Inactivation of DNA mismatch repair by increased expression of yeast MLH1

Inactivation of DNA mismatch repair by mutation or by transcriptional silencing of the MLH1 gene results in genome instability and cancer predisposition. We recently found (P. V. Shcherbakova and T. A. Kunkel, Mol. Cell. Biol. 19:3177-3183, 1999) that an elevated spontaneous mutation rate can also result from increased expression of yeast MLH1. Here we investigate the mechanism of this mutator effect. Hybridization of poly(A)(+) mRNA to DNA microarrays containing 96.4% of yeast open reading frames revealed that MLH1 overexpression did not induce changes in expression of other genes involved in DNA replication or repair. MLH1 overexpression strongly enhanced spontaneous mutagenesis in yeast strains with defects in the 3'-->5' exonuclease activity of replicative DNA polymerases delta and epsilon but did not enhance the mutation rate in strains with deletions of MSH2, MLH1, or PMS1. This suggests that overexpression of MLH1 inactivates mismatch repair of replication errors. Overexpression of the PMS1 gene alone caused a moderate increase in the mutation rate and strongly suppressed the mutator effect caused by MLH1 overexpression. The mutator effect was also reduced by a missense mutation in the MLH1 gene that disrupted Mlh1p-Pms1p interaction. Analytical ultracentrifugation experiments showed that purified Mlh1p forms a homodimer in solution, albeit with a K(d) of 3.14 microM, 36-fold higher than that for Mlh1p-Pms1p heterodimerization. These observations suggest that the mismatch repair defect in cells overexpressing MLH1 results from an imbalance in the levels of Mlh1p and Pms1p and that this imbalance might lead to formation of nonfunctional mismatch repair complexes containing Mlh1p homodimers.

The effect of vitamin E and vitamin C supplementation on LDL oxidizability and neutrophil respiratory burst in young smokers

OBJECTIVE

The purpose of this study was to determine the effect of vitamin E and/or vitamin C supplementation on low-density lipoprotein (LDL) oxidizability and neutrophil (PMN) superoxide anion production in young smokers.

METHODS

Thirty smokers with a <5 pack-year history were randomly assigned to take placebo; vitamin C (1 g/day); vitamin E (400 IU/day), or both vitamins in a double-blind fashion. Subjects took the supplements for 8 weeks. At weeks 0 and 8, blood was collected for isolation of LDL and PMN, and for antioxidant vitamin analysis. LDL was oxidized with a copper (Cu) catalyst, and oxidation was measured by formation of conjugated dienes over a 5-hour time course. Lag times and maximum oxidation rates were calculated from the time course data. PMN superoxide anion release was assessed by respiratory burst after stimulation with phorbol ester and opsonized zymosan, and their ability to oxidize autologous LDL following treatment with the above stimuli was measured with the conjugated diene assay.

RESULTS

Subjects who received vitamin E alone had a significant increase in the lag phase of Cu-catalyzed LDL oxidation (week 0, 118+/-31 min vs. week 8, 193+/-80 min, mean +/- SD, p < 0.05), whereas the vitamin C and placebo groups had no changes in LDL oxidation kinetics. The group receiving both vitamins E and C had a significant reduction in oxidation rate (week 0. 7.4+/-2.3 vs. week 8, 5.1+/-2.1, p < 0.05). There were no significant changes for any group in PMN superoxide anion production or PMN LDL oxidation after stimulation with either phorbol ester or opsonized zymosan. Plasma and LDL vitamin E concentrations were significantly increased in both groups that received vitamin E. The subjects who received vitamin C alone had no significant change in plasma vitamin C concentrations; however, when data were pooled from both groups who received vitamin C, the increases were significant.

CONCLUSION

Vitamin E supplementation of young smokers was effective in reducing Cu-catalyzed LDL oxidizability; however, vitamin E and/or C supplementation showed few significant effects on the more physiologically relevant PMN function. This casts doubt on the ability of antioxidant supplementation to reduce oxidative stress in smokers in vivo. Therefore, smoking cessation remains the only means by which young smokers can prevent premature coronary heart disease.

Linking gene expression patterns to therapeutic groups in breast cancer

A major objective of current cancer research is to develop a detailed molecular characterization of tumor cells and tissues that is linked to clinical information. Toward this end, we have identified approximately one-quarter of all genes that were aberrantly expressed in a breast cancer cell line using differential display. The cancer cells lost the expression of many genes involved in cell adhesion, communication, and maintenance of cell shape, while they gained the expression of many synthetic and metabolic enzymes important for cell proliferation. High-density, membrane-based hybridization arrays were used to study mRNA expression patterns of these genes in cultured cells and archived tumor tissue. Cluster analysis was then used to identify groups of genes, the expression patterns of which correlated with clinical information. Two clusters of genes, represented by p53 and maspin, had expression patterns that strongly associated with estrogen receptor status. A third cluster that included HSP-90 tended to be associated with clinical tumor stage, whereas a forth cluster that included keratin 14 tended to be associated with tumor size. Expression levels of these clinically relevant gene clusters allowed breast tumors to be grouped into distinct categories. Gene expression fingerprints that include these four gene clusters have the potential to improve prognostic accuracy and therapeutic outcomes for breast cancer patients.

Therapy of secondary hyperparathyroidism with 19-nor-1alpha,25-dihydroxyvitamin D2

Secondary hyperparathyroidism contributes to significant morbidity in patients with chronic renal failure. The treatment of this disorder with vitamin D compounds, such as calcitriol, although effective at suppressing parathyroid hormone (PTH) secretion, may promote the development of hypercalcemia and hyperphosphatemia, thus increasing the risk for metastatic calcification. A new vitamin D analogue, 19-nor-1alpha,25-(OH)2D2 (paricalcitol; Zemplar, Abbott Laboratories, Inc, Chicago, IL) has recently been developed for the treatment of secondary hyperparathyroidism, and, in experimental animals, it was found to be less calcemic and phosphatemic than calcitriol. In double-blind clinical trials, paricalcitol effectively decreased the levels of PTH by 60%, yet the mean serum calcium values remained within the normal range. The few episodes of hypercalcemia that occurred in the paricalcitol-treated patients (8 of 400 determinations > or =11.0 mg/dL in 7 patients) were associated with marked decreases in PTH levels (87% +/- 2% less than baseline) and absolute values of PTH less than 100 pg/mL in four of the seven patients. PTH values less than 100 pg/mL, however, occurred in 15 patients, but were not invariably associated with frank hypercalcemia, although serum calcium levels increased to 10.63 +/- 0.3 mg/dL, slightly greater than the upper limits of normal. Additional studies to evaluate the conversion from calcitriol to paricalcitol therapy showed that a dose ratio of 1:4 (calcitriol:paricalcitol) could maintain control of high levels of PTH without significant alterations in serum calcium and phosphorus levels. These studies indicate that effective control of hyperparathyroidism can be achieved with paricalcitol therapy with minimal perturbation of serum calcium and phosphorus levels, and may have a therapeutic advantage over current treatment strategies.

Down-regulation of laminin-5 in breast carcinoma cells

BACKGROUND

Laminin-5 (ln-5), a large heterotrimeric glycoprotein consisting of an alpha 3, beta 3, and gamma 2 chain, is a component of epithelial cell basement membranes that functions as a ligand of the alpha 3 beta 1 and alpha 6 beta 4 integrins to regulate cell adhesion, migration, and morphogenesis. The ln-5 chains show tissue-specific patterns of regulation in tumors derived from different tissues. For example, ln-5 is often up-regulated in gliomas, gastric carcinomas, and squamous carcinomas and down-regulated in prostate and basal cell carcinomas. Ln-5 expression patterns may represent useful tumor markers and help to elucidate the role of ln-5 in tumor progression in different tissue types.

MATERIALS AND METHODS

We have studied ln-5 expression patterns in the breast. mRNA levels were examined in tumor and normal breast epithelial cell lines, tissue samples, and immunomagnetically sorted primary cultures using differential display, Northern blotting, and hybridization arrays. Protein levels were examined by immunoprecipitation. Gene integrity was assessed by Southern blotting of representative cell types.

RESULTS

Ln-5 alpha 3, beta 3, and gamma 2 mRNA expression was found to be markedly down-regulated in a panel of breast tumor cell lines when compared with normal breast epithelial cells. Ln-5 mRNA was expressed at relatively high levels in MCF-10A immortal normal breast epithelial cells, long-term cultures of normal breast cells, and sorted primary cultures of normal breast luminal epithelial and myoepithelial cells. Reduced, but detectable, levels of ln-5 tended to be expressed in cell lines derived from early-stage breast tumors, whereas expression was generally not detected in cell lines derived from later-stage tumors. In breast tumor tissue specimens, expression of ln alpha 3 and beta 3 mRNAs tended to be reduced relative to levels observed in adjacent nontumor tissue, whereas in gamma 2 levels were elevated in specimens with increased amounts of myoepithelial cells. These ln-5 expression changes could not be attributed to large-scale mutations or gene rearrangements. Ln-5 protein levels were found to reflect mRNA levels in representative cell lines. At senescence, a growth state believed to suppress tumorigenesis, expression of all three ln-5 mRNAs was up-regulated.

CONCLUSION

The down-regulation of ln-5 mRNA expression in breast tumors cells provides a new molecular marker and suggests that ln-5 functions to control tumor progression in the breast.

19-Nor-1-alpha-25-dihydroxyvitamin D2 (Paricalcitol) safely and effectively reduces the levels of intact parathyroid hormone in patients on hemodialysis

Paricalcitol (19-nor-1alpha-25-dihydroxyvitamin D2), a new vitamin D analog developed for the treatment of secondary hyperparathyroidism, was evaluated in three double-blind, placebo-controlled, dose-escalating, randomized multicenter trials. A total of 78 patients (40 Paricalcitol injection, 38 placebo) achieved treatment phase eligibility, which included intact parathyroid hormone (iPTH) > or = 400 pg/ml, normalized serum calcium levels between 8.0 and 10.0 mg/dl, and calcium x phosphorus product values less than 75. Study end points included a decrease in iPTH of at least 30% or a maximum of five dose escalations. After a 4-wk washout, paricalcitol or placebo was administered intravenously three times per week after dialysis for 12 wk. Study drug was started at a dose of 0.04 microg/kg and was increased by 0.04 microg/kg every 2 wk to a maximal allowable dose of 0.24 microg/kg or until at least a 30% decrease in serum iPTH was achieved. The dose of paricalcitol that decreased iPTH by at least 30% became the maintenance dose. Of 40 patients receiving paricalcitol, 27 (68%) had at least a 30% decrease in serum iPTH for 4 consecutive weeks, compared with three of 38 patients (8%) receiving placebo (P < 0.001). For patients who received 12 wk of treatment with paricalcitol, the levels of iPTH decreased significantly from 795+/-86 to 406+/-106 pg/ml (P < 0.001), whereas the values for PTH were 679+/-41 pg/ml before and 592+/-41 pg/ml after 12 wk of therapy in patients receiving placebo (P=NS). Also, there was a significant difference between treatment groups for the change from baseline PTH levels (P < 0.001). Paricalcitol treatment resulted in a significant reduction in serum alkaline phosphatase from 148+/-23 U/L to 101+/-14 U/L (P < 0.001) in patients treated for 12 wk compared with 120+/-9 U/L to 130+/-11 U/L (P=NS) in patients receiving placebo for 12 wk. Importantly, hypercalcemia did not occur before achieving target serum iPTH levels in any of the paricalcitol-treated patients. There was no significant difference for the change from baseline in serum phosphorus within or between treatment groups. There was no significant difference in adverse events between the paricalcitol and placebo-treated groups. These studies demonstrate that paricalcitol safely and effectively suppresses iPTH levels in hemodialysis patients. This second generation vitamin D analog may have a wider therapeutic window than current vitamin D preparations, and thus may allow reduction in PTH with less hypercalcemia.

Identification and verification of differential display cDNAs using gene-specific primers and hybridization arrays

An accurate and streamlined approach to differential display (DD) band identification and verification is described. To minimize false positives, the strategy avoids the use of impure Northern blot probes obtained from PCR-amplified DD bands. To increase throughput, the cloning of DD bands is replaced by a gene-specific primer approach, and hybridization arrays are used in place of Northern blots. In summary, DD bands obtained with long primers were directly sequenced to allow the design and synthesis of gene-specific primers, which were then used to PCR-amplify homogeneous probes for the verification of expression patterns by hybridization array analysis. Differential expression of 60 of the 63 genes tested was confirmed. Thus, false positives are not inherent to DD. The results demonstrate the power of DD used with hybridization arrays to rapidly generate information on expression patterns of differentially expressed genes.

Terminal differentiation of human breast cancer through PPAR gamma

We have previously demonstrated that PPAR gamma stimulates the terminal differentiation of adipocyte precursors when activated by synthetic ligands, such as the antidiabetic thiazolidinedione (TZD) drugs. We show here that PPAR gamma is expressed at significant levels in human primary and metastatic breast adenocarcinomas. Ligand activation of this receptor in cultured breast cancer cells causes extensive lipid accumulation, changes in breast epithelial gene expression associated with a more differentiated, less malignant state, and a reduction in growth rate and clonogenic capacity of the cells. Inhibition of MAP kinase, shown previously to be a powerful negative regulator of PPAR gamma, improves the TZD ligand sensitivity of nonresponsive cells. These data suggest that the PPAR gamma transcriptional pathway can induce terminal differentiation of malignant breast epithelial cells and thus may provide a novel, nontoxic therapy for human breast cancer.

Expression genetics: a different approach to cancer diagnosis and prognosis

Expression genetics is a new approach to the identification of cancer-related genes. Instead of studying gene mutations at the genome level, it focuses on the investigation of heredity at the RNA level. By isolating genes whose expression is up or down regulated in cancers, expression geneticists study their function in the context of gene regulation. A major goal of expression genetics in cancer is to correct gene expression in tumors by the application of potential therapeutic agents.

Complications associated with insertion of jugular venous catheters for hemodialysis: the value of postprocedural radiograph

It is routine in hemodialysis units to require a chest radiograph after the insertion of an internal jugular line for venous access before dialysis is commenced. There are two principal reasons for this: (1) to ensure that no procedural complications have occurred and (2) to verify correct catheter placement. Knowledge of the time delay involved may prompt nephrologists to opt for femoral access (with increased hemodialysis recirculation and need for repeated line placement). The benefit of the postprocedural chest radiograph has never been evaluated in the hemodialysis population. We retrospectively reviewed the data on internal jugular access placement from two large nephrology training centers. Over a 36-month period, 460 internal jugular dialysis catheters were placed in 312 patients. Wherever possible, 15-cm lines were used for the left internal jugular vein and 12-cm lines for the right internal jugular vein. Ultrasound guidance was used in 105 cases (22.8%). There were a total of 90 (19.6%) clinical complications in 62 patients (13.5%). These consisted of carotid artery puncture (n = 35, 7.6%) and hematoma (n = 55, 12%). All of these patients had a normal post-internal jugular chest radiograph. Carotid artery puncture did not occur if ultrasound guidance was used. There was no case of associated pneumothorax. Of the 370 line insertions in 250 patients in whom it was believed clinically that no complication had occurred, the chest radiograph only showed unsuspected line malposition in four cases (1.08%). Routine chest radiographs rarely contribute to the diagnosis of any procedural complications and are of little value after internal jugular access placement, especially if it is believed clinically that no complication occurred.

Coordinate regulation of PTH/PTHrP receptors by PTH and calcitriol in UMR 106-01 osteoblast-like cells

High levels of PTH result in desensitization of target cells to further stimulation with PTH in vivo and in vitro. While studies in vitro demonstrate that the effect of PTH can be direct, it is also possible that studies in vivo may be complicated by the fact that other potential regulators of PTH action, such as increased levels of calcitriol, may play a role. Thus, we examined the actions of calcitriol and PTH on PTH/PTHrP-receptor expression in confluent cultures of UMR 106-01 osteoblast-like cells treated with calcitriol, PTH or both hormones for one to three days. Following these treatments, studies of PTH receptor binding, cAMP generation, and steady-state levels of PTH/PTHrP receptor mRNA were performed. Exposure to PTH resulted in a decrease in PTH stimulated cAMP generation by 88 +/- 2%, and PTH binding by 63 +/- 3%. Levels of PTH/PTHrP-receptor mRNA decreased progressively reaching 20% of control values after three days of PTH (100 nM) treatment. Calcitriol also resulted in a dose and time-dependent decrease in PTH/PTHrP-receptor mRNA, decreasing by 72 +/- 4% after 48 hours. PTH receptor binding and cAMP generation were diminished by 42 +/- 3% and 42 +/- 4%, respectively. Co-incubation of UMR 106-01 cells with submaximal doses of calcitriol and PTH together revealed that the levels of PTH/PTHrP-receptor mRNA were decreased by both hormones together to a greater extent than with either alone. These studies show that both calciotropic hormones, PTH and calcitriol, are potent regulators of PTH/PTHrP-receptor gene expression in UMR 106-01 osteoblast-like cells. Thus, stimulation of calcitriol production by PTH may result in a coordinated down-regulation of PTH receptor expression by these hormones.

Retinoids modulate the effect of PTH and calcitriol on EGF receptor expression in UMR 106-01 cells

Although osteoblast proliferation is a prominent feature of osteitis fibrosa, studies in vitro using osteoblast-like cells have shown that parathyroid hormone (PTH) impairs cell growth. Recent studies in our laboratory have shown that PTH increases epidermal growth factor (EGF) receptor expression in UMR 106-01 osteoblast-like cells, and thus, osteoblast proliferation may occur as a result of an enhanced response of the osteoblast to EGF. In the present studies we investigated the effect of calcitriol and the influence of retinoids on the regulation of EGF receptors. Calcitriol increased 125I-EGF binding 2.5-3-fold after 72 hours of incubation and was maximal at a calcitriol dose of 100 nM. Scatchard analysis showed that this effect was due to increased receptor number. In contrast, all-trans retinoic acid or 9-cis retinoic acid alone, even at 10 microM, caused less than a 50% increase in 125I-EGF binding. However, the effect of calcitriol was totally abolished in the presence of all-trans retinoic acid. 9-cis retinoic acid was equivalent with all-trans retinoic acid in this regard. In the presence of either retinoid, the stimulatory effect of PTH was totally eliminated and EGF binding was actually decreased below control values. Additional studies revealed that retinoic acid decreased PTH-stimulated cAMP generation in a dose-dependent manner. These data are consistent with our previous studies which showed that the effect of PTH on the induction of EGF receptors was mediated by a cAMP-dependent mechanism. The inhibition of the calcitriol effect by retinoids is consistent with the requirement of the retinoid-X-receptor (RXR) for binding of the vitamin D receptor (VDR) to its target sequences in DNA. These data indicate that EGF receptors in UMR 106-01 cells are up-regulated by PTH and calcitriol and that this process can be modulated by retinoids. Retinoids, therefore, may play a major role in the regulation of osteoblast function by PTH and calcitriol.

The synthetic phosphagen cyclocreatine phosphate inhibits the growth of a broad spectrum of solid tumors

BACKGROUND

The brain isoform of creatine kinase (CKBB), an enzyme involved in energy metabolism, has been implicated in cellular transformation process. Cyclocreatine (CCr), a creatine kinase (CK) substrate analogue, was shown to inhibit the growth of a broad spectrum of solid tumors expressing high levels of CK. Cyclocreatine phosphate (CCrP) generated by CK, was proposed to be the active form responsible for growth inhibition.

MATERIALS AND METHODS

We synthesized CCrP and tested its cellular uptake and anti tumor activity in stem cell assays and in athymic mouse models.

RESULTS

CCrP seems to be taken up by cells and inhibits the growth of solid tumors with high levels of CK. CCr and CCrP have similar specificity and potency.

CONCLUSION

The observation that only high-CK cell lines were responsive to CCrP, similar to CCr, indicates that the enzyme requirement was not bypassed. We propose that CK is a target for CCrP, and is involved in mediating its antiproliferative activity.

Oral iron absorption test in patients on CAPD: comparison of ferrous sulfate and a polysaccharide ferric complex

We prospectively compared the absorption of ferrous sulfate to that of a polysaccharide ferric complex (Niferex) in 5 healthy controls and 7 stable patients on continuous ambulatory peritoneal dialysis (CAPD). All study subjects received an equivalent of 150 mg of elemental iron of either preparation, in a random fashion. After a baseline fasting serum iron level was obtained, the serum iron concentration was measured at 2 h in the control group and at 2 and 4 h in the CAPD patients. One to 2 months later, all study subjects received the alternative iron compound and were studied in an identical manner. A significant rise in serum iron was only observed in the healthy subjects after the ingestion of ferrous sulfate and not Niferex (ferrous sulfate 102 +/- (SE) 9 vs. 142 +/- 7 Mg/dl, p = 0.0005; Niferex 96 +/- (SE) 10 vs. 102 +/- 12 mg/dl; baseline vs. 2 h, respectively). The absorption of both compounds was poor in the patients on CAPD, with the 2- and 4-hour serum iron levels not significantly higher than the baseline values (ferrous sulfate 73 +/- 7 vs. 107 +/- 21 vs. 109 +/- 21 mg/dl, p = NS; Niferex 57 +/- 11 vs. 65 +/- 14 vs. 60 +/- 11 mg/dl, p = NS; baseline vs. 2 vs. 4 h, respectively). Our data suggest that the absorption of both ferrous sulfate and ferric polysaccharide complex is poor in patients on CAPD.

Questions from practice: a basis for research

Occupational health nurses in clinical practice are in an excellent position to identify unanswered questions that affect the health and well being of employees. Once these questions have been asked, the occupational health nurses may proceed with structured research to find answers. The research begins with a thorough review of existing literature to learn the background of the issue and clearly define a research question. This question is then framed conceptually to guide the study. The theoretical framework may be supported or refuted by the research project. The study method is dictated by the research question and the theoretical framework. Two basic research methods are intervention and descriptive studies. Intervention studies, with treatment and control groups, attempt to show differences between groups when one receives a certain treatment and the other group does not. Descriptive studies generally survey attitudes or activities, then test for associations. Data analysis is determined by the type of study and type of data collected. Descriptive statistics generate frequencies and correlations; inferential statistics yield stronger information about associations of the variables. Interpretation of research findings must include consideration of threats to validity. Internal validity allows the investigator to state with confidence that the intervention was responsible for the difference between the groups. External validity allows for generalizability of the findings to other populations. The purpose of nursing research is to advance the discipline of nursing. Research refines nursing theories and guides practice. It is through research that occupational health nurses gain confidence to alter procedures and provide interventions that have been shown to be effective.

Antiproliferative effects of cyclocreatine on human prostatic carcinoma cells

Creatine kinase (CK; EC 2.7.3.2) isoenzymes and their substrates have an important function in cellular energy generation and utilization. The brain isoform (CK-BB) has been implicated in cellular transformation processes involving the oncogenic products of the Ela virus and the p53 tumor suppressor gene. Cyclocreatine, an analogue of creatine, has been previously shown to inhibit the growth of a broad spectrum of cancer cells derived from solid tumors. Results reported herein indicate an increased level of creatine kinase activity in human prostate carcinoma cell lines and inhibitory effects of cyclocreatine alone and in combination with adriamycin on the growth of these cells in vitro and in vivo, in immune-deprived mice. Our results suggest the possible use of cyclocreatine in the treatment of prostatic carcinoma.

Microtubule stabilization and potentiation of taxol activity by the creatine analog cyclocreatine

Creatine kinase (CK), a key enzyme of cellular energetics, has been implicated in tumorigenesis. Cyclocreatine (CCr), which forms a stable phosphagen with a reduced rate of ATP regeneration through CK, inhibits the growth of many solid tumors. We report that CCr induces the formation of unusually stable microtubules that resist depolymerization by nocodazole. By reducing ATP availability, CCr may modulate the activity of kinases that regulate microtubule dynamics. Further, combinations of CCr and taxol resulted in the synergistic killing of breast tumor cells indicating that CCr may be a useful addition to chemotherapy's that include taxanes.

Workers' compensation: case management strategies

1. Comprehensive workers' compensation case management involves goals at all levels of prevention. The goal for primary prevention is decreasing the risk of job injury; for secondary prevention, preparing for early intervention in injury events; and for tertiary prevention, assisting injured employees to regain maximum health. 2. The major roles of the occupational health nurse in implementing a case management program are: assessing workplace safety and health, establishing treatment networks, assisting employees with choices from among treatment options, and creating a continuous communication feedback loop among all parties involved. 3. Case management systems may be evaluated from four perspectives: consumer satisfaction, process, outcome, and cost effectiveness. A combination of the four methods will yield a strong indication of program value and highlight areas in need of improvement.