Training: putting the pieces together

What steps are needed to develop and successfully manage a comprehensive safety and health program for your institution? Don't overlook a long-term action plan and remember that safety is a shared responsibility, says the author.

The anticytomegaloviral activity of raltitrexed is abrogated in quiescent mouse fibroblasts that overexpress thymidylate synthase

Cytomegalovirus (CMV) replication in non-proliferating cells requires the coordinated expression of the host enzymes responsible for deoxyribonucleotide synthesis. Thymidylate synthase (TS) is an essential cellular enzyme that catalyzes de novo synthesis of thymidylic acid (dTMP). In this report we show that murine CMV (MCMV) replication and DNA synthesis are inhibited in quiescent 3T6 fibroblasts by raltitrexed, a quinazoline-based folate analog that specifically inhibits TS. This antiviral activity was abrogated in LU3-7 cells, a 3T6 derivative that overproduces TS by about 50-fold. These observations indicate that the anticytomegaloviral activity of raltitrexed is associated with TS inhibition and suggest that cellular TS activity is required for efficient CMV replication in quiescent cells.

Inhibition of the mammalian transcription factor LSF induces S-phase-dependent apoptosis by downregulating thymidylate synthase expression

The thymidylate synthase (TS) gene, which is induced at the G(1)-S transition in growth-stimulated cells, encodes an enzyme that is essential for DNA replication and cell survival. Here we demonstrate that LSF (LBP-1c, CP2) binds to sites within the TS promoter and intronic regions that are required for this induction. Mutation of the LSF binding sites inhibits G(1)-S induction of mRNA derived from a TS minigene. Furthermore, expression of dominant-negative LSF (LSFdn) prevents the increase in TS enzyme levels during G(1)-S, and induces apoptosis in growth- stimulated mouse and human cell lines. Such apoptosis can be prevented either by circumventing the TS requirement through addition of low concentrations of thymidine, or by coexpression of the TS gene driven by a heterologous promoter. Induction of apoptosis by LSFdn parallels the process known as thymineless death, which is induced by the TS inhibitor and chemotherapeutic drug 5-fluorodeoxyuridine. Thus, LSF is a novel regulatory factor that supports progression through S-phase by targeting a single gene that is critical for cell survival.

Progress and problems in achieving the United States national target for completion of antituberculosis treatment

SETTING

The target for antituberculosis treatment in the United States is for 90% of patients to complete therapy within 12 months.

OBJECTIVE

To assess progress in achieving the US national target for tuberculosis treatment.

DESIGN

A comparison of treatment outcome in two cohorts of patients with drug-susceptible tuberculosis in California-those reported in 1993-1994 (8488 patients) and 1995-1996 (7823 patients). Risk factors for delay in treatment completion (more than 12 months) were assessed.

RESULTS

The percentage of cases completing treatment within 12 months increased in the 1995-1996 cohort (to 68.2%), primarily due to concomitant reductions in delays in treatment completion (to 11.1%) and defaulting (to 2.4%). Disparities in timely treatment completion narrowed over time and in nearly all subpopulations, especially in groups with lowest treatment completion in the 1993-1994 cohort. Remaining risk factors for delay in treatment completion included AIDS and older ages. A substantial percentage of patients died or moved before treatment completion.

CONCLUSIONS

Despite recent improvements, completion of antituberculosis treatment in California has not reached the national target. Reaching this target will require further reductions in delays in treatment completion and deaths during treatment, and ensuring that patients who move eventually complete treatment.

Intramural tracking: a feature of esophageal intramural pseudodiverticulosis

OBJECTIVE

Our purpose was to determine the frequency of intramural tracking in patients with esophageal intramural pseudodiverticulosis and to characterize the morphologic features of this finding on barium studies.

MATERIALS AND METHODS

A review of radiology files at two institutions revealed 30 cases of esophageal intramural pseudodiverticulosis diagnosed at esophagography. In all cases, the radiographs were reviewed retrospectively to determine the frequency and morphologic features of intramural tracking in these patients. The number and distribution of pseudodiverticula and the presence or absence of strictures or esophagitis were also noted.

RESULTS

Fifteen (50%) of 30 patients with esophageal intramural pseudodiverticulosis had intramural tracking on esophagography. The tracks had an average length of 1.2 cm (length range, 0.3-7 cm) and an average width of 1.6 mm (width range, 1-4 mm). The pseudodiverticula were more numerous and had a more diffuse distribution in patients with tracking than in patients without tracking. Although patients with and without tracking had a similar frequency of strictures and esophagitis, patients with tracking were more likely to have strictures involving the upper or mid esophagus, whereas patients without tracking were more likely to have strictures in the distal esophagus. These findings indicate that intramural tracking is more likely to occur in patients with the diffuse form of esophageal intramural pseudodiverticulosis.

CONCLUSION

Intramural tracking was detected on esophagography in 50% of patients with esophageal intramural pseudodiverticulosis, so this type of tracking is a more common radiographic finding than has previously been recognized. Although intramural tracking has little or no known clinical significance, it is important to be aware of this finding so that it is not mistaken for a large flat ulcer in the esophagus or for an extramural collection associated with esophageal peridiverticulitis.

Transcriptional control elements of the rat thymidylate synthase promoter: evolutionary conservation of regulatory features

The sequence elements that are important for the transcription and regulation of the rat thymidylate synthase (TS) gene were analyzed. The rat TS promoter lacks a TATA box and directs transcriptional initiation at multiple sites between 60 and 20 nt upstream of the AUG translational start codon. Promoter deletion analyses showed that the region between -100 and -42 nt relative to the AUG codon was both necessary and sufficient for high level promoter activity and was designated the essential promoter region. The essential region also had bidirectional promoter activity. Site-directed mutagenesis revealed that four elements were especially important for promoter activity. These include Ets motifs at -85 and -50, an Sp1 motif at -80, and an LSF motif that overlapped the upstream Ets and Sp1 motifs. Inactivation of E2F motifs that are upstream and downstream of the essential promoter region had no measurable effect on promoter activity in transient transfection assays. The rat TS promoter region directed S-phase-specific expression of a stably transfected minigene if a spliceable intron was included in the transcribed region. When the intron was deleted or the E2F motifs were inactivated, expression of the minigene changed very little during the G1 to S transition.

Murine cytomegalovirus stimulates cellular thymidylate synthase gene expression in quiescent cells and requires the enzyme for replication

Herpesviruses accomplish DNA replication either by expressing their own deoxyribonucleotide biosynthetic genes or by stimulating the expression of the corresponding cellular genes. Cytomegalovirus (CMV) has adopted the latter strategy to allow efficient replication in quiescent cells. In the present report, we show that murine CMV (MCMV) infection of quiescent fibroblasts induces both mRNA and protein corresponding to the cellular thymidylate synthase (TS) gene, which encodes the enzyme that catalyzes the de novo synthesis of thymidylic acid. The increase in TS gene expression was due to an increase in gene transcription, since the activity of a reporter gene driven by the mouse TS promoter was induced following MCMV infection. Mutagenesis of the potential E2F-responsive element immediately upstream from the TS essential promoter region abolished the virus-mediated stimulation of the TS promoter, suggesting that the transactivating activity of MCMV infection was E2F dependent. Cotransfection experiments revealed that expression of the viral immediate-early 1 protein was sufficient to mediate the increase in TS promoter activity. Finally, MCMV replication and viral DNA synthesis were found to be inhibited by ZD1694, a quinazoline-based folate analog that inhibits TS activity. These results demonstrate that upregulation of cellular TS expression is required for efficient MCMV replication in quiescent cells.