Role of monocarboxylate transporters in human cancers: state of the art

Monocarboxylate transporters (MCTs) belong to the SLC16 gene family, presently composed by 14 members. MCT1-MCT4 are proton symporters, which mediate the transmembrane transport of pyruvate, lactate and ketone bodies. The role of MCTs in cell homeostasis has been characterized in detail in normal tissues, however, their role in cancer is still far from understood. Most solid tumors are known to rely on glycolysis for energy production and this activity leads to production of important amounts of lactate, which are exported into the extracellular milieu, contributing to the acidic microenvironment. In this context, MCTs will play a dual role in the maintenance of the hyper-glycolytic acid-resistant phenotype of cancer, allowing the maintenance of the high glycolytic rates by performing lactate efflux, and pH regulation by the co-transport of protons. Thus, they constitute attractive targets for cancer therapy, which have been little explored. Here we review the literature on the role of MCTs in solid tumors in different locations, such as colon, central nervous system, breast, lung, gynecologic tract, prostate, stomach, however, there are many conflicting results and in most cases there are no functional studies showing the dependence of the tumors on MCT expression and activity. Additional studies on MCT expression in other tumor types, confirmation of the results already published as well as additional functional studies are needed to deeply understand the role of MCTs in cancer maintenance and aggressiveness.     

Gene cloning and functional characterization of four novel antimicrobial-like peptides from scorpions of the family Vaejovidae

From the cDNA libraries made from the venom glands of two scorpions belonging to the Vaejovidae family, four different putative non disulfide-bridged antimicrobial peptides were identified: VmCT1 and VmCT2 from Vaejovis mexicanus smithi plus VsCT1 and VsCT2 from Vaejovis subcristatus. These short peptides (with only 13 amino acid residues each) share important amino acid sequence similarities among themselves and with other reported antimicrobial peptides, but their biological activities vary dramatically. This communication reports the cloning, chemical synthesis and characterization of these peptides. Two peptides, VmCT1 and VmCT2 showed broad-spectrum antibacterial activity with minimum inhibitory concentrations MICs in the range of 5-25 μM and 10-20 μM respectively, whereas their hemolytic activity at these concentrations was low. Structure-function relationships that might determine the differences in activities are discussed.     

Detection of microRNA Expression in Human Peripheral Blood Microvesicles

Background

MicroRNAs (miRNA) are small non-coding RNAs that regulate translation of mRNA and protein. Loss or enhanced expression of miRNAs is associated with several diseases, including cancer. However, the identification of circulating miRNA in healthy donors is not well characterized. Microvesicles, also known as exosomes or microparticles, circulate in the peripheral blood and can stimulate cellular signaling. In this study, we hypothesized that under normal healthy conditions, microvesicles contain miRNAs, contributing to biological homeostasis.

Methodology/Principal Findings

Microvesicles were isolated from the plasma of normal healthy individuals. RNA was isolated from both the microvesicles and matched mononuclear cells and profiled for 420 known mature miRNAs by real-time PCR. Hierarchical clustering of the data sets indicated significant differences in miRNA expression between peripheral blood mononuclear cells (PBMC) and plasma microvesicles. We observed 71 miRNAs co-expressed between microvesicles and PBMC. Notably, we found 33 and 4 significantly differentially expressed miRNAs in the plasma microvesicles and mononuclear cells, respectively. Prediction of the gene targets and associated biological pathways regulated by the detected miRNAs was performed. The majority of the miRNAs expressed in the microvesicles from the blood were predicted to regulate cellular differentiation of blood cells and metabolic pathways. Interestingly, a select few miRNAs were also predicted to be important modulators of immune function.

Conclusions

This study is the first to identify and define miRNA expression in circulating plasma microvesicles of normal subjects. The data generated from this study provides a basis for future studies to determine the predictive role of peripheral blood miRNA signatures in human disease and will enable the definition of the biological processes regulated by these miRNA.     

Photoprotective implications of leaf variegation in E. dens-canis L. and P. officinalis L

Variegated leaves occur rarely in nature, but there are some species, primarily in the forest understory, that possess this characteristic. We recently studied two variegated plants: Erytronium dens-canis L., which is characterised by a pattern of red patches and Pulmonaria officinalis L., with light green spots. These non-green areas could attenuate light reaching mesophyll cells with respect to green sections. The aim of the study was to verify whether such red and light green parts are more photoprotected than green ones and if this trait could be of adaptive value. Red patches in E. dens-canis were due to a single layer of red cells in the upper parenchyma, which accumulated anthocyanins. Light green spots in P. officinalis were caused by the presence of loosely arranged cells instead of a well-established layer of packed cells in the palisade parenchyma. Chlorophyll fluorescence imaging was performed under light treatment, showing a greater decrease of photochemical efficiency in red and light green patches than in green sections. Differences in the extent of photochemical efficiency among patches were not attributable to different activation of the xanthophyll cycle. These observations failed to confirm our initial hypothesis, but they questioned the physiological reason for this higher sensitivity in red and light green patches of photosynthetic tissues. Chlorophyll fluorescence imaging was therefore performed in the field. The same pattern of photochemical efficiency was maintained only in E. dens-canis. The current results demonstrate that in both species the benefits of variegation, if any, are different from enhanced photosynthetic performance.     

Transthyretin interacts with metallothionein 2

Transthyretin (TTR) is a 55 kDa homotetrameric protein known for the transport of thyroxine and the indirect transportation of retinol. Within the central nervous system, TTR is primary synthesized and secreted into the cerebral spinal fluid by the choroid plexus (CP), whereas most TTR in the systemic circulation is produced and secreted by the liver. TTR is involved in two types of amyloid disease, the senile systemic amyloidosis and the familial amyloidotic polyneuropathy. TTR has also been implicated in the sequestration of amyloid beta peptide (Abeta), preventing its deposition. To explore other biological roles for TTR, we searched for protein-protein interactions using the yeast two-hybrid system with the full-length human TTR cDNA as bait. We found a novel interaction between TTR and metallothionein 2 (MT2) in human liver. This interaction was confirmed by competition binding assays, co-immunoprecipitation, cross-linking, and Western blotting experiments. Binding studies using MT1 showed a saturable specific interaction with TTR with a Kd of 244.8 +/- 44.1 nM. Western blotting experiments revealed a TTR-MT1/2 protein complex present in rat CP and kidney tissue extracts. Immunofluorescence experiments, in CP primary cell cultures and in CP paraffin sections, showed co-localization of TTR and MT1/2 in the cytoplasm of epithelial CP cells and localization of MT1/2 in the endoplasmic reticulum. Moreover, dot blot immunoassays of rat CSF provided the first evidence, to our knowledge, of circulating metallothionein in CSF. Taken together, we suggest that TTR-MT1/2 complexes may be functionally significant not only in healthy conditions but also in Abeta deposition in Alzheimer disease, thereby providing a novel potential therapeutic target.     

Phospholipin, a novel heterodimeric phospholipase A2 from Pandinus imperator scp6pion venom.

The primary structure of a phospholipase A2, with unique structural and functional characteristics, was determined. The large subunit has 108 amino acid residues, linked by a disulfide bridge to the small subunit, which contains 17 residues. Its gene was cloned from a cDNA library. The nucleotide sequence showed that the same RNA messenger encodes both subunits, separated only by a pentapeptide, that is processed during maturation.     

Dynamics of the α-tocopherol pool as affected by external (environmental) and internal (leaf age) factors in Buxus sempervirens leaves

The pools of photoprotective molecules respond to changes in the environmental conditions and sometimes to leaf ageing. We asked to what extent both factors contribute to the contents of α-tocopherol and xanthophyll cycle [V + A + Z (VAZ)] pigments. To address this question, we used boxtree ( Buxus sempervirens ) as model species because its leaves are long-lived and evergreen and are subjected to a succession of different stress conditions during their lifespan. In three age classes of sun and shade leaves of this species, seasonal changes in photoprotective compounds were followed during 15 months and a leaf age interval of 40 months was covered. As could be expected, VAZ and α-tocopherol pools increased in parallel during stress periods (summer and winter), but only VAZ recovered to the initial pools once stress disappeared. As a result, the basal α-tocopherol level increased linearly in a time-dependent manner that was also higher in sun leaves of this species when compared with shade leaves, and in fact, the rate of tocopherol increase was directly proportional to irradiance in another evergreen ( Laurus nobilis ). To study whether light dependency of tocopherol accumulation is observed in other species, we performed a literature survey that revealed that this age-dependent tocopherol increase was significant in sun leaves from 65% of the species for which age-dependent tocopherol changes have been reported, and it was on average 2.2-fold higher in sun leaves as compared with shade leaves. We conclude that there are two components in the α-tocopherol pool, one dynamic that responds to environmental changes and one age-related which increases linearly with time in a light-dependent manner. The physiological meaning of the latter remains obscure.     

Long-term effects of nitrate on lucerne (Medicago sativa L.) nitrogen fixation is not influenced by the denitrification status of the microsymbiont

Studies on the inhibitory effects of combined nitrogen on biological nitrogen fixation in legume crops have been usually carried out after short-term nitrate treatments at high concentrations. As these treatments are quite different from field conditions, a study was conducted to evaluate the effects of the continuous presence of nitrate (0, 1, 5 and 10 mM) throughout three months on lucerne (Medicago sativa L.). Plants were grown in a greenhouse with perlite as substrate and were inoculated with a denitrifying Sinorhizobium meliloti strain (102-F-51) and a non-denitrifying strain (102-F-65). During the first 60 days of growth, the highest nitrate treatment resulted in a complete inhibition of the main symbiotic parameters (nodule initiation and development and specific nitrogen fixation) in plants inoculated with either strain. However, after 3 months of growth in the presence of nitrate, this inhibition was partly abolished, with a high number of new functioning nodules being formed. Acetylene reduction activity (ARA) of these plants was 70% of the control plants. As this process was observed in plants nodulated with either strain, it is concluded that this was not related to the denitrifying ability of the strain, but is an intrinsic property of the lucerne nitrogen fixing system. As legume plants usually grow under natural field conditions in the continuous presence of nitrate, the ability to use simultaneously nitrate and atmospheric nitrogen could be of adaptive and agronomic importance. This revised version was published online in June 2006 with corrections to the Cover Date.     

Plant characterization of genetically modified maize hybrids MON-89Ø34-3 × MON-88Ø17-3, MON-89Ø34-3 × MON-ØØ6Ø3-6, and MON-ØØ6Ø3-6: alternatives for maize production in Mexico

Environmental risk assessment (ERA) of genetically modified (GM) crops is a process to evaluate whether the biotechnology trait(s) in a GM crop may result in increased pest potential or harm to the environment. In this analysis, two GM insect-resistant (IR) herbicide-tolerant maize hybrids (MON-89Ø34-3 × MON-88Ø17-3 and MON-89Ø34-3 × MON-ØØ6Ø3-6) and one herbicide-tolerant GM hybrid (MON-ØØ6Ø3-6) were compared with conventional maize hybrids of similar genetic backgrounds. Two sets of studies, Experimental Phase and Pilot Phase, were conducted across five ecological regions (ecoregions) in Mexico during 2009–2013, and data were subject to meta-analysis. Results from the Experimental Phase studies, which were used for ERA, indicated that the three GM hybrids were not different from conventional maize for early stand count, days-to-silking, days-to-anthesis, root lodging, stalk lodging, or final stand count. Statistically significant differences were observed for seedling vigor, ear height, plant height, grain moisture, and grain yield, particularly in the IR hybrids; however, none of these phenotypic differences are expected to contribute to a biological or ecological change that would result in an increased pest potential or ecological risk when cultivating these GM hybrids. Overall, results from the Experimental Phase studies are consistent with those from other world regions, confirming that there are no additional risks compared to conventional maize. Results from Pilot Phase studies indicated that, compared to conventional maize hybrids, no differences were detected for the agronomic and phenotypic characteristics measured on the three GM maize hybrids, with the exception of grain moisture and grain yield in the IR hybrids. Since MON-89Ø34-3 × MON-88Ø17-3 and MON-89Ø34-3 × MON-ØØ6Ø3-6 confer resistance to target insect pests, they are an alternative for farmers in Mexico to protect the crop from insect damage. Additionally, the herbicide tolerance conferred by all three GM hybrids enables more cost-effective weed management.