Biomedical subjects

Lene Pedersen

Publications and source records attributed to Lene Pedersen.

11 recordsLinked to original sources

PubMed2007

Revised procedures for yeast metabolites extraction: application to a glucose pulse to carbon-limited yeast cultures, which reveals a transient activation of the purine salvage pathway.

In this study we have revised our original procedure of yeast metabolites extraction. We showed that: (a) less than 5% of intracellular metabolites leaks out during the step of rapid arrest of cellular metabolism by quenching yeast cells into a 60% methanol solution kept at -40 degrees C; and (b) with a few exception, the stability of metabolites were not altered during the 3 min boiling procedure in a buffered ethanol solution. However, there was a loss of external added metabolites of 5-30%, depending on the type of metabolites. This was mainly attributable to their retention on cellular debris after ethanol treatment, which prevented centrifugation of the cellular extracts before evaporation of ethanol. We further simplified our previous high-performance ionic chromatography (HPIC) techniques for easier, more reliable and robust quantitative measurements of organic acids, sugar phosphates and sugar nucleotides, and extended these techniques to purine and pyrimidine bases, using a variable wavelength detector set at 220 and 260 nm in tandem with a pulsed electrochemical or suppressed conductivity detector. These protocols were successfully applied to a glucose pulse to carbon-limited yeast cultures on purines metabolism. This study showed that glucose induced a fast activation of the purine salvage pathway, as indicated by a transient drop of ATP and ADP with a concomitant rise of IMP and inosine. This metabolic perturbation was accompanied by a rapid increase in the activity of the ISN1-encoded specific IMP-5'-nucleotidase. The mechanism of this activation remains to be determined.

Adenine Nucleotides↗

PubMed2006

Characterization of transport mechanisms and determinants critical for Na+-dependent Pi symport of the PiT family paralogs human PiT1 and PiT2.

The general phosphate need in mammalian cells is accommodated by members of the P(i) transport (PiT) family (SLC20), which use either Na(+) or H(+) to mediate inorganic phosphate (P(i)) symport. The mammalian PiT paralogs PiT1 and PiT2 are Na(+)-dependent P(i) (NaP(i)) transporters and are exploited by a group of retroviruses for cell entry. Human PiT1 and PiT2 were characterized by expression in Xenopus laevis oocytes with (32)P(i) as a traceable P(i) source. For PiT1, the Michaelis-Menten constant for P(i) was determined as 322.5 +/- 124.5 microM. PiT2 was analyzed for the first time and showed positive cooperativity in P(i) uptake with a half-maximal activity constant for P(i) of 163.5 +/- 39.8 microM. PiT1- and PiT2-mediated Na(+)-dependent P(i) uptake functions were not significantly affected by acidic and alkaline pH and displayed similar Na(+) dependency patterns. However, only PiT2 was capable of Na(+)-independent P(i) transport at acidic pH. Study of the impact of divalent cations Ca(2+) and Mg(2+) revealed that Ca(2+) was important, but not critical, for NaP(i) transport function of PiT proteins. To gain insight into the NaP(i) cotransport function, we analyzed PiT2 and a PiT2 P(i) transport knockout mutant using (22)Na(+) as a traceable Na(+) source. Na(+) was transported by PiT2 even without P(i) in the uptake medium and also when P(i) transport function was knocked out. This is the first time decoupling of P(i) from Na(+) transport has been demonstrated for a PiT family member. Moreover, the results imply that putative transmembrane amino acids E(55) and E(575) are responsible for linking P(i) import to Na(+) transport in PiT2.

Animals↗

PubMed2006

Amphotropic murine leukemia virus is preferentially attached to cholesterol-rich microdomains after binding to mouse fibroblasts.

BACKGROUND: We have recently shown that amphotropic murine leukemia virus (A-MLV) can enter the mouse fibroblast cell line NIH3T3 via caveola-dependent endocytosis. But due to the size and omega-like shape of caveolae it is possible that A-MLV initially binds cells outside of caveolae. Rafts have been suggested to be pre-caveolae and we here investigate whether A-MLV initially binds to its receptor Pit2, a sodium-dependent phosphate transporter, in rafts or caveolae or outside these cholesterol-rich microdomains. RESULTS: Here, we show that a high amount of cell-bound A-MLV was attached to large rafts of NIH3T3 at the time of investigation. These large rafts were not enriched in caveolin-1, a major structural component of caveolae. In addition, they are rather of natural occurrence in NIH3T3 cells than a result of patching of smaller rafts by A-MLV. Thus cells incubated in parallel with vesicular stomatitis virus glycoprotein (VSV-G) pseudotyped MLV particles showed the same pattern of large rafts as cells incubated with A-MLV, but VSV-G pseudotyped MLV particles did not show any preference to attach to these large microdomains. CONCLUSION: The high concentration of A-MLV particles bound to large rafts of NIH3T3 cells suggests a role of these microdomains in early A-MLV binding events.

Animals↗

PubMed2005

Amphotropic murine leukaemia virus envelope protein is associated with cholesterol-rich microdomains.

BACKGROUND: Cholesterol-rich microdomains like lipid rafts were recently identified as regions within the plasma membrane, which play an important role in the assembly and budding of different viruses, e.g., measles virus and human immunodeficiency virus. For these viruses association of newly synthesized viral proteins with lipid rafts has been shown. RESULTS: Here we provide evidence for the association of the envelope protein (Env) of the 4070A isolate of amphotropic murine leukaemia virus (A-MLV) with lipid rafts. Using density gradient centrifugation and immunocytochemical analyses, we show that Env co-localizes with cholesterol, ganglioside GM1 and caveolin-1 in these specific regions of the plasma membrane. CONCLUSIONS: These results show that a large amount of A-MLV Env is associated with lipid rafts and suggest that cholesterol-rich microdomains are used as portals for the exit of A-MLV.

Animals↗

PubMed2005

Central corneal thickness in high myopia.

PURPOSE: To examine if central corneal thickness (CCT) is different in emmetropia and high myopia. METHODS: 57 emmetropic subjects (0 to + 1.5 D) and 48 high myopes (all more than - 6 D in spherical equivalent refraction) were studied. CCT was measured by a Haag-Streit Optical Low-Coherence Reflectometry (OLCR) pachymeter, a recently developed high precision pachymeter with a standard deviation (SD) for repeated measurements of 1 microm. RESULTS: Mean CCT for the emmetropic group was 538.6 microm (SD = 32.1), and for the myopic group 527.7 microm (SD = 35.0). Neither the mean CCT nor the variance from the two groups showed a statistically significant different (p > 0.05). CONCLUSION: CCT is not systematically altered in myopia. The process by which the myopia progresses does not to a measurable degree influence the central cornea.

Adolescent↗

PubMed2005

Evolutionary and experimental analyses of inorganic phosphate transporter PiT family reveals two related signature sequences harboring highly conserved aspartic acids critical for sodium-dependent phosphate transport function of human PiT2.

The mammalian members of the inorganic phosphate (P(i)) transporter (PiT) family, the type III sodium-dependent phosphate (NaP(i)) transporters PiT1 and PiT2, have been assigned housekeeping P(i) transport functions and are suggested to be involved in chondroblastic and osteoblastic mineralization and ectopic calcification. The PiT family members are conserved throughout all kingdoms and use either sodium (Na+) or proton (H+) gradients to transport P(i). Sequence logo analyses revealed that independent of their cation dependency these proteins harbor conserved signature sequences in their N- and C-terminal ends with the common core consensus sequence GANDVANA. With the exception of 10 proteins from extremophiles all 109 proteins analyzed carry an aspartic acid in one or both of the signature sequences. We changed either of the highly conserved aspartates, Asp28 and Asp506, in the N- and C-terminal signature sequences, respectively, of human PiT2 to asparagine and analyzed P(i) uptake function in Xenopus laevis oocytes. Both mutant proteins were expressed at the cell surface of the oocytes but exhibited knocked out NaP(i) transport function. Human PiT2 is also a retroviral receptor and we have previously shown that this function can be exploited as a control for proper processing and folding of mutant proteins. Both mutant transporters displayed wild-type receptor functions implying that their overall architecture is undisturbed. Thus the presence of an aspartic acid in either of the PiT family signature sequences is critical for the Na+-dependent P(i) transport function of human PiT2. The conservation of the aspartates among proteins using either Na+- or H+-gradients for P(i) transport suggests that they are involved in H+-dependent P(i) transport as well. Current results favor a membrane topology model in which the N- and C-terminal PiT family signature sequences are positioned in intra- and extracellular loops, respectively, suggesting that they are involved in related functions on either side of the membrane. The present data are in agreement with a possible role of the signature sequences in translocation of cations.

Amino Acid Sequence↗

PubMed2005

Caveola-dependent endocytic entry of amphotropic murine leukemia virus.

Early results suggested that the amphotropic murine leukemia virus (A-MLV) does not enter cells via endocytosis through clathrin-coated pits and this gammaretrovirus has therefore been anticipated to fuse directly with the plasma membrane. However, here we present data implicating a caveola-mediated endocytic entry route for A-MLV via its receptor Pit2. Caveolae belong to the cholesterol-rich microdomains characterized by resistance to nonionic detergents such as Triton X-100. Extraction of murine fibroblastic NIH 3T3 cells in cold Triton X-100 showed the presence of the A-MLV receptor Pit2 in detergent-insoluble microdomains. Using coimmunoprecipitation of cell extracts, we were able to demonstrate direct association of Pit2 with caveolin-1, the structural protein of caveolae. Other investigations revealed that A-MLV infection in contrast to vesicular stomatitis virus infection is a slow process (t(1/2) approximately 5 h), which is dependent on plasma membrane cholesterol but independent of NH4Cl treatment of cells; NH4Cl impairs entry via clathrin-coated pits. Furthermore, expression of dominant-negative caveolin-1 decreased the susceptibility to infection via Pit2 by approximately 70%. These results show that A-MLV can enter cells via a caveola-dependent entry route. Moreover, increase in A-MLV infection by treatment with okadaic acid as well as entry of fusion-defective fluorescent A-MLV virions in NIH 3T3 cells further confirmed our findings and show that A-MLV can enter mouse fibroblasts via an endocytic entry route involving caveolae. Finally, we also found colocalization of fusion-defective fluorescent A-MLV virions with caveolin-1 in NIH 3T3 cells. This is the first time substantial evidence has been presented implicating the existence of a caveola-dependent endocytic entry pathway for a retrovirus.

Animals↗

PubMed2004

The central half of Pit2 is not required for its function as a retroviral receptor.

The type III sodium-dependent phosphate (NaPi) cotransporter, Pit2, is a receptor for amphotropic murine leukemia virus (A-MuLV) and 10A1 MuLV. In order to determine what is sufficient for Pit2 receptor function, a deletion mutant lacking about the middle half of the protein was made. The mutant supported entry for both viruses, unequivocally narrowing down the identification of the sequence that is sufficient to specify the receptor functions of Pit2 to its N-terminal 182 amino acids and C-terminal 170 amino acids.

Animals↗

PubMed2002

Two highly conserved glutamate residues critical for type III sodium-dependent phosphate transport revealed by uncoupling transport function from retroviral receptor function.

Type III sodium-dependent phosphate (NaP(i)) cotransporters, Pit1 and Pit2, have been assigned housekeeping P(i) transport functions and suggested involved in chondroblastic and osteoblastic mineralization and ectopic calcification. Both proteins exhibit dual function, thus, besides being transporters, they also serve as receptors for several gammaretroviruses. We here show that it is possible to uncouple transport and receptor functions of a type III NaP(i) cotransporter and thus exploit the retroviral receptor function as a control for proper processing and folding of mutant proteins. Thus exchanging two putative transmembranic glutamate residues in human Pit2, Glu(55) and Glu(575), with glutamine or with lysine severely impaired or knocked out, respectively, P(i) transport function, but left viral receptor function undisturbed. Both glutamates are conserved in type III NaP(i) cotransporters, in fungal NaP(i) cotransporters PHO-4 and Pho89, and in other known or putative phosphate permeases from a number of species and are the first residues shown to be critical for type III NaP(i) cotransport. Their putative transmembranic positions together with the presented data are consistent with Glu(55) and Glu(575) being parts of a cation liganding site or playing roles in conformational changes associated with substrate transport. Finally, the results also show that Pit2 retroviral receptor function per se is not dependent on Pit2 P(i) transport function.

Amino Acid Substitution↗

PubMed2002

A transmissible human endogenous retrovirus.

The transmissibility of the human endogenous retrovirus HERV-H/RGH-2 was investigated by marker rescue: intraspecies transmission of HERV-H/RGH-2 retrovirus particles was attempted by cocultivation of virion-producing, long-term cell cultures spontaneously formed from peripheral blood mononuclear cells from several multiple sclerosis patient cultures with a retroviral vector construct-harboring cell line. Transmissibility was assessed by assays for productive infection (reverse transcriptase activity), and assays for rescue of the retroviral vector construct in indicator cells. Our studies show that the human endogenous retrovirus HERV-H/RGH-2 is transmissible, albeit at a very low level. The human endogenous retrovirus HERV-H/RGH-2 is associated with multiple sclerosis (MS). Previously, we demonstrated sequence variants of the human endogenous retrovirus HERV-H family in virion form, by applying RT-PCR to virion RNA from the supernatants of long-term MS cell cultures, and to the particulate fraction of a series of MS patient plasma samples.

Cell Line↗

PubMed2002

Overexpression of gibbon ape leukemia virus (GALV) receptor (GLVR1) on human CD34(+) cells increases gene transfer mediated by GALV pseudotyped vectors.

Retroviral transduction of CD34(+) cells on Retronectin using gibbon ape leukemia virus (GALV) pseudotyped vectors is inhibited by high concentrations of vector containing medium (VCM). Furthermore, this inhibitory activity is stable for at least 48 hours at 37 degrees C and partially blocks a second hit with a GALV pseudotyped vector. We hypothesized that this inhibition was due to interference at the receptor level between infectious and noninfectious vector particles and that it might be possible to overcome it by increasing receptor expression on target cells. Activation of protein kinase C in CD34(+) cells with the phorbol ester PMA (phorbol 12-myristate 13-acetate) increased the mRNA level of the GALV receptor (GLVR1) and the transduction efficiency (TE), and fully reversed the inhibition of transduction seen with high-titer GALV VCM. A murine stem cell virus (MSCV) vector with the GLVR1 receptor and green fluorescent protein cDNAs (MGLIG) was used to transduce fibroblasts, and clones expressing different levels of GLVR1 were isolated. The TE of these cells using a GALV vector correlated with the level of GLVR1 expression. When CD34(+) cells or K562 cells were first transduced with MGLIG and then with high-titer GALV VCM, no inhibition of transduction was seen. The low level of GLVR1 expression limits gene transfer to K562 and CD34(+) cells using GALV pseudotyped vectors, especially in the presence of high-titer VCMs.

Antigens, CD34↗