Liver kinase B1 (LKB1) in the pathogenesis of UVB-induced murine basal cell carcinoma

LKB1, a known tumor suppressor, is mutated in Peutz–Jeghers Syndrome (PJS). It is responsible for the enhanced cancer risk in patients with PJS. Dysregulation of LKB1-dependent signaling also occurs in various epithelial cancers. UVB alters the expression of LKB1, though its role in the pathogenesis of skin cancer is unknown. Here we describe upregulation of LKB1 expression in UVB-induced murine basal cell carcinoma (BCC) and in human skin tumor keratinocytes. AMP-kinase and acetyl Co-A carboxylase, the downstream LKB1 targets, are also enhanced in this neoplasm. In addition, p-Akt, a kinase which inactivates GSK3β by its phosphorylation, is enhanced in BCCs. Consistently, an accumulation of p-GSK3β and an increase in activated nuclear β-catenin are found. mTOR signaling, which is also inhibited by LKB1, remains upregulated in BCCs. However, a marked decrease in the expression of sestrins, which function as potent negative regulators of mTOR is observed. Metformin, a known chemical inducer of this pathway, was found effective in immortalized HaCaT keratinocytes, but failed to activate the LKB1-dependent signaling in human carcinoma A431 cells. Thus, our data show that the LKB1/AMPK axis fails to regulate mTOR pathway, and a complex regulatory mechanism exists for the persistent mTOR activation in murine BCCs.     

Rewiring of Glutamine Metabolism Is a Bioenergetic Adaptation of Human Cells with Mitochondrial DNA Mutations

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乌苏里江流域的伞菌及其它大型担子菌

报告了中国东北和俄罗斯远东地区乌苏里江流域伞菌及其它大型担子菌种类。基于作者2003年和2004年在中国黑龙江抚远、饶河、虎林和密山及俄罗斯滨海边疆区和哈巴罗夫斯克边疆区所采得的1200余号标本。记载了132属328种,其中有27种为中国新记录(用星号标注)。此名录包括种的名称及其文献出处、采集地和引证的标本号,不列举同物异名。标本保存于吉林农业大学菌物标本馆(HMJAU)及俄罗斯科学院生物与土壤研究所植物标本馆菌物部(VLA-M)。     

HPLC determination of α-ketoglutaramate [5-amino-2,5-dioxopentanoate] in biological samples

α-Ketoglutaramate is an important glutamine metabolite in mammals, plants, and many bacteria. It is also a nicotine metabolite in certain bacteria. Previously published methods for the determination of α-ketoglutaramate in biological samples have considerable drawbacks. Here, we describe a relatively simple high-performance liquid chromatography (HPLC)-based method for measurement of α-ketoglutaramate in plasma and deproteinized tissues that overcomes these drawbacks. Concentrations of α-ketoglutaramate in normal rat liver, kidney, brain, and plasma were found to be approximately 216, 13, 6, and 19 μM, respectively. The HPLC method should be useful for studying the role of α-ketoglutaramate in eukaryotic glutamine metabolism and in bacterial nicotine metabolism.     

Activation of Akt Signaling Reduces the Prevalence and Intensity of Malaria Parasite Infection and Lifespan in Anopheles stephensi Mosquitoes

Malaria (Plasmodium spp.) kills nearly one million people annually and this number will likely increase as drug and insecticide resistance reduces the effectiveness of current control strategies. The most important human malaria parasite, Plasmodium falciparum, undergoes a complex developmental cycle in the mosquito that takes approximately two weeks and begins with the invasion of the mosquito midgut. Here, we demonstrate that increased Akt signaling in the mosquito midgut disrupts parasite development and concurrently reduces the duration that mosquitoes are infective to humans. Specifically, we found that increased Akt signaling in the midgut of heterozygous Anopheles stephensi reduced the number of infected mosquitoes by 60–99%. Of those mosquitoes that were infected, we observed a 75–99% reduction in parasite load. In homozygous mosquitoes with increased Akt signaling parasite infection was completely blocked. The increase in midgut-specific Akt signaling also led to an 18–20% reduction in the average mosquito lifespan. Thus, activation of Akt signaling reduced the number of infected mosquitoes, the number of malaria parasites per infected mosquito, and the duration of mosquito infectivity.     

Self-renewal and differentiation capabilities are variable between human embryonic stem cell lines I3, I6 and BG01V

Background  

A unique and essential property of embryonic stem cells is the ability to self-renew and differentiate into multiple cell lineages. However, the possible differences in proliferation and differentiation capabilities among independently-derived human embryonic stem cells (hESCs) are not well known because of insufficient characterization. To address this question, a side-by-side comparison of 1) the ability to maintain an undifferentiated state and to self-renew under standard conditions; 2) the ability to spontaneously differentiate into three primary embryonic germ lineages in differentiating embryoid bodies; and 3) the responses to directed neural differentiation was made between three NIH registered hES cell lines I3 (TE03), I6 (TE06) and BG01V. Lines I3 and I6 possess normal XX and a normal XY karyotype while BG01V is a variant cell line with an abnormal karyotype derived from the karyotypically normal cell line BG01.     

COX-1 and COX-2 contribute differentially to the LPS-induced release of PGE2 and TxA2 in liver macrophages

LPS induces an immediate release of thromboxane TxA2 and a delayed release of PGE2. Dexamethasone suppresses the LPS-induced release of TxA2 and PGE2. In the first 8 h after LPS addition, the specific COX-2 inhibitor SC236 inhibits the PGE2 and TxA2 release by about 80% and 20%, whereas the release of PGE2 and TxA2 between 8 and 24 h is inhibited by about 40% and 35%, respectively. Resident liver macrophages express substantial amounts of COX-1, TxAS, cPGES and mPGES-2, small amounts of COX-2 but almost no detectable amounts of mPGES-1. LPS induces an increase of COX-2 and mPGES-1, but does not change COX-1, cPGES, mPGES-2 and TxAS at protein level. Dexamethasone suppresses almost completely the LPS-induced effects on COX-2 and mPGES-1. It is concluded that (1) COX-1 and COX-2 are involved in the LPS-induced synthesis of TxA2 and PGE2; (2) TxA2 release is catalyzed at early time-points by the combined action of COX-1 and TxAs, whereas at later time points the newly expressed COX-2 couples to TxAS and contributes to the TxA2 release; (3) PGE2 release within the first 8 h is predominantly catalyzed by COX-2, whereas at later time-points COX-1 couples to the newly expressed mPGES-1 and contributes to the PGE2 release.     

The GCR1, GPA1, PRN1, NF-Y signal chain mediates both blue light and abscisic acid responses in Arabidopsis

Different classes of biotic (e.g. plant hormones) and abiotic (e.g. different wavelengths of light) signals act through specific signal transduction mechanisms to coordinate higher plant development. While a great deal of progress has been made, full signal transduction chains have not yet been described for most blue light- or abscisic acid-mediated events. Based on data derived from T-DNA insertion mutants and yeast (Saccharomyces cerevisiae) two-hybrid and coprecipitation assays, we report a signal transduction chain shared by blue light and abscisic acid leading to light-harvesting chlorophyll a/b-binding protein expression in etiolated Arabidopsis (Arabidopsis thaliana) seedlings. The chain consists of GCR1 (the sole Arabidopsis protein coding for a potential G-protein-coupled receptor), GPA1 (the sole Arabidopsis Galpha-subunit), Pirin1 (PRN1; one of four members of an iron-containing subgroup of the cupin superfamily), and a nuclear factor Y heterotrimer comprised of A5, B9, and possibly C9. We also demonstrate that this mechanism is present in imbibed seeds wherein it affects germination rate.     

Restricting conformational flexibility of the switch II region creates a dominant-inhibitory phenotype in Obg GTPase Nog1

Nog1 is a conserved eukaryotic GTPase of the Obg family involved in the biogenesis of 60S ribosomal subunits. Here we report the unique dominant-inhibitory properties of a point mutation in the switch II region of mouse Nog1; this mutation is predicted to restrict conformational mobility of the GTP-binding domain. We show that although the mutation does not significantly affect GTP binding, ectopic expression of the mutant in mouse cells disrupts productive assembly of pre-60S subunits and arrests cell proliferation. The mutant impairs processing of multiple pre-rRNA intermediates, resulting in the degradation of the newly synthesized 5.8S/28S rRNA precursors. Sedimentation analysis of nucleolar preribosomes indicates that defective Nog1 function inhibits the conversion of 32S pre-rRNA-containing complexes to a smaller form, resulting in a drastic accumulation of enlarged pre-60S particles in the nucleolus. These results suggest that conformational changes in the switch II element of Nog1 have a critical importance for the dissociation of preribosome-bound factors during intranucleolar maturation and thereby strongly influence the overall efficiency of the assembly process.