Apoptosis and inactivation of the PI3-kinase pathway by tetrocarcin A in breast cancers

Metabolomic and genomic insights into Micromonospora carbonacea subsp. caeruleus for anti-colorectal compound

Cancer is a predominant contributor to global morbidity and mortality, affecting populations worldwide. Marine Micromonospora species have been identified as significant sources of anticancer compounds. This work aimed to perform a polyphasic approach of isolated strain and conduct comparative metabolomic and genomic analyses to identify compounds with anticancer activity. The study utilized a polyphasic approach on isolated strains for anticancer compound identification. Taxonomic analysis of strain 2MTK254 revealed unique pigment and fatty acid patterns, designating it as a novel Micromonospora carbonacea subsp. caeruleus. Its crude extract displayed significant anti-colorectal activity (66.03% inhibition). Molecular network analysis classified metabolites into eight classes, highlighting a polycyclic tetramate macrolactams (PTMs) compound (P1, C29H38N2O4) with 99.31% inhibitory activity against HCT-116 cell lines (IC50 at 0.125 µM). Genome analysis identified 32 biosynthetic gene clusters (BGCs), including unique PTMs BGCs (83% similarity) linked to the P1 compound. Thus, M. carbonacea subsp. caeruleus 2MTK254 holds promise as a source of novel PTMs with anti-colorectal cancer potential. KEY POINTS: • A novel strain of Micromonospora carbonacea subsp. caeruleus 2MTK254 was isolated in Thailand • A new polycyclic tetramate macrolactam (PTM) with anticancer activity was identified in 2MTK254 • The genome of 2MTK254 has unique secondary metabolite gene clusters.

SF3B1 thermostability as an assay for splicing inhibitor interactions

The spliceosome protein, SF3B1, is associated with U2 snRNP during early spliceosome assembly for pre-mRNA splicing. Frequent somatic mutations in SF3B1 observed in cancer necessitates the characterization of its role in identifying the branchpoint adenosine of introns. Remarkably, SF3B1 is the target of three distinct natural product drugs, each identified by their potent anti-tumor properties. Structural studies indicate that SF3B1 conformational flexibility is functionally important, and suggest that drug binding blocks the transition to a closed state of SF3B1 required for the next stage of spliceosome assembly. This model is confounded, however, by the antagonistic property of an inactive herboxidiene analog. In this study, we established an assay for evaluating the thermostability of SF3B1 present in the nuclear extract preparations employed for in vitro splicing studies, to investigate inhibitor interactions with SF3B1 in a functional context. We show that both active and antagonistic analogs of natural product inhibitors affect SF3B1 thermostability, consistent with binding alone being insufficient to impair SF3B1 function. Surprisingly, SF3B1 thermostability differs among nuclear extract preparations, likely reflecting its conformational status. We also investigated a synthetic SF3B1 ligand, WX-02-23, and found that it increases SF3B1 thermostability and interferes with in vitro splicing by a mechanism that strongly resembles the activity of natural product inhibitors. We propose that altered SF3B1 thermostability can serve as an indicator of inhibitor binding to complement functional assays of their general effect on splicing. It may also provide a means to investigate the factors that influence SF3B1 conformation.

Micromonospora: A Prolific Source of Bioactive Secondary Metabolites with Therapeutic Potential

Micromonospora, one of the most important actinomycetes genera, is well-known as the treasure trove of bioactive secondary metabolites (SMs). Herein, together with an in-depth genomic analysis of the reported Micromonospora strains, all SMs from this genus are comprehensively summarized, containing structural features, bioactive properties, and mode of actions as well as their biosynthetic and chemical synthesis pathways. The perspective enables a detailed view of Micromonospora-derived SMs, which will enrich the chemical diversity of natural products and inspire new drug discovery in the pharmaceutical industry.

The genus Micromonospora as a model microorganism for bioactive natural product discovery

This review covers the development of the genus Micromonospora as a model for natural product research and the timeline of discovery progress from the classical bioassay-guided approaches through the application of genome mining and genetic engineering techniques that target specific products. It focuses on the reported chemical structures along with their biological activities and the synthetic and biosynthetic studies they have inspired. This survey summarizes the extraordinary biosynthetic diversity that can emerge from a widely distributed actinomycete genus and supports future efforts to explore under-explored species in the search for novel natural products.

Marine Spirotetronates: Biosynthetic Edifices That Inspire Drug Discovery

Spirotetronates are actinomyces-derived polyketides that possess complex structures and exhibit potent and unexplored bioactivities. Due to their anticancer and antimicrobial properties, they have potential as drug hits and deserve further study. In particular, abyssomicin C and tetrocarcin A have shown significant promise against antibiotic-resistant S. aureus and tuberculosis, as well as for the treatment of various lymphomas and solid tumors. Improved synthetic routes to these compounds, particularly the class II spirotetronates, are needed to access sufficient quantities for structure optimization and clinical applications.

Natural compound Tetrocarcin-A downregulates Junctional Adhesion Molecule-A in conjunction with HER2 and inhibitor of apoptosis proteins and inhibits tumor cell growth

Overexpression of the tight junction protein Junctional Adhesion Molecule-A (JAM-A) has been linked to aggressive disease in breast and other cancers, but JAM-targeting drugs remain elusive. Screening of a natural compound library identified the antibiotic Tetrocarcin-A as a novel downregulator of JAM-A and human epidermal growth factor receptor-2 (HER2) protein expression in breast cancer cells. Lysosomal inhibition partially rescued the downregulation of JAM-A and HER2 caused by Tetrocarcin-A, and attenuated its cytotoxic activity. Tetrocarcin-A treatment or JAM-A silencing reduced AKT and ERK phosphorylation, inhibited c-FOS phosphorylation at Threonine-232 (its transcriptional regulation site), inhibited nuclear localization of c-FOS, and downregulated expression of the inhibitor of apoptosis proteins (IAP). This was accompanied by Tetrocarcin-A-induced caspase-dependent apoptosis. To begin evaluating the potential clinical relevance of our findings, we extended our studies to other models. Encouragingly, Tetrocarcin-A downregulated JAM-A expression and caused cytotoxicity in primary breast cells and lung cancer stem cells, and inhibited the growth of xenografts in a semi-in vivo model involving invasion across the chicken egg chorioallantoic membrane. Taken together, our data suggest that Tetrocarcin-A warrants future evaluation as a novel cancer therapeutic by virtue of its ability to downregulate JAM-A expression, reduce tumorigenic signaling and induce apoptosis.

A novel RON splice variant lacking exon 2 activates the PI3K/AKT pathway via PTEN phosphorylation in colorectal carcinoma cells

Abnormal expression of the Recepteur d'Origine Nantais (RON) receptor tyrosine kinase is accompanied by the generation of multiple splice or truncated variants, which mediate many critical cellular functions that contribute to tumor progression and metastasis. Here, we report a new RON splice variant in the human colorectal cancer (CRC) cell line HT29. This variant is a 165 kda protein generated by alternative pre-mRNA splicing that eliminates exon 2, causing an in-frame deletion of 63 amino acids in the extracellular domain of the RON β chain. The deleted transcript was a single chain expressed in the intracellular compartment. Although it lacked tyrosine phosphorylation activity, the RONΔ165E2 variant could phosphorylate phosphatase and tensin homolog (PTEN), thereby activating the PI3K/AKT pathway. In addition, in vitro and in vivo experiments showed that the RONΔ165E2 promoted cell migration and tumor growth. Finally, in an investigation of 67 clinical CRC samples, the variant was highly expressed in about 58% of the samples, and was positively correlated with the invasive depth of the tumor (P < 0.05). These results demonstrate that the novel RONΔ165E2 variant promoted tumor progression while activating the PI3K/AKT pathway via PTEN phosphorylation.

Modulating splicing with small molecular inhibitors of the spliceosome

Small molecule inhibitors that target components of the spliceosome have great potential as tools to probe splicing mechanism and dissect splicing regulatory networks in cells. These compounds also hold promise as drug leads for diseases in which splicing regulation plays a critical role, including many cancers. Because the spliceosome is a complicated and dynamic macromolecular machine comprised of many RNA and protein components, a variety of compounds that interfere with different aspects of spliceosome assembly is needed to probe its function. By screening chemical libraries with high-throughput splicing assays, several labs have added to the collection of splicing inhibitors, although the mechanistic insight into splicing yielded from the initial compound hits is somewhat limited so far. In contrast, SF3B1 inhibitors stand out as a great example of what can be accomplished with small molecule tools. This group of compounds were first discovered as natural products that are cytotoxic to cancer cells, and then later shown to target the core spliceosome protein SF3B1. The inhibitors have since been used to uncover details of SF3B1 mechanism in the spliceosome and its impact on gene expression in cells. Continuing structure activity relationship analysis of the compounds is also making progress in identifying chemical features key to their function, which is critical in understanding the mechanism of SF3B1 inhibition. The knowledge is also important for the design of analogs with new and useful features for both splicing researchers and clinicians hoping to exploit splicing as pressure point to target in cancer therapy. WIREs RNA 2017, 8:e1381. doi: 10.1002/wrna.1381 For further resources related to this article, please visit the WIREs website.

Tetrocarcins N and O, glycosidic spirotetronates from a marine-derived Micromonospora sp. identified by PCR-based screening

Two new glycosidic spirotetronate antibiotics, tetrocarcins N (1) and O (2), were isolated and identified from the marine-derived Micromonospora sp. 5-297 using a PCR-based genetic screening method targeting the dTDP-glucose-4,6-dehydratase gene.

Natural products containing 'decalin' motif in microorganisms

Microorganisms are well-known producers of a wide variety of bioactive compounds that are utilized not only for their primary metabolism but also for other purposes such as defense, detoxification, or communication with other micro- and macro-organisms. Natural products containing a 'decalin ring' occur often in microorganisms. They exhibit diverse and remarkable biological activities, including antifungal, antibacterial, anticancer and immunosuppressive activities, to name a few. This review surveys the natural decalin-type compounds that have been isolated from microorganisms, with emphasis on both chemical and biological implications. Total syntheses of some important decalin moiety-containing natural products are also highlighted.

Spirotetronate polyketides as leads in drug discovery

The discovery of chlorothricin (1) defined a new family of microbial metabolites with potent antitumor antibiotic properties collectively referred to as spirotetronate polyketides. These microbial metabolites are structurally distinguished by the presence of a spirotetronate motif embedded within a macrocyclic core. Glycosylation at the periphery of this core contributes to the structural complexity and bioactivity of this motif. The spirotetronate family displays impressive chemical structures, potent bioactivities, and significant pharmacological potential. This review groups the family members based on structural and biosynthetic considerations and summarizes synthetic and biological studies that aim to elucidate their mode of action and explore their pharmacological potential.

The SARS-coronavirus membrane protein induces apoptosis via interfering with PDK1-PKB/Akt signalling

A number of viral gene products are capable of inducing apoptosis by interfering with various cellular signalling cascades. We previously reported the pro-apoptotic property of the SARS-CoV (severe acute respiratory syndrome coronavirus) M (membrane)-protein and a down-regulation of the phosphorylation level of the cell-survival protein PKB (protein kinase B)/Akt in cells expressing M-protein. We also showed that overexpression of PDK1 (3-phosphoinositide-dependent protein kinase 1), the immediate upstream kinase of PKB/Akt, suppressed M-induced apoptosis. This illustrates that M-protein perturbs the PDK1 and PKB/Akt cell survival signalling pathway. In the present study, we demonstrated that the C-terminus of M-protein interacts with the PH (pleckstrin homology) domain of PDK1. This interaction disrupted the association between PDK1 and PKB/Akt, and led to down-regulation of PKB/Akt activity. This subsequently reduced the level of the phosphorylated forkhead transcription factor FKHRL1 and ASK (apoptosis signal-regulating kinase), and led to the activation of caspases 8 and 9. Altogether, our data demonstrate that the SARS-CoV M-protein induces apoptosis through disrupting the interaction of PDK1 with PKB/Akt, and this causes the activation of apoptosis. Our work highlights that the SARS-CoV M protein is highly pro-apoptotic and is capable of simultaneously inducing apoptosis via initiating caspases 8 and 9. Preventing the interaction between M-protein and PDK1 is a plausible therapeutic approach to target the pro-apoptotic property of SARS-CoV.

Far beyond the usual biomarkers in breast cancer: a review

Research investigating biomarkers for early detection, prognosis and the prediction of treatment responses in breast cancer is rapidly expanding. However, no validated biomarker currently exists for use in routine clinical practice, and breast cancer detection and management remains dependent on invasive procedures. Histological examination remains the standard for diagnosis, whereas immunohistochemical and genetic tests are utilized for treatment decisions and prognosis determinations. Therefore, we conducted a comprehensive review of literature published in PubMed on breast cancer biomarkers between 2009 and 2013. The keywords that were used together were breast cancer, biomarkers, diagnosis, prognosis and drug response. The cited references of the manuscripts included in this review were also screened. We have comprehensively summarized the performance of several biomarkers for diagnosis, prognosis and predicted drug responses of breast cancer. Finally, we have identified 15 biomarkers that have demonstrated promise in initial studies and several miRNAs. At this point, such biomarkers must be rigorously validated in the clinical setting to be translated into clinically useful tests for the diagnosis, prognosis and prediction of drug responses of breast cancer.

Biomedical techniques in translational studies: The journey so far

Biomedical techniques have wide clinical application in many fields of medicine such as oncology, rheumatology, immunology, genomics, cardiology and diagnostics; among others. This has been made possible with the use of genetic engineering and a number of techniques like Immunohistochemistry (IHC), Fluorescent Microscopy, Cell Culture, Genetically Modified (GM) Cells, Monoclonal Antibodies (MAbs), Polymerase Chain Reaction (PCR) and Western blotting. The aim of this literature review is to explore the foundations and bases of the commonly used biomedical techniques, as well as their applications in biomedical research and clinical medicine in general. This review also aims to shed some light on more recent advances in genetic engineering, especially in relation to genetically modified cells and use of monoclonal antibodies which have found more increasing use and relevance in genomics, oncology, rheumatology, immunology, cardiology as well as diagnostics, and have revolutionised patient care, while at the same time resulting in improved standard of health care. Unfortunately, some of these new techniques are associated with unwanted side effects which may pose a risk to the people they are actually intended for. Therefore, there is need for strict regulations and guidelines to control the use and implementation of some of these novel techniques.

Identification of compounds by high-content screening that induce cytoplasmic to nuclear localization of a fluorescent estrogen receptor α chimera and exhibit agonist or antagonist activity in vitro

We have completed a robust high-content imaging screen for novel estrogen receptor α (ERα) agonists and antagonists by quantitation of cytoplasmic to nuclear translocation of an estrogen receptor chimera in 384-well plates. The screen was very robust, with Z' values >0.7 and coefficients of variation (CV) <5%. The screen utilized a stably transfected green fluorescent protein-tagged glucocorticoid/estrogen receptor (GFP-GRER) chimera, which consisted of the N-terminus of the glucocorticoid receptor fused to the human ERα ligand binding domain. The GFP-GRER exhibited cytoplasmic localization in the absence of ERα ligands and translocated to the nucleus in response to stimulation with ERα agonists and antagonists. The BD Pathway 435 imaging system was used for image acquisition, analysis of translocation dynamics, and cytotoxicity measurements. We screened 224,891 samples from our synthetic, pure natural product libraries, prefractionated natural product extracts library, and crude natural product extracts library, which produced a 0.003% hit rate. In addition to identifying several known ER ligands, five compounds were discovered that elicited significant activity in the screen. Transactivation potential studies demonstrated that two hit compounds behave as agonists, while three compounds elicited antagonist activity in MCF-7 cells.

Phosphatase and tensin homologue deleted on chromosome 10

Phosphatase and tensin homologue deleted on chromosome 10 (PTEN) is a tumor suppressor gene deleted or mutated in many human cancers such as glioblastoma, spinal tumors, prostate, bladder, adrenals, thyroid, breast, endometrium, and colon cancers. They result from loss of heterozygosity (LOH) for the PTEN gene on chromosome 10q23. Previous studies reported that various drugs, chemicals, and foods can up-regulate PTEN mRNA and protein expression in different cell lines, and they may be useful in the future prevention and/or treatment of these cancers. PTEN has also been observed to have prognostic significance and is gradually being accepted as an independent prognostic factor. This will help in monitoring disease progression and/or recurrence, with a view to improving treatment outcomes and reducing the associated morbidity and mortality from these cancers. Neprilysin (NEP) is a zinc-dependent metallopeptidase that cleaves and inactivates some biologically active peptides thus switching off signal transduction at the cell surface. Decreased NEP expression in many cancers has been reported. NEP can form a complex with PTEN and enhance PTEN recruitment to the plasma membrane as well as stabilize its phosphatase activity. MicroRNA-21 (miR-21) post-transcriptionally down-regulates the expression of PTEN and stimulates growth and invasion in non-small cell lung cancer (NSCLC) (lung Ca), suggesting that this may be a potential therapeutic target in the future treatment of NSCLC. PTEN is a tumor suppressor gene associated with many human cancers. This has diagnostic, therapeutic, and prognostic significance in the management of many human cancers, and may be a target for new drug development in the future.

A high-throughput splicing assay identifies new classes of inhibitors of human and yeast spliceosomes

The spliceosome is the macromolecular machine responsible for pre-mRNA splicing, an essential step in eukaryotic gene expression. During splicing, myriad subunits join and leave the spliceosome as it works on the pre-mRNA substrate. Strikingly, there are very few small molecules known to interact with the spliceosome. Splicing inhibitors are needed to capture transient spliceosome conformations and probe important functional components. Such compounds may also have chemotherapeutic applications, as links between splicing and cancer are increasingly uncovered. To identify new splicing inhibitors, we developed a high-throughput assay for in vitro splicing using a reverse transcription followed by quantitative PCR readout. In a pilot screen of 3080 compounds, we identified three small molecules that inhibit splicing in HeLa extract by interfering with different stages of human spliceosome assembly. Two of the compounds similarly affect spliceosomes in yeast extracts, suggesting selective targeting of conserved components. By examining related molecules, we identified chemical features required for the activity of two of the splicing inhibitors. In addition to verifying our assay procedure and paving the way to larger screens, these studies establish new compounds as chemical probes for investigating the splicing machinery.

Features of the reversible sensitivity-resistance transition in PI3K/PTEN/AKT signalling network after HER2 inhibition

Systems biology approaches that combine experimental data and theoretical modelling to understand cellular signalling network dynamics offer a useful platform to investigate the mechanisms of resistance to drug interventions and to identify combination drug treatments. Extending our work on modelling the PI3K/PTEN/AKT signalling network (SN), we analyse the sensitivity of the SN output signal, phospho-AKT, to inhibition of HER2 receptor. We model typical aberrations in this SN identified in cancer development and drug resistance: loss of PTEN activity, PI3K and AKT mutations, HER2 overexpression, and overproduction of GSK3β and CK2 kinases controlling PTEN phosphorylation. We show that HER2 inhibition by the monoclonal antibody pertuzumab increases SN sensitivity, both to external signals and to changes in kinetic parameters of the proteins and their expression levels induced by mutations in the SN. This increase in sensitivity arises from the transition of SN functioning from saturation to non-saturation mode in response to HER2 inhibition. PTEN loss or PIK3CA mutation causes resistance to anti-HER2 inhibitor and leads to the restoration of saturation mode in SN functioning with a consequent decrease in SN sensitivity. We suggest that a drug-induced increase in SN sensitivity to internal perturbations, and specifically mutations, causes SN fragility. In particular, the SN is vulnerable to mutations that compensate for drug action and this may result in a sensitivity-to-resistance transition. The combination of HER2 and PI3K inhibition does not sensitise the SN to internal perturbations (mutations) in the PI3K/PTEN/AKT pathway: this combination treatment provides both synergetic inhibition and may prevent the SN from acquired mutations causing drug resistance. Through combination inhibition treatments, we studied the impact of upstream and downstream interventions to suppress resistance to the HER2 inhibitor in the SN with PTEN loss. Comparison of experimental results of PI3K inhibition in the PTEN upstream pathway with PDK1 inhibition in the PTEN downstream pathway shows that upstream inhibition abrogates resistance to pertuzumab more effectively than downstream inhibition. This difference in inhibition effect arises from the compensatory mechanism of an activation loop induced in the downstream pathway by PTEN loss. We highlight that drug target identification for combination anti-cancer therapy needs to account for the mutation effects on the upstream and downstream pathways.

Combined structural and functional investigation of a C-3''-ketoreductase involved in the biosynthesis of dTDP-L-digitoxose

l-Digitoxose is an unusual dideoxysugar found attached to various pharmacologically active natural products, including the antitumor antibiotic tetrocarcin A and the antibiotics kijanimicin and jadomycin B. Six enzymes are required for its production starting from glucose 1-phosphate. Here we describe a combined structural and functional investigation of KijD10, an NADPH-dependent C-3''-ketoreductase that catalyzes the third step of l-digitoxose biosynthesis in the African soil-dwelling bacterium Actinomadura kijaniata. KijD10 belongs to the glucose-fructose oxidoreductase superfamily. For this investigation, both binary and ternary complexes of KijD10 were crystallized, and their structures were determined to 2.0 Å resolution or better. On the basis of these high-resolution structures, two potential active site acids were identified, Lys 102 and Tyr 186. These residues were individually mutated and the resultant proteins investigated both kinetically and structurally. The Y186F mutant protein demonstrated significant catalytic activity, and its structure was virtually identical to that of the wild-type enzyme except for the positioning of the nicotinamide ring. All lysine mutations, on the other hand, resulted in proteins with either abolished or drastically reduced catalytic activities. Structures for the K102A and K102E mutant proteins were determined and showed that the abrogation of catalytic activity was not a result of large conformational changes. Taken together, these data suggest that Lys 102 donates a proton to the C-3'' keto group during the reaction and that Tyr 186 serves only an auxiliary role. This is in contrast to that proposed for glucose-fructose oxidoreductase and other family members in which the tyrosines, or in some cases similarly positioned histidines, are thought to play major catalytic roles.

The impact of PTEN regulation by CK2 on PI3K-dependent signaling and leukemia cell survival

Gene alterations affecting elements of PI3K signaling pathway do not appear to be sufficient to explain the extremely high frequency of PI3K signaling hyperactivation in leukemia. It has been known for long that PTEN phosphorylation at the C-terminal tail, in particular by CK2, contributes to the stabilization and simultaneous inhibition of this critical tumor suppressor. However, direct evidence of the involvement of this mechanism in cancer has been gathered only recently. It is now known that CK2-mediated posttranslational, non-deleting, inactivation of PTEN occurs in T-ALL, CLL and probably other leukemias and solid tumors. To explore this knowledge for therapeutic purposes remains one of the challenges ahead.

Antitumor compounds from actinomycetes: from gene clusters to new derivatives by combinatorial biosynthesis

Covering: up to October 2008. Antitumor compounds produced by actinomycetes and novel derivatives generated by combinatorial biosynthesis are reviewed (with 318 references cited.) The different structural groups for which the relevant gene clusters have been isolated and characterized are reviewed, with a description of the strategies used for the generation of the novel derivatives and the activities of these compounds against tumor cell lines.

A cell-based high-throughput screen to identify synergistic TRAIL sensitizers

We have developed a high-throughput screen (HTS) to search for novel molecules that can synergize with TRAIL, thus promoting apoptosis of ACHN renal tumor cells in a combinatorial fashion. The HTS detects synthetic compounds and pure natural products that can pre-sensitize the cancer cells to TRAIL-mediated apoptosis, yet have limited toxicity on their own. We have taken into account the individual effects of the single agents, versus the combination, and have identified hits that are synergistic, synergistic-toxic, or additive when combined with TRAIL in promoting tumor cell death. Preliminary mechanistic studies indicate that a subset of the synergistic TRAIL sensitizers act very rapidly to promote cleavage and activation of caspase-8 following TRAIL binding. Caspase-8 is an apical enzyme that initiates programmed cell death via the extrinsic apoptotic pathway. Thus, these TRAIL sensitizers may potentially reduce resistance of tumor cells to TRAIL-mediated apoptosis. Two representative sensitizers were found to increase levels of p53 but did not inhibit the proteasome, suggesting that early DNA damage-sensing pathways may be involved in their mechanisms of action.

PTEN posttranslational inactivation and hyperactivation of the PI3K/Akt pathway sustain primary T cell leukemia viability

Mutations in the phosphatase and tensin homolog (PTEN) gene leading to PTEN protein deletion and subsequent activation of the PI3K/Akt signaling pathway are common in cancer. Here we show that PTEN inactivation in human T cell acute lymphoblastic leukemia (T-ALL) cells is not always synonymous with PTEN gene lesions and diminished protein expression. Samples taken from patients with T-ALL at the time of diagnosis very frequently showed constitutive hyperactivation of the PI3K/Akt pathway. In contrast to immortalized cell lines, most primary T-ALL cells did not harbor PTEN gene alterations, displayed normal PTEN mRNA levels, and expressed higher PTEN protein levels than normal T cell precursors. However, PTEN overexpression was associated with decreased PTEN lipid phosphatase activity, resulting from casein kinase 2 (CK2) overexpression and hyperactivation. In addition, T-ALL cells had constitutively high levels of ROS, which can also downmodulate PTEN activity. Accordingly, both CK2 inhibitors and ROS scavengers restored PTEN activity and impaired PI3K/Akt signaling in T-ALL cells. Strikingly, inhibition of PI3K and/or CK2 promoted T-ALL cell death without affecting normal T cell precursors. Overall, our data indicate that T-ALL cells inactivate PTEN mostly in a nondeletional, posttranslational manner. Pharmacological manipulation of these mechanisms may open new avenues for T-ALL treatment.

Cloning and characterization of the tetrocarcin A gene cluster from Micromonospora chalcea NRRL 11289 reveals a highly conserved strategy for tetronate biosynthesis in spirotetronate antibiotics

Tetrocarcin A (TCA), produced by Micromonospora chalcea NRRL 11289, is a spirotetronate antibiotic with potent antitumor activity and versatile modes of action. In this study, the biosynthetic gene cluster of TCA was cloned and localized to a 108-kb contiguous DNA region. In silico sequence analysis revealed 36 putative genes that constitute this cluster (including 11 for unusual sugar biosynthesis, 13 for aglycone formation, and 4 for glycosylations) and allowed us to propose the biosynthetic pathway of TCA. The formation of D-tetronitrose, L-amicetose, and L-digitoxose may begin with D-glucose-1-phosphate, share early enzymatic steps, and branch into different pathways by competitive actions of specific enzymes. Tetronolide biosynthesis involves the incorporation of a 3-C unit with a polyketide intermediate to form the characteristic spirotetronate moiety and trans-decalin system. Further substitution of tetronolide with five deoxysugars (one being a deoxynitrosugar) was likely due to the activities of four glycosyltransferases. In vitro characterization of the first enzymatic step by utilization of 1,3-biphosphoglycerate as the substrate and in vivo cross-complementation of the bifunctional fused gene tcaD3 (with the functions of chlD3 and chlD4) to Delta chlD3 and Delta chlD4 in chlorothricin biosynthesis supported the highly conserved tetronate biosynthetic strategy in the spirotetronate family. Deletion of a large DNA fragment encoding polyketide synthases resulted in a non-TCA-producing strain, providing a clear background for the identification of novel analogs. These findings provide insights into spirotetronate biosynthesis and demonstrate that combinatorial-biosynthesis methods can be applied to the TCA biosynthetic machinery to generate structural diversity.