Effects of branched chain alpha-ketoacids on the metabolism of isolated rat liver cells. I. Regulation of branched chain alpha-ketoacid metabolism.

alpha-Ketoisocaproate (ketoleucine) is shown to be metabolized to ketone bodies rapidly by isolated rat liver cells. Acetoacetate is the major end product and maximum rates were observed with 2 mM substrate. Studies with 2-tetradecylglycidic acid (an inhibitor of long chain fatty acid oxidation) showed that ketogenesis from alpha-ketoisocaproate and from endogenous fatty acids were additive. With alpha-ketoisocaproate present as soole substrate at 2 mM, leucine production was less than 10% of alpha-ketoisocaproate uptake and only 30% of the acetyl coenzyme A generated was oxidized in the citric acid cycle. Metabolism of alpha-ketoisocaproate was inhibited by fatty acids, alpha-ketoisovalerate, alpha-keto-beta-methylvalerate, and pyruvate. Oxidation of acetyl-CoA generated from alpha-ketoisocaproate was suppressed by oleate and by pyruvate, but was enhanced by lactate. Metabolism between the different branched chain alpha-ketoacids was mutually competitive. When alpha-ketoisocaproate (2 mM) was added in the presence of high pyruvate concentrations (4.4 mM), flux through pyruvate dehydrogenase was decreased, and the proportion of total pyruvate dehydrogenase in the active form (PDHa) also fell. With lactate as substrate, PDHa was only 25% of total activity and was little affected by addition of alpha-ketoisocaproate. These data suggest that enhanced oxidation of acetyl-CoA from alpha-ketoisocaproate by lactate addition is caused by a low activity of pyruvate dehydrogenase combined with increased flux through the citric acid cycle in response to the energy requirements for gluconeogenesis. However, acetyl-CoA generation from pyruvate is apparently insufficiently inhibited by alpha-ketoisocaproate to cause a diversion of acetyl-CoA formed during alpha-ketoisocaproate metabolism from ketone body formation to oxidation in the citric acid cycle. Measurements of the cell contents of CoASH, acetyl-CoA, acid-soluble acyl-CoA, and acid-insoluble fatty acyl-CoA indicated that when the branched chain alpha-ketoacids were added as sole substrate, their oxidation was limited at a step distal to the branched chain alpha-ketoacid dehydrogenase. Acid-soluble acyl-CoA derivatives were depleted after oleate addition in the presence of alpha-ketoisocaproate, suggesting an inhibition of the branched chain alpha-ketoacid dehydrogenase by the elevation of the mitochondrial NADH/NAD+ ratio observed during fatty acid oxidation. This effect was not observed in the presence of oleate and 2-tetradecylglycidic acid.     

Cloning and nucleotide sequence of celA1, and endo-beta-1,4-glucanase-encoding gene from Streptomyces halstedii JM8.

The celA1 gene encoding an endo-beta-1,4-glucanase from a mesophilic actinomycete, strain JM8, identified as Streptomyces halstedii, was cloned and expressed in S. lividans JI66. From the nucleotide sequence of a 1.7-kb DNA fragment we identified an open reading frame of 963 nucleotides encoding a protein of 321 amino acids, starting at TTG (instead of ATG). The Cel1 mature enzyme is a protein of 294 amino acids (after signal peptide cleavage) and can be included in the beta-glycanase family B (N. R. Gilkes, B. Henrissat, D. G. Kilburn, R. C. Miller, Jr., and R. A. J. Warren, Microbiol. Rev. 55:303-315, 1991). The Cel1 enzyme lacks a cellulose-binding domain as predicted by computer analysis of the sequence and confirmed by Avicel binding experiments. The promoter region of celA1 was identified by S1 mapping; the -35 region closely resembles those of housekeeping Streptomyces promoters. Three imperfectly repeated sequences of 15, 15, and 14 nucleotides were found upstream from celA1 [ATTGGGACCGCTTCC-(N85)-ATTGGGACCGCTTCC-(N2)-TGGGAGC GCTCCCA]; The 14-nucleotide sequence has a perfect palindrome identical to that found in several cellulase-encoding genes from Thermomonospora fusca, an alkalophilic Streptomyces strain, and Streptomyces lividans. This sequence has been implicated in the mechanism of induction exerted by cellobiose. Using an internal celA1 probe, we detected similar genes in several other Streptomyces species, most of them cellulase producers.     

Insulin and IGF receptors are developmentally regulated in the chick embryo eye lens

We have previously reported that insulin-like growth factor (IGF) receptors appear to predominate over insulin receptors in early stages of embryogenesis in the chick (days 2-3 whole embryo membranes). Overall, [125I]IGF I and II binding to specific receptors was maximal when the rate of brain growth is highest. In the present study we used the embryonic chick lens, a well-defined tissue composed of a single type of cell, to analyse whether changes of insulin and IGF I binding are correlated with changes in growth rate and differentiation state of the cells. We show that both insulin receptors and IGF receptors are present in the lens epithelial cells, and that each type is distinctly regulated throughout development. While there is a direct correlation between IGF-binding capability and growth rate of the cells, there is less relation to differentiation status and embryo age. Insulin receptors, by contrast, appear to be mostly related to the differentiated state of cells, decreasing sharply in fibers, irrespective of their developmental age.     

v-mil induces autocrine growth and enhanced tumorigenicity in v-myc-transformed avian macrophages

MH2, an avian retrovirus containing the v-myc and v-mil oncogenes, rapidly transforms chick hematopoietic cells in vitro. The transformed cells belong to the macrophage lineage and proliferate in the absence of exogenous growth factors. Here we analyze a series of MH2 deletion mutants and show that these two oncogenes together establish an autocrine growth system in which v-myc stimulates cell proliferation, while v-mil induces the production of chicken myelomonocytic growth factor (cMGF). We also demonstrate that these two oncogenes cooperate in vivo. MH2 efficiently induces monocytic leukemias and liver tumors, while deletion mutants lacking either a functional v-mil or v-myc do not.     

The Crystal Structure and Small-Angle X-Ray Analysis of CsdL/TcdA Reveal a New tRNA Binding Motif in the MoeB/E1 Superfamily

Cyclic N⁶-threonylcarbamoyladenosine (‘cyclic t⁶A’, ct⁶A) is a non-thiolated hypermodification found in transfer RNAs (tRNAs) in bacteria, protists, fungi and plants. In bacteria and yeast cells ct⁶A has been shown to enhance translation fidelity and efficiency of ANN codons by improving the faithful discrimination of aminoacylated tRNAs by the ribosome. To further the understanding of ct⁶A biology we have determined the high-resolution crystal structures of CsdL/TcdA in complex with AMP and ATP, an E1-like activating enzyme from Escherichia coli, which catalyzes the ATP-dependent dehydration of t⁶A to form ct⁶A. CsdL/TcdA is a dimer whose structural integrity and dimer interface depend critically on strongly bound K⁺ and Na⁺ cations. By using biochemical assays and small-angle X-ray scattering we show that CsdL/TcdA can associate with tRNA with a 1:1 stoichiometry and with the proper position and orientation for the cyclization of t⁶A. Furthermore, we show by nuclear magnetic resonance that CsdL/TcdA engages in transient interactions with CsdA and CsdE, which, in the latter case, involve catalytically important residues. These short-lived interactions may underpin the precise channeling of sulfur atoms from cysteine to CsdL/TcdA as previously characterized. In summary, the combination of structural, biophysical and biochemical methods applied to CsdL/TcdA has afforded a more thorough understanding of how the structure of this E1-like enzyme has been fine tuned to accomplish ct⁶A synthesis on tRNAs while providing support for the notion that CsdA and CsdE are able to functionally interact with CsdL/TcdA.     

Tree dynamics and co‐existence in the montane–sub‐alpine ecotone: the role of different light‐induced strategies

Questions: Is light availability the main factor driving forest dynamics in Pyrenean sub‐alpine forests? Do pines and firs differ in growth, mortality and morphological response to low light availability? Can differences in shade tolerance affect predictions of future biome changes in Pyrenean sub‐alpine forests in the absence of thermal limitation? Location: Montane–sub‐alpine ecotones of the Eastern Pyrenees (NE Spain). Methods: We evaluated morphological plasticity, survival and growth response of saplings of Scots pine, mountain pine and silver fir to light availability in a mixed forest ecotone. For each species, we selected 100 living and 50 dead saplings and measured size, crown morphology and light availability. A wood disk at root collar was then removed for every sapling, and models relating growth and mortality to light were obtained. Results: Fir had the lowest mortality rate (<0.1) for any given light condition. Pines had comparable responses to light availability, although in deep shade Scots pine risked higher mortality (0.35) than mountain pine (0.19). Pines and fir developed opposing strategies to light deprivation: fir employed a conservative strategy based on sacrificing height growth, whereas pines enhanced height growth to escape from shade, but at the expense of higher mortality risk. Scots pine showed higher plasticity than mountain pine for all architectural and morphological traits analysed, having higher adaptive capacity to a changing environment. Conclusions: Our results support the prediction of future biome changes in Pyrenean sub‐alpine forests as silver fir and Scots pine may find appropriate conditions for colonizing mountain pine‐dominated stands due to land‐use change‐related forest densification and climate warming‐related temperature increases, respectively.     

Presence of Blastocystis in gut microbiota is associated with cognitive traits and decreased executive function

Growing evidence implicates the gut microbiome in cognition. Blastocystis is a common gut single-cell eukaryote parasite frequently detected in humans but its potential involvement in human pathophysiology has been poorly characterized. Here we describe how the presence of Blastocystis in the gut microbiome was associated with deficits in executive function and altered gut bacterial composition in a discovery (n = 114) and replication cohorts (n = 942). We also found that Blastocystis was linked to bacterial functions related to aromatic amino acids metabolism and folate-mediated pyrimidine and one-carbon metabolism. Blastocystis-associated shifts in bacterial functionality translated into the circulating metabolome. Finally, we evaluated the effects of microbiota transplantation. Donor’s Blastocystis subtypes led to altered recipient’s mice cognitive function and prefrontal cortex gene expression. In summary, Blastocystis warrant further consideration as a novel actor in the gut microbiome-brain axis.Subject terms: Biomarkers, Pathogenesis, Diagnosis     

Melanoma RBPome identification reveals PDIA6 as an unconventional RNA-binding protein involved in metastasis

RNA-binding proteins (RBPs) have been relatively overlooked in cancer research despite their contribution to virtually every cancer hallmark. Here, we use RNA interactome capture (RIC) to characterize the melanoma RBPome and uncover novel RBPs involved in melanoma progression. Comparison of RIC profiles of a non-tumoral versus a metastatic cell line revealed prevalent changes in RNA-binding capacities that were not associated with changes in RBP levels. Extensive functional validation of a selected group of 24 RBPs using five different in vitro assays unveiled unanticipated roles of RBPs in melanoma malignancy. As proof-of-principle we focused on PDIA6, an ER-lumen chaperone that displayed a novel RNA-binding activity. We show that PDIA6 is involved in metastatic progression, map its RNA-binding domain, and find that RNA binding is required for PDIA6 tumorigenic properties. These results exemplify how RIC technologies can be harnessed to uncover novel vulnerabilities of cancer cells.