The mRNA-binding Protein TTP/ZFP36 in Hepatocarcinogenesis and Hepatocellular Carcinoma.

Hepatic lipid deposition and inflammation represent risk factors for hepatocellular carcinoma (HCC). The mRNA-binding protein tristetraprolin (TTP, gene name ZFP36) has been suggested as a tumor suppressor in several malignancies, but it increases insulin resistance. The aim of this study was to elucidate the role of TTP in hepatocarcinogenesis and HCC progression. Employing liver-specific TTP-knockout (lsTtp-KO) mice in the diethylnitrosamine (DEN) hepatocarcinogenesis model, we observed a significantly reduced tumor burden compared to wild-type animals. Upon short-term DEN treatment, modelling early inflammatory processes in hepatocarcinogenesis, lsTtp-KO mice exhibited a reduced monocyte/macrophage ratio as compared to wild-type mice. While short-term DEN strongly induced an abundance of saturated and poly-unsaturated hepatic fatty acids, lsTtp-KO mice did not show these changes. These findings suggested anti-carcinogenic actions of TTP deletion due to effects on inflammation and metabolism. Interestingly, though, investigating effects of TTP on different hallmarks of cancer suggested tumor-suppressing actions: TTP inhibited proliferation, attenuated migration, and slightly increased chemosensitivity. In line with a tumor-suppressing activity, we observed a reduced expression of several oncogenes in TTP-overexpressing cells. Accordingly, ZFP36 expression was downregulated in tumor tissues in three large human data sets. Taken together, this study suggests that hepatocytic TTP promotes hepatocarcinogenesis, while it shows tumor-suppressive actions during hepatic tumor progression.

Polyunsaturated fatty acid production by Yarrowia lipolytica employing designed myxobacterial PUFA synthases.

Long-chain polyunsaturated fatty acids (LC-PUFAs), particularly the omega-3 LC-PUFAs eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA), and docosahexaenoic acid (DHA), have been associated with beneficial health effects. Consequently, sustainable sources have to be developed to meet the increasing demand for these PUFAs. Here, we demonstrate the design and construction of artificial PUFA biosynthetic gene clusters (BGCs) encoding polyketide synthase-like PUFA synthases from myxobacteria adapted for the oleaginous yeast Yarrowia lipolytica. Genomic integration and heterologous expression of unmodified or hybrid PUFA BGCs yielded different yeast strains with specific LC-PUFA production profiles at promising yield and thus valuable for the biotechnological production of distinct PUFAs. Nutrient screening revealed a strong enhancement of PUFA production, when cells were phosphate limited. This represents, to the best of our knowledge, highest concentration of DHA (16.8 %) in total fatty acids among all published PUFA-producing Y. lipolytica strains.

A polyphasic approach leads to seven new species of the cellulose-decomposing genus Sorangium, Sorangium ambruticinum sp. nov., Sorangium arenae sp. nov., Sorangium bulgaricum sp. nov., Sorangium dawidii sp. nov., Sorangium kenyense sp. nov., Sorangium orientale sp. nov. and Sorangium reichenbachii sp. nov.

Seventy-three strains of Sorangium have been isolated from soil samples collected from all over the world. The strains were characterized using a polyphasic approach and phenotypic, genotypic and chemotype analyses clarified their taxonomic relationships. 16S rRNA, xynB1, groEL1, matrix-assisted laser desorption/ioniziation time-of-flight mass spectrometry and API-ZYM analyses were conducted. In addition, from selected representative strains, fatty acids, quinones and phospholipids were analysed. In silico DNA-DNA hybridization and DNA-DNA hybridization against the current type species of Sorangiumcellulosum strain Soce 1871T (DSM 14627T) completed the analyses. Finally, our study revealed seven new species of Sorangium: Sorangium ambruticinum (Soce 176T; DSM 53252T, NCCB 100639T, sequence accession number ERS2488998), Sorangium arenae (Soce 1078T; DSM 105768T, NCCB 100643T, ERS2489002), Sorangium bulgaricum (Soce 321T; DSM 53339T, NCCB 100640T, ERS2488999), Sorangium dawidii (Soce 362T; DSM 105767T, NCCB 100641T, ERS2489000), Sorangium kenyense (Soce 375T; DSM 105741T, NCCB 100642T, ERS2489001), Sorangium orientale (Soce GT47T; DSM 105742T, NCCB 100638T, ERS2501484) and Sorangium reichenbachii (Soce 1828T; DSM 105769T, NCCB 100644T, ERS2489003).

Metabolic and Biosynthetic Diversity in Marine Myxobacteria.

Prior to 2005, the vast majority of characterized myxobacteria were obtained from terrestrial habitats. Since then, several species of halotolerant and even obligate marine myxobacteria have been described. Chemical analyses of extracts from these organisms have confirmed their ability to produce secondary metabolites with unique chemical scaffolds. Indeed, new genera of marine-derived myxobacteria, particularly Enhygromyxa, have been shown to produce novel chemical scaffolds that differ from those observed in soil myxobacteria. Further studies have shown that marine sponges and terrestrial myxobacteria are capable of producing similar or even identical secondary metabolites, suggesting that myxobacterial symbionts may have been the true producers. Recent in silico analysis of the genome sequences available from six marine myxobacteria disclosed a remarkably versatile biosynthetic potential. With access to ever-advancing tools for small molecule and genetic evaluation, these studies suggest a bright future for expeditions into this yet untapped resource for secondary metabolites.

Nannocystis konarekensis sp. nov., a novel myxobacterium from an Iranian desert.

An orange-coloured myxobacterium, MNa11734T, was isolated from desert in Iran. MNa11734T had rod-shaped vegetative cells, moved by gliding and was bacteriolytic. No real fruiting body formation could be observed, but sporangioles were produced on water agar. The strain was mesophilic, strictly aerobic and chemoheterotrophic. 16S rRNA gene analyses revealed that MNa11734T belonged to the family Nannocystaceae, genus Nannocystis and was closely related to Nannocystis pusilla Na p29T (DSM 14622T) and Nannocystis exedens Na e1T (DSM 71T), with 97.8 and 97.6 % 16S rRNA gene sequence similarity, respectively. Laboratory-measured DNA-DNA hybridization showed only 9.5/15.7 % (reciprocal) similarity between the novel strain and N. pusilla Na p29T, and 14.1/20.4 % between the strain and N. exedens Na e1T, whereas DNA-DNA hybridization estimates derived from draft genome sequences were 21.8-23.0 % and 22.2-23.7 %, respectively, depending on the calculation method. The G+C content of DNA from Nannocystis konarekensis MNa11734T was 73.3 mol%, for N. pusilla Nap29T it was 71.8 mol% and for N. exedens Nae1T it was 72.2 mol%. The major fatty acids of the new strain were C16 : 1 (56.2 %), iso-C17 : 0 (14.4 %), C14 : 0 (8.2 %), C16 : 0 (6.6 %) and iso-C15 : 0 (5.9 %). Strain MNa11734T exhibited phylogenetic and physiological similarities to the two other species of Nannocystis, i.e. N. pusilla and N. exedens, but the differences were sufficient enough to represent a novel species, for which the name Nannocystiskonarekensis sp. nov. is proposed. The type strain is MNa11734T (=DSM 104509T=NCCB 100618T).

Synthetic biology approaches to establish a heterologous production system for coronatines.

Coronatine (COR) represents a phytotoxin produced by several pathovars of Pseudomonas syringae. It mediates multiple virulence activities by mimicking the plant stress hormone jasmonoyl-l-isoleucine. Structurally, COR consists of a bicyclic polyketide moiety, coronafacic acid (CFA), which is linked via an amide bond to an unusual ethylcyclopropyl amino acid moiety, coronamic acid (CMA). In our studies, we aimed at establishing and engineering of heterologous COR and CFA production platforms using P. putida KT2440 as host. Based on genetic information of the native producer P. syringae pv. tomato DC3000 a COR biosynthetic gene cluster was designed and reconstituted from synthetic DNA fragments. The applied constructional design facilitated versatile pathway modifications and the generation of various expression constructs, which were evaluated for the production of CFA, COR and its derivatives. By modifications of the gene cluster composition production profiles were directed towards target compounds and valuable information about the function and impact of selected pathway proteins on COR biosynthesis were obtained. Additional engineering of expression vector features, including the use of the constitutive PrpsH promoter and a p15Aori-based transposon backbone, led to the development of an expression strain with promising CFA production yields of > 90mg/l.

Vitiosangium cumulatum gen. nov., sp. nov. and Vitiosangium subalbum sp. nov., soil myxobacteria, and emended descriptions of the genera Archangium and Angiococcus, and of the family Cystobacteraceae.

Bacterial strains MCy10943T and MCy10944T were isolated in 2014 from dried Nepalese soil samples collected in 2013 from Phukot, Kalikot, Western Nepal, and Godawari, Lalitpur, Central Nepal. The novel organisms showed typical myxobacterial growth characteristics, which include swarming colony and fruiting body formation on solid surfaces, and a predatory ability to lyse micro-organisms. The strains were aerobic, mesophilic, chemoheterotrophic and showed resistance to various antibiotics. The major cellular fatty acids common to both organisms were C17 : 0 2-OH, iso-C15 : 0, C16 : 1 and iso-C17 : 0. The G+C content of the genomic DNA was 72-75 mol%. Phylogenetic analysis showed that the strains belong to the family Cystobacteraceae, suborder Cystobacterineae, order Myxococcales. The 16S rRNA gene sequences of both strains showed 97-98 % similarity to Archangium gephyra DSM 2261T andCystobacter violaceus DSM 14727T, and 96.7-97 % to Cystobacter fuscus DSM 2262T and Angiococcus disciformis DSM 52716T. Polyphasic taxonomic characterization suggested that strains MCy10943T and MCy10944T represent two distinct species of a new genus, for which the names Vitiosangium cumulatum gen. nov., sp. nov. and Vitiosangium subalbum sp. nov. are proposed. The type strain of Vitiosangium cumulatum is MCy10943T (=DSM 102952T=NCCB 100600T) while that for Vitiosangium subalbum is MCy10944T (=DSM 102953T=NCCB 100601T). In addition, emended descriptions of the genera Archangium and Angiococcus, and of the family Cystobacteraceaeare provided.

Racemicystis persica sp. nov., a myxobacterium from soil.

A novel myxobacterium, strain MSr11462T, was isolated in 2015 from a soil sample collected form Kish Island beach, Persian Gulf, Iran. It displayed general myxobacterial features like Gram-negative staining, rod-shaped vegetative cells, gliding on solid surfaces, microbial lytic activity, fruiting-body-like aggregates and myxospore-like structures. The strain was mesophilic, aerobic and showed a chemoheterotrophic mode of nutrition. It was resistant to many antibiotics like gentamycin, polymyxin, fusidic acid and trimethoprim, and the key fatty acids of whole-cell hydrolysates were iso-C15 : 0, C16 : 0, iso-C17 : 0, C18 : 1, iso-C17 : 1 2-OH, C18 : 1 2-OH, iso-C15 : 0 OAG (O-alkylglycerol) and C16 : 1 OAG. The 16S rRNA gene sequence showed highest similarity (98.6 %) to Racemicystis crocea strain MSr9521T (GenBank accession no. KT591707). The phylogenetic analysis based on 16S rRNA gene sequences and matrix-assisted laser-desorption/ionization time-of-flight (MALDI-TOF) spectroscopy data supports a novel species of the family Polyangiaceae and the genus Racemicystis. DNA-DNA hybridization showed only about 50 % similarity between the novel strain and the phylogenetically closest species, Racemicystis. crocea MSr9521T. On the basis of a comprehensive taxonomic study, we propose a novel species, Racemicystis persica sp. nov., for strain MSr11462T (=DSM 103165T=NCCB 100606T).

Corrigendum: Transient Hepatic Overexpression of Insulin-Like Growth Factor 2 Induces Free Cholesterol and Lipid Droplet Formation.

[This corrects the article on p. 147 in vol. 7, PMID: 27199763.].

Susceptibility of Different Mouse Wild Type Strains to Develop Diet-Induced NAFLD/AFLD-Associated Liver Disease.

Although non-alcoholic and alcoholic fatty liver disease have been intensively studied, concerning pathophysiological mechanisms are still incompletely understood. This may be due to the use of different animal models and resulting model-associated variation. Therefore, this study aimed to compare three frequently used wild type mouse strains in their susceptibility to develop diet-induced features of non-alcoholic/alcoholic fatty liver disease. Fatty liver disease associated clinical, biochemical, and histological features in C57BL/6, CD-1, and 129Sv WT mice were induced by (i) high-fat diet feeding, (ii) ethanol feeding only, and (iii) the combination of high-fat diet and ethanol feeding. Hepatic and subcutaneous adipose lipid profiles were compared in CD-1 and 129Sv mice. Additionally hepatic fatty acid composition was determined in 129Sv mice. In C57BL/6 mice dietary regimens resulted in heterogeneous hepatic responses, ranging from pronounced steatosis and inflammation to a lack of any features of fatty liver disease. Liver-related serum biochemistry showed high deviations within the regimen groups. CD-1 mice did not exhibit significant changes in metabolic and liver markers and developed no significant steatosis or inflammation as a response to dietary regimens. Although 129Sv mice showed no weight gain, this strain achieved most consistent features of fatty liver disease, apparent from concentration alterations of liver-related serum biochemistry as well as moderate steatosis and inflammation as a result of all dietary regimens. Furthermore, the hepatic lipid profile as well as the fatty acid composition of 129Sv mice were considerably altered, upon feeding the different dietary regimens. Accordingly, diet-induced non-alcoholic/alcoholic fatty liver disease is most consistently promoted in 129Sv mice compared to C57BL/6 and CD-1 mice. As a conclusion, this study demonstrates the importance of genetic background of used mouse strains for modeling diet-induced non-alcoholic/alcoholic fatty liver disease.

Transient Hepatic Overexpression of Insulin-Like Growth Factor 2 Induces Free Cholesterol and Lipid Droplet Formation.

Although insulin-like growth factor 2 (IGF2) has been reported to be overexpressed in steatosis and steatohepatitis, a causal role of IGF2 in steatosis development remains elusive. Aim of our study was to decipher the role of IGF2 in steatosis development. Hydrodynamic gene delivery of an Igf2 plasmid used for transient Igf2 overexpression employing codon-optimized plasmid DNA resulted in a strong induction of hepatic Igf2 expression. The exogenously delivered Igf2 had no influence on endogenous Igf2 expression. The downstream kinase AKT was activated in Igf2 animals. Decreased ALT levels mirrored the cytoprotective effect of IGF2. Serum cholesterol was increased and sulfo-phospho-vanillin colorimetric assay confirmed lipid accumulation in Igf2-livers while no signs of inflammation were observed. Interestingly, hepatic cholesterol and phospholipids, determined by thin layer chromatography, and free cholesterol by filipin staining, were specifically increased. Lipid droplet (LD) size was not changed, but their number was significantly elevated. Furthermore, free cholesterol, which can be stored in LDs and has been reported to be critical for steatosis progression, was elevated in Igf2 overexpressing mice. Accordingly, Hmgcr/HmgCoAR was upregulated. To have a closer look at de novo lipid synthesis we investigated expression of the lipogenic transcription factor SREBF1 and its target genes. SREBF1 was induced and also SREBF1 target genes were slightly upregulated. Interestingly, the expression of Cpt1a, which is responsible for mitochondrial fatty acid oxidation, was induced. Hepatic IGF2 expression induces a fatty liver, characterized by increased cholesterol and phospholipids leading to accumulation of LDs. We therefore suggest a causal role for IGF2 in hepatic lipid accumulation.

Aetherobacter fasciculatus gen. nov., sp. nov. and Aetherobacter rufus sp. nov., novel myxobacteria with promising biotechnological applications.

Bacterial strains SBSr002T and SBSr003T were isolated in 2007 from dried soil samples containing decaying plant material. The organisms were recognized as myxobacteria by growth-stage characteristics, forming swarming colonies and fruiting bodies on agar and on filter paper. These strains were unusual for their ring-like or halo colony appearance in an agar. Both isolates were characterized as bacteriolytic, non-cellulolytic, mesophilic, aerobic and chemoheterotrophic and showed resistance to various antibiotics. GC-MS analysis of their cellular fatty acids revealed rather large quantities of docosahexaenoic acid, and they also both contained eicosapentaenoic acid, arachidonic acid and docosapentaenoic acid. Strain SBSr003T was previously identified as the producer organism of a novel class of potent antiviral metabolites that were called aetheramides. The G+C content of the genomic DNA was 68.0-68.9 mol%. Phylogenetic analysis revealed that both strains belong within the family Polyangiaceae, suborder Sorangiineae, order Myxococcales. Their 16S rRNA gene sequences showed the highest similarity (97-99 %) to sequences derived from clones of uncultured bacteria, 95-96 % similarity to Byssovorax cruenta and Sorangium cellulosum and 94 % similarity to Chondromyces apiculatus. The results of a polyphasic taxonomic characterization suggested that strains SBSr002T and SBSr003T represent two distinct species of a novel genus, Aetherobacter gen. nov., for which the names Aetherobacter fasciculatus sp. nov. (type strain SBSr002T = DSM 24601T = NCCB 100377T) and Aetherobacter rufus sp. nov. (type strain SBSr003T = DSM 24628T = NCCB 100378T) are proposed. The type species of Aetherobacter is Aetherobacter fasciculatus.

Metabolic engineering of Pseudomonas putida for production of docosahexaenoic acid based on a myxobacterial PUFA synthase.

Long-chain polyunsaturated fatty acids (LC-PUFAs) can be produced de novo via polyketide synthase-like enzymes known as PUFA synthases, which are encoded by pfa biosynthetic gene clusters originally discovered from marine microorganisms. Recently similar gene clusters were detected and characterized in terrestrial myxobacteria revealing several striking differences. As the identified myxobacterial producers are difficult to handle genetically and grow very slowly we aimed to establish heterologous expression platforms for myxobacterial PUFA synthases. Here we report the heterologous expression of the pfa gene cluster from Aetherobacter fasciculatus (SBSr002) in the phylogenetically distant model host bacteria Escherichia coli and Pseudomonas putida. The latter host turned out to be the more promising PUFA producer revealing higher production rates of n-6 docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA). After several rounds of genetic engineering of expression plasmids combined with metabolic engineering of P. putida, DHA production yields were eventually increased more than threefold. Additionally, we applied synthetic biology approaches to redesign and construct artificial versions of the A. fasciculatus pfa gene cluster, which to the best of our knowledge represents the first example of a polyketide-like biosynthetic gene cluster modulated and synthesized for P. putida. Combination with the engineering efforts described above led to a further increase in LC-PUFA production yields. The established production platform based on synthetic DNA now sets the stage for flexible engineering of the complex PUFA synthase.

Elevated free cholesterol in a p62 overexpression model of non-alcoholic steatohepatitis.

AIM: To characterize how insulin-like growth factor 2 (IGF2) mRNA binding protein p62/IMP2-2 promotes steatohepatitis in the absence of dietary cholesterol. METHODS: Non-alcoholic steatohepatitis (NASH) was induced in wild-type mice and in mice overexpressing p62 specifically in the liver by feeding the mice a methionine and choline deficient (MCD) diet for either two or four weeks. As a control, animals were fed a methionine and choline supplemented diet. Serum triglycerides, cholesterol, glucose, aspartate aminotransferase and alanine transaminase were determined by standard analytical techniques. Hepatic gene expression was determined by real-time reverse transcription-polymerase chain reaction. Generation of reactive oxygen species in liver tissue was quantified as thiobarbituric acid reactive substances using a photometric assay and malondialdehyde as a standard. Tissue fatty acid profiles and cholesterol levels were analyzed by gas chromatography-mass spectrometry after hydrolysis. Hepatocellular iron accumulation was determined by Prussian blue staining in paraffin-embedded formalin-fixed tissue. Filipin staining on frozen liver tissue was used to quantify hepatic free cholesterol levels. Additionally, nuclear localization of the nuclear factor kappa B (NF-κB) subunit p65 was examined in frozen tissues. RESULTS: Liver-specific overexpression of the insulin-like growth factor 2 mRNA binding protein 2-2 (IGF2BP2-2/IMP2-2/p62) induces steatosis with regular chow and amplifies NASH-induced fibrosis in the MCD mouse model. Activation of NF-κB and expression of NF-κB target genes suggested an increased inflammatory response in p62 transgenic animals. Analysis of hepatic lipid composition revealed an elevation of monounsaturated fatty acids as well as increased hepatic cholesterol. Moreover, serum cholesterol was significantly elevated in p62 transgenic mice. Dietary cholesterol represents a critical factor for the development of NASH from hepatic steatosis. Filipin staining revealed increased free cholesterol in p62 transgenic livers, which were not diet-derived. The mRNA levels of the rate-limiting enzyme for cholesterol synthesis 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMG-CoA reductase or HMGCR) were not significantly upregulated, potentially due to increased cholesterol biosynthesis via elevated sterol regulatory element binding transcription factor 2 (SREBF2) gene expression and increased iron deposition in transgenic animals. CONCLUSION: This study provides evidence that p62/IGF2BP2-2 drives the progression of NASH through elevation of hepatic iron deposition and increased production of hepatic free cholesterol.

Minicystis rosea gen. nov., sp. nov., a polyunsaturated fatty acid-rich and steroid-producing soil myxobacterium.

A bacterial strain designated SBNa008(T) was isolated from a Philippine soil sample. It exhibited the general characteristics associated with myxobacteria, such as swarming of Gram-negative vegetative rod cells, fruiting body and myxospore formation and predatory behaviour in lysing micro-organisms. The novel strain was characterized as mesophilic, chemoheterotrophic and aerobic. The major fatty acids were C(20:4)ω6,9,12,15 all cis (arachidonic acid), iso-C(15 : 0), C(17 : 1) 2-OH and iso-C(15 : 0) dimethylacetal. Interestingly, SBNa008(T) contained diverse fatty acids belonging to the commercially valuable polyunsaturated omega-6 and omega-3 families, and a highly conjugated dihydroxylated C28 steroid. The G+C content of the genomic DNA was 67.3 mol%. The 16S rRNA gene sequence revealed 95-96% similarity to sequences derived from clones of uncultured bacteria and 94-95% similarity to cultured members of the suborder Sorangiineae. Phylogenetic analysis revealed that strain SBNa008(T) formed a novel lineage in the suborder Sorangiineae. Based on a polyphasic taxonomic characterization, we propose that strain SBNa008(T) represents a novel genus and species, Minicystis rosea gen. nov., sp. nov. The type strain of Minicystis rosea is SBNa008(T) ( =DSM 24000(T) =NCCB 100349(T)).

Fatty acid elongation in non-alcoholic steatohepatitis and hepatocellular carcinoma.

Non-alcoholic steatohepatitis (NASH) represents a risk factor for the development of hepatocellular carcinoma (HCC) and is characterized by quantitative and qualitative changes in hepatic lipids. Since elongation of fatty acids from C16 to C18 has recently been reported to promote both hepatic lipid accumulation and inflammation we aimed to investigate whether a frequently used mouse NASH model reflects this clinically relevant feature and whether C16 to C18 elongation can be observed in HCC development. Feeding mice a methionine and choline deficient diet to model NASH not only increased total hepatic fatty acids and cholesterol, but also distinctly elevated the C18/C16 ratio, which was not changed in a model of simple steatosis (ob/ob mice). Depletion of Kupffer cells abrogated both quantitative and qualitative methionine-and-choline deficient (MCD)-induced alterations in hepatic lipids. Interestingly, mimicking inflammatory events in early hepatocarcinogenesis by diethylnitrosamine-induced carcinogenesis (48 h) increased hepatic lipids and the C18/C16 ratio. Analyses of human liver samples from patients with NASH or NASH-related HCC showed an elevated expression of the elongase ELOVL6, which is responsible for the elongation of C16 fatty acids. Taken together, our findings suggest a detrimental role of an altered fatty acid pattern in the progression of NASH-related liver disease.

The IGF2 mRNA binding protein p62/IGF2BP2-2 induces fatty acid elongation as a critical feature of steatosis.

Liver-specific overexpression of the insulin-like growth factor 2 (IGF2) mRNA binding protein p62/IGF2BP2-2 induces a fatty liver, which highly expresses IGF2 Because IGF2 expression is elevated in patients with steatohepatitis, the aim of our study was to elucidate the role and interconnection of p62 and IGF2 in lipid metabolism. Expression of p62 and IGF2 highly correlated in human liver disease. p62 induced an elevated ratio of C18:C16 and increased fatty acid elongase 6 (ELOVL6) protein, the enzyme catalyzing the elongation of C16 to C18 fatty acids and promoting nonalcoholic steatohepatitis in mice and humans. The p62 overexpression induced the activation of the ELOVL6 transcriptional activator sterol regulatory element binding transcription factor 1 (SREBF1). Recombinant IGF2 induced the nuclear translocation of SREBF1 and a neutralizing IGF2 antibody reduced ELOVL6 and mature SREBF1 protein levels. Concordantly, p62 and IGF2 correlated with ELOVL6 in human livers. Decreased palmitoyl-CoA levels, as found in p62 transgenic livers, can explain the lipogenic action of ELOVL6. Accordingly, p62 represents an inducer of hepatic C18 fatty acid production via a SREBF1-dependent induction of ELOVL6. These findings underline the detrimental role of p62 in liver disease.

Insights into the complex biosynthesis of the leupyrrins in Sorangium cellulosum So ce690.

The anti-fungal leupyrrins are secondary metabolites produced by several strains of the myxobacterium Sorangium cellulosum. These intriguing compounds incorporate an atypically substituted γ-butyrolactone ring, as well as pyrrole and oxazolinone functionalities, which are located within an unusual asymmetrical macrodiolide. Previous feeding studies revealed that this novel structure arises from the homologation of four distinct structural units, nonribosomally-derived peptide, polyketide, isoprenoid and a dicarboxylic acid, coupled with modification of the various building blocks. Here we have attempted to reconcile the biosynthetic pathway proposed on the basis of the feeding studies with the underlying enzymatic machinery in the S. cellulosum strain So ce690. Gene products can be assigned to many of the suggested steps, but inspection of the gene set provokes the reconsideration of several key transformations. We support our analysis by the reconstitution in vitro of the biosynthesis of the pyrrole carboxylic starter unit along with gene inactivation. In addition, this study reveals that a significant proportion of the genes for leupyrrin biosynthesis are located outside the core cluster, a 'split' organization which is increasingly characteristic of the myxobacteria. Finally, we report the generation of four novel deshydroxy leupyrrin analogues by genetic engineering of the pathway.