Mock Transfectants Research Articles

Proteolytic Processing Causes Extensive Heterogeneity of Tissue Matrilin Forms

The matrilins are a family of multidomain extracellular matrix proteins with adapter functions. The oligomeric proteins have a bouquet-like structure and bind to a variety of different ligands whereby the avidity of their interactions is dependent on the number of subunits and domains present. Here we show the contribution of post-translational proteolytic processing to the heterogeneity of matrilins seen in tissue extracts and cell culture supernatants. A cleavage site after two glutamate residues in the hinge region close to the C-terminal coiled-coil oligomerization domain is conserved among the matrilins. Cleavage at this site yields molecules that lack almost complete subunits. The processing is least pronounced in matrilin-1 and particularly complex in matrilin-2, which contains additional cleavage sites. Replacement of the hinge region in matrilin-4 by the matrilin-1 hinge region had no marked effect on the processing. A detailed study revealed that matrilin-4 is processed already in the secretory pathway and that the activation of the responsible enzymes is dependent on proprotein convertase activity. Matrilin-3 and -4, but not matrilin-1 subunits present in matrilin-1/-3 hetero-oligomers, were identified as substrates for ADAMTS4 and ADAMTS5, whereas ADAMTS1 did not cleave any matrilin. A neo-epitope antibody raised against the N terminus of the C-terminal cleavage product of matrilin-4 detected processed matrilin-4 in cultures of primary chondrocytes as well as on cartilage sections showing that the conserved cleavage site is used in vivo.

Hereditary folate malabsorption: A positively charged amino acid at position 113 of the proton-coupled folate transporter (PCFT/SLC46A1) is required for folic acid binding

The proton-coupled folate transporter (PCFT/SLC46A1) mediates intestinal folate uptake at acidic pH. Some loss of folic acid (FA) transport mutations in PCFT from hereditary folate malabsorption (HFM) patients cluster in R113, thereby suggesting a functional role for this residue. Herein, unlike non-conservative substitutions, an R113H mutant displayed 80-fold increase in the FA transport Km while retaining parental Vmax, hence indicating a major fall in folate substrate affinity. Furthermore, consistent with the preservation of 9% of parental transport activity, R113H transfectants displayed a substantial decrease in the FA growth requirement relative to mock transfectants. Homology modeling based on the crystal structures of the Escherichia coli transporter homologues EmrD and glycerol-3-phosphate transporter revealed that the R113H rotamer properly protrudes into the cytoplasmic face of the minor cleft normally occupied by R113. These findings constitute the first demonstration that a basic amino acid at position 113 is required for folate substrate binding.

Polymeric Osteopontin Employs Integrin α9β1 as a Receptor and Attracts Neutrophils by Presenting a de Novo Binding Site

Osteopontin (OPN) is a cytokine and ligand for multiple members of the integrin family. OPN undergoes the in vivo polymerization catalyzed by cross-linking enzyme transglutaminase 2, which consequently increases the bioactivity through enhanced interaction with integrins. The integrin alpha9beta1, highly expressed on neutrophils, binds to the sequence SVVYGLR only after intact OPN is cleaved by thrombin. The SVVYGLR sequence appears to be cryptic in intact OPN because alpha9beta1 does not recognize intact OPN. Because transglutaminase 2-catalyzed polymers change their physical and chemical properties, we hypothesized that the SVVYGLR site might also be exposed on polymeric OPN. As expected, alpha9beta1 turned into a receptor for polymeric OPN, a result obtained by cell adhesion and migration assays with alpha9-transfected cells and by detection of direct binding of recombinant soluble alpha9beta1 with colorimetry and surface plasmon resonance analysis. Because the N-terminal fragment of thrombin-cleaved OPN, a ligand for alpha9beta1, has been reported to attract neutrophils, we next examined migration of neutrophils to polymeric OPN using time-lapse microscopy. Polymeric OPN showed potent neutrophil chemotactic activity, which was clearly inhibited by anti-alpha9beta1 antibody. Unexpectedly, mutagenesis studies showed that alpha9beta1 bound to polymeric OPN independently of the SVVYGLR sequence, and further, SVVYGLR sequence of polymeric OPN was cryptic because SVVYGLR-specific antibody did not recognize polymeric OPN. These results demonstrate that polymerization of OPN generates a novel alpha9beta1-binding site and that the interaction of this site with the alpha9beta1 integrin is critical to the neutrophil chemotaxis induced by polymeric OPN.

Cancer Metastasis Is Accelerated through Immunosuppression during Snail-Induced EMT of Cancer Cells

Epithelial-mesenchymal transition (EMT) is a key step toward cancer metastasis, and Snail is a major transcription factor governing EMT. Here, we demonstrate that Snail-induced EMT accelerates cancer metastasis through not only enhanced invasion but also induction of immunosuppression. Murine and human melanoma cells with typical EMT features after snail transduction induced regulatory T cells and impaired dendritic cells in vitro and in vivo partly through TSP1 production. Although Snail(+) melanoma did not respond to immunotherapy, intratumoral injection with snail-specific siRNA or anti-TSP1 monoclonal antibody significantly inhibited tumor growth and metastasis following increase of tumor-specific tumor-infiltrating lymphocytes and systemic immune responses. These results suggest that inhibition of Snail-induced EMT could simultaneously suppress both tumor metastasis and immunosuppression in cancer patients.

The E693Δ Mutation in Amyloid Precursor Protein Increases Intracellular Accumulation of Amyloid β Oligomers and Causes Endoplasmic Reticulum Stress-Induced Apoptosis in Cultured Cells

The E693Delta mutation within the amyloid precursor protein (APP) has been suggested to cause dementia via the enhanced formation of synaptotoxic amyloid beta (Abeta) oligomers. However, this mutation markedly decreases Abeta secretion, implying the existence of an additional mechanism of neuronal dysfunction that is independent of extracellular Abeta. We therefore examined the effects of this mutation on both APP processing to produce Abeta as well as subcellular localization and accumulation of Abeta in transfected HEK293 and COS-7 cells. Both beta- and gamma-cleavage of mutant APP increased, indicating a lack of inhibition in Abeta production. Instead, this mutation promoted Abeta accumulation within cells, including the endoplasmic reticulum (ER), Golgi apparatus, early and late endosomes, lysosomes, and autophagosomes, all of which have been proposed as intracellular sites of Abeta generation and/or degradation, suggesting impairment of APP/Abeta trafficking. Notably, the intracellular mutant Abeta was found to predominantly form oligomers. Concomitant with this accumulation, the ER stress markers Grp78 and phosphorylated eIF2alpha were both strongly induced. Furthermore, the activation of caspase-4 and -3 as well as DNA fragmentation were detected in these cells. These results suggest that mutant Abeta induces alteration of Abeta trafficking and subsequent ER stress-induced apoptosis via enhancement of its intracellular oligomerization. Our findings suggest that Abeta oligomers exhibit toxicity in the extracellular space and within the cells themselves.

The Chemokine Receptor CXCR4 and the Metalloproteinase MT1-MMP Are Mutually Required during Melanoma Metastasis to Lungs

Melanoma is the most aggressive skin cancer once metastasis begins; therefore, it is important to characterize the molecular players involved in melanoma dissemination. The chemokine receptor CXCR4 and the membrane-bound metalloproteinase MT1-MMP are expressed on melanoma cells and represent candidate molecules for the control of metastasis. Using human melanoma transfectants that either overexpress or silence CXCR4 or MT1-MMP, or that have a combination of overexpression and interference of these proteins, we show that CXCR4 and MT1-MMP coordinate their activities at different steps along melanoma cell metastasis into the lungs. Results from in vivo xenograft mouse models of melanoma lung colonization and mice survival and short-term, homing nested polymerase chain reaction experiments from lung samples indicated that CXCR4 is required at early phases of melanoma cell arrival in the lungs. In contrast, MT1-MMP is not needed for these initial steps but promotes subsequent invasion and dissemination of the tumor with CXCR4. Investigation of potential cross talk between CXCR4 and MT1-MMP revealed that MT1-MMP accumulates intracellularly after melanoma cell stimulation with the CXCR4 ligand CXCL12, and that this process involves the activation of the Rac-Erk1/2 pathway. Subsequent to cell contact with specific basement membrane proteins, MT1-MMP redistributes to the cell membrane in a phosphatidylinositol 3-kinase-dependent manner. These results suggest that combination therapies that target CXCR4 and MT1-MMP should improve the limitations of the current therapies for metastatic melanoma.

Targeting Hypoxia-inducible Factor-1α With Tf–PEI–shRNA Complex via Transferrin Receptor–mediated Endocytosis Inhibits Melanoma Growth

Malignant melanoma (MM) is a major public health problem. The development of effective, systemic therapies for MM is highly desired. We showed here that the transferrin receptor (TfR) was a suitable surface marker for targeting of gene therapy in MM and that the hypoxia-inducible factor-1α (HIF-1α) was an attractive therapeutic molecular target in MM. We observed that inhibition of HIF-1α blocked cell proliferation and induced cell apoptosis in vitro. We then showed that a transferrin–polyethylenimine–HIF-1α–short-hairpin RNA (Tf–PEI–HIF-1α–shRNA) complex could target MM specifically and efficiently both in vivo and in vitro, exploiting the high expression of the TfR in MM. The systemic delivery of sequence-specific small-interfering RNA (siRNA) against HIF-1α by the Tf– PEI–HIF-1α–shRNA complex dramatically inhibited tumor growth in the A375 MM xenograft model. The underlying concept of transfecting a HIF-1α shRNA expression vector complexed with Tf–PEI to block HIF-1α holds promise as a clinical approach to gene therapy for MM.

A Role for the Proton-coupled Folate Transporter (PCFT-SLC46A1) in Folate Receptor-mediated Endocytosis

Recently, this laboratory identified a proton-coupled folate transporter (PCFT), with optimal activity at low pH. PCFT is critical to intestinal folate absorption and transport into the central nervous system because there are loss-of-function mutations in this gene in the autosomal recessive disorder, hereditary folate malabsorption. The current study addresses the role PCFT might play in another transport pathway, folate receptor (FR)-mediated endocytosis. FRalpha cDNA was transfected into novel PCFT(+) and PCFT(-) HeLa sublines. FRalpha was shown to bind and trap folates in vesicles but with minimal export into the cytosol in PCFT(-) cells. Cotransfection of FRalpha and PCFT resulted in enhanced folate transport into cytosol as compared with transfection of FRalpha alone. Probenecid did not inhibit folate binding to FR, but inhibited PCFT-mediated transport at endosomal pH, and blocked FRalpha-mediated transport into the cytosol. FRalpha and PCFT co-localized to the endosomal compartment. These observations (i) indicate that PCFT plays a role in FRalpha-mediated endocytosis by serving as a route of export of folates from acidified endosomes and (ii) provide a functional role for PCFT in tissues in which it is expressed, such as the choroid plexus, where the extracellular milieu is at neutral pH.

Neprilysin gene expression requires binding of the amyloid precursor protein intracellular domain to its promoter: implications for Alzheimer disease

Amyloid beta-peptide (Abeta) accumulation leads to neurodegeneration and Alzheimer disease; however, amyloid metabolism is a dynamic process and enzymic mechanisms exist for Abeta removal. Considerable controversy surrounds whether the intracellular domain of the amyloid precursor protein (AICD) regulates expression of the Abeta-degrading metalloprotease, neprilysin (NEP). By comparing two neuroblastoma cell lines differing substantially in NEP expression, we show by chromatin immunoprecipitation (ChIP) that AICD is bound directly to the NEP promoter in high NEP-expresser (NB7) cells but not in low-expresser (SH-SY5Y) cells. The methylation status of the NEP promoter does not regulate expression in these cells, whereas the histone deacetylase inhibitors trichostatin A and valproate partly restore NEP expression and activity in SH-SY5Y cells. ChIP analysis also reveals AICD binding to the NEP promoter in rat primary neurons but not in HUVEC cells. Chromatin remodelling of crucial Alzheimer disease-related genes by valproate could provide a new therapeutic strategy.

Contribution of Guanine Nucleotide Exchange Factor Vav2 to Hyperhomocysteinemic Glomerulosclerosis in Rats

We currently reported that Vav2, a member of the guanine nucleotide exchange factor-Vav subfamily, participates in homocysteine-induced increases in Rac1 activity and consequent activation of NADPH oxidase in rat mesangial cells. However, the physiological relevance of this cellular action of Vav2 remains unknown. The present study tested a hypothesis that Vav2 importantly mediates the injurious action of homocysteine on glomeruli and thereby contributes to the development of glomerulosclerosis during hyperhomocysteinemia. We found that, among Vav members, Vav2 was abundantly expressed in glomeruli. When Vav2 short hairpin RNA was transfected into the kidneys of Sprague-Dawley rats, hyperhomocysteinemia induced by folate-free diet failed to significantly enhance Rac1 activity and increase NADPH-dependent superoxide production. In these rats with silenced renal Vav2 gene, glomerular injury during hyperhomocysteinemia was markedly attenuated compared with those rats only receiving mock vector transfection, as shown by ameliorated albuminuria and extracellular matrix metabolism. In the rat kidneys with transfection of a dominant-active Vav2 variant (onco-Vav2), we found that overexpression of Vav2 led to significant increases in Rac1 activity, superoxide production, and glomerular injury, which was similar to that induced by hyperhomocysteinemia. However, this Vav2 overexpression was unable to further enhance homocysteine-induced glomerular injury. We concluded that Vav2-mediated activation of NADPH oxidase is an important initiating mechanism resulting in hyperhomocysteinemic glomerular injury through enhanced local oxidative stress.

CD40-Induced Signaling in Human Endothelial Cells Results in mTORC2- and Akt-Dependent Expression of Vascular Endothelial Growth Factor In Vitro and In Vivo

We have examined CD40-dependent signals in endothelial cells (EC) mediating the expression of vascular endothelial growth factor (VEGF) and VEGF-induced angiogenesis. We treated confluent cultures of EC with soluble CD40L (sCD40L), and by Western blot found a marked increase in the phosphorylation of Akt, 4EBP-1, and S6K1, compared with untreated cells. EC were transfected with a full-length VEGF promoter-luciferase construct and cultured in the absence or presence of rapamycin and sCD40L. We found that rapamycin, which blocks mTORC1 and mTORC2 signaling, inhibited sCD40L-mediated transactivation of VEGF. In addition, by Western blot, we found that the transfection of EC with small interfering RNA (siRNA) to rictor (to inhibit mTORC2), and not raptor (to inhibit mTORC1), inhibited sCD40L-dependent protein expression of VEGF. In additions, we found that basal levels of phosphorylated Akt as well as VEGF were increased in EC transfected with the raptor siRNA. Also, rapamycin failed to inhibit VEGF promoter activation, as well as VEGF protein expression in EC transfected with a constitutively active construct of Akt, further demonstrating that mTORC1 is not necessary for CD40- and Akt-induced expression of VEGF. Finally, we injected human CD40L-transfected fibroblasts or mock transfectants into human skin on SCID mice. We found that the injection of CD40L transfectants, but not mock cells, resulted in VEGF expression and mediated a marked angiogenesis reaction, and this response was reduced in mice treated with rapamycin. Together, these observations indicate that mTORC2 and Akt facilitate CD40-inducible expression of VEGF in EC, which is of clinical importance in tumor growth and the progression of chronic inflammatory diseases.

Lentivirus-Mediated RNA Interference Targeting Vascular Endothelial Growth Factor Gene Enhances the Sensitivity of K562 Cells to Imatinib

Background: Vascular endothelial growth factor (VEGF), one of the most potent mediators of angiogenesis, plays an important role in tumor cell proliferation and migration. Elevated VEGF levels are found in both the plasma and the bone marrow of patients with chronic myelogeneous leukemia(CML). Moreover, the CML-associated oncogene Bcr-Abl induces endogenous secretion of VEGF. The aim of this study was to construct a lentiviral vector-mediated RNA interference (RNAi) of vascular endothelial growth factor (VEGF) gene and to investigate the effects of RNAi inhibiting VEGF gene alone or in combination with imatinib on the proliferation and apoptosis of K562 leukemic cell line.Methods: A lentiviral expression vector containing short hairpin RNA (shRNA ) targeting VEGF was constructed and cotransfected with the pPACKH1 packaging plasmids mixture into 293T cells by Lipofectamine 2000. K562 cells were infected with the packaged lentivirus. The levels of VEGF mRNA and protein were detected by real-time quantitative RT- PCR, Western blot and ELISA. Cellular proliferation was determined by trypan blue exclusion and MTT assay. imatinib -induced apoptosis was analyzed by flow cytometry.Results: The lentiviral shRNA vector targeting VEGF has been constructed and transfected into K562 cells successfully. The expression of VEGF mRNA and protein in K562-shVEGF cells transfected with pRNAT-shRNA were significantly inhibited when compared with those of K562 and K562–con cells (mock transfection). The proliferation rate of K562-shVEGF cells slowed down. After imatinib treatment, the percentages of apoptotic cells in K562-shVEGF cells increased more significantly than those of K562 and K562–con cells.Conclusion: Suppression of VEGF by lentivirus-mediated RNAi could effectively inhibit proliferation and increase the sensitivity of K562 cells to imatinib. These results indicate that Bcr/Abl-targeting compound in combination with anti-angiogenic therapies may provide a potent therapeutic strategy to CML.

Effects of green tea extract on expression of human papillomavirus type 16 oncoproteins-induced hypoxia-inducible factor-1alpha and vascular endothelial growth factor in human cervical carcinoma cells

To investigate the effects of green tea extract (GTE) and its major component (-)-epigallocatechin-3-gallate (EGCG) on the human papillomavirus (HPV) type 16 oncoproteins (E6 and E7)-induced expression of hypoxia-inducible factor-1alpha (HIF-1alpha) and vascular endothelial growth factor (VEGF) in human cervical carcinoma cells. Human cervical carcinoma cells of the line C-33A were divided to 4 groups to be transiently transfected with the plasmid HA-pSG5-HPV-16E6 containing the HPV type 16 oncoprotein E6, HA-pSG5-HPV-16 E7, or empty plasmid HA-pSG5, or just exposed to the transfection reagent Lipofectamine 2000 as mock transfection control group. Western blotting and ELISA were used to detect the protein expression of HIF-1alpha and the protein expression of VEGF 18, 24, and 48 h after the transfection. Twenty-four hours after the transfection, the transfected-cells were treated with GTE (40 microg/ml) or EGCG (50 micromol/L) for 8, 16, and 24 h respectively, or treated with GTE of the concentrations of 20, 40, and 80 microg/ml or EGCG of the concentrations of 25, 50, and 100 micromol/L respectively for 16 h. The HIF-1alpha and VEGF protein levels were analyzed by Western blotting and ELISA respectively and the HIF-1alpha and VEGF mRNA levels were determined with real-time PCR. Twenty-four hours after transfection, the HIF-1alpha protein expression of the 16E6 and 16E7 groups were significantly decreased, and the VEGF protein levels of the 16E6 and 16E7 groups were (870+/-66) and (1487+/-51) pg/ml respectively, both significantly higher than that of the empty plasmid group [(366+/-65) pg/ml, both P<0.01]. Treated by 40 microg/ml of GTE or 50 micromol/L of EGCG for 16 h, (1) the HIF-1alpha protein levels of the 16E6 and 16E7 groups were significantly decreased; (2) the VEGF protein levels of the 16E6 group were (476+/-34) and (477+/-65) pg/ml respectively, and the VEGF mRNA levels of the 16E6 group were 1.208+/-0.196 and 1.174+/-0.208 respectively, all significantly lower than those of the untreated group [(870+/-66) pg/ml and 1.805+/-0.081 respectively, all P<0.01]; and (3) the VEGF protein levels of the 16E7 group were (649+/-55) and (514+/-37) pg/ml respectively, and the VEGF mRNA levels of the 16E7 group were 1.442+/-0.136 and 1.399+/-0.064 respectively, all significantly lower than those of untreated group [(1487+/-51) pg/ml and 2.123+/-0.120 respectively, all P<0.01]. The 80 microg/ml of GTE or 100 micromol/L of EGCG showed much stronger effects on the inhibition of VEGF protein expression than 40 microg/ml of GTE or 50 micromol/L of EGCG (both P<0.01). GTE and EGCG can remarkably inhibit the HPV-16 oncoproteins-induced expression of HIF-1alpha protein, and VEGF protein and mRNA in human cervical carcinoma cells. Moreover, GTE and EGCG decrease the VEGF protein expression dose-dependently.

Abstract 3955: Chemokines Fused to a Fractalkine Backbone and a GPI-Anchor Attract Embryonic Endothelial Progenitor Cells to the Site of Ischemia

Recruitment of endothelial progenitor cells to the sites of ischemia is a prerequisite for efficient therapeutic neovascularization via vasculogenesis. Chemokines play a major role in the homing of EPCs at the ischemic vasculature, a mechanism fading in chronic ischemia. To overcome this limitation, we constructed an artificial adhesion molecule consisting of a GPI-anchor, a fractalkine-backbone and an SDF-1 head (SDF-1-fra-GPI), which was applied for enhanced recruitment of embryonic EPCs (eEPCs: CXCR4++, Tie2++, Thrombomodulin++, CD34-, MHCI-, vWF inducible, eNOS inducible) in vitro and in vivo . Methods: In a flow chamber adhesion assay, Control plasmids (pcDNA or GPI-SDF-1 cDNA) were compared to the SDF-1-fra-GPI construct for eEPC recruitment 24h after liposomal transfection of rat endothelial cells. In vivo, in rabbits (n=5 per group) at day 7 (d7) after femoral artery excision, 1 mg of the SDF-1-fra-GPI or eGFP cDNA was transfected into the ischemic limb. At d9, ischemic hindlimbs were retroinfused with 5x10 6 eEPCs. Angiography was performed for collateral quantification and frame count score at d9 and d37 (% of d9), capillary density was assessed via PECAM-1-staining (capillaries/muscle fiber = c/mf). Results: In vitro, eEPC adhesion (16±12 cells/field) was increased to a higher extent by SDF-1-fra-GPI (79±13) than SDF1-GPI (54±8) or control vector (37±8). In vivo , eEPC adhesion in the ischemic hindlimb after SDF-1-fra-GPI transfection compared to mock transfection (30±3 vs. 9±1 cells/field). Whereas capillary density was unaffected (1.66±0.30 SDF-1-Fra-GPI vs. 1.56±0.29 eEPCs), collateral growth (152±10% SDF-1-fra-GPI vs. 124±13%) as well as perfusion score (198±17% SDF-1-fra-GPI vs.160±6% eEPCs) further increased after SDF-1-fra-GPI transfection (controls: 1.24±0.12 c/mf, collaterals 105±8%, perfusion score 112±11%). We conclude that recruitment of EPCs expressing CXCR4 (the SDF-1 receptor) may benefit from pre-treatment of the recipient vasculature with SDF-1-Fra-GPI, an artificial adhesion molecule. This approach might be valuable for enhancing EPC recruitment in the scenario of therapeutic neovascular-ization of chronic ischemic syndromes.

N-Acetylglucosaminyltransferase V Regulates Extravillous Trophoblast Invasion through Glycosylation of α5β1 Integrin

For successful human placentation, invasion of trophoblast cells into the uterus and its associated vasculature is essential, and the regulation of this process is controlled by many factors at the fetal-maternal interface. N-acetylglucosaminyltransferase V (GnT-V) is a key enzyme that catalyzes beta1, 6-N-acetylglucosamine (beta1-6GlcNAc) branching on asparagine-linked oligosaccharides of cell proteins. GnT-V and its product, beta1-6GlcNAc, are known to regulate cellular transformation and correlate with the metastatic potential of various cancer cells. The aim of the present study was to determine whether extravillous trophoblast (EVT) expressed this molecule and examine the role of GnT-V in the regulation of human trophoblast invasion. Immunohistochemistry showed that GnT-V was strongly expressed within the cytoplasm of EVT in the anchoring villi; this expression was down-regulated in EVTs invading the decidua. Suppression of beta1-6GlcNAc glycosylation by swainsonine enhanced the migratory potential and invasive capability of both primary EVTs and the EVT cell line, HTR-8/SVneo. Down-regulation of GnT-V expression by small interfering RNA in the choriocarcinoma cell line Jar consistently enhanced the migration and invasive capacity of these cells and elevated cellular adhesion to extracellular matrix proteins, such as fibronectin and collagen type I/IV. The extent of beta1-6 branching of alpha5beta1 integrin was significantly reduced in small interfering GnT-V-transfected Jar cells compared with mock transfectants, although the expression of alpha1, alpha5, alpha6, and beta1 integrin on the cell surface was not changed. These results suggest that GnT-V is expressed in human EVT and is involved in regulating trophoblast invasion through modifications of the oligosaccharide chains of alpha5beta1 integrin.

A novel loss-of-function mutation in the proton-coupled folate transporter from a patient with hereditary folate malabsorption reveals that Arg 113 is crucial for function

AbstractHereditary folate malabsorption (HFM) patients harbor inactivating mutations including R113S in the proton-coupled folate transporter (PCFT), an intestinal folate transporter with optimal activity at acidic pH. Here we identified and characterized a novel R113C mutation residing in the highly conserved first intracellular loop of PCFT. Stable transfectants overexpressing a Myc-tagged wild-type (WT) and mutant R113C PCFT displayed similar transporter targeting to the plasma membrane. However, whereas WT PCFT transfectants showed a 22-fold increase in [3H]folic acid influx at pH 5.5, R113C or mock transfectants showed no increase. Moreover, WT PCFT transfectants displayed a 50% folic acid growth requirement concentration of 7 nM, whereas mock and R113C transfectants revealed 24- to 27-fold higher values. Consistently, upon fluorescein-methotrexate labeling, WT PCFT transfectants displayed a 50% methotrexate displacement concentration of 50 nM, whereas mock and R113C transfectants exhibited 12- to 14-fold higher values. Based on the crystal structure of the homologous Escherichia coli glycerol-3-phosphate transporter, we propose that the cationic R113 residue of PCFT is embedded in a hydrophobic pocket formed by several transmembrane helices that may be part of a folate translocation pore. These findings establish a novel loss of function mutation in HFM residing in an intracellular loop of PCFT crucial for folate transport.

ShRNA-triggered RNAi inhibits expression of NDV NP gene in chicken embryo fibroblast.

RNA interference (RNAi) technology is a powerful tool for identifying gene functions. Chicken embryo fibroblast (CEF) is an ideal model for studying the interaction between avian viruses and their hosts. To establish a methodological platform for RNAi studies in CEF, three plasmid vectors expressing short hairpin RNAs (shRNAs) targeted against the Newcastle disease virus (NDV) NP gene were constructed. One of them, ndv1, was proven effective on blocking viral replication in CEF and chicken embryos. Four hours prior to infection with NDV, the CEF was transfected with the plasmids by Silent-fect. An unrelated shRNA sequence (HK) was used in mock transfection. The expression of a potent shRNA resulted in up to 2.3, 21.1 and 9.8 fold decreases in NP gene expression at 3, 6 and 9 h post infection in CEF, respectively. The ndv1 was able to completely inhibit the replication of the virus in CEF within 48 post infection. Furthermore, the pathological changes in CEF caused by NDV were delayed, and the degree of pathological changes was lighter compared with the mock transfection in the presence of ndv1. When the complex of shRNA-Silent-fect and NDV was co-injected into the allantoic cavity of 10-day-old embryonated eggs with 105 or 106 ELD50 NDV, NDV replication was decreased by 94.14% and 62.15% after 17 h, respectively. These findings suggest that the newly synthesized NP protein is critical for NDV transcription and replication and provide a basis for identifying the functions of viral genes and screening for effective siRNAs against viruses in CEF and chicken embryo by RNAi.

Problem‐solving test: Expression cloning of the erythropoietin receptor

Terms to be familiar with before you start to solve the test: cytokines, cytokine receptors, cDNA library, cDNA synthesis, poly(A)⁺ RNA, primer, template, reverse transcriptase, restriction endonucleases, cohesive ends, expression vector, promoter, Shine-Dalgarno sequence, poly(A) signal, DNA helicase, DNA ligase, topoisomerases, [¹²⁵I] labeling, transfection, mock transfection, SDS-polyacrylamide gel electrophoresis, β-mercaptoethanol, autoradiography.

AKR1C2 and AKR1C3 mediated prostaglandin D2 metabolism augments the PI3K/Akt proliferative signaling pathway in human prostate cancer cells

Members of the aldo-keto reductase (AKR) superfamily have been implicated in prostaglandin (PG) metabolism and prostate cancer. AKR1C3 possesses 11-ketoprostaglandin reductase activity and is capable of converting PGD2 to 9alpha, 11beta-PGF2alpha, whereas AKR1C2-mediated PG metabolism remains unclear. The accumulation of PGF2alpha may generate proliferative signals to promote prostate cell growth. Levels of AKR1C2 and AKR1C3 expression are elevated in localized and advanced prostate cancer. To study the significance of AKR1C2- and AKR1C3-mediated PGD2 conversion in human prostate cell proliferation, we stably transfected androgen insensitive human prostate cancer PC-3 cells with AKR1C2 or AKR1C3 cDNA. PC-3 cells overexpressing AKR1C2 and AKR1C3 had elevated cell proliferation in response to PGD2 stimulation as compared to mock transfectants. Overexpression of AKR1C2 or AKR1C3 did not alter levels of PGF receptor (FP) expression. Inclusion of an FP antagonist (AL8810) significantly suppressed PGD2-stimulated PC-3 cell proliferation in these stable transfectants. In addition, PGD2 significantly elevated levels of total Akt protein expression and Akt Ser473 phosphorylation in AKR1C2 and AKR1C3 stable transfectants; and inclusion of a phosphatidylinositol 3-kinase (PI3K) chemical inhibitor (LY294002) attenuated PGD2-stimulated cell proliferation in these transfectants. Our results suggested that both AKR1C2 and AKR1C3 mediate similar PGD2 conversion toward the accumulation of proliferative signals through FP and PI3K/Akt signaling pathways to promote prostate cell proliferation.

Overexpression of fucosyltransferase VII (FUT7) promotes embryo adhesion and implantation

To investigate the effect of increased fucosyltransferase VII (FUT7) on sialyl Lewis X (sLeX) synthesis and their impact on embryo implantation. Cell and animal study. Liaoning Provincial Core Lab of Glycobiology and Glycoengineering, Department of Biochemistry and Molecular Biology, Dalian Medical University. Adult female mice of Kunming species. A pIRES2-EGFP-FUT7 expression plasmid containing full-length human FUT7 cDNA was constructed and transiently transfected into RL95-2 or injected into the uteri of early pregnant mice. Control subjects received the mock pIRES2-EGFP or anti-sLeX antibody. The expression of FUT7 and sLeX was detected by reverse transcriptase polymerase chain reaction (RT-PCR) and indirect immunofluorescence. The embryo adhesion rate was assayed in vitro with the cocultured RL95-2 and JAR implantation model. In vivo embryo implantation was investigated using a mouse model. Expression of FUT7 was significantly increased after transfection of pIRES2-EGFP-FUT7 into RL95-2 cells compared with the parental control and mock vector transfectants, as demonstrated by fluorescent microscopy and RT-PCR. Expression of sLeX was also increased in FUT7 overexpressers, as detected by indirect immunofluorescence. Consistent with the elevated expression of FUT7 and sLeX, embryo adhesion rate and embryo implantation competence were significantly increased (P<.01) in both in vitro and in vivo models. Overexpression of FUT7 up-regulates sLeX synthesis and enhances sLeX-mediated embryo implantation.