Multiple functions for the poly(A)-binding protein in mRNA decapping and deadenylation in yeast

The first step in the decay of many eukaryotic mRNAs is shortening of the poly(A) tail. In yeast, deadenylation leads to mRNA decapping and subsequent 5' --> 3' exonucleolytic degradation of the transcript body. We have determined that the major poly(A)-binding protein Pab1p plays at least two critical roles in this pathway. First, mRNAs in pab1 delta strains were decapped prior to deadenylation. This observation defines a new function for Pab1p as an inhibitor of mRNA decapping. Moreover, mutations that inhibit mRNA turnover suppress the inviability of a pab1 delta mutation, suggesting that premature mRNA decapping in pab1 delta strains contributes to cell death. Second, we find that Pab1p is not required for deadenylation, although in its absence poly(A) tail shortening rates are significantly reduced. In addition, in the absence of Pab1p, newly synthesized mRNAs had poly(A) tails longer than those in wild-type strains and showed an unexpected temporal delay prior to the initiation of deadenylation and degradation. These results define new and critical functions for Pab1p in the regulation of mRNA decapping and deadenylation, two important control points in the specification of mRNA half-lives. Moreover, these results suggest that Pab1p functions in additional phases of mRNA metabolism such as mRNP maturation.

Partial characterization of a Cisplatin-resistant subline of murine rif-1 tumor-cells

We have developed a drug-resistant cell line (RIF/Ptr1) (R) from the murine radiation-induced fibrosarcoma (RIF-1) also designated Pts or (S). This subline has been characterized previously by an increased resistance to cisplatin (cis-diamminedichloroplatinum(II) or CDDP), lowered intracellular CDDP concentrations, and elevated intracellular glutathione (GSH) levels (1.4-2.5-fold) but unaltered formation of CDDP-DNA interstrand cross-links. In this work, we have shown that RIF/Ptr1 cells were also resistant to carmustine (BCNU) and X-irradiation. Neither cell line had P-glycoprotein 170. The intrastrand CDDP-DNA adduct level was proportional to the concentration of intracellular CDDP. The oxygen consumption, ATP level, and glycolysis were similar in both cell lines. The cisplatin influx and efflux showed that the RIF/Ptr1 cells had lower drug influx and higher drug efflux compared to RIF-1. We conclude that the major difference between the cisplatin sensitive and cisplatin-resistant cells in this model is the regulation of cisplatin transport probably at the cell membrane level suggesting that a membrane active transport system other than P-glycoprotein 170 is involved. Whether glutathione is linked to the putative membrane transporter needs further investigation.

[The effect of x-rays on experimental arthritis in the rat]

AIMS

We investigated the therapeutic efficacy of low doses of X-rays on different in-vivo models of monoarticular arthritis which have been developed for the investigation of anti-inflammatory drugs.

MATERIAL AND METHODS

Zymosan or heat-inactivated mycobacterium tuberculosis was injected into 1 knee joint of Wistar rats to produce, via different pathogenetic mechanisms, an acute monoarticular arthritis. Five days later, the amount of joint swelling, bone destruction and cartilage catabolism were measured. Immediately after arthritis induction, the knees were irradiated with a single dose of 5 Gy or with 4 daily fractions of 1 Gy.

RESULTS

X-irradiation with daily doses of 1 Gy significantly reduced bone loss and cartilage degradation in Zymosan-induced arthritis and joint swelling in mycobacterium tuberculosis induced arthritis. However, a single high radiation dose significantly increased bone loss in mycobacterium tuberculosis induced arthritis.

CONCLUSIONS

These data confirm the hypothesis of an anti-inflammatory effect of low radiation doses which so far has been based only on clinical experience. By using an established model of monoarticular arthritis we have now the opportunity to study the mechanism of the anti-inflammatory radiation effect in comparison to that of anti-inflammatory drugs. This way, we hope to provide a scientific basis for the use of radiotherapy in various painful degenerative joint disorders.

The effect of transient temperatures on the growth of Salmonella typhimurium LT2. II: Excursions outside the growth region

The effect of fluctuating temperatures on microbial growth is important in the passage of foods from production to consumption. Suspensions of Salmonella typhimurium have been subjected to sinusoidally time-varying temperatures of periods from 60 to 240 min between 4 degrees and 22 degrees C, that is within and below the growth temperature range. The suspensions were prepared with two concentrations of sodium chloride and adjusted to two different values of pH. The change in the numbers of viable bacteria was measured with time and the experimental growth curves and average generation times compared with predictions based on isothermal growth data. Generally, the experimental average generation times exceeded the predictions by not more than 10%. In enumerating viable bacteria in the suspensions containing 3.5% (w/v) sodium chloride it was necessary to use sodium chloride in the diluent and recovery medium in order to recover the bacteria quantitatively.

The Use of Nonaqueous Fractionation to Assess the Ionic Composition of the Apoplast during Fruit Ripening

We have examined the possibility that pectin solubilization and cell separation in fruit may be due to organic acids disrupting calcium bridges between pectic polysaccharides. With fruit from a wild tomato (Lycopersicon pimpinellifolium [Dunal]) we demonstrated the validity of a nonaqueous fractionation method to obtain reliable estimates of the ionic content of the apoplast. In unripe fruit no organic acids were associated with the cell wall, which contained 67% of the total calcium and 47% of the magnesium. In ripe fruit 4% of the malate, 10% of the citrate, and 15% of the oxalate were estimated to be in the cell wall, together with 84% of the calcium and 52% of the magnesium. In contrast to the cultivated tomato, we did not find a consistent decrease in the degree of methyl esterification between unripe and ripe fruit, and an overall average of 75% was observed. In the cell walls of ripe fruit the ratio of calcium:magnesium:organic acid:unesterified uronic acid, on the basis of charge, was 15:4:4:16. The use of a computer program to predict the proportions of different ionic species in complex mixtures suggested that in ripe fruit 70% of the unesterified uronic acid would be complexed with calcium. Our results show that organic acids do not accumulate in the cell wall sufficiently to disrupt calcium cross-linking, nor is the calcium removed from the wall into the cell. We therefore conclude that organic acids do not contribute to cell separation during the ripening of tomato fruit.

Surgical management of ventricular tachycardia in subannular left ventricular aneurysm

Submitral left ventricular aneurysms typically affect young adults of African ancestry. These aneurysms are characterized by heart failure and mitral insufficiency, and occur in the absence of coronary disease. We report a rare case of symptomatic ventricular tachycardia in association with submitral left ventricular aneurysm (and no mitral insufficiency). Ventricular tachycardia was abolished by aneurysm resection and ventricular reconstruction. We suggest surgical management is indicated for ventricular tachycardia associated with this unusual condition, and may be curative.

Prevention of premature birth by screening and treatment for common genital tract infections: results of a prospective controlled evaluation

OBJECTIVE

Our purpose was to analyze (1) the effects of prevalent lower reproductive tract infections and (2) the effect of systematic diagnosis and treatment to reduce risks of early pregnancy loss (< 22 weeks), preterm premature rupture of membrances, and overall preterm birth.

STUDY DESIGN

A prospective, controlled treatment trial was conducted on 1260 women. During the first 7 months of the program (observation, phase I), women were examined at initiation of prenatal care for a panel of lower genital tract microorganisms and bacterial vaginosis. Women were followed up with reexaminations at 22 to 29 weeks and after 32 weeks' gestation. The recommended treatments of the Centers for Disease Control (i.e., 300 mg of clindamycin orally twice daily for 7 days for bacterial vaginosis) were used for infected women during the second 8 months of the study (treatment, phase II). Data were analyzed according to intent to treat by means of univariate and multivariate methods.

RESULTS

Overall, presence of bacterial vaginosis (32.5%) at enrollment was associated with pregnancy loss at < 22 weeks' gestation (relative risk 3.1, 95% confidence interval 1.4 to 6.9). Among women in the observation phase bacterial vaginosis was associated with increased risk of both preterm birth (relative risk 1.9, 95% confidence interval 1.2 to 3.0) and preterm premature rupture of membranes (relative risk 3.5, 95% confidence interval 1.4 to 8.9). Within this population (phase I) 21.9% of preterm birth overall (43.8% premature rupture of membranes) is estimated as attributable to bacterial vaginosis. Among women with bacterial vaginosis phase II (treatment) was associated with reduced preterm birth (relative risk 0.5, 95% confidence interval 0.3 to 0.9); there was a similar reduction for women with preterm premature rupture of membranes (relative risk 0.5, 95% confidence interval 0.2 to 1.4). Women with both bacterial vaginosis and trichomoniasis were at highest risk of preterm birth (28%); treatment of both conditions (phase II) reduced preterm birth (17%) but did not eliminate this risk. Earlier patient enrollment and oral antibiotic treatment were associated with reduced preterm birth.

CONCLUSIONS

This prospective, controlled trial confirms that the presence of bacterial vaginosis is associated with increased risks of pregnancy loss at < 22 weeks, preterm premature rupture of membranes, and preterm birth. Orally administered clindamycin treatment is associated with a 50% reduction of bacterial vaginosis-linked preterm birth and preterm premature rupture of membranes. Women at risk for preterm birth or preterm premature rupture of membranes because of bacterial vaginosis or common genital tract infections should be screened, treated, reevaluated for cure, and re-treated if necessary.

Diversity of cytoplasmic functions for the 3' untranslated region of eukaryotic transcripts

The 3' untranslated region (3' UTR) can control gene expression by affecting the localization, stability and translation of mRNAs. The recent finding that 3' UTRs can control the decapping rate of mRNAs, in combination with their ability to influence the initiation of translation, suggests that 3' UTRs act through a direct or indirect interaction between the 3' and 5' ends of mRNAs.

Effects of interleukin-1 alpha on DNA repair in human ovarian carcinoma (NIH:OVCAR-3) cells: implications in the mechanism of sensitization of cis-diamminedichloroplatinum(II)

The cytokine interleukin-1 alpha (IL-1 alpha) showed a cytostatic effect on human ovarian carcinoma cells and significantly enhanced the antiproliferative activity of cis-diamminedichloroplatinum(II) (cisplatin) toward the NIH:OVCAR-3 tumor cell line in culture. The factor of sensitization was 15-20-fold. The maximum levels of sensitization were observed both with simultaneous exposure to cisplatin and IL-1 alpha and with 24-hr pretreatment with IL-1 alpha. Synergy between these agents was diminished when cells were pretreated with an IL-1 alpha-specific receptor antagonist, indicating that synergistic interaction was receptor mediated. Using atomic absorption spectroscopy, we evaluated the cellular accumulation of cisplatin and the DNA platination; the results showed that IL-1 alpha increased cellular accumulation of cisplatin and DNA platination. Cisplatin did not affect IL-1 alpha accumulation in NIH:OVCAR-3 cells. Further studies showed that IL-1 alpha reduced the removal of platinum from DNA. These results strongly suggest that IL-1 alpha inhibits DNA repair, and this decrease in DNA repair may explain, in part, the strong synergistic interaction between IL-1 alpha and cisplatin in NIH:OVCAR-3 cells.

Degradation of mRNA in eukaryotes

Based on the above mechanisms of mRNA degradation, an integrated model of mRNA turnover can be proposed (Figure 1). In this model, all polyadenylated mRNAs would be degraded by the deadenylation-dependent pathway at some rate. In addition to this default pathway, another layer of complexity would come from degradation mechanisms specific to individual mRNAs or to classes of mRNAs. Such mRNA-specific mechanisms would include sequence-specific endonuclease cleavage and deadenylation-independent decapping. Thus, the overall decay rate of an individual transcript will be a function of its susceptibility to these turnover pathways. In addition, cis-acting sequences that specify mRNA decay rate, as well as regulatory inputs that control mRNA turnover, are likely to affect all the steps of these decay pathways. One important goal in future work will be to identify the gene products that are responsible for the nucleolytic events in these pathways and to delineate how specific mRNA features act to affect the function of these degradative activities. The identification of distinct mRNA decay pathways should allow, genetic and biochemical approaches that can be designed to identify these gene products. A second important goal is to understand the nature of the interaction between the 5' and 3' termini, which may also be critical for efficient translation.

The glass-transition behaviour of wheat gluten proteins

The glass-transition behaviour of four hydrated wheat gluten proteins (alpha-gliadin, gamma-gliadin, omega-gliadin and high-molecular-weight (HMW) subunits of glutenin) was studied using differential scanning calorimetry (DSC). By fitting the data to the Gordon-Taylor equation, which has previously been used to describe the plasticization of polymers by diluents, the glass-transition temperatures (Tg) for the dry proteins were found by extrapolation. The values for Tg were within the range 397-418 K. Values for the heat capacity increment delta Cp at Tg for the plasticized proteins were also determined and ranged from 0.29-0.47 J g-1 K-1 with no dependence on water content. The differences in glass-transition behaviour of the proteins are discussed in relation to their secondary structure.

Turnover mechanisms of the stable yeast PGK1 mRNA

The first step in the decay of several yeast mRNAs is the shortening of the poly(A) tail, which for the MFA2 transcript triggers decapping and 5'-to-3' degradation. To understand the basis for differences in mRNA decay rates, it is important to determine if deadenylation-dependent decapping is specific to the unstable MFA2 transcript or is a general mechanism of mRNA degradation. To this end, we analyzed the turnover of the stable PGK1 mRNA by monitoring the decay of a pulse of newly synthesized transcripts while using two strategies to trap decay intermediates. First, we used strains deleted for the XRN1 gene, which encodes a major 5'-to-3' exonuclease in Saccharomyces cerevisiae. In xrn1 delta cells, PGK1 transcripts lacking the 5' cap structure and a few nucleotides at the 5' end were detected after deadenylation. Second, we inserted into the PGK1 5' untranslated region strong RNA secondary structures, which can slow exonucleolytic digestion and thereby trap decay intermediates. These secondary structures led to the accumulation of PGK1 mRNA fragments, following deadenylation, trimmed from the 5' end to the site of the secondary structure. The insertion of strong secondary structures into the 5' untranslated region also inhibited translation of the mRNA and greatly stimulated the decay of the PGK1 transcripts, suggesting that translation of the PGK1 mRNA is required for its normally slow rate of decay. These results suggest that one mechanism of degradation of the PGK1 transcript is deadenylation followed by decapping and subsequent 5'-to-3' exonucleolytic degradation. In addition, by blocking the 5'-to-3' degradation process, we observed PGK1 mRNA fragments that are consistent with a 3'-to-5' pathway of mRNA turnover that is slightly slower than the decapping/5'-to-3' decay pathway. These observations indicate that there are multiple mechanisms by which an individual transcript can be degraded following deadenylation.

Premature translational termination triggers mRNA decapping

The degradation of messenger RNA in eukaryotic cells is initiated by endonucleolytic cleavage or by shortening of the poly(A) tail, which for some mRNAs activates a deadenylation-dependent decapping reaction. One type of rapid mRNA degradation in eukaryotes is caused by premature termination of translation. This turnover process prevents the translation of aberrant mRNAs, may affect the abundance and splicing pattern of nuclear transcripts, and may be involved in the aetiology of human genetic disease. Here we show that premature translational termination in yeast triggers decapping, independent of deadenylation, thereby exposing the transcript to 5'-to-3' degradation. Inactivation of the 5'-to-3' exonuclease reveals an additional 3'-to-5' pathway of mRNA turnover. These observations provide in vivo evidence for two new mechanisms of mRNA decay.

Mechanisms of mRNA degradation in eukaryotes

Recent experiments have identified distinct mechanisms of eukaryotic RNA turnover. In one mechanism, deadenylation triggers decapping, exposing the messenger RNA to 5' to 3' degradation. This pathway may act at different rates on the majority of messenger RNAs. There are also degradation mechanisms, such as endonucleolytic cleavage, limited to messenger RNAs containing specific sequence elements.

The effect of transient temperatures on the growth of Salmonella typhimurium LT2. I: Cycling within the growth region

The effect of fluctuating temperatures on microbial growth is important in the passage of foods through the food chain. Suspensions of Salmonella typhimurium were subjected to sinusoidally time-varying temperatures of periods from 40 to 480 min within their growth temperature range. The change in the numbers of viable bacteria was measured with time and the experimental growth curves and average generation times compared with predictions based on isothermal growth data. The experimental average generation times exceeded the predictions by less than 30%, although the discrepancy increased with cycle frequency. Instantaneous growth rates obtained for the 480 min cycles were in agreement with those predicted from isothermal behaviour.

Differential effects of translational inhibition in cis and in trans on the decay of the unstable yeast MFA2 mRNA

Several observations in eukaryotic cells suggest that the processes of translation and mRNA turnover are interrelated. To understand this relationship, we examined the effects of translational inhibition on the decay of the unstable yeast MFA2 mRNA, which is degraded in a 5' to 3' direction following deadenylation (1). Although inhibition of translation in cis stabilizes several unstable mammalian transcripts, inhibiting translation of the MFA2 mRNA in cis, by the insertion of a large stem-loop structure in the 5'-untranslated region (UTR), did not affect the half-life, deadenylation rate, or appearance of specific decay intermediates. Therefore, efficient translational elongation on the MFA2 mRNA is not a requirement for the normal rate, or mechanism, of degradation of this transcript. In contrast, inhibition of translation in trans, by the addition of cycloheximide, stabilized the deadenylated form of MFA2 mRNA. Furthermore, the MFA2 transcripts that were not translated due to a stem-loop in the 5'-UTR were also stabilized in the presence of cycloheximide, suggesting that cycloheximide is likely to affect mRNA stability indirectly. These results suggest possible relationships between the mechanisms of mRNA decay and the translational process.

A cost analysis of approved antiretroviral strategies in persons with advanced human immunodeficiency virus disease and zidovudine intolerance

Treatment with zidovudine has been standard therapy for patients with advanced HIV infection, but intolerance is common. Previously, management of intolerance has consisted of symptomatic therapy, dose interruption/discontinuation, and, when appropriate, transfusion. The availability of new antiretroviral agents such as didanosine as well as adjunctive recombinant hematopoietic growth factors makes additional strategies possible for the zidovudine-intolerant patient. Because all of these agents are costly, we evaluated the cost implications of these various strategies for the management of zidovudine-intolerant individuals within a population of persons with advanced HIV disease. We performed a decision analysis using iterative algorithmic models of 1 year of antiretroviral care under various strategies. The real costs providing antiretroviral therapy were estimated by deflating medical center charges by specific Medi-Cal (Medicaid) charge-to-payment ratios. Clinical data were extracted from the medical literature, product package inserts, investigator updates, and personal communications. Sensitivity analysis was used to test the effect of error in the estimation of parameters. The models predict that a strategy of dose interruption and transfusion for zidovudine intolerance will provide an average of 46 weeks of therapy per year to the average patient at a cost of $5,555/year of therapy provided (1991 U.S. dollars). The models predict that a strategy of adding hematopoietic growth factors to the regimen of appropriate patients would increase the average amount of therapy provided to the average patient by 3 weeks (6%) and the costs attributable to therapy by 77% to $9,805/year of therapy provided.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacterial vaginosis is associated with prematurity and vaginal fluid mucinase and sialidase: results of a controlled trial of topical clindamycin cream

OBJECTIVE

The pathogenesis of preterm birth and other adverse pregnancy outcomes linked with reproductive tract infection remains poorly understood. Mucolytic enzymes, including mucinases and sialidases (neuraminidase), are recognized virulence factors among enteropathogens and bacteria that cause periodontal infection. Perturbation of maternal cervicovaginal mucosa membrane host defenses by such enzyme-producing microorganisms may increase the risk of subclinical intrauterine infection during pregnancy and thus increase risks of preterm birth.

STUDY DESIGN

We prospectively evaluated vaginal fluid mucinase and sialidase and selected cervicovaginal bacteria along with pregnancy outcomes in 271 women. Within this study, women with bacterial vaginosis (16 to 27 week' gestation) were treated with 2% clinadmycin vaginal cream or placebo. Enzyme, microbial findings, treatment effects, and pregnancy outcomes were compared among drug- and placebo-treated women and control women without bacterial vaginosis.

RESULTS

Presence of bacterial vaginosis at intake was associated with increased risk of preterm birth (relative risk 3.3, 95% confidence interval 1.2 to 9.1, p = 0.02), premature rupture of membranes (relative risk 3.8, 95% confidence interval 1.6 to 9.0, p = 0.002), and preterm premature rupture of membranes. Mucinase and sialidase activities were more commonly identified, and they occurred in higher concentrations, if present, in women with bacterial vaginosis (mucinase: 44.3% with bacterial vaginosis vs 27.4% without, p = 0.007; sialidase: 45% with bacterial vaginosis vs 12% without p < 0.001). Sialidase activity was associated with bacterial vaginosis-linked organisms (Gardnerella vaginalis, Mobiluncus spp, and Mycoplasma hominis) and Chlamydia trachomatis and yeast species; mucinase activity was associated only with bacterial vaginosis-linked microorganisms. Clindamycin, 2% cream, was effective treatment for bacterial vaginosis and temporarily reduced mucinase and sialidase activities. Topical treatment of bacterial vaginosis did not reduce risks of perinatal morbidity. Women with persistent or recurrent sialidase 8 weeks after treatment were at increased risk of preterm birth (15.6% vs 7.4%) premature rupture of membranes (30% vs 15%), and low birth weight (20% vs 3%, relative risk 6.8, 95% confidence interval 1.6 to 28.1).

CONCLUSIONS

Persistence of sialidase-producing vaginal microorganisms in numbers sufficient to increase vaginal fluid sialidase activity may be a risk factor for possibly preventable subclinical intrauterine infection and preterm birth. This study confirms and further informs our understanding of the association of bacterial vaginosis and preterm birth; studies to evaluate whether systemic treatment for bacterial vaginosis can effectively reduce vaginal mucolytic enzymes and risks of prematurity and other morbid outcomes are continuing.