No abstract

Site-1 protease (S1P) cleaves membrane-bound sterol regulatory element-binding proteins (SREBPs), allowing their transcriptionstimulating domains to translocate to the nucleus where they activate genes governing lipid synthesis. S1P is a potential target for lipidlowering drugs, but the effect of S1P blockade in animals is unknown. Here, we disrupt the S1P gene in mice. Homozygous germ-line disruptions of S1P were embryonically lethal. To disrupt the gene inducibly in liver, we generated mice homozygous for a floxed S1P allele and heterozygous for a transgene encoding Cre recombinase under control of the IFN-inducible MX1 promoter. When IFN was produced, 70 -90% of S1P alleles in liver were inactivated, and S1P mRNA and protein were reduced. Nuclear SREBPs declined, as did mRNAs for SREBP target genes. Cholesterol and fatty acid biosynthesis in hepatocytes declined by 75%. Low density lipoprotein (LDL) receptor mRNA declined by 50%, as did the clearance of 125 I-labeled LDL from plasma, but plasma cholesterol fell, suggesting that LDL production was reduced. These data raise the possibility that S1P inhibitors may be effective lipid-lowering agents, but they suggest that nearly complete inhibition will be required.sterol regulatory element-binding proteins ͉ cholesterol ͉ fatty acids ͉ knockout mice T he proteolytic release of sterol regulatory element-binding proteins (SREBPs) from cell membranes stimulates lipid synthesis in hepatocytes and other cells. Inhibition of this proteolytic release in liver might lead to reduced lipid synthesis and reduced lipid accumulation in liver, blood, and other organs. The consequences of blocking hepatic SREBP proteolysis can now be investigated as a result of the recent molecular identification of the proteins that mediate this process (1).SREBPs are synthesized as membrane-bound precursors of Ϸ1,150 aa in length (1). The NH 2 terminal domain of Ϸ480 aa is a transcription factor of the basic helix-loop-helix leucine zipper family. This domain is followed by a hairpin membraneattachment domain of Ϸ80 aa, which consists of two transmembrane helices separated by a short 30-aa hydrophilic loop that projects into the lumen of the endoplasmic reticulum. The COOH-terminal domain of Ϸ590 aa faces the cytosol where it performs a regulatory function.Immediately after their synthesis, SREBPs form complexes with SREBP cleavage-activating protein (SCAP), an endoplasmic reticulum protein that contains eight membrane-spanning helices followed by a cytoplasmic domain of 545 aa (2).

If neuropilin-2 and the growth factor VEGF-C don’t come together, lymphatic vessels don’t branch apart.

Insulin signaling in the liver leads to accumulation of phosphatidylinositol (3,4,5)-trisphosphate (PIP 3 ). Deletion of the phosphatase Pten (phosphatase and tensin homologue deleted on chromosome 10) reduces PIP 3 levels and leads to fatty liver development. The purpose of this study was to investigate the mechanisms underlying lipogenesis that result from PIP 3 accumulation using liver Pten-deletion mice. To explore the role of AKT2, the major liver AKT isoform in steatosis induced by deletion of Pten, we created mice lacking both Pten and Akt2 in hepatocytes and compared the effect of deleting Akt2 and Pten in the double mutants to the Pten deletion mice alone. Hepatic lipid accumulation was significantly reduced in mice lacking both PTEN and AKT2, as compared with Pten mutant mice alone. This effect was due to the role of AKT2 in maintaining expression of genes involved in de novo lipogenesis. We showed that lipid accumulation in the double mutant hepatocytes was partially reversed by expression of constitutive active FOXO1, a transcription factor downstream of AKT not dependent on inhibition of atypical protein kinase C. In summary, this study delineated Lipid phosphatase and tensin homologue deleted on chromosome 10 (PTEN) functions to convert phosphotidylinositol-3,4,5-trisphosphate (PIP 3 ) to phosphatidylinositol bisphosphate.1 Thus, PTEN antagonizes the insulin-phosphoinositide 3-kindase (PI3K)/AKT pathway by reducing the levels of PIP 3 . In the liver, insulin activates PI3K signal to drive hepatic lipid accumulation. Mice lacking all PI3K activities are hypolipidemic and exhibit reduced expression of lipogenic genes in the liver.2 Previous studies reported a liver steatosis phenotype in mice when PTEN is lost in the hepatocytes. 3,4 In hepatocyte-specific Pten deletion mice, liver becomes a lipogenic organ, and accumulates triglyceride (TG) even though there is systemic hypoglycemia. 4 Both sterol regulatory element-binding proteins (SREBP-1c) and fatty acid synthase (FAS) are markedly elevated when PTEN is lost in the hepatocyte.3,4 This model, thus, is relevant to study how activation of the PI3K/AKT signaling pathway, specifically PIP 3 accumulation, induces lipogenesis.In this study, we considered the role of AKT2 in mediating the lipogenic effect of insulin/PI3K signaling. AKT2 is the major isoform of AKT that is expressed in the liver. AKT plays a pivotal role in hepatic insulin action.5 Adenovirus expression of constitutively activated AKT in vivo led to a similar fatty liver phenotype as loss of PTEN. 6 We hypothesized that AKT2 may mediate the metabolic phenotypes observed in the livers of Pten mutant animals. We investigated this hypothesis by crossing the hepatocytespecific Pten mutant mice 4 with the Akt2 Ϫ/Ϫ mice. 7 Our results indicate that loss of AKT2 can effectively block the fatty deposition in the liver of the Pten mutant mice. Our

Investigating microbial response to environmental variables is of great importance for understanding of microbial acclimatization and evolution in natural environments. However, little is known about how microbial communities responded to environmental factors (e.g. salinity, geographic distance) in lake surface sediments of the Qinghai-Tibetan Plateau (QTP). In this study, microbial diversity and community structure in the surface sediments of nine lakes on the QTP were investigated by using the Illumina Miseq sequencing technique and the resulting microbial data were statistically analyzed in combination with environmental variables. The results showed total microbial community of the studied lakes was significantly correlated (r = 0.631, P < 0.001) with lake salinity instead of geographic distance. This suggests that lake salinity is more important than geographic distance in shaping the microbial diversity and community structure in the studied samples. In addition, the abundant and rare taxa (OTUs with relative abundance higher than 1% and lower than 0.01% within one sample, respectively) were significantly (P < 0.05) correlated (r = 0.427 and 0.783, respectively) with salinity, suggesting rare taxa might be more sensitive to salinity than their abundant counterparts, thus cautions should be taken in future when evaluating microbial response (abundant vs. rare sub-communities) to environmental conditions.

The thiazolidinedione (TZD) family of PPARγ agonists, especially troglitazone and ciglitazone, induce cell cycle arrest, differentiation, and apoptosis in cancer cells. Mounting evidence indicates that TZDs interfere with multiple signaling mechanisms independently of PPARγactivation, which affect many aspects of cellular functions governing cell cycle progression and survival of cancer cells. Here, we review the "off-target" mechanisms that underlie the antitumor effects of TZDs with emphasis on three key pathways, namely, inhibition of Bcl-2/Bcl-xL function, proteasomal degradation of cell cycle-and apoptosis-regulatory proteins, and transcriptional repression of androgen receptor (AR) through Sp1 degradation. Relative to tumor cells, nonmalignant cells are resistant to these PPARγ-independent antitumor effects, which underscores the translational potential of these agents. Furthermore, dissociation of these antitumor effects from their PPARγ agonist activity provides a rationale for using TZDs as scaffolds for lead optimization to develop a novel class of antitumor agents with a unique mode of mechanism.

No abstract

Aquaporin-1 (AQP1) water channels are expressed widely in epithelia and capillary endothelia involved in fluid transport. To test whether AQP1 facilitates water movement from capillaries into the peritoneal cavity, osmotically induced water transport rates were compared in AQP1 knockout [(−/−)], heterozygous [(+/−)], and wild-type [(+/+)] mice. In (+/+) mice, RT-PCR showed detectable transcripts for AQP1, AQP3, AQP4, AQP7, and AQP8. Immunofluorescence showed AQP1 protein in capillary endothelia and mesangium near the peritoneal surface and AQP4 in adherent muscle plasmalemma. For measurement of water transport, 2 ml of saline containing 300 mM sucrose (600 mosM) were infused rapidly into the peritoneal cavity via a catheter. Serial fluid samples (50 μl) were withdrawn over 60 min, with albumin as a volume marker. The albumin dilution data showed significantly decreased initial volume influx in AQP1 (−/−) mice: 101 ± 8, 107 ± 5, and 42 ± 4 (SE) μl/min in (+/+), (+/−), and (−/−) mice, respectively [ n = 6–10, P < 0.001, (−/−) vs. others]. Volume influx for AQP4 knockout mice was 100 ± 8 μl/min. In the absence of an osmotic gradient,3H2O uptake [half time = 2.3 and 2.2 min in (+/+) and (−/−) mice, respectively], [14C]urea uptake [half time = 7.9 and 7.7 min in (+/+) and (−/−) mice, respectively], and spontaneous isosmolar fluid absorption from the peritoneal cavity [0.47 ± 0.05 and 0.46 ± 0.04 ml/h in (+/+) and (−/−) mice, respectively] were not affected by AQP1 deletion. Therefore, AQP1 provides a major route for osmotically driven water transport across the peritoneal barrier in peritoneal dialysis.