Algal extracellular organic matter pre-treatment enhances microalgal biofilm adhesion onto microporous substrate.

Adhesive biocoating has microstructure composed of biomolecules to entrap viable cells in a stabilized matrix over exposed surfaces. Although marine benthic diatoms are a common group of algae excreting substantial amount of extracellular polymeric substances (EPS), studies regarding the utilization of these EPS are scarce. Using the soluble EPS derived from Navicula incerta and pre-deposition of it as a thin conditioning layer on microporous polyvinylidene fluoride (PVDF) membranes, the pre-coated surface was used to investigate the cell binding affinity of three marine microalgae, namely Amphora coffeaeformis, Cylindrotheca fusiformis and Navicula incerta. Microalgae actively engaged themselves on the pre-coated membranes which was 10 times greater than the initial cell adhesion degree. Soluble EPS is mainly comprised of polysaccharide while bounded EPS is mainly comprised of protein. On EPS pre-coated membranes, N. incerta released the least amount of bounded polysaccharides (<100 mg m-2) and vice versa for the other two because EPS production is usually maximized to assist cell adhesion onto unfavorable substrates. In stark contrast, when the adaptation period (first 6 h) ended, cells began to secrete more bounded protein for cell growth, and an increasing trend of protein content found in N. incerta has verified its optimal adaptation onto the biocoating itself. On pristine PVDF membranes, the adhesion degree was ranked in ascending order: C. fusiformis, N. incerta and A. coffeaeformis. Interestingly, after the pre-coating process, the order was reported as: A. coffeaeformis, N. incerta and C. fusiformis, but it should be noted that C. fusiformis demonstrated fluctuating cell colonization degree and bounded EPS production over time. In other words, the biofilm's susceptibility was confirmed since the cells latched loosely on the membranes rather than in a biofilm matrix. Biocoating enables uniform cell distribution and firmer biofilm growth, opening the door to vast future applications in environmental bioremediation and sensing.

Evaluating health benefits and cost-effectiveness of a mass-media campaign for improving participation in the National Bowel Cancer Screening Program in Australia.

OBJECTIVES: The Australian National Bowel Cancer Screening Program (NBCSP) offers free 2-yearly immunochemical faecal occult blood testing to individuals aged 50-74 years; national participation in 2015-2016 was 41%. In 2017, a 7-week television-led mass-media campaign to increase participation in the Australian state of Victoria was associated with a 1.31-fold increase in participation for 11 weeks. We aimed to evaluate the cost-effectiveness and health benefits of the 2017 campaign and scaled-up equivalent campaigns run over 4 years in Victoria and nationally. STUDY DESIGN: This study used microsimulation modelling. METHODS: A comprehensive microsimulation model of colorectal cancer (CRC), Policy1-Bowel, was used to simulate three scenarios. Scenario 1 simulated the 2017 campaign in Victoria; Scenarios 2 and 3 assumed that campaigns were run three times annually from 2019 to 2022 in Victoria and Australia-wide, respectively. Total campaign costs of AUD$1million, AUD$10million, and AUD$40million were assumed for Scenarios 1, 2, and 3, respectively. The incremental effects and costs of the campaign on the NBCSP were assessed. A governmental perspective was used. RESULTS: All campaign scenarios were predicted to be highly cost-effective, with cost-effectiveness ratios under AUD$4,800/life-year saved. The actual 2017 campaign in Victoria is estimated to prevent 319 CRC cases and 183 deaths over the following 40 years. A 4-year campaign would prevent 1,750 CRC cases and 987 deaths if conducted in Victoria, and 8,100 cases and 4,330 deaths if conducted Australia-wide. CONCLUSION: Mass-media participation campaigns could be highly cost-effective and maximise the potential life-saving impact of bowel screening. These results support ongoing investment in major bowel screening campaigns.

Routine use of HbA1c amongst inpatients hospitalised with decompensated heart failure and the association of dysglycaemia with outcomes.

Diabetes is an independent risk factor for development of heart failure and has been associated with poor outcomes in these patients. The prevalence of diabetes continues to rise. Using routine HbA1c measurements on inpatients at a tertiary hospital, we aimed to investigate the prevalence of diabetes amongst patients hospitalised with decompensated heart failure and the association of dysglycaemia with hospital outcomes and mortality. 1191 heart failure admissions were identified and of these, 49% had diabetes (HbA1c ≥ 6.5%) and 34% had pre-diabetes (HbA1c 5.7-6.4%). Using a multivariable analysis adjusting for age, Charlson comorbidity score (excluding diabetes and age) and estimated glomerular filtration rate, diabetes was not associated with length of stay (LOS), Intensive Care Unit (ICU) admission or 28-day readmission. However, diabetes was associated with a lower risk of 6-month mortality. This finding was also supported using HbA1c as a continuous variable. The diabetes group were more likely to have diastolic dysfunction and to be on evidence-based cardiac medications. These observational data are hypothesis generating and possible explanations include that more diabetic patients were on medications that have proven mortality benefit or prevent cardiac remodelling, such as renin-angiotensin system antagonists, which may modulate the severity of heart failure and its consequences.

Advanced glycation end-products increase IL-6 and ICAM-1 expression via RAGE, MAPK and NF-κB pathways in human gingival fibroblasts.

BACKGROUND AND OBJECTIVES: Diabetes mellitus (DM) is a risk factor for periodontal diseases and may exacerbate the progression of the pathogenesis of periodontitis. Advanced glycation end-products (AGEs) cause DM complications relative to levels of glycemic control and larger amounts accumulate in the periodontal tissues of patients with periodontitis and DM. In the present study, we investigated the effects of AGEs on the expression of inflammation-related factors in human gingival fibroblasts (HGFs) to elucidate the impact of AGEs on DM-associated periodontitis. MATERIAL AND METHODS: HGFs were cultured with or without AGEs. Cell viability was examined, and RNA and protein fractions were isolated from AGE-treated cells. The expression of interleukin (IL)-6, intercellular adhesion molecule-1 (ICAM-1), and the receptor for AGE (RAGE) was investigated using reverse transcription-polymerase chain reaction, quantitative real-time polymerase chain reaction and enzyme-linked immunosorbent assay, and reactive oxygen species activity was measured using a kit with 2',7'-dichlorofluorescin diacetate. Human monocytic cells (THP-1) labeled with a fluorescent reagent were co-cultured with HGFs treated with AGEs and IL-6 siRNA, and the adhesive activity of THP-1 cells to HGFs was assessed. The expression of IL-6 and ICAM-1 was examined when HGFs were pretreated with recombinant human IL-6, the siRNAs of RAGE and IL-6, and inhibitors of MAPK and NF-κB, and then cultured with and without AGEs. The phosphorylation of MAPK and NF-κB was assessed using western blotting. RESULTS: AGEs increased the mRNA and protein expressions of RAGE, IL-6, ICAM-1 and reactive oxygen species activity in HGFs, and promoted the adhesion of THP-1 cells to HGFs, but had no effect on cell viability until 72 hours. Recombinant human IL-6 increased ICAM-1 expression in HGFs, while the siRNAs of RAGE and IL-6 inhibited AGE-induced IL6 and ICAM1 mRNA expression, and IL-6 siRNA depressed AGE-induced THP-1 cell adhesion. AGEs increased the phosphorylation of p38 and ERK MAPKs, p65 NF-κB and IκBα, while inhibitors of p38, ERK MAPKs and NF-κB significantly decreased AGE-induced IL-6 and ICAM-1 expression. CONCLUSION: AGEs increase IL-6 and ICAM-1 expression via the RAGE, MAPK and NF-κB pathways in HGFs and may exacerbate the progression of the pathogenesis of periodontal diseases.

The 2S albumin allergens of Arachis hypogaea, Ara h 2 and Ara h 6, are the major elicitors of anaphylaxis and can effectively desensitize peanut-allergic mice.

BACKGROUND: Ara h 2 and Ara h 6, co-purified together in a 13-25 kD fraction (Ara h 2/6; 20 kD fraction) on gel filtration chromatography, account for the majority of effector activity in a crude peanut extract (CPE) when assayed with RBL SX-38 cells sensitized with IgE from human peanut allergic sera. OBJECTIVES: To determine if Ara h 2/6 are the primary peanut allergens responsible for allergic reactions in vivo and to determine if Ara h 2/6 would be sufficient to prevent allergic reactions to a complete CPE. METHODS: An oral sensitization mouse model of peanut allergy was used to assess the activity of Ara h 2/6 (20 kD) and CPE without the 20 kD fraction (CPE w/o 20 kD) for allergic provocation challenge and immunotherapy. The activity of these preparations was also tested in an assay of histamine release from human basophils in whole blood. RESULTS: Compared with mice challenged with control CPE, mice challenged with CPE w/o 20 kD experienced reduced symptoms (P < 0.05) and a smaller decrease in body temperature (P < 0.01). Results with the basophil histamine release assay corroborated these findings (P < 0.01). The mouse model was also used to administer Ara h 2/6 (20 kD) in an immunotherapy protocol, in which peanut-allergic mice treated with the 20 kD fraction experienced significantly reduced symptoms, changes in body temperature, and mast cell protease (MMCP-1) release compared with placebo (P < 0.01 for all parameters). Importantly, immunotherapy with the 20 kD fraction was just as effective as treatment with CPE, whereas CPE w/o 20 kD was significantly less effective for higher dose peanut challenges. CONCLUSIONS AND CLINICAL RELEVANCE: Ara h 2/6 are the most potent peanut allergens in vivo and can be used to desensitize peanut-allergic mice. These results have potential implications for clinical research in the areas of diagnosis and immunotherapy for peanut allergy.

Alcohol consumption and risk of renal cell cancer: the NIH-AARP diet and health study.

BACKGROUND: The effect of moderate to heavy drinking (>15 g per day) on renal cell cancer (RCC) risk is unclear. METHOD: The relationship between alcohol consumption and RCC was examined in the NIH-AARP Diet and Health Study (n=49 2187, 1814 cases). RESULTS: Compared with >0 to <5 g per day of alcohol consumption, the multivariate relative risk (95% confidence intervals) for 15 to <30 and 30 g per day was, 0.75 (0.63-0.90) and 0.71 (0.59-0.85), respectively, in men and 0.67 (0.42-1.07) and 0.43 (0.22-0.84), respectively, in women. CONCLUSION: Alcohol consumption was inversely associated with RCC in a dose-response manner. The inverse association may be extended to 30 g per day of alcohol intake.

Mucosal graft-vs-host disease.

Graft-vs-host disease (GVHD) is a serious complication of hematopoietic stem cell transplantation (HSCT). Indications for HSCT have greatly expanded, and more patients are undergoing HSCT today than ever before. In addition, the options for immunosuppressive therapy for both prevention and treatment of GVHD have also expanded. These changes have in turn altered the landscape of this disease. We have reviewed the current literature on this subject and presented an update on this disease with a particular emphasis on mucosal manifestations.

Intra-operative parathyroid hormone monitoring in patients with parathyroid cancer.

BACKGROUND: Intra-operative parathyroid hormone (PTH) monitoring (IPM) is 97% accurate in predicting postoperative eucalcemia in sporadic primary hyperparathyroidism (SPHPT). However, its usefulness in parathyroid cancer has not been demonstrated. This study reports IPM accuracy during surgical resections for parathyroid cancer. METHODS: Eight of 556 consecutive patients with SPHPT underwent parathyroidectomy using IPM and had parathyroid cancer. Operative success was defined as eucalcemia > six months and operative failure/persistent cancer as hypercalcemia within six months of parathyroidectomy. The IPM criterion for operative success was defined as a >50% decrease of peripheral PTH levels from the highest either pre-incision or pre-excision values, 10 minutes after resection. RESULTS: In eight patients, 11 operations were performed. Ten operations (91%) resulted in >50% intra-operative PTH decrease. However, in only seven (70%) of these resections, eucalcemia was achieved for >6 months with five of these seven (71%) procedures being initial en bloc resections. The remaining 3/10 (30%) operations with >50% intra-operative PTH decrease resulted in operative failures. In the last operation, intraoperative parathormone monitoring (IPM) correctly predicted operative failure. IPM sensitivity, specificity, positive predictive value, negative predictive value, and overall accuracy in predicting outcome were 100, 40, 70, 100, and 75%, respectively. CONCLUSIONS: IPM with the criterion of >50% PTH drop from the highest level is less accurate in predicting operative success in parathyroid cancer when compared to SPHPT. A >50% intra-operative PTH level decrease in patients with parathyroid cancer, particularly in reoperative cases, is less predictive of complete resection. The initial recognition of this disease followed by proper resection remains essential in the treatment of parathyroid cancer.

The hunt for an elusive source of pyrexia in a foreign worker.

We report a 23-year-old Bangladeshi man who presented with fever and hepatosplenomegaly. The initial laboratory findings were bicytopenia with elevated serum globulins. The diagnosis of visceral leishmaniasis (Kala Azar) was suspected. The parasite Leishmania donovani was found on bone marrow aspiration. He was treated with liposomal amphotericin B and had a good response to treatment. The case highlights the need to be aware of this disease occurring in a foreign national from an endemic region when he presents with fever and hepatosplenomegaly.

Preoperative esophageal manometry and outcome of laparoscopic adjustable silicone gastric banding.

BACKGROUND: Laparoscopic adjustable silicone gastric banding (LASGB) for morbid obesity has been reported to provide long-term weight loss with a low risk of operative complications. Nevertheless, esophageal dilation leading to achalasia-like and reflux symptoms is a feared complication of LASGB. This study evaluates the clinical benefit of routine preoperative esophageal manometry in predicting outcome after LASGB in morbidly obese patients. METHOD: A review of prospectively collected data on 77 patients who underwent routine esophageal manometry prior to LASGB for morbid obesity from February 2001 to September 2003 was performed. Aberrant motility, abnormal lower esophageal sphincter (LES) pressures, and other nonspecific esophageal motility disorders noted on preoperative esophageal manometry defined patients of the abnormal manometry group. Outcome differences in weight loss, emesis, band complications, and gastroesophageal reflux disease (GERD) resolution or improvement were compared between patients of the abnormal and normal manometry groups after LASGB. Analysis of variance (ANOVA) and chi-square tests were performed to determine the significance of these outcomes. RESULTS: Of the patients tested, 14 had abnormal esophageal manometry results, whereas 63 had normal manometry results before LASGB. There was no significant difference in percent excess weight loss (%EWL) at 6 and 12 months between the groups after gastric banding. Severe postoperative emesis occurred more frequently in patients with abnormal manometry results than in those with normal manometry results. There were two band-related complications, both of which occurred in patients of the normal manometry group. CONCLUSIONS: Preoperative esophageal manometry does not predict weight loss or GERD outcomes after LASGB in morbidly obese patients. Postoperative emesis was more common in patients with abnormal manometry findings, but such symptoms were manageable and did not lead to poor weight loss or to band removal or increased band-related complications.

Effects of rice bran oil on plasma lipid concentrations, lipoprotein composition, and glucose dynamics in mares.

Plasma lipid concentrations, lipoprotein composition, and glucose dynamics were measured and compared between mares fed diets containing added water, corn oil (CO), refined rice bran oil (RR), or crude rice bran oil (CR) to test the hypothesis that rice bran oil lowers plasma lipid concentrations, alters lipoprotein composition, and improves insulin sensitivity in mares. Eight healthy adult mares received a basal diet fed at 1.5 times the DE requirement for maintenance and each of the four treatments according to a repeated 4 x 4 Latin square design consisting of four 5-wk feeding periods. Blood samples were collected for lipid analysis after mares were deprived of feed overnight at 0 and 5 wk. Glucose dynamics were assessed at 0 and 4 wk in fed mares by combined intravenous glucose-insulin tolerance tests. Plasma glucose and insulin concentrations were measured, and estimated values of insulin sensitivity (SI), glucose effectiveness, and net insulin response were obtained using the minimal model. Mean BW increased (P = 0.014) by 29 kg (range = 10 to 50 kg) over 5 wk. Mean plasma concentrations of NEFA, triglyceride (TG), and very low-density lipoprotein (VLDL) decreased (P < 0.001) by 55, 30, and 39%, respectively, and plasma high-density lipoprotein and total cholesterol (TC) concentrations increased (P < 0.001) by 15 and 12%, respectively, over 5 wk. Changes in plasma NEFA (r = 0.58; P < 0.001) and TC (r = 0.44; P = 0.013) concentrations were positively correlated with weight gain over 5 wk. Lipid components of VLDL decreased (P < 0.001) in abundance over 5 wk, whereas the relative protein content of VLDL increased by 39% (P < 0.001). Addition of oil to the basal diet instead of water lowered plasma NEFA and TG concentrations further (P = 0.002 and 0.020, respectively) and increased plasma TC concentrations by a greater magnitude (P = 0.072). However, only plasma TG concentrations and VLDL free cholesterol content were affected (P = 0.024 and 0.009, respectively) by the type of oil added to the diet. Mean plasma TG concentration decreased by 14.2 mg/dL over 5 wk in the CR group, which was a larger (P < 0.05) decrease than the one (-5.3 mg/dL) detected in mares that received water. Consumption of experimental diets lowered S(I), but glucose dynamics were not affected by oil supplementation. Addition of oil to the diet altered blood lipid concentrations, and supplementation with CR instead of water specifically affected plasma TG concentrations and VLDL free cholesterol content.

Construct validity for the LAPSIM laparoscopic surgical simulator.

BACKGROUND: The skills required for laparoscopic surgery are amenable to simulator-based training. Several computerized devices are now available. We hypothesized that the LAPSIM simulator can be shown to distinguish novice from experienced laparoscopic surgeons, thus establishing construct validity. METHODS: We tested residents of all levels and attending laparoscopic surgeons. The subjects were tested on eight software modules. Pass/fail (P/F), time (T), maximum level achieved (MLA), tissue damage (TD), motion, and error scores were compared using the t-test and analysis of variance. RESULTS: A total of 54 subjects were tested. The most significant difference was found when we compared the most (seven attending surgeons) and least experienced (10 interns) subjects. Grasping showed significance at P/F and MLA (p < 0.03). Clip applying was significant for P/F, MLA, motion, and errors (p < 0.02). Laparoscopic suturing was significant for P/F, MLA, T, TD, as was knot error (p < 0.05). This finding held for novice, intermediate, and expert subjects (p < 0.05) and for suturing time between attending surgeons and residents (postgraduate year [PGY] 1-4) (p < 0.05). CONCLUSIONS: LAPSIM has construct validity to distinguish between expert and novice laparoscopists. Suture simulation can be used to discriminate between individuals at different levels of residency and expert surgeons.

Suspected case of venous air embolism in an infant undergoing hip arthrogram.

An otherwise well ten-week-old girl underwent an air contrast hip arthrogram and application of a hip spica for a developmentally dislocated hip. The child displayed signs consistent with venous air embolism after injection of 5 ml of air into the hip joint. These signs included a decrease in arterial haemoglobin oxygen saturation as measured by pulse oximetry, decreased end-tidal carbon dioxide level and tachycardia. The signs initially resolved, but the patient deteriorated with injection of a further 5 ml of air. The patient responded to cessation of injection and resuscitative measures. The infant remained well postoperatively. The need for the use of air to confirm intra-articular placement of the needle prior to injection of contrast during a hip arthrogram is questioned.

Complete 5-year follow-up of a prospective phase II trial of preoperative chemoradiotherapy for esophageal cancer.

BACKGROUND: Conclusive evidence supporting the routine use of multimodality therapy in esophageal cancer is lacking. However, since long-term survival after esophagectomy alone is unusual, clinical trials designed to identify effective therapeutic regimens are essential. We report here the 5-year results of a phase II induction chemoradiotherapy trial. METHODS: From August 1991 to January 1995, 44 patients with esophageal or gastroesophageal junction carcinoma were treated with a combination of 5-fluorouracil, cisplatin, and interferon-alpha with concurrent external beam radiotherapy. RESULTS: Forty-one (93%) patients completed chemoradiotherapy, with most toxic events recorded as grade I or II. Curative resection (all gross tumor removed) was achieved in 36 of 37 surgical explorations, with 10 tumors demonstrating complete pathologic response and 23 showing partial pathologic response. Median follow-up for survivors was 75 months (range, 60-100 months). Five-year survival for all patients was 32%, with a median survival of 28 months. Five-year disease-free survival in patients with curative resection was 36% (median, 26 months) and overall survival was 39% (median, 34 months). Five-year survival for patients with curative resection whose disease responded to chemoradiotherapy was 42% (median overall survival, 36 months). Local-regional recurrence alone occurred in 3 patients, distant failure alone in 12 patients, and combined local-regional and distant failure in 2 patients. A Cox proportional hazards model identified both pathologic tumor and nodal stage as independent predictors of disease-free survival. Fourteen patients (32%) were 5-year survivors; 1 of these patients later experienced disease recurrence and died. CONCLUSIONS: Preoperative chemoradiotherapy can result in a long-term and durable disease-free state. Only large, multi-institutional phase III trials can determine whether combined modality therapy is superior to resection alone.

Long-term survival following induction chemoradiotherapy and esophagectomy for esophageal carcinoma.

HYPOTHESIS: Long-term survival is rare in patients treated for esophageal carcinoma. Several clinical trials suggest the possibility of prolonged survival in patients who undergo induction chemoradiotherapy plus esophagectomy. DESIGN: Prospective uncontrolled study. SETTING: University hospital. PATIENTS AND METHODS: Forty-four patients with carcinoma of the esophagus or gastroesophageal junction were prospectively entered into a phase II trial of preoperative 5-fluorouracil, cisplatin, and interferon alfa with concurrent external beam radiotherapy before esophagectomy. Curative resection was performed on 36 of 41 patients who completed the induction chemoradiotherapy. RESULTS: Of the 44 patients, 17 are alive at a median follow-up of 50 months. Of these 17 patients, 15 show no evidence of recurrent disease. Of the 14 patients with long-term survival (> or =3 years), 1 patient died of disease, and another patient is alive with disease. The remaining 12 patients are alive and disease-free (median follow-up, 54 months). Six patients have survived longer than 4 years and 3 patients longer than 5 years. Subsequent primary tumors have developed in 2 patients. One patient had a recurrence at 11 months following initiation of treatment and remains disease-free 43 months postresection of a single brain metastasis. Standard clinicopathologic parameters (age, sex, histologic findings, chemoradiotherapy regimen, and clinical and pathologic stages) were not significantly associated with a survival time of 3 years or longer (Fisher exact test, 2-tailed). Although not significant, p 53 mutational status suggested long-term survival. In 11 of 14 patients who are alive with no history of recurrence, p53 genotyping demonstrated no point mutations in 10 patients. Median survival time for the long-term survivors has not been reached. CONCLUSIONS: Long-term survival can be achieved in patients with esophageal carcinoma who undergo induction chemoradiotherapy and esophagectomy. Recurrence is unlikely in patients who survive for 3 years or longer after undergoing this multimodality treatment.

The complete pathway for catalytic activation of the mitogen-activated protein kinase, ERK2.

The mitogen-activated protein (MAP) kinase ERK2 is an essential signal transduction molecule that mediates extracellular signaling by all polypeptide growth factors. Full activation of ERK2 requires phosphorylation at both a threonine residue (Thr(183)) conserved in most protein kinases as well as a tyrosine residue (Tyr(185)) unique to members of the mitogen-activated protein kinase family. We have characterized the kinetic role of phosphorylation at each site with respect to the overall activation mechanism, providing a complete picture of the reaction steps involved. Phosphorylation at Tyr(185) serves to configure the ATP binding site, while phosphorylation at both residues is required to stabilize binding of the protein substrate, myelin basic protein. Similar control mechanisms are employed to stabilize ATP and myelin basic protein in the phosphoryl group transfer reaction, accounting for the enormous increase in turnover rate. The mechanism of ERK2 activation is kinetically similar to that of the cell cycle control protein, cdk2/cyclinA. Phosphorylation of Tyr(185) in ERK2 and association of cyclinA with cdk2 both serve to stabilize ATP binding. Subsequent phosphorylation of both enzymes on threonine serves to stabilize binding of the phosphoacceptor substrate.

Induction of 7-ethoxyresorufin-O-deethylase activity by planar chlorinated hydrocarbons and polycyclic aromatic hydrocarbons in cell lines from the rainbow trout pituitary.

The induction of 7-ethoxyresorufin-o-deethylase (EROD) activity was examined in three rainbow trout pituitary cell lines: RTP-91E, RTP-91F and RTP-2. RTP-91E and RTP-91F were developed from the pituitary of a male and have epithelial-like and fibroblast-like morphologies, respectively. RTP-2, which was described previously, was developed from the pituitary of a female and has an epithelial-like shape. In all cell lines EROD activity was induced by 2,3,7,8- tetrachlorodibenzo-p-dioxin (TCDD). Immunoblotting with the polyclonal antibody, anti-trout CYP1A1(277-294)/KLH, confirmed induction of a 58-kDa polypeptide. Potential inhibitors of the aryl hydrocarbon receptor, geldanamycin and alpha-naphthoflavone, inhibited EROD induction by TCDD. Other compounds inducing EROD activity were 1,2,3,7,8-pentachlorodibenzo-p-dioxin (PCDD), 2,3,7,8-tetrachlorodibenzofuran (TCDF), 3,3',4,4',5-pentachlorobiphenyl (PCB 126), and 3-methylcholanthrene (3MC). When judged by the concentration eliciting 50% of the maximal response (EC50), induction was similar in RTP-2 and RTP-91E, and less effective in RTP-91F. Regardless of the cell line, the rank order from most to least potent inducer on the basis of EC50 value was TCDD> or =PCDD>TCDF>PCB 126>>3MC. When induction potencies were expressed relative to TCDD, the values obtained with the pituitary cell lines were similar to previously published values derived with a rainbow trout liver cell line.

Mechanism of activation of ERK2 by dual phosphorylation.

The mitogen-activated protein (MAP) kinases are characterized by their requirement for dual phosphorylation at a conserved threonine and tyrosine residue for catalytic activation. The structural consequences of dual-phosphorylation in the MAP kinase ERK2 (extracellular signal-regulated kinase 2) include active site closure, alignment of key catalytic residues that interact with ATP, and remodeling of the activation loop. In this study, we report the specific effects of dual phosphorylation on the individual catalytic reaction steps in ERK2. Dual phosphorylation leads to an increase in overall catalytic efficiency and turnover rate of approximately 600,000- and 50,000-fold, respectively. Solvent viscosometric studies reveal moderate decreases in the equilibrium dissociation constants (K(d)) for both ATP and myelin basic protein. However, the majority of the overall rate enhancement is due to an increase in the rate of the phosphoryl group transfer step by approximately 60,000-fold. By comparison, the rate of the same step in the ATPase reaction is enhanced only 2000-fold. This suggests that optimizing the position of the invariant residues Lys(52) and Glu(69), which stabilize the phosphates of ATP, accounts for only part of the enhanced rate of phosphoryl group transfer in the kinase reaction. Thus, significant stabilization of the protein phosphoacceptor group must also occur. Our results demonstrate similarities between the activation mechanisms of ERK2 and the cell cycle control enzyme, Cdk2 (cyclin-dependent kinase 2). Rather than dual phosphorylation, however, activation of the latter is controlled by cyclin binding followed by phosphorylation at Thr(160).

Kinetic basis for activation of CDK2/cyclin A by phosphorylation.

The activation of most protein kinases requires phosphorylation at a conserved site within a structurally defined segment termed the activation loop. A classic example is the regulation of the cell cycle control enzyme, CDK2/cyclin A, in which catalytic activation depends on phosphorylation at Thr(160) in CDK2. The structural consequences of phosphorylation have been revealed by x-ray crystallographic studies on CDK2/cyclin A and include changes in conformation, mainly of the activation loop. Here, we describe the kinetic basis for activation by phosphorylation in CDK2/cyclin A. Phosphorylation results in a 100,000-fold increase in catalytic efficiency and an approximate 1,000-fold increase in the overall turnover rate. The effects of phosphorylation on the individual steps in the catalytic reaction pathway were determined using solvent viscosometric techniques. It was found that the increase in catalytic power arises mainly from a 3,000-fold increase in the rate of the phosphoryl group transfer step with a more moderate increase in substrate binding affinity. In contrast, the rate of phosphoryl group transfer in the ATPase pathway was unaffected by phosphorylation, demonstrating that phosphorylation at Thr(160) does not serve to stabilize ATP in the ATPase reaction. Thus, we hypothesize that the role of phosphorylation in the kinase reaction may be to specifically stabilize the peptide phosphoacceptor group.