured in leaves, flowers and ripening fruits of tomato. In contrast to genes which encode enzymes of early steps in the carotenoid biosynthesis pathway, whose transcription increases during the 'breaker' stage of fruit ripening, the level of CrtL mRNA decreases at this stage. Hence, the accumulation of lycopene in tomato fruits is apparently due to a down-regulation of the lycopene cyclase gene that occurs at the breaker stage of fruit development. This conclusion supports the hypothesis that transcriptional regulation of gene expression is a predominant mechanism of regulating carotenogenesis.

A single ataxia telangiectasia gene with a product similar to PI-3 kinase

A gene, ATM, that is mutated in the autosomal recessive disorder ataxia telangiectasia (AT) was identified by positional cloning on chromosome 11q22-23. AT is characterized by cerebellar degeneration, immunodeficiency, chromosomal instability, cancer predisposition, radiation sensitivity, and cell cycle abnormalities. The disease is genetically heterogeneous, with four complementation groups that have been suspected to represent different genes. ATM, which has a transcript of 12 kilobases, was found to be mutated in AT patients from all complementation groups, indicating that it is probably the sole gene responsible for this disorder. A partial ATM complementary DNA clone of 5.9 kilobases encoded a putative protein that is similar to several yeast and mammalian phosphatidylinositol-3' kinases that are involved in mitogenic signal transduction, meiotic recombination, and cell cycle control. The discovery of ATM should enhance understanding of AT and related syndromes and may allow the identification of AT heterozygotes, who are at increased risk of cancer.

Cloning and characterization of the gene for phytoene desaturase (Pds) from tomato (Lycopersicon esculentum)

The gene Pds encodes phytoene desaturase, a key enzyme in carotenoid biosynthesis that converts phytoene to zeta-carotene. We have cloned and analyzed the genomic DNA sequence of Pds from tomato. In tomato Pds is comprised of 15 exons that, together with the introns occupy over 8 kb. A putative promoter sequence has been identified by comparison with the cDNA sequence of Pds. A consensus nucleotide sequence around intron splicing sites in tomato genes was determined by compiling data on 137 introns in 34 genes. This consensus sequence generally agrees with the consensus sequence of other higher plants with only minor differences that are unique to tomato.

A single polypeptide catalyzing the conversion of phytoene to zeta-carotene is transcriptionally regulated during tomato fruit ripening

The cDNA of the gene pds from tomato, encoding the carotenoid biosynthesis enzyme phytoene desaturase, was cloned, and its nucleotide sequence was determined. Cells of Escherichia coli that expressed the tomato pds gene could convert phytoene to zeta-carotene. This result suggests that one polypeptide, the product of the pds gene, can carry out phytoene desaturation in the carotenoid biosynthetic pathway. Transcripts of the pds gene accumulate in orange tomato fruit, indicating transcriptional control of pds expression during fruit ripening. The deduced amino acid sequence of phytoene desaturase indicates that this enzyme in tomato contains 583 amino acids that are highly conserved with respect to the homologous enzymes in cyanobacteria and algae. The deduced amino acid sequences of the phytoene desaturases from other microorganisms (purple bacteria and fungi) appear to be evolutionarily unrelated to those from green photosynthetic organisms.

Functional complementation in Escherichia coli of different phytoene desaturase genes and analysis of accumulated carotenes

Three different phytoene desaturase genes, from Rhodobacter capsulatus, Erwinia uredovora, and Synechococcus PCC 7942, have been functionally complemented with a gene construct from E. uredovora which encodes all enzymes responsible for formation of 15-cis phytoene in Escherichia coli. As indicated by the contrasting reaction products detected in the pigmented E. coli cells after co-transformation, a wide functional diversity of these three different types of phytoene desaturases can be concluded. The carotenes formed by the phytoene desaturase from R. capsulatus were trans-neurosporene with three additional double bonds and two cis isomers. Furthermore, small amounts of three zeta-carotene isomers (2 double bonds more than phytoene) and phytofluene (15-cis and all-trans with + 1 double bond) were detected as intermediates. When the subsequent genes from E. uredovora which encode for lycopene cyclase and beta-carotene hydroxylase were present, neurosporene, the phytoene desaturase product of R. capsulatus, was subsequently converted to the monocyclic beta-zeacarotene and its monohydroxylation product. The most abundant carotene resulting from phytoene desaturation by the E. uredovora enzyme was trans-lycopene together with a cis isomer. In addition, bisdehydrolycopene was also formed. The reaction products of Synechococcus phytoene desaturase were two cis isomers of zeta-carotene and only small amounts of trans-zeta-carotene including 15-cis. The I50 values for flurtamone and diphenylamine to inhibit phytoene desaturation were determined and differential inhibition was observed for diphenylamine.

Molecular cloning and expression in photosynthetic bacteria of a soybean cDNA coding for phytoene desaturase, an enzyme of the carotenoid biosynthesis pathway

Carotenoids are orange, yellow, or red photo-protective pigments present in all plastids. The first carotenoid of the pathway is phytoene, a colorless compound that is converted into colored carotenoids through a series of desaturation reactions. Genes coding for carotenoid desaturases have been cloned from microbes but not from plants. We report the cloning of a cDNA for pds1, a soybean (Glycine max) gene that, based on a complementation assay using the photosynthetic bacterium Rhodobacter capsulatus, codes for an enzyme that catalyzes the two desaturation reactions that convert phytoene into zeta-carotene, a yellow carotenoid. The 2281-base-pair cDNA clone analyzed contains an open reading frame with the capacity to code for a 572-residue protein of predicted Mr 63,851. Alignment of the deduced Pds1 peptide sequence with the sequences of fungal and bacterial carotenoid desaturases revealed conservation of several amino acid residues, including a dinucleotide-binding motif that could mediate binding to FAD. The Pds1 protein is synthesized in vitro as a precursor that, upon import into isolated chloroplasts, is processed to a smaller mature form. Hybridization of the pds1 cDNA to genomic blots indicated that this gene is a member of a low-copy-number gene family. One of these loci was genetically mapped using restriction fragment length polymorphisms between Glycine max and Glycine soja. We conclude that pds1 is a nuclear gene encoding a phytoene desaturase enzyme that, as its microbial counterparts, contains sequence motifs characteristic of flavoproteins.

The molecular basis of resistance to the herbicide norflurazon

We have cloned and sequenced a gene, pds, from the cyanobacterium Synechococcus PCC7942 that is responsible for resistance to the bleaching herbicide norflurazon. A point mutation in that gene, leading to an amino acid substitution from valine to glycine in its polypeptide product, was found to confer this resistance. Previous studies with herbicide-resistant mutants have indicated that this gene encodes phytoene desaturase (PDS), a key enzyme in the biosynthesis of carotenoids. A short amino acid sequence that is homologous to conserved motifs in the binding sites for NAD(H) and NADP(H) was identified in PDS, suggesting the involvement of these dinucleotides as cofactors in phytoene desaturation.

Cloning a gene coding for norflurazon resistance in cyanobacteria

The herbicide norflurazon inhibits carotene biosynthesis in photosynthetic organisms by blocking the enzyme phytoene dehydrogenase (= phytoene desaturase). We have isolated norflurazon-resistant mutants of the cyanobacterium Synechococcus PCC7942. The herbicide-resistance gene from the mutant NFZ4 has been cloned by genetic complementation of the resistance trait in wild type cells. The experiment described here illustrates the usefulness of employing cyanobacteria to clone herbicide-resistance genes in a quick and simple way.

Isolation and Characterization of Herbicide Resistant Mutants in the Cyanobacterium Synechococcus R2

Department of Genetics, The Hebrew University of Jerusalem. Jerusalem. A variety of mutants which are resistant to triazine - and urea - classes of herbicides have been isolated in the cyanobacterium Synechococcus R2.

All the mutants that have been analyzed, show some cross-resistance to different herbicides suggesting that these herbicides share a common binding site in photosystem II.

Three psbA genes have been identified in Synechococcus R2. The psbA-copy I gene was cloned from three mutants and used in DNA-mediated genetic transformation. It was found that in all three mutants this gene could transfer the mutation for herbicide resistance indicating that this gene codes for the herbicide resistant protein.

Isolation and Characterization of Herbicide Resistant Mutants in the Cyanobacterium Synechococcus R2

A variety of mutants which are resistant to triazine - and urea - classes of herbicides have been isolated in the cyanobacterium Synechococcus R2.

All the mutants that have been analyzed, show some cross-resistance to different herbicides suggesting that these herbicides share a common binding site in photosystem II.

Three psbA genes have been identified in Synechococcus R2. The psbA-copy I gene was cloned from three mutants and used in DNA-mediated genetic transformation. It was found that in all three mutants this gene could transfer the mutation for herbicide resistance indicating that this gene codes for the herbicide resistant protein.