cDNA sequence and genomic characterization of intracisternal A-particle-related retroviral elements containing an envelope gene

Intracisternal A-particle retrotransposons (IAPs) are retroviruslike elements that are defective in envelope protein synthesis and exist without an extracellular stage. We have isolated a novel class of cDNAs that are related to known IAP elements in the nucleotide and deduced protein sequence of gag and pol genes but also contain a previously unidentified reading frame between the pol gene and putative U3 region. Analysis of the deduced protein sequence reveals features of the putative protein that are characteristic of retroviral envelope proteins. The isolated cDNAs represent transcripts of multiple retroid elements in the mouse genome that were termed IAPE (intracisternal A-particle-related elements coding for envelope). IAPE env genes exist in approximately 200 copies per haploid genome as integral parts of the majority of these retroid elements. Four major IAPE subgroups could be distinguished after EcoRI digestion of genomic DNA.

Glutamine attenuates leukocyte-endothelial cell adhesion in indomethacin-induced intestinal inflammation in the rat

BACKGROUND

Glutamine (Gln) is a major energy source for the intestinal mucosa. Its depletion results in epithelial atrophy and in bacterial translocation. Clinical substitution of this nonessential amino acid in critically ill persons results in a reduction of epithelial atrophy and in an accelerated recovery. The objective of this study was to assess the effect of Gln on leukocyte-endothelial cell interaction in an indomethacin (Indo)-induced long-lasting ileitis in Sprague-Dawley rats.

METHODS

Indo (7.5 mg/kg subcutaneously) was injected at time 0 and 24 hours later. Animals were fed with standard rat chow (ST) for 10 days until 12 hours before intravital microscopy analysis. Gln (3 g/kg body wt) was gavaged twice a day in the morning 4 hours apart (1) for 10 days between Indo administration and the experiment (ST/Gln, therapy), (2) for 14 days before Indo (Gln/ST, prophylaxis), or (3) from 14 days before Indo until the experiment (Gln/Gln, prophylaxis and therapy). Ten mesenteric venules (30 microm diameter) per animal (n = 5 per group) were observed using intravital microscopy, and the following parameters were monitored: number of adherent and emigrated leukocytes, leukocyte rolling velocity, erythrocyte velocity, venular blood flow, and shear rate. Macroscopically visible injury was scored 0 to 5.

RESULTS

Ten days after Indo treatment the macroscopic score was 3.5+/-0.4 vs. 0.6+/-0.2 of controls, and leukocyte adherence and emigration were increased (2.2-fold and 3.3-fold vs. control, respectively), whereas leukocyte rolling velocity and venular wall shear rate were reduced (both parameters to 81% of control). Glutamine prophylaxis, therapy, and the combination of both significantly attenuated macroscopic damage and prevented the microcirculatory disturbances to a similar extent. The beneficial effects of glutamine were accompanied by a normalization of fecal pH to control level, which had been lowered by Indo treatment.

CONCLUSIONS

The long-lasting Indo-induced ileitis was accompanied by macroscopic ulceration and microcirculatory disturbances. Oral therapy and prophylaxis with glutamine reduced macroscopic and microcirculatory inflammatory activity, indicating a special demand for glutamine in this type of inflammation.

Acute changes in vitamin B6 status in endurance athletes before and after a marathon

The vitamin B6 status of 13 endurance athletes was determined by whole blood B6 (microbiological) and urine 4-pyridoxic acid (4-PA) (HPLC), serum vitamin B6 (pyridoxal, pyridoxol, pyridoxamine) (HPLC), and erythrocyte alpha-EGOT measurements with the aid of 7-day records. In addition, blood and serum samples and urine were collected before (Time A), directly after (Time B), and 2 hr after a marathon race (Time C). The total energy intake was 12,303 +/- 3,464 kJ/day (34% fat, 48% carbohydrates, 14% protein). The vitamin B6 intake, serum concentrations, alpha-EGOT value, and 4-PA excretion were higher than the reference values at Time A. Only the vitamin B6 whole blood levels were below the normal level at Time A. The vitamin B6 status of the athletes corresponded essentially to reference values obtained for untrained individuals. There was a mean loss of about 1 mg vitamin B6 as a result of the marathon race. Vitamin B6 supplementation does not appear necessary if a balanced diet is consumed.

Assessment of vitamin B6 status of strength and speedpower athletes

OBJECTIVE

The investigation was designed to obtain information concerning the vitamin B6 status in high-performance athletes.

SUBJECTS

Fifty-seven strength and speedpower athletes were available for examination.

METHODS

Vitamin B6 status was determined by a 7-day weighed food record, enzyme activity (alpha-EGOT) measurement, whole blood concentrations (Saccharomyces carlsbergenisis and 4-pyridoxinic acid (4-PA) excretion (high-pressure liquid chromatography).

RESULTS

The absolute vitamin B6 intake in > 30% of the athletes was below the German recommended dietary allowance (GRDA) and, in relation to the protein intake (GRDA 0.20 mg vitamin B6/g protein), > 60% of the athletes had values below the GRDA. More than 90% of the athletes did not attain the reference value (0.88 nmol/mL) for untrained individuals in vitamin B6 whole blood concentration, and only a few athletes (< 5%) had alpha-EGOT values above the reference value of alpha-EGOT > 1.50). The 4-PA excretion was below the reference value of > 2.73 mumol/g creatinine in 18% of all athletes examined.

CONCLUSIONS

Vitamin B6 status can be quantified using the weighed food record, microbiological whole blood determination, and 4-PA excretion; however, limits of the individual methods must be taken into account. Vitamin B6 supply of the athletes still cannot be definitively assessed because there are no generally valid reference values.

Mouse mammary tumor virus superantigen expression in B cells is regulated by a central enhancer within the pol gene

Expression of mouse mammary tumor virus (MMTV)-encoded superantigens in B lymphocytes is required for viral transmission and pathogenesis. The mechanism of superantigen expression from the viral sag gene in B cells is largely unknown, due to problems with detection and quantification of these low-abundance proteins. We have established a sensitive superantigen-luciferase reporter assay to study the expression and regulation of the MMTV sag gene in B-cell lymphomas. The regulatory elements for retroviral gene expression are generally located in the 5' long terminal repeat (LTR) of the provirus. However, we found that neither promoters nor enhancers in the MMTV 5' LTR play a significant role in superantigen expression in these cells. Instead, the essential regulatory regions are located in the pol and env genes of MMTV. We report here that maximal sag expression in B-cell lines depends on an enhancer within the viral pol gene which can be localized to a minimal 183-bp region. Regulation of sag gene expression differs between B-cell lymphomas and pro-B cells, where an enhancer within the viral LTRs is involved. Thus, MMTV sag expression during B-cell development is achieved through the use of two separate enhancer elements.

Stimulation of mouse mammary tumor virus superantigen expression by an intragenic enhancer

The mechanisms regulating expression of mouse mammary tumor virus (MMTV)-encoded superantigens from the viral sag gene are largely unknown, due to problems with detection and quantification of these low-abundance proteins. To study the expression and regulation of the MMTV sag gene, we have developed a sensitive and quantitative reporter gene assay based on a recombinant superantigen-human placental alkaline phosphatase fusion protein. High sag-reporter expression in Ba/F3, an early B-lymphoid cell line, depends on enhancers in either of the viral long terminal repeats (LTRs) and is largely independent of promoters in the 5' LTR. The same enhancer region is also required for general expression of MMTV genes from the 5' LTR. The enhancer was mapped to a 548-bp fragment of the MMTV LTR lying within sag and shown to be sufficient to stimulate expression from a heterologous simian virus 40 promoter. No enhancer activity of the MMTV LTR was observed in XC sarcoma cells, which are permissive for MMTV. Our results demonstrate a major role for this enhancer in MMTV gene expression in early B-lymphoid cells.

Genetics of intracisternal-A-particle-related envelope-encoding proviral elements in mice

Intracisternal-A-particle-related envelope-encoding (IAPE) proviral elements in the mouse genome encode and express an envelope-like protein that may allow transmission of IAPEs as infectious agents. To test IAPE mobility and potential transmission in mice, we have analyzed the distribution of IAPE elements in the genomes of Mus spretus and Mus musculus inbred strains and wild-caught animals. Potential full-length (IAPE-A) proviral elements are present as repetitive copies in DNA from male but not female animals of M. musculus inbred strains and Mus musculus castaneus. Analysis of IAPE-cellular junction fragments indicates that fixation of most IAPEs in the germ line occurred in M. musculus and M. spretus after speciation but before M. musculus inbred strains were derived.

Expression of intracisternal A-particle-related retroviral element-encoded envelope proteins detected in cell lines

Intracisternal A-particle (IAP) retrotransposons of rodents express gag and pol proteins for assembly of intracellular viruslike particles but lack an env gene. The recently described IAP-related family of retroviral elements contains a reading frame with close resemblance to retroviral env genes (IAPEs) (F. U. Reuss and H. C. Schaller, J. Virol. 65:5702-5709, 1991). I now report the analysis of cellular IAPE mRNAs and detection of IAPE env proteins. IAPE elements are transcribed in cell lines NH15-CA2 and AtT20. Four major transcripts of 4.2, 3.9, 2.8, and 1.3 kb are detected and characterized by probes specific for defined regions of the cloned IAPE-1 cDNA. The 2.8-kb mRNA is shown to lack gag and pol genes but comprises an env gene and U3 region, as expected for a subgenomic env mRNA. Polymerase chain reaction amplification and cloning of such mRNAs confirmed the absence of gag and pol genes 5' from the env gene and implicates env mRNA generation by a splicing event. A polyclonal anti-IAPE env antiserum, raised against a bacterial IAPE-env fusion protein, specifically detects N-glycosylated env proteins of 91 kDa or less in cell lines positive for IAPE mRNA. IAPE env proteins of different sizes represent independent translation products. After inhibition of N-glycosylation, env proteins in the size predicted from the env gene sequence or smaller are present. These results provide evidence that putative IAPE env proteins are synthesized in vivo. Envelope protein expression by an IAP-related retroviral element identifies IAPEs as a possible missing link between IAP retrotransposons and retroviruses.

Replication of enhancer-deficient amphotropic murine leukemia virus in human cells

Amphotropic murine leukemia virus (MLV) replicates in cells from various mammalian species, including humans, and is a potential contaminant in MLV vector preparations for human gene transfer studies. The generation of replication-competent virus is considered less likely with vectors that delete the viral transcription elements. This conclusion is based on data obtained in rodents, where MLV replication depends on the expression of viral genes under the control of 75-bp enhancer elements in the long terminal repeat. We demonstrate here that in some human cells replication of amphotropic MLV is possible in the absence of these enhancer elements. Replication of the enhancer-deficient virus MLV-(MOA)Delta E is observed in selected human sarcoma and B lymphoma lines and proceeds at a lower rate than that of the intact virus. No insertion of a foreign promoter or enhancer into the long terminal repeat was detected. Our data suggest the presence of a secondary enhancer element within the MLV provirus that can in selected human cells mediate virus transcription and replication in the absence of the 75-bp U3 enhancers.

Amphotropic murine leukemia virus replication in human mammary epithelial cells and the formation of cytomegalovirus-promoter recombinants

Amphotropic murine leukemia virus (MLV) can replicate in human cells and is a potential contaminant in vector preparations for human gene transfer studies. We have recently shown that replication of amphotropic MLV in specific human sarcoma and lymphoma lines is possible in the absence of the viral 75-bp transcription enhancer elements. Here, we have tested the replication of an amphotropic MLV, MLV-(MOA), and an enhancer-deficient mutant of this virus in human breast carcinoma-derived cell lines. The proviral expression plasmids use a cytomegalovirus (CMV) promoter for the initial transcription of virus RNA. We found that all cells analyzed are permissive for replication of MLV-(MOA). Enhancer-deficient virus is unable to replicate. However, in two lines the replication defect can be rescued by the spontaneous insertion of a CMV promoter and enhancer into the U3 region. This recombinant virus MLV-(RCMV) replicates with kinetics similar to that of MLV-(MOA) but is restricted to specific cell lines. The potential formation of RCMV recombinants during MLV vector preparation must be considered.

The mouse mammary tumor virus transcription enhancers for hematopoietic progenitor and mammary gland cells share functional elements

Expression of mouse mammary tumor virus (MMTV)-encoded superantigens in B lymphocytes is required for viral transmission and pathogenesis. We have previously established a critical role of an enhancer element within the long terminal repeat (LTR) for MMTV sag gene expression in B-lymphoid progenitor cells. We now demonstrate enhancer activity of this element in a promyelocytic progenitor cell line. We also map the position of the enhancer within the U3 region of the MMTV LTR and show that the progenitor cell enhancer shares functional elements with a previously described mammary gland-specific enhancer.

Enhancer-deficient amphotropic murine leukemia virus and recombinants with heterologous transcription elements can be efficiently amplified and detected in Mus dunni fibroblasts

Amphotropic murine leukemia virus (MLV) replicates in cells from various mammalian species, including humans, and is a potential contaminant in MLV vector preparations for human gene transfer studies. Mus dunni fibroblasts are routinely used for amplification and detection of contaminating virus. We have recently characterized an amphotropic MLV mutant lacking the 75-bp viral enhancer elements and spontaneous MLV-(RCMV) recombinants that have acquired cytomegalovirus (CMV) transcription elements. Both of these viruses replicate in specific human cell types. To test whether the formation of such viruses can be detected and controlled with current routine procedures, we have analyzed the replication of these amphotropic MLV mutants in Mus dunni fibroblasts. We find that M. dunni cells are permissive for enhancer-deficient and CMV promoter-recombinant MLV from several human cell lines. Thus, M. dunni fibroblasts are suitable for the amplification and subsequent detection of enhancer-deficient and enhancer-recombinant MLV in vector preparations.

[Pantothenic acid levels in blood of athletes at rest and after aerobic exercise]

Ninety-six high-performance athletes of various disciplines were available for this investigation. All athletes had many years of training and competition experience. The pantothenic acid contents in the blood were determined by means of microbiological measurements. In addition to the pantothenic acid level at rest, measurements were made resp. physical exertion in 14 marathon runners and nine body builders. Blood was collected for determination of pantothenic acid before (a), after (b) and 2 h after exercise. Compared to the reference values for untrained persons (1.34 +/- 0.13 nmol/mL), the marathon runners with 0.76 (0.31-0.94) nmol/mL and soccer players with 1.19 (0.37-2.64) nmol/mL were below the reference values. According to relative frequencies, more than 30% of all athletes were below the lower limit (< 1.20 nmol/mL). The values in body builders/racing cyclists differed significantly from those in marathon racers (p < 0.001), which is presumably due to unallowed supplementation. During exercise, there was a significant increase in the pantothenic acid level in marathon runners (p < 0.01).

Mouse mammary tumor virus superantigen expression is reduced by glucocorticoid treatment

Expression of mouse mammary tumor virus (MMTV)-encoded superantigens in B lymphocytes are required for viral transmission and pathogenesis. Due to problems with detection and quantification of the superantigen protein, most reports about the mechanism of superantigen expression from the viral sag gene rely on the quantitative analysis of putative sag mRNAs. The description of multiple promoters as a source of putative sag mRNA has complicated the situation even further. All conclusions about the level of superantigen protein expression based on these data remain circumstantial. To test the effect of the glucocorticoid hormone dexamethasone on the total superantigen expression from an infectious MMTV provirus we used a quantitative assay that is based on a superantigen-luciferase fusion protein. MMTV gene expression from the major promoter in the 5' long terminal repeat (LTR) is strongly induced in the presence of glucocorticoid hormones. We now demonstrate that, in the presence of dexamethasone, sag gene expression is reduced despite increased transcription from the MMTV 5' LTR and increased amounts of putative sag mRNA initiated at the LTR promoter. These data show that the expression of the MMTV sag gene does not correlate with the activity of the major LTR promoter and thus differs from all other MMTV genes.