David Rodríguez

Deubiquitinases in cancer: new functions and therapeutic options.

Deubiquitinases (DUBs) have fundamental roles in the ubiquitin system through their ability to specifically deconjugate ubiquitin from targeted proteins. The human genome encodes at least 98 DUBs, which can be grouped into 6 families, reflecting the need for specificity in their function. The activity of these enzymes affects the turnover rate, activation, recycling and localization of multiple proteins, which in turn is essential for cell homeostasis, protein stability and a wide range of signaling pathways. Consistent with this, altered DUB function has been related to several diseases, including cancer. Thus, multiple DUBs have been classified as oncogenes or tumor suppressors because of their regulatory functions on the activity of other proteins involved in tumor development. Therefore, recent studies have focused on pharmacological intervention on DUB activity as a rationale to search for novel anticancer drugs. This strategy may benefit from our current knowledge of the physiological regulatory mechanisms of these enzymes and the fact that growth of several tumors depends on the normal activity of certain DUBs. Further understanding of these processes may provide answers to multiple remaining questions on DUB functions and lead to the development of DUB-targeting strategies to expand the repertoire of molecular therapies against cancer.

POT1 mutations cause telomere dysfunction in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is the most frequent leukemia in adults. We have analyzed exome sequencing data from 127 individuals with CLL and Sanger sequencing data from 214 additional affected individuals, identifying recurrent somatic mutations in POT1 (encoding protection of telomeres 1) in 3.5% of the cases, with the frequency reaching 9% when only individuals without IGHV@ mutations were considered. POT1 encodes a component of the shelterin complex and is the first member of this telomeric structure found to be mutated in human cancer. Somatic mutation of POT1 primarily occurs in gene regions encoding the two oligonucleotide-/oligosaccharide-binding (OB) folds and affects key residues required to bind telomeric DNA. POT1-mutated CLL cells have numerous telomeric and chromosomal abnormalities that suggest that POT1 mutations favor the acquisition of the malignant features of CLL cells. The identification of POT1 as a new frequently mutated gene in CLL may facilitate novel approaches for the clinical management of this disease.

Functional Analysis of OleY L-Oleandrosyl 3-O-Methyltransferase of the Oleandomycin Biosynthetic Pathway in Streptomyces antibioticus

Oleandomycin, a macrolide antibiotic produced by Streptomyces antibioticus, contains two sugars attached to the aglycon: L-oleandrose and D-desosamine. oleY codes for a methyltransferase involved in the biosynthesis of L-oleandrose. This gene was overexpressed in Escherichia coli to form inclusion bodies and in Streptomyces lividans, producing a soluble protein. S. lividans overexpressing oleY was used as a biotransformation host, and it converted the precursor L-olivosyl-erythronolide B into its 3-O-methylated derivative, L-oleandrosyl-erythronolide B. Two other monoglycosylated derivatives were also substrates for the OleY methyltransferase: L-rhamnosyl- and L-mycarosyl-erythronolide B. OleY methyltransferase was purified yielding a 43-kDa single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The native enzyme showed a molecular mass of 87 kDa by gel filtration chromatography, indicating that the enzyme acts as a dimer. It showed a narrow pH range for optimal activity, and its activity was clearly stimulated by the presence of several divalent cations, being maximal with Co(2+). The S. antibioticus OleG2 glycosyltransferase is proposed to transfer L-olivose to the oleandolide aglycon, which is then converted into L-oleandrose by the OleY methyltransferase. This represents an alternative route for L-oleandrose biosynthesis from that in the avermectin producer Streptomyces avermitilis, in which L-oleandrose is transferred to the aglycon by a glycosyltransferase.

Iodoarylation Reactions of Allenes: Inter‐ and Intramolecular Processes

Polar addition reactions to allenes are well established and various processes involving this mechanistic pathway are known. The reaction of arenes with electrophiles is a conceptually powerful method to functionalize C H bonds. Therefore, the feasibility of using carbon-based electrophiles, in reactions with arenes, was soon recognized as an entry for C C bond formation. The Friedel–Crafts alkylation of arenes with alkenes is a relevant example. Nevertheless, the related alkenylation reaction involving alkynes was more sluggishly developed and only recent advances involving metal-catalyzed transformations have made this target practicable. The reaction of arenes with the transitory species generated upon interaction of iodonium ions with alkenes or alkynes represents a powerful route for preparing cyclic compounds involving related C C bondforming processes. Moreover, examples of Friedel–Crafts arylation reactions of allenes are rare. Recent advances involve formally related processes using precious metal catalysts and are mainly intramolecular transformations. Herein, we report the first solid evidence on the use of iodonium ions as the trigger for an unprecedented b iodoallylation of a C H bond of an arene by reaction with an allene (Scheme 1). Both, intraand intermolecular processes are presented. The iodonium approach would complement the requirements of the powerful carbometallation reaction of allenes. The intermolecular process requires a substituted arene, whereas in the intramolecular process the assembled skeleton is endowed with further functionality. Interestingly, the application of this technology to ring elaboration enables a direct entry into the 2-iodo-1,4-dihydronaphthalene core, an elusive and valuable building block for crosscoupling chemistry that will also be highlighted. The iodonium-promoted carbocyclization was first tested on 2,3-butadienyl benzene (1 a), a demanding model substrate considering that the participation of an electronically activated arene is mandatory in most allene hydroarylation reactions. Several iodinating reagents were tested in an effort to synthesize 2-iodo-1,4-dihydronaphthalene (2 a) through a straightforward iodoarylation strategy. Some key experiments are outlined in Table 1.

Frequent somatic mutations in components of the RNA processing machinery in chronic lymphocytic leukemia.

Frequent somatic mutations in components of the RNA processing machinery in chronic lymphocytic leukemia

The genomic landscape of chronic lymphocytic leukemia: clinical implications

A precise understanding of the genomic and epigenomic features of chronic lymphocytic leukemia (CLL) may benefit the study of the disease’s staging and treatment. While recent reports have shed some light on these aspects, several challenges need to be addressed before translating this research into clinical practice. Thus, even the best candidate driver genes display low mutational rates compared to other tumors. This means that a large percentage of cases do not display clear tumor-driving point mutations, or show candidate driving point mutations with no obvious biochemical relationship to the more frequently mutated genes. This genomic landscape probably reflects either an unknown underlying biochemical mechanism playing a key role in CLL or multiple biochemical pathways independently driving the development of this tumor. The elucidation of either scenario will have important consequences on the clinical management of CLL. Herein, we review the recent advances in the definition of the genomic landscape of CLL and the ongoing research to characterize the underlying biochemical events that drive this disease.

Purification and Characterization of a Monooxygenase Involved in the Biosynthetic Pathway of the Antitumor Drug Mithramycin

A monooxygenase encoded by the mtmOIV gene from the mithramycin gene cluster of Streptomyces argillaceus was purified 21-fold by a three-step purification procedure. This monooxygenase catalyzes the oxidative cleavage of the fourth ring of premithramycin B. The enzyme was dependent on NADPH and flavin adenine dinucleotide for activity with optimal pH at 9.5, and the K(m) values for NADPH and premithramycin B were 269.22 and 23.35 micro M, respectively. The reaction catalyzed by MtmOIV yields two possible isomers of the same basic shortened aliphatic chain molecule. One of the reaction products showed important biological activity, thus highlighting the importance of the cleavage of the fourth ring of the aglycon for biological activity.

Functional analysis of sucrase–isomaltase mutations from chronic lymphocytic leukemia patients

Next-generation sequencing techniques have emerged as powerful tools for the understanding of cancer genomes. In recent years, whole-exome and whole-genome sequencing strategies have enabled the annotation of a comprehensive mutation landscape of chronic lymphocytic leukemia (CLL), the most frequent leukemia in western countries. Several recurrently mutated genes have been identified, with a subset being validated as neoplastic drivers. Still, a main challenge remains for the differentiation between driver and passenger mutations among candidates as well as for the functional description of the newly discovered leukemogenic genes that could be utilized for personalized anti-tumor strategies. In this scenario, we have identified the metabolic enzyme sucrase-isomaltase (SI) as one of the most frequently mutated genes in a cohort of 105 CLL patients. Here, we demonstrate that these SI mutations result in loss of enzyme function by preventing the biosynthesis of catalytically competent SI at the cell surface. Transcriptome analyses of RNA from CLL patients with SI loss-of-function mutations have uncovered gene expression patterns that depict ample metabolic reprogramming, pinpointing SI as a putative player in the cancer-associated metabolic switch. These results highlight SI as a relevant target for clinical evaluation in future CLL studies.

Next-generation sequencing reveals the secrets of the chronic lymphocytic leukemia genome

The study of the detailed molecular history of cancer development is one of the most promising techniques to understand and fight this diverse and prevalent disease. Unfortunately, this history is as diverse as cancer itself. Therefore, even with next-generation sequencing techniques, it is not easy to distinguish significant (driver) from random (passenger) events. The International Cancer Genome Consortium (ICGC) was formed to solve this fundamental issue by coordinating the sequencing of samples from 50 different cancer types and/or sub-types that are of clinical and societal importance. The contribution of Spain in this consortium has been focused on chronic lymphocytic leukemia (CLL). This approach has unveiled new and unexpected events in the development of CLL. In this review, we introduce the approaches utilized by the consortium for the study of the CLL genome and discuss the recent results and future perspectives of this work.

MtmMII-mediated C-Methylation during Biosynthesis of the Antitumor Drug Mithramycin Is Essential for Biological Activity and DNA-Drug Interaction

The antitumor drug mithramycin consists of a polyketide chromophore glycosylated with a trisaccharide and a disaccharide. Two post-polyketide methylations take place during mithramycin biosynthesis. One of these methylations has been shown to be very relevant for biological activity, that is the introduction of a methyl group at aromatic C-7. We have purified to 282- fold the MtmMII methyltransferase involved in this reaction. The protein is a monomer, and results from kinetic studies were consistent with a model for the enzyme acting via a compulsory order mechanism. The enzyme showed high substrate specificity and was unable to operate on structurally closely related molecules. Structural predictions suggest that the molecule is integrated by two domains, an essentially all α-amino domain and an α/β-carboxyl domain displaying a variation of a Rossmann-fold containing the cofactor binding site. Although 7-demethyl-mithramycin did not show any biological activity, it was able to reach the nucleus of eukaryotic cells, with subsequent binding to DNA. Mithramycin and 7-demethylmithramycin were able to form similar complexes with Mg2+, although their respective DNA binding isotherms were very different. The dinucleotide binding model fit well the isotherms recorded for both compounds, predicting that the C-7 methyl group was essential for high affinity binding to specific GC and CG sequences. Considering previous structural studies, we propose that this effect is performed by positioning the group in the floor of the minor groove, allowing the interaction with the third sugar moiety of the trisaccharide, d-mycarose, which is involved in sequence selectivity.