Stable gene silencing in human monocytic cell lines using lentiviral-delivered small interference RNA. Silencing of the p110alpha isoform of phosphoinositide 3-kinase reveals differential regulation of adherence induced by 1alpha,25-dihydroxycholecalciferol and bacterial lipopolysaccharide

Liver regulatory mechanisms of noncoding variants at lipid and metabolic trait loci

Genome-wide association studies (GWASs) have identified hundreds of risk loci for liver disease and lipid-related metabolic traits, although identifying their target genes and molecular mechanisms remains challenging. We predicted target genes at GWAS signals by integrating them with molecular quantitative trait loci for liver gene expression (eQTL) and liver chromatin accessibility QTL (caQTL). We predicted specific regulatory caQTL variants at four GWAS signals located near EFHD1, LITAF, ZNF329, and GPR180. Using transcriptional reporter assays, we determined that caQTL variants rs13395911, rs11644920, rs34003091, and rs9556404 exhibit allelic differences in regulatory activity. We also performed a protein binding assay for rs13395911 and found that FOXA2 differentially interacts with the alleles of rs13395911. For variants rs13395911 and rs11644920 in putative enhancer regulatory elements, we used CRISPRi to demonstrate that repression of the enhancers altered the expression of the predicted target and/or nearby genes. Repression of the element at rs13395911 reduced the expression of EFHD1, and repression of the element at rs11644920 reduced the expression of LITAF, SNN, and TXNDC11. Finally, we showed that EFHD1 is a metabolically active gene in HepG2 cells. Together, these results provide key steps to connect genetic variants with cellular mechanisms and help elucidate the causes of liver disease.

Identification of different gene expressions between diffuse- and intestinal-type spheroid-forming gastric cancer cells

BACKGROUND

Three-dimensional in vitro spheroid models are unique because they are considered for enrichment of specific cell populations with self-renewal ability. In this study, we explored the different mechanisms of gastric cancer spheroid-forming cells according to the Lauren classification.

METHODS

We isolated and enriched cells with self-renewal ability using spheroid-forming methods from gastric cancer cell lines. The expression of candidate target genes was investigated using western blot and qRT-PCR analysis. Lentiviral shRNA knockdown of target gene expression was performed and the effects on spheroid, colony forming, and tumorigenic ability were analyzed.

RESULTS

The SNU-638, SNU-484, MKN-28, and NCI-N87 successfully formed spheroid from single cell and enriched for self-renewal ability from 11 gastric cancer cell lines, including diffuse and intestinal types. The expression of SOX2 and E-cadherin increased in spheroid-forming cells in a diffuse-type cell line (SNU-638 and SNU-484), but not in the intestinal type (MKN-28 and NCI-N87). In contrast, ERBB3 expression was only increased in intestinal-type spheroid cells. The depletion of each candidate target gene expression suppressed self-renewal ability to grow as spheroids and colonies in a soft agar assay. In particular, down-regulated ERBB3 in the intestinal-type cell lines inhibited tumor growth in a mouse xenograft model. We found that high ERBB3 gene expression correlates with decreased survival in the intestinal type of gastric cancer.

CONCLUSIONS

Our results suggest that diffuse- and intestinal-type spheroid-forming cells express genes differently. Our data suggest that these candidate genes from spheroid-forming cells can be used in applications in targeted therapy.

Regulation of ROS-NF-κB axis by tuna backbone derived peptide ameliorates inflammation in necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is the most common life-threatening gastrointestinal disease encountered in the premature infant. It has been shown that the intercellular reactive oxygen species (ROS) generation activated by lipopolysaccharide involved in the nuclear factor kappa B (NF-κB) activation and pathogenesis of NEC. Here, we report that an antioxidant peptide from tuna backbone protein (APTBP) reduces the inflammatory cytokines transcription and release. APTBP directly scavenges the free radical through 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide (PTIO) assay. In addition, APTBP reduces the intracellular ROS level, exhibiting an antioxidant activity within cells. Remarkably, gavage with APTBP attenuates the phenotype of NEC in the mice model. Mechanically, the NF-κB activation, together with the expression of inflammatory cytokines are decreased significantly when intracellular ROS are eliminated by APTBP. Therefore, our findings demonstrated that an antioxidant peptide, APTBP, ameliorates inflammation in NEC through attenuating ROS-NF-κB axis.

Macrophage migration inhibitory factor is critical for dengue NS1-induced endothelial glycocalyx degradation and hyperpermeability

Vascular leakage is one of the salient characteristics of severe dengue. Nonstructural protein 1 (NS1) of dengue virus (DENV) can stimulate endothelial cells to secrete endothelial hyperpermeability factor, macrophage migration inhibitory factor (MIF), and the glycocalyx degradation factor heparanase 1 (HPA-1). However, it is unclear whether MIF is directly involved in NS1-induced glycocalyx degradation. In this study, we observed that among NS1, MIF and glycocalyx degradation-related molecules, the HPA-1, metalloproteinase 9 (MMP-9) and syndecan 1 (CD138) serum levels were all increased in dengue patients, and only NS1 and MIF showed a positive correlation with the CD138 level in severe patients. To further characterize and clarify the relationship between MIF and CD138, we used recombinant NS1 to stimulate human cells in vitro and challenge mice in vivo. Our tabulated results suggested that NS1 stimulation could induce human endothelial cells to secrete HPA-1 and immune cells to secrete MMP-9, resulting in endothelial glycocalyx degradation and hyperpermeability. Moreover, HPA-1, MMP-9, and CD138 secretion after NS1 stimulation was blocked by MIF inhibitors or antibodies both in vitro and in mice. Taken together, these results suggest that MIF directly engages in dengue NS1-induced glycocalyx degradation and that targeting MIF may represent a possible therapeutic approach for preventing dengue-induced vascular leakage.

LINCRNA00273 promotes cancer metastasis and its G-Quadruplex promoter can serve as a novel target to inhibit cancer invasiveness

Discovery of anti-metastatic drugs is of immense clinical significance as metastasis is responsible for 90% of all cancer deaths. Here we report the inhibitory effect of a bis schiff base (M2) on cancer cell migration and invasion in vitro and in vivo. M2 has shown good solubility and permeability across the intestinal cell wall and hence can be classified as BCS (Biopharmaceutical classification system) class I. Microarray studies identified a long non coding intergenic RNA, LINC00273 as a novel molecular target of M2. We report that LINC00273 harbors a unique (4n-1) parallel G-Quadruplex structure in its promoter as validated by DMS footprint. M2 is proposed to stabilize this G-quadruplex structure resulting in the down-regulation of LINC00273 expression. Dual Luciferase reporter assay also suggests inhibition of LINC00273 promoter activity by M2. Involvement of this linc in metastasis is proven by siRNA and shRNA mediated knock down of LINC00273 in vitro and in vivo in nude mice which significantly decelerates cancer cell migration and invasion and also makes the cells unresponsive to TGF-β's pro-metastatic effects. Furthermore, the real time expression of LINC00273 in thirty seven human clinical samples is found to be positively correlated with the histopathological staging of metastasis.

Construction and identification of an RNA interference lentiviral vector targeting the mouse TNF-α gene

The aim of this study was to construct RNA interference (RNAi) lentiviral vector particles targeting the mouse tumor necrosis factor-α (TNF-α) gene. Three types of small interfering RNA (siRNA) targeting the mouse TNF-α gene were designed, synthesized and transfected into RAW264.7 cells. Screening was performed to identify the siRNA sequence exhibiting the highest inhibition efficiency; based on this, recombinant lentiviral plasmids were constructed and co-transfected into 293T cells with packaging plasmids for the production of lentiviral particles. The screening results showed that the TNF-α mRNA expression levels of the three siRNA groups were significantly lower than those of the negative control group, with the highest inhibition rate in the siRNA2 group (83.09%). Similarly, the expression levels of TNF-α protein in the three siRNA groups were significantly lower than those of the negative control group, and the highest inhibition rate was found in the siRNA2 group (51.16%). The mRNA expression of interleukin (IL)-1β and IL-6 showed no significant difference among the siRNA groups and the negative control. The recombinant lentiviral shuttle plasmid was constructed, and electrophoresis revealed the polymerase chain reaction product to be 343 bp, while that of the empty vector was 306 bp; DNA sequencing showed partial insertion. The virus titer was calculated to be 2×10⁶ TU/µl. In conclusion, RNAi lentiviral vector particles targeting the mouse TNF-α gene were successfully obtained in the present study. This method may be used to produce lentiviral vector for the in vivo study of RNAi gene therapy targeting TNF-α.

Mechanistic insights into Lp(a)-induced IL-8 expression: a role for oxidized phospholipid modification of apo(a)

Elevated lipoprotein (a) [Lp(a)] levels are a causal risk factor for coronary heart disease. Accumulating evidence suggests that Lp(a) can stimulate cellular inflammatory responses through the kringle-containing apolipoprotein (a) [apo(a)] component. Here, we report that recombinant apo(a) containing 17 kringle (17K) IV domains elicits a dose-dependent increase in interleukin (IL)-8 mRNA and protein expression in THP-1 and U937 macrophages. This effect was blunted by mutation of the lysine binding site in apo(a) kringle IV type 10, which resulted in the loss of oxidized phospholipid (oxPL) on apo(a). Trypsin-digested 17K had the same stimulatory effect on IL-8 expression as intact apo(a), while enzymatic removal of oxPL from apo(a) significantly blunted this effect. Using siRNA to assess candidate receptors, we found that CD36 and TLR2 may play roles in apo(a)-mediated IL-8 stimulation. Downstream of these receptors, inhibitors of MAPKs, Jun N-terminal kinase and ERK1/2, abolished the effect of apo(a) on IL-8 gene expression. To assess the roles of downstream transcription factors, luciferase reporter gene experiments were conducted using an IL-8 promoter fragment. The apo(a)-induced expression of this reporter construct was eliminated by mutation of IL-8 promoter binding sites for either NF-κB or AP-1. Our results provide a mechanistic link between oxPL modification of apo(a) and stimulation of proinflammatory intracellular signaling pathways.

Overexpression of Csk-binding protein decreases growth, invasion, and migration of esophageal carcinoma cells by controlling Src activation

AIM: To investigate the mechanisms by which Csk-binding protein (CBP) inhibits tumor progression in esophageal carcinoma.

METHODS: A CBP overexpressing esophageal carcinoma cell line (TE-1) was established. The growth, invasion, and migration of CBP-TE-1 cells, as well as the expression of Src were then determined and compared with those in normal TE-1 cells.

RESULTS: The expression of Src was decreased by the overexpression of CBP in TE-1 cells. The growth, invasion, and migration of TE-1 cells were decreased by the overexpression of CBP.

CONCLUSION: This study indicates that CBP may decrease the metastasis of esophageal carcinoma by inhibiting the activation of Src. CBP may be a potential tumor suppressor and targeting the CBP gene may be an alternative strategy for the development of therapies for esophageal carcinoma.

Signaling via class IA Phosphoinositide 3-kinases (PI3K) in human, breast-derived cell lines

We have addressed the differential roles of class I Phosphoinositide 3-kinases (PI3K) in human breast-derived MCF10a (and iso-genetic derivatives) and MDA-MB 231 and 468 cells. Class I PI3Ks are heterodimers of p110 catalytic (α, β, δ and γ) and p50-101 regulatory subunits and make the signaling lipid, phosphatidylinositol (3,4,5)-trisphosphate (PtdIns(3,4,5)P3) that can activate effectors, eg protein kinase B (PKB), and responses, eg migration. The PtdIns(3,4,5)P3-3-phosphatase and tumour-suppressor, PTEN inhibits this pathway. p110α, but not other p110s, has a number of onco-mutant variants that are commonly found in cancers. mRNA-seq data shows that MCF10a cells express p110β>>α>δ with undetectable p110γ. Despite this, EGF-stimulated phosphorylation of PKB depended upon p110α-, but not β- or δ- activity. EGF-stimulated chemokinesis, but not chemotaxis, was also dependent upon p110α, but not β- or δ- activity. In the presence of single, endogenous alleles of onco-mutant p110α (H1047R or E545K), basal, but not EGF-stimulated, phosphorylation of PKB was increased and the effect of EGF was fully reversed by p110α inhibitors. Cells expressing either onco-mutant displayed higher basal motility and EGF-stimulated chemokinesis.This latter effect was, however, only partially-sensitive to PI3K inhibitors. In PTEN(-/-) cells, basal and EGF-stimulated phosphorylation of PKB was substantially increased, but the p110-dependency was variable between cell types. In MDA-MB 468s phosphorylation of PKB was significantly dependent on p110β, but not α- or δ- activity; in PTEN(-/-) MCF10a it remained, like the parental cells, p110α-dependent. Surprisingly, loss of PTEN suppressed basal motility and EGF-stimulated chemokinesis. These results indicate that; p110α is required for EGF signaling to PKB and chemokinesis, but not chemotaxis; onco-mutant alleles of p110α augment signaling in the absence of EGF and may increase motility, in part, via acutely modulating PI3K-activity-independent mechanisms. Finally, we demonstrate that there is not a universal mechanism that up-regulates p110β function in the absence of PTEN.

CXCL1 contributes to β-amyloid-induced transendothelial migration of monocytes in Alzheimer's disease

Background

Bone marrow-derived microglia that originates in part from hematopoietic cells, and more particularly from monocytes preferentially attach to amyloid deposition in brains of Alzheimer’s disease (AD). However, the mechanism of monocytes recruited into the amyloid plaques with an accelerated process in AD is unclear.

Methodology/Principal Findings

Here we reported that monocytes from AD patients express significantly higher chemokine (C-X-C motif) ligand 1 (CXCL1) compared to age-matched controls. AD patient’s monocytes or CXCL1-overexpressing THP-1 cells had enhanced ability of β-amyloid (Aβ)-induced transendothelial migration and Aβ-induced transendothelial migration for AD patient’s monocytes or CXCL1-overexpressing THP-1 cells was almost abrogated by anti-CXCL1 antibody. Furthermore, monocytes derived from a transgenic mouse model of AD also expressed significantly higher CXCL1. CD11b⁺CD45^hi population of cells that were recruited from the peripheral blood were markedly bolcked in APP mouse brain by anti-CXCL1 antibody. Accordingly, in response to Aβ, human brain microvascular endothelial cells (HBMEC) significantly up-regulated CXC chemokine receptor 2 (CXCR2) expression, which was the only identified receptor for CXCL1. In addition, a high level expression of CXCR2 in HBMEC significantly promoted the CXCL1-overexpressing THP-1 cells transendothelial migration, which could be was abrogated by anti-CXCR2 antibody. Further examination of possible mechanisms found that CXCL1-overexpressing THP-1 cells induced transendothelial electrical resistance decrease, horseradish peroxidase flux increase, ZO-1 discontinuous and occludin re-distribution from insoluble to soluble fraction through interacting with CXCR2. ROCK inhibitor, Y27632, could block CXCL1-overexpressing THP-1 cells transendothelial migration, whereas other inhibitors had no effects.

Conclusions/Significance

The present data indicate that monocytes derived from AD patients overexpressing CXCL1, which is a determinant for Aβ-induced transendothelial migration. CXCL1 expressed by monocytes and CXCR2 on HBMEC is involved in monocytes migrating from blood to brain in AD patients.

Effective non-viral delivery of siRNA to acute myeloid leukemia cells with lipid-substituted polyethylenimines

Use of small interfering RNA (siRNA) is a promising approach for AML treatment as the siRNA molecule can be designed to specifically target proteins that contribute to aberrant cell proliferation in this disease. However, a clinical-relevant means of delivering siRNA molecules must be developed, as the cellular delivery of siRNA is problematic. Here, we report amphiphilic carriers combining a cationic polymer (2 kDa polyethyleneimine, PEI2) with lipophilic moieties to facilitate intracellular delivery of siRNA to AML cell lines. Complete binding of siRNA by the designed carriers was achieved at a polymer:siRNA ratio of ∼0.5 and led to siRNA/polymer complexes of ∼100 nm size. While the native PEI2 did not display cytotoxicity on AML cell lines THP-1, KG-1 and HL-60, lipid-modification on PEI2 slightly increased the cytotoxicity, which was consistent with increased interaction of polymers with cell membranes. Cellular delivery of siRNA was dependent on the nature of lipid substituent and the extent of lipid substitution, and varied among the three AML cell lines used. Linoleic acid-substituted polymers performed best among the prepared polymers and gave a siRNA delivery equivalent to better performing commercial reagents. Using THP-1 cells and a reporter (GFP) and an endogenous (CXCR4) target, effective silencing of the chosen targets was achieved with 25 to 50 nM of siRNA concentrations, and without adversely affecting subsequent cell growth. We conclude that lipid-substituted PEI2 can serve as an effective delivery of siRNA to leukemic cells and could be employed in molecular therapy of leukemia.

Class IA phosphatidylinositol 3-kinase p110α regulates phagosome maturation

Of the various phosphatidylinositol 3- kinases (PI3Ks), only the class III enzyme Vps34 has been shown to regulate phagosome maturation. During studies of phagosome maturation in THP-1 cells deficient in class IA PI3K p110α, we discovered that this PI3K isoform is required for vacuole maturation to progress beyond acquisition of Rab7 leading to delivery of lysosomal markers. Bead phagosomes from THP-1 cells acquired p110α and contained PI3P and PI(3,4,5)P3; however, p110α and PI(3,4,5)P3 levels in phagosomes from p110α knockdown cells were decreased. Phagosomes from p110α knock down cells showed normal acquisition of both Rab5 and EEA-1, but were markedly deficient in the lysosomal markers LAMP-1 and LAMP-2, and the lysosomal hydrolase, β-galactosidase. Phagosomes from p110α deficient cells also displayed impaired fusion with Texas Red dextran-loaded lysosomes. Despite lacking lysosomal components, phagosomes from p110α deficient cells recruited normal levels of Rab7, Rab-interacting lysosomal protein (RILP) and homotypic vacuole fusion and protein sorting (HOPs) components Vps41 and Vps16. The latter observations demonstrated that phagosomal Rab7 was active and capable of recruiting effectors involved in membrane fusion. Nevertheless, active Rab7 was not sufficient to bring about the delivery of lysosomal proteins to the maturing vacuole, which is shown for the first time to be dependent on a class I PI3K.

Enhanced cartilage formation by inhibiting cathepsin K expression in chondrocytes expanded in vitro

Although engineered cartilage has great potential in cartilage regeneration and reconstruction, dedifferentiation of chondrocytes during in vitro expansion remains a technical bottleneck in the clinical application. To overcome the problem, a gene modification approach was developed to knock-down the key gene involving dedifferentiation of human chondrocytes. A microarray assay revealed 84 up-regulated genes and 56 down-regulated genes in passage 4 (dedifferentiated) human chondrocytes compared to passage 1 cells. Among them, cathepsin K (CTSK) was the key gene (with 28 folds of increased gene expression), which was further confirmed by RT-PCR and Western-Blot. Furthermore, over-expression of CTSK led to reduced matrix production in cultured human chondrocytes in vitro and poor formation of engineered cartilage in vivo. In contrast, CTSK knock-down could better maintain the chondrogenic phenotype of in vitro expanded cells with increased gene and protein expression of collagen II and aggrecan when compared to control cells. More importantly, after 6 passages, the knock-down cells formed much better engineered cartilage than the control cells after in vivo implantation with 30% Pluronic F127 for 8 weeks as the experimental group formed much bigger sized cartilages with significantly increased weight and glycosaminoglycan content (p < 0.05) than the control group. Histologically, the knock-down cells formed a more homogenous cartilage structure with enhanced production of collagen II and proteoglycans. Overall, these results suggest that CTSK knock-down may provide a feasible way to expand functional human chondrocytes in vitro for engineering good quality human cartilage and thus may have its great potential in the clinical translation of engineered cartilage in the future, given the fact that biosafe RNA interference techniques are already available.

Phosphoinositides in chemotaxis

Phosphatidylinositol lipids generated through the action of phosphinositide 3-kinase (PI3K) are key mediators of a wide array of biological responses. In particular, their role in the regulation of cell migration has been extensively studied and extends to amoeboid as well as mesenchymal migration. Through the emergence of fluorescent probes that target PI3K products as well as the use of specific inhibitors and knockout technologies, the spatio-temporal distribution of PI3K products in chemotaxing cells has been shown to represent a key anterior polarity signal that targets downstream effectors to actin polymerization. In addition, through intricate cross-talk networks PI3K products have been shown to regulate signals that control posterior effectors. Yet, in more complex environments or in conditions where chemoattractant gradients are steep, a variety of cell types can still chemotax in the absence of PI3K signals. Indeed, parallel signal transduction pathways have been shown to coordinately regulate cell polarity and directed movement. In this chapter, we will review the current role PI3K products play in the regulation of directed cell migration in various cell types, highlight the importance of mathematical modeling in the study of chemotaxis, and end with a brief overview of other signaling cascades known to also regulate chemotaxis.

PIPKIγ regulates β-catenin transcriptional activity downstream of growth factor receptor signaling

Increased β-catenin transcriptional activity downstream of the Wnt/Wingless signaling pathway has been observed in many human tumors, most notably colorectal carcinomas. However, β-catenin activation is also observed in many human malignancies with no observable Wnt activity. Wnt-independent pathways that activate β-catenin remain undefined, yet have the potential to play a significant role during tumorigenesis. Here, we report that phosphotidylinositol phosphate kinase Iγ (PIPKIγ), an enzyme that generates phosphoinositide messengers in vivo, directly associates with β-catenin and increases β-catenin activity downstream of growth factor stimulation. PIPKIγ expression and kinase activity enhance β-catenin phosphorylation on residues that promote nuclear importation and transcriptional activity. Lastly, we show that β-catenin is required for PIPKIγ-dependent increased cell proliferation. These results reveal a novel mechanism in which PIPKIγ expression and catalytic activity enhance β-catenin nuclear translocation and expression of its target genes to promote tumorigenic phenotypes.

Efficient non-viral transfection of THP-1 cells

Macrophages are an important part of the cellular immune system and play a key role during immune responses. Thus, macrophages are interesting targets in basic and clinical research. Primary monocytes or monocyte-derived macrophages do not proliferate on a suitable scale so that their use for functional studies in vitro is limited. Immortal proliferating cell lines, such as the human THP-1 monocytic leukemia cell line, are therefore often used instead of primary cells. Transfection is a useful tool to study the function of gene products, but transfection of THP-1 monocytes and pre-differentiated THP-1 macrophages with subsequent differentiation into mature THP-1 macrophages using phorbol esters is usually accompanied by a progressive loss of cell viability. In this study, we describe a simple and rapid approach for efficient transfection of THP-1 monocytes and pre-differentiated THP-1 macrophages using a modified Nucleofection-based approach. The protocol maintains cell viability and functionality, thus allowing efficient transfection of THP-1 cells combined with subsequent differentiation of transfected THP-1 cells into mature macrophages.

Phosphoinositide 3-kinases in cell migration

Cell migration is essential for many biological processes in animals and is a complex highly co-ordinated process that involves cell polarization, actin-driven protrusion and formation and turnover of cell adhesions. The PI3K (phosphoinositide 3-kinase) family of lipid kinases regulate cell migration in many different cell types, both through direct binding of proteins to their lipid products and indirectly through crosstalk with other pathways, such as Rho GTPase signalling. Emerging evidence suggests that the involvement of PI3Ks at different stages of migration varies even within one cell type, and is dependent on the combination of external stimuli, as well as on the signalling status of the cell. In addition, it appears that different PI3K isoforms have distinct roles in cell polarization and migration. This review describes how PI3K signalling is regulated by pro-migratory stimuli, and the diverse ways in which PI3K-mediated signal transduction contributes to different aspects of cell migration.

Stable lentiviral vector-mediated gene silencing in human monocytic cell lines

A major obstacle in studying monocyte cell biology has been the resistance of these cells to genetic manipulation, particularly when using nonviral methods. In the approach outlined in this chapter, we describe a strategy for stable gene silencing of monocytic cells. Using a vesicular stomatitis virus (VSV)-pseudotyped lentiviral vector expressing short hairpin RNA (shRNA), stable silencing of the p110alpha isoform of PI3-kinase in the human monocytic cell lines THP-1 and U-937 was achieved.

Modifications in low-density lipoprotein receptor expression affects Cyclosporin A cellular uptake and cytotoxicity

The purpose of this study was to test the effect of modulating the expression of the human low-density lipoprotein receptor (LDLr) in human embryonic kidney (293T) cells on Cyclosporin A (CsA) cellular uptake and CsA-mediated cytotoxicity. LDLr expression was modulated using RNA interference (RNAi) and an LDLr overexpression plasmid. One of the small-interfering RNA (siRNA) constructs, LDLr-792, showed a 60% decrease in LDLr protein expression. The downregulation effect was specific as transfection with an annexin V (AxV) siRNA construct did not decrease LDLr expression levels. AxV and ABCA1 expression levels were not affected in the cells transfected with LDLr-792 (LDLr(LOW) cells) compared to the controls. At a functional level, fluorescent low-density lipoprotein (LDL) (DiI-LDL) internalization in the LDLr(LOW) cells was decreased (30%) compared to control cells. We tested the dose-dependent cytotoxicity induced by CsA using a respiration assay. We found a decrease in CsA-mediated cytotoxicity in the range of CsA doses studied (1-10 microg/mL) in the LDLr(LOW) cells compared to the pSHAG-transfected cells, reaching a statistical significance at 10 microg/mL CsA. At higher CsA doses we found a significant decrease in LDLr expression. When the control and LDLr(LOW) cells were treated with another cytotoxic drug, gentamycin, there was no difference in the cell viability, suggesting that this effect is specific for CsA. We confirmed the association of LDLr expression levels with CsA uptake by overexpressing the LDLr. The LDLr overexpressing cells showed an enhanced uptake of radiolabelled CsA. Taken together these results suggest that CsA internalization and cytotoxicity are affected by the LDL receptor expression levels.

Differential control of CXCR4 and CD4 downregulation by HIV-1 Gag

Background

The ESCRT (endosomal sorting complex required for transport) machinery functions to sort cellular receptors into the lumen of the multivesicular body (MVB) prior to lysosomal degradation. ESCRT components can also be recruited by enveloped viruses to sites of viral assembly where they have been proposed to mediate viral egress. For example, HIV-1 budding is dependent on Gag-mediated recruitment of the cellular ESCRTs-I, -III, AIP1/Alix and Vps4 proteins. Viral recruitment of ESCRT proteins could therefore impact on host cell processes such as receptor downregulation.

Results

Here we show that downregulation of the HIV-1 co-receptor, CXCR4, by its ligand SDF-1, is ESCRT-I dependent. Expression of HIV-1 Gag attenuated downregulation of CXCR4, resulting in accumulation of undegraded receptors within intracellular compartments. The effect of Gag was dependent on an ESCRT-I interacting motif within the C-terminal p6 region of Gag. In contrast, PMA-induced downregulation of the HIV-1 receptor CD4 was independent of ESCRT-I and Vps4; HIV-1 Gag had no effect on this process.

Conclusion

These results establish that the HIV-1 receptor, CD4, and co-receptor, CXCR4 are differentially regulated by ESCRT proteins. HIV-1 Gag selectively modulates protein sorting at the MVB, interfering with ESCRT-I dependent but not ESCRT-I independent processes.

The vitamin D receptor-mediated activation of phosphatidylinositol 3-kinase (PI3Kα) plays a role in the 1α,25-dihydroxyvitamin D3-stimulated increase in steroid sulphatase activity in myeloid leukaemic cell lines

In this article we show that 1alpha,25-dihydroxyvitamin D(3) (1alpha,25(OH)(2)D(3)) stimulates the activity of the class IA phosphatidylinositol 3-kinase PI3Kalpha and its downstream target Akt in HL60, U937 and THP-1 myeloid leukaemic cell lines. Furthermore, we show that the classical nuclear vitamin D receptor (VDR(nuc)) is involved in this activation of the PI3K/Akt signalling in these cell lines. We have previously shown that the activity of steroid sulphatase is stimulated in HL60, U937 and THP-1 myeloid leukaemic cell lines by 1alpha,25(OH)(2)D(3) (Hughes et al., [2001] Biochem J 355:361-371; Hughes et al., [2005] J Cell Biochem 94:1175-1189; Hughes and Brown [2006] J Cell Biochem 98:590-617). In this article we show that the 1alpha,25(OH)(2)D(3)-stimulated increase in signalling via the PI3K/Akt pathway plays a role in the increase in steroid sulphatase activity in the HL60 U937 and THP-1 cell lines. We used a variety of pharmacological and biochemical approaches to show that activation of PI3Kalpha mediates the 1alpha,25(OH)(2)D(3)-stimulated increase in steroid sulphatase activity in myeloid leukaemic cells. We also show that the PI3K/Akt dependent activation of NF-kappaB plays a role in the 1alpha,25(OH)(2)D(3)-stimulated increase in steroid sulphatase activity in myeloid leukaemic cells.

Human ribosomal protein L13a is dispensable for canonical ribosome function but indispensable for efficient rRNA methylation

Previously, we demonstrated that treatment of monocytic cells with IFN-gamma causes release of ribosomal protein L13a from the 60S ribosome and subsequent translational silencing of Ceruloplasmin (Cp) mRNA. Here, evidence using cultured cells demonstrates that Cp mRNA silencing is dependent on L13a and that L13a-deficient ribosomes are competent for global translational activity. Human monocytic U937 cells were stably transfected with two different shRNA sequences for L13a and clonally selected for more than 98% abrogation of total L13a expression. Metabolic labeling of these cells showed rescue of Cp translation from the IFN-gamma mediated translational silencing activity. Depletion of L13a caused significant reduction of methylation of ribosomal RNA and of cap-independent translation mediated by Internal Ribosome Entry Site (IRES) elements derived from p27, p53, and SNAT2 mRNAs. However, no significant differences in the ribosomal RNA processing, polysome formation, global translational activity, translational fidelity, and cell proliferation were observed between L13a-deficient and wild-type control cells. These results support the notion that ribosome can serve as a depot for releasable translation-regulatory factors unrelated to its basal polypeptide synthetic function. Unlike mammalian cells, the L13a homolog in yeast is indispensable for growth. Thus, L13a may have evolved from an essential ribosomal protein in lower eukaryotes to having a role as a dispensable extra-ribosomal function in higher eukaryotes.

Monocyte p110alpha phosphatidylinositol 3-kinase regulates phagocytosis, the phagocyte oxidase, and cytokine production

Mononuclear phagocytes are critical modulators and effectors of innate and adaptive immune responses, and PI-3Ks have been shown to be multifunctional monocyte regulators. The PI-3K family includes eight catalytic isoforms, and only limited information is available about how these contribute to fine specificity in monocyte cell regulation. We examined the regulation of phagocytosis, the phagocyte oxidative burst, and LPS-induced cytokine production by human monocytic cells deficient in p110alpha PI-3K. We observed that p110alpha PI-3K was required for phagocytosis of IgG-opsonized and nonopsonized zymosan in differentiated THP-1 cells, and the latter was inhibitable by mannose. In contrast, p110alpha PI-3K was not required for ingestion serum-opsonized zymosan. Taken together, these results suggest that FcgammaR- and mannose receptor-mediated phagocytosis are p110alpha-dependent, whereas CR3-mediated phagocytosis involves a distinct isoform. It is notable that the phagocyte oxidative burst induced in response to PMA or opsonized zymosan was also found to be dependent on p110alpha in THP-1 cells. Furthermore, p110alpha was observed to exert selective and bidirectional effects on the secretion of pivotal cytokines. Incubation of p110alpha-deficient THP-1 cells with LPS showed that p110alpha was required for IL-12p40 and IL-6 production, whereas it negatively regulated the production of TNF-alpha and IL-10. Cells deficient in p110alpha also exhibited enhanced p38 MAPK, JNK, and NF-kappaB phosphorylation. Thus, p110alpha PI-3K appears to uniquely regulate important monocyte functions, where other PI-3K isoforms are uninvolved or unable to fully compensate.

Cyclosporin A and FK506 inhibit IL-12p40 production through the calmodulin/calmodulin-dependent protein kinase-activated phosphoinositide 3-kinase in lipopolysaccharide-stimulated human monocytic cells

Cyclosporine-A (CyA) and FK506 are potent immunosuppressive agents because of their ability to suppress the production of Th1 cytokines including interleukin (IL)-12. However, the mechanisms underlying the inhibitory effects of CyA and FK506 on the production of IL-12p40, a critical component of IL-12, remain unknown. Both CyA and FK506 are potent inhibitors of calcineurin in the calcium signaling pathway. Interestingly, calcium and phosphoinositide 3-kinase (PI3K) signaling pathways have been shown to negatively regulate lipopolysaccharide (LPS)-induced murine IL-12p40 production. Contrary to these observations, we show that LPS-induced IL-12p40 production in human monocytic cells is positively regulated by the calcium pathway and in particular by calmodulin-(CaM) and CaM-dependent protein kinase-II (CaMK-II)-activated PI3K. Furthermore, LPS-induced IL-12p40 production was regulated by the p110alpha catalytic subunit of PI3K. Moreover, LPS induced IL-12p40 production through the CaM/CaMK-II-activated NFkappaB and AP-1 transcription factors. LPS-induced IL-12p40 production is known to be regulated by the c-Jun N-terminal kinase (JNK) pathway. Importantly, both CyA and FK506 down-regulated LPS-induced IL-12p40 transcription by inhibiting CaM/CaMK-II-activated PI3K and their downstream transcription factors NFkappaB and AP-1 independent of the JNK pathway.

1alpha,25-dihydroxycholecalciferol activates binding of CREB to a CRE site in the CD14 promoter and drives promoter activity in a phosphatidylinositol-3 kinase-dependent manner

1,25-dihydroxycholecalciferol, also known as 1alpha,25-dihydroxyvitamin D3 or calcitriol, regulates the differentiation and functional properties of mononuclear phagocytes. Many of these effects involve nongenomic signaling pathways, which are not fully understood. Activation of CD14 expression, a monocyte differentiation marker and coreceptor with TLR-2 for bacterial LPS, by calcitriol was shown previously to be PI-3K-dependent [1]; however, the mechanism of gene activation remained undefined. Using a transcription factor-binding array screen coupled with EMSA, we found evidence for PI-3K-dependent activation of CREB in THP-1 cells incubated with calcitriol. Furthermore, analysis of the proximal promoter of human CD14 identified regions that contained up to seven sequences, which showed significant similarity to a canonical CRE sequence, 5'-TGACGTCA-3'. Treatment of THP-1 cells with calcitriol activated CREB binding to one of these regions at Positions -37 to -55, relative to the transcription start site in a PI-3K-dependent manner. This 19-mer region also became transcriptionally active in a reporter assay in response to calcitriol, again dependent on PI-3K. Mutation of the CRE within the 19-mer abolished this activity. Taken together, these results show that calcitriol signaling, leading to activation of the CD14 promoter, involves CREB activation downstream of PI-3K.

Inhibition of viruses by RNA interference

RNA-mediated interference (RNAi) is a recently discovered process by which dsRNA is able to silence specific gene functions. Although initially described in plants, nematodes and Drosophila, the process is currently considered to be an evolutionarily conserved process that is present in the entire eukaryotic kingdom in which its original function was as a defense mechanism against viruses and foreign nucleic acids. Similarly to the silencing of genes by RNAi, viral functions can be also silenced by the same mechanism, through the introduction of specific dsRNA molecules into cells, where they are targeted to essential genes or directly to the viral genome in case RNA viruses, thus arresting viral replication. Since the pioneering work of Elbashir and coworkers, who identified RNAi activity in mammalian cells, many publications have described the inhibition of viruses belonging to most if not all viral families, by targeting and silencing diverse viral genes as well as cell genes that are essential for virus replication. Moreover, virus expression vectors were developed and used as vehicles with which to deliver siRNAs into cells. This review will describe the use of RNAi to inhibit virus replication directly, as well as through the silencing of the appropriate cell functions.

Phosphoinositide3-kinase regulates actin polymerization during delayed phagocytosis of Helicobacter pylori

We have shown previously that ulcerogenic (type I) strains of Helicobacter pylori (Hp) retard their entry into macrophages. However, the signaling pathways that regulate Hp phagocytosis are largely undefined. We show here that Hp strongly activated class IA phosphoinositide3-kinases (PI3Ks) in macrophages, coincident with phagocytosis, and endogenous p85 and active protein kinase Balpha accumulated on forming phagosomes. PI3K inhibitors, wortmannin and LY294002, inhibited phagocytosis of Hp in a dose-dependent manner, and blockade of engulfment correlated directly with loss of 3'-phosphoinositides in the membrane subjacent to attached bacteria. During uptake of large immunoglobulin G (IgG)-coated particles, PI3Ks regulate pseudopod extension and phagosome closure. In marked contrast, we show here that 3'-phosphoinositides regulated actin polymerization at sites of Hp uptake. Moreover, Hp and IgG beads activated distinct PI3K isoforms. Phagosomes containing IgG-coated particles accumulated 3'-phosphatase and tensin homologue deleted on chromosome 10 and Src homology 2 domain-containing inositol 5'-phosphatase, yet Hp phagosomes did not. Finally, rapid uptake of IgG-opsonized Hp or a less-virulent type II Hp was PI3K-independent. We conclude that Hp and IgG beads are ingested by distinct mechanisms and that PI3Ks regulate the actin cytoskeleton during slow phagocytosis of ulcerogenic Hp.

An interfering RNA protocol for primary porcine alveolar macrophages

RNA interference (RNAi) is a cellular process of post-transcriptional gene silencing in which a short interfering dsRNA (siRNA, 21-23 nt) targets a homologous mRNA for degradation by ribonuclease. RNAi has been used successfully to inhibit targeted gene expression and viral replication in mammalian cells. In this study we established an RNAi transfection protocol for primary porcine alveolar macrophages and evaluated potential off-target effects of siRNA introduction into these cells. Porcine alveolar macrophages were transfected using a fluorescence-labeled siRNA to compare transfection reagents from different suppliers. Under optimized transfection conditions, up to 95% of macrophages were fluorescent at 12 and 24 h post-transfection using an amine-based transfection reagent. An siRNA targeting GAPDH suppressed macrophage endogenous GAPDH transcript levels as much as 60% through 24h. Further, we did not detect a significant interferon response following siRNA transfection. These data suggest that RNAi will be an efficient and convenient approach for studying loss of gene function in primary porcine alveolar macrophages.

Signalling by PI3K isoforms: insights from gene-targeted mice

Phosphoinositide 3-kinases (PI3Ks) generate lipids that control a wide variety of intracellular signalling pathways. Part of this diversity in PI3K actions stems from the broad range of protein effectors of the PI3K lipids. A further layer of complexity is added by the existence of multiple isoforms of PI3K. Gene-targeting studies in the mouse have recently uncovered key roles for specific PI3K isoforms in immunity, metabolism and cardiac function. Remarkably, some of these actions do not require PI3K catalytic activity. In addition, loss-of-expression of certain PI3K genes leads to increased PI3K signalling following insulin stimulation. PI3K gene targeting has, in many cases, led to altered expression of the non-targeted PI3K subunits, making it difficult to exclude that some of the reported phenotypes result from 'knock-on' effects of PI3K gene deletion. Targeting strategies that take into account the complex interplay between members of the PI3K family will be crucial to gain a full understanding of the physiological roles of the isoforms of PI3K.

Deficiency in the p110alpha subunit of PI3K results in diminished Tie2 expression and Tie2(-/-)-like vascular defects in mice

Phosphoinositide 3-kinase (PI3K) is activated by transmembrane tyrosine kinases such as vascular endothelial growth factor (VEGF) receptors and Tie2 (tunica intima endothelial kinase 2), both of which are key regulators of vascular development. However, the in vivo role of PI3K during developmental vascularization remains to be defined. Here we demonstrate that mice deficient in the p110alpha catalytic subunit of PI3K display multiple vascular defects, including dilated vessels in the head, reduced branching morphogenesis in the endocardium, lack of hierarchical order of large and small branches in the yolk sac, and impaired development of anterior cardinal veins. These vascular defects are strikingly similar to those in mice defective in the Tie2 signaling pathway. Indeed, Tie2 protein levels were significantly lower in p110alpha-deficient mice. Furthermore, RNA interference of p110alpha in cultured endothelial cells significantly reduced Tie2 protein levels. These findings raise the possibility that PI3K may function as an upstream regulator of Tie2 expression during mouse development.

1?,25-dihydroxyvitamin D3 stimulates steroid sulphatase activity in HL60 and NB4 acute myeloid leukaemia cell lines by different receptor-mediated mechanisms

Steroid sulphatase is a key enzyme in the biosynthesis of bioactive estrogens and androgens from highly abundant inactive circulating sulphated steroid precursors. Little is known about how the expression/activity of this enzyme is regulated. In this article, we show that of 1alpha,25(OH)2D3 stimulates an increase steroid sulphatase activity in the HL60 myeloid leukaemic cell line that is inhibited by a specific nuclear VDR (VDRnuc) antagonist and unaffected by plasma membrane-associated vitamin D receptor (VDRmem) agonists and antagonists. 1alpha,25(OH)2D3-mediated up-regulation of steroid sulphatase activity in HL60 cells was augmented by RXR agonists, blocked by RXR-specific antagonists, and RAR specific agonists and antagonists had no effect. In contrast, the 1alpha,25(OH)2D3-mediated up-regulation of steroid sulphatase activity in the NB4 myeloid leukaemic cell line was unaffected by the specific VDRnuc and RXR antagonists, but was blocked by a VDRmem-specific antagonist and was increased by VDRmem-specific agonists. The findings reveal that VDRnuc-RXR-heterodimers play a key role in the 1alpha,25(OH)2D3-mediated up-regulation of steroid sulphatase activity in HL60 cells. However, in NB4 cells, VDRnuc-derived signals do not play an obligatory role, and non-genomic VDRmem-derived signals are important.

Cutting edge: direct interaction of TLR4 with NAD(P)H oxidase 4 isozyme is essential for lipopolysaccharide-induced production of reactive oxygen species and activation of NF-kappa B

LPS, the primary constituent of the outer membrane of Gram-negative bacteria, is recognized by TLR4. Binding of TLR4 to LPS triggers various cell signaling pathways including NF-kappaB activation and reactive oxygen species (ROS) production. In this study, we present the data that LPS-induced ROS generation and NF-kappaB activation are mediated by a direct interaction of TLR4 with (NAD(P)H oxidase 4 (Nox) 4), a protein related to gp91phox (Nox2) of phagocytic cells, in HEK293T cells. Yeast two hybrid and GST pull-down assays indicated that the COOH-terminal region of Nox4 interacted with the cytoplasmic tail of TLR4. Knockdown of Nox4 by transfection of small interference RNA specific to the Nox4 isozyme in HEK293T cells expressing TLR4 along with MD2 and CD14 resulted in inhibition of LPS-induced ROS generation and NF-kappaB activation. Taken together, these results indicate that direct interaction of TLR4 with Nox4 is involved in LPS-mediated ROS generation and NF-kappaB activation.