IGF2BP2 promotes colorectal cancer progression by upregulating the expression of TFRC and enhancing iron metabolism

BACKGROUND

Colorectal cancer (CRC) is one of the most common malignant tumors of the digestive system, ranking third for morbidity and mortality worldwide. At present, no effective control method is available for this cancer type. In tumor cells, especially iron metabolization, is necessary for its growth and proliferation. High levels of iron are an important feature to maintain tumor growth; however, the overall mechanism remains unclear.

METHODS

We used western blotting, immunohistochemistry (IHC) and real-time quantitative PCR to analyze the expression of IGF2BP2 in cell lines and tissues. Further, RNA-sequencing, RNA immunoprecipitation and methylated RNA immunoprecipitation experiments explored the specific binding of target genes. Moreover, the RNA stability assay was performed to determine the half-life of genes downstream of IGF2BP2. In addition, the Cell Counting Kit-8, colony formation assay, 5-ethynyl-2'-deoxyuridine assay and flow cytometry were used to evaluate the effects of IGF2BP2 on proliferation and iron metabolism. Lastly, the role of IGF2BP2 in promoting CRC growth was demonstrated in animal models.

RESULTS

We observed that IGF2BP2 is associated with iron homeostasis and that TFRC is a downstream target of IGF2BP2. Further, overexpression of TFRC can rescue the growth of IGF2BP2-knockdown CRC cells. Mechanistically, we determined that IGF2BP2 regulates TFRC methylation via METTL4, thereby regulating iron metabolism and promoting CRC growth. Furthermore, using animal models, we observed that IGF2BP2 promotes CRC growth.

CONCLUSION

IGF2BP2 regulates TFRC mRNA methylation via METTL4, thereby regulating iron metabolism and promoting CRC growth. Our study highlights the key roles of IGF2BP2 in CRC carcinogenesis and the iron transport pathways.

[Outcomes at discharge of preterm infants born <34 weeks' gestation]

Objective: To investigate the incidence and trend of short-term outcomes among preterm infants born <34 weeks' gestation. Methods: A secondary analysis of data from the standardized database established by a multicenter cluster-randomized controlled study "reduction of infection in neonatal intensive care units (NICU) using the evidence-based practice for improving quality (REIN-EPIQ) study". This study was conducted in 25 tertiary NICU. A total of 27 192 infants with gestational age <34 weeks at birth and admitted to NICU within the first 7 days of life from May 2015 to April 2018 were enrolled. Infants with severe congenital malformation were excluded. Descriptive analyses were used to describe the mortality and major morbidities of preterm infants by gestational age groups and different admission year groups. Cochran-Armitage test and Jonckheere-Terpstra test were used to analyze the trend of incidences of mortality and morbidities in 3 study-years. Multiple Logistic regression model was constructed to analyze the differences of outcomes in 3 study-years adjusting for confounders. Results: A total of 27 192 preterm infants were enrolled with gestational age of (31.3±2.0) weeks at birth and weight of (1 617±415) g at birth. Overall, 9.5% (2 594/27 192) of infants were discharged against medical advice, and the overall mortality rate was 10.7% (2 907/27 192). Mortality for infants who received complete care was 4.7% (1 147/24 598), and mortality or any major morbidity was 26.2% (6 452/24 598). The incidences of moderate to severe bronchopulmonary dysplasia, sepsis, severe intraventricular hemorrhage or periventricular leukomalacia, proven necrotizing enterocolitis, and severe retinopathy of prematurity were 16.0% (4 342/27 192), 11.9% (3 225/27 192), 6.8% (1 641/24 206), 3.6% (939/25 762) and 1.5% (214/13 868), respectively. There was a decreasing of the overall mortality (P<0.001) during the 3 years. Also, the incidences for sepsis and severe retinopathy of prematurity both decreased (both P<0.001). However, there were no significant differences in the major morbidity in preterm infants who received complete care during the 3-year study period (P=0.230). After adjusting for confounders, infants admitted during the third study year showed significantly lower risk of overall mortality (adjust OR=0.62, 95%CI 0.55-0.69, P<0.001), mortality or major morbidity, moderate to severe bronchopulmonary dysplasia, sepsis and severe retinopathy of prematurity, compared to those admitted in the first study year (all P<0.05). Conclusions: From 2015 to 2018, the mortality and major morbidities among preterm infants in Chinese NICU decreased, but there is still space for further efforts. Further targeted quality improvement is needed to improve the overall outcome of preterm infants.

[Analysis of clinical phenotype and genotype of Chinese children with disorders of sex development]

Objective: To explore the heterogeneity and correlation of clinical phenotypes and genotypes in children with disorders of sex development (DSD). Methods: A retrospective study of 1 235 patients with clinically proposed DSD in 36 pediatric medical institutions across the country from January 2017 to May 2021. After capturing 277 DSD-related candidate genes, second-generation sequencing was performed to analyzed the heterogeneity and correlation combined with clinical phenotypes. Results: Among 1 235 children with clinically proposed DSD, 980 were males and 255 were females of social gender at the time of initial diagnosis with the age ranged from 1 day of age to 17.92 years. A total of 443 children with pathogenic variants were detected through molecular genetic studies, with a positive detection rate of 35.9%. The most common clinical phenotypes were micropenis (455 cases), hypospadias (321 cases), and cryptorchidism (172 cases) and common mutations detected were in SRD5A2 gene (80 cases), AR gene (53 cases) and CYP21A2 gene (44 cases). Among them, the SRD5A2 mutation is the most common in children with simple micropenis and simple hypospadias, while the AMH mutation is the most common in children with simple cryptorchidism. Conclusions: The SRD5A2 mutation is the most common genetic variant in Chinese children with DSD, and micropenis, cryptorchidism, and hypospadias are the most common clinical phenotypes. Molecular diagnosis can provide clues about the biological basis of DSD, and can also guide clinicians to perform specific clinical examinations. Target sequence capture probes and next-generation sequencing technology can provide effective and economical genetic diagnosis for children with DSD.

Money Talks: Pilot Financial Wellness Programs to Promote Positive Financial Planning Behaviors Among Residents

PROBLEM

Graduate medical education programs and national organizations are becoming more involved in promoting trainee financial wellness. Current literature reports residents have poor financial knowledge, high debt levels, low concern about their finances, and deficits in financial preparedness, but there has been little published on best practices for implementing financial wellness programs for residents or measuring meaningful outcomes of such programs.

APPROACH

From June 2017 to 2019, the authors invited 277 internal medicine residents from the Stony Brook University Hospital, Montefiore Medical Center, and Johns Hopkins Bayview Medical Center residency programs to participate in financial wellness programs. Each institution held at least one 90-minute financial planning session; Stony Brook also had biannual financial wellness check-ins. Participants were invited to complete a presession, an immediate postsession, and a year-end survey to assess changes in financial planning behaviors.

OUTCOMES

Survey response rates were 49% (135/277) for the presession survey, 47% (130/277) for the immediate postsession survey, and 22% (61/277) for the year-end survey. Ninety-six percent (125/130) found the sessions helpful and 98% (120/123) recommended continuing the program in the future. At year-end, the most frequent completed financial planning actions prompted by the session included saving emergency funds, creating a monthly budget, consolidating loans via the Public Service Loan Forgiveness program, contributing to retirement savings, and participating in an employer's retirement plan. Residents liked that some sessions were during intern orientation before the selection of retirement plans. Postgraduate year (PGY) 1 residents were more likely to complete positive financial planning actions and to agree or strongly agree that the session prompted them to take financial planning actions than PGY-2 and PGY-3 residents.

NEXT STEPS

While financial wellness programs are well received by internal medicine residents, more robust evidence is needed on curricular delivery methods and program features that promote positive financial planning behaviors.

Biosynthesis of silver nanoparticles with antimicrobial and anticancer properties using two novel yeasts

AgNPs are nanomaterials with many potential biomedical applications. In this study, the two novel yeast strains HX-YS and LPP-12Y capable of producing biological silver nanoparticles were isolated. Sequencing of ribosomal DNA-ITS fragments, as well as partial D1/D2 regions of 26S rDNA indicated that the strains are related to species from the genus Metschnikowia. The BioAgNPs produced by HX-YS and LPP-12Y at pH 5.0-6.0 and 26 °C ranged in size from 50 to 500 nm. The antibacterial activities of yeast BioAgNPs against five pathogenic bacteria were determined. The highest antibacterial effect was observed on P. aeruginosa, with additional obvious effects on E. coli ATCC8099 and S. aureus ATCC10231. Additionally, the BioAgNPs showed antiproliferative effects on lung cancer cell lines H1975 and A579, with low toxicity in Beas 2B normal lung cells. Therefore, the AgNPs biosynthesized by HX-YS and LPP-12Y may have potential applications in the treatment of bacterial infections and cancer.

[A rare anatomical variation of ileocolic veins involving in gastrocolic vein trunk: case report and literature review]

Objective: Due to its various anatomical variations and numerous branches, the gastrocolic vein trunk (Henle trunk) is the most common site to develop bleeding and other complications in laparoscopic right hemicolectomy for colon cancer. This study aims to investigate the role of ileocolic vein (ICV) joining with Henle trunk, a rare anatomical variation. Methods: A rare case whose ICV was newly found to involve in the formation of Henle trunk during laparoscopic resection of right hemicolon cancer was reported as right gastroepiploic vein+ right colic vein+superior right colic vein+ICV. This anatomical variation was confirmed by multi-slice spiral CT coronal two-dimensional reconstruction of right hemicolon angiography. The literatures about ICV participating in formation of Henle trunk were systematically searched from PubMed, The Cochran Library, CNKI net and Wanfang database, and the occurrence probability and composition of its anatomical variation were analyzed. Results: This was a 47-year-old female patient who underwent laparoscopic right hemicolectomy. When the vessels were dissected during operation, it was found that ICV did not accompany the ileocolic artery, but directly flowed into Henle trunk. Two-dimensional reconstructed CT images of right hemicolon vessels showed that the composition of Henle trunk was rarely varied, which was composed of right gastroepiploic vein, right colonic vein, superior right colonic vein and ICV. Five literatures were enrolled from literature retrieval. A total of 12 cases with ICV participating in the construction of Henle trunk were reported, with a probability of 0.27%-6.31% and 6 forms of the formation of Henle trunk. In this case, Henle trunk was made up of right gastroepiploic vein, right colonic vein, upper right colonic vein and ICV, which was reported for the first time. Conclusions: ICV involving in Henle trunk is a rare vascular variation, and this type of variation should be fully recognized. Careful dissection during operation is necessary to prevent intraoperative bleeding caused by improper operation.

[Comparative analysis of serum glutamate and gamma-aminobutyric acid levels in patients with bipolar depressive disorder and major depression disorder]

Objective: To investigate the difference of serum glutamate (Glu) and gamma- aminobutyric acid (GABA) levels between depressive patients and bipolar disorder patients with depressive episodes. Methods: From May 2018 to March 2019, forty-seven patients with depression (depression group) and 45 patients with bipolar depressive episode (bipolar depression group) were selected from the department of psychiatry, the First Affiliated Hospital of Jinan University, and 41 healthy controls (healthy control group) were simultaneously recruited from the community. The subjects' depression and anxiety were assessed by 17 items of Hamilton depression scale (HAMD-17) and Hamilton Anxiety Scale (HAMA). The serum levels of Glu, GABA and Glu decarboxylase (GAD) were detected by enzyme-linked immunosorbent assay (ELISA) . Results: The serum Glu level ( (36±7) mg/L, (37±7) mg/L vs (28±4) mg/L, F=10.97, P<0.01) and Glu/GABA ratio (5.77±0.35, 8.18±0.24 vs 3.35±0.33, F=37.68, P<0.01) in depression and bipolar depression groups were higher than those of healthy control group, while the GABA level ((6.1±0.7) μmol/L,(4.1±0.8) μmol/L vs (8.1±1.2) μmol/L, F=21.61, P<0.01) and GAD ((31±6) U/L, (31±6) U/L vs (35±6) U/L, F=5.61, P<0.01) were lower than those of healthy control group. The level of serum GABA in bipolar depression group was lower than that in depression group. However, Glu/GABA was higher in bipolar depression group than that in depression group (P<0.01). The level of serum GABA in depression group was negatively correlated with HAMD sleep disorder factor (r=-0.46, P=0.01). Conclusions: Both depression and bipolar depression have abnormal levels of Glu, GABA neurotransmitters and imbalance between Glu and GABA in peripheral blood circulation. Moreover, these abnormalities are more obvious in patients with bipolar depression.

Hsa-miR-329 exerts tumor suppressor function through down-regulation of MET in non-small cell lung cancer

MicroRNAs (miRNAs) act as key regulators of multiple cancers. Hsa-miR-329 (miR-329) functions as a tumor suppressor in some malignancies. However, its role on lung cancer remains poorly understood. In this study, we investigated the role of miR-329 on the development of lung cancer. The results indicated that miR-329 was decreased in primary lung cancer tissues compared with matched adjacent normal lung tissues and very low levels were found in a non-small cell lung cancer (NSCLC) cell lines. Ectopic expression of miR-329 in lung cancer cell lines substantially repressed cell growth as evidenced by cell viability assay, colony formation assay and BrdU staining, through inhibiting cyclin D1, cyclin D2 and up-regulatiing p57(Kip2) and p21(WAF1/CIP1). In addition, miR-329 promoted NSCLC cell apoptosis, as indicated by up-regulation of key apoptosis gene cleaved caspase-3, and down-regulation of anti-apoptosis gene Bcl2. Moreover, miR-329 inhibited cellular migration and invasiveness through inhibiting matrix metalloproteinases (MMP)-7 and MMP-9. Further, oncogene MET was revealed to be a putative target of miR-329, which was inversely correlated with miR-329 expression. Furthermore, down-regulation of MET by siRNA performed similar effects to over-expression of miR-329. Collectively, our results demonstrated that miR-329 played a pivotal role in lung cancer through inhibiting cell proliferation, migration, invasion, and promoting apoptosis by targeting oncogenic MET.

miR-206/133b Cluster: A Weapon against Lung Cancer?

Lung cancer is a deadly disease that ends numerous lives around the world. MicroRNAs (miRNAs) are a group of non-coding RNAs involved in a variety of biological processes, such as cell growth, organ development, and tumorigenesis. The miR-206/133b cluster is located on the human chromosome 6p12.2, which is essential for growth and rebuilding of skeletal muscle. The miR-206/133b cluster has been verified to be dysregulated and plays a crucial role in lung cancer. miR-206 and miR-133b participate in lung tumor cell apoptosis, proliferation, migration, invasion, angiogenesis, drug resistance, and cancer treatment. The mechanisms are sophisticated, involving various target genes and molecular pathways, such as MET, EGFR, and the STAT3/HIF-1α/VEGF signal pathway. Hence, in this review, we summarize the role and potential mechanisms of the miR-206/133b cluster in lung cancer.

miR-134: A Human Cancer Suppressor?

MicroRNAs (miRNAs) are small noncoding RNAs approximately 20-25 nt in length, which play crucial roles through directly binding to corresponding 3' UTR of targeted mRNAs. It has been reported that miRNAs are involved in numerous of diseases, including cancers. Recently, miR-134 has been identified to dysregulate in handles of human cancers, such as lung cancer, glioma, breast cancer, colorectal cancer, and so on. Increasing evidence indicates that miR-134 is essential for human carcinoma and participates in tumor cell proliferation, apoptosis, invasion and metastasis, drug resistance, as well as cancer diagnosis, treatment, and prognosis. Nevertheless, its roles in human cancer are still ambiguous, and its mechanisms are sophisticated as well, referring to a variety of targets and signal pathways, such as STAT5B, KRAS, MAPK/ERK signal pathway, Notch pathway, etc. Herein, we review the crucial roles of miR-134 in scores of human cancers via analyzing latest investigations, which might provide evidence for cancer diagnose, treatment, prognosis, or further investigations.

Cutaneous protothecosis on the bilateral wrists of a food handler

Cutaneous protothecosis is caused by the achlorophyllic algae Prototheca, typically presenting as a localized plaque in immunocompetent individuals. We report a patient with bilateral erythematous plaques and pustules on her forearms, which had initially been treated with steroids for presumed eczema. Histology showed spherical spore-like bodies with internal morula-like septation, which were positive for periodic-acid-Schiff (PAS) staining, consistent with cutaneous protothecosis. Definitive treatment with oral itraconazole resulted in resolution of the lesions.

Papular angiolymphoid hyperplasia and lymphoplasmacytic plaque: a clinical and histological spectrum

Acral pseudolymphomatous angiokeratoma of children (APACHE) is a rare form of cutaneous pseudolymphoma characterized byangiomatous papules with a predilection for the acral regions of children. Classically, a dense dermal lymphocytic infiltrate composed of both T and B cells is seen in histological specimens, together with prominent vessels lined by plump endothelial cells. Increasing evidence suggests that this condition is neither necessarily acral, pseudolymphomatous, nor angiokeratomatous. It may not always be a pediatric disease. Therefore, the correctness of its nomenclature has been questioned. Herein, we report threecases whose clinical and histological features were consistent with the diagnosis of APACHE. To our knowledge, this is the first report of APACHE from Southeast Asia. We also discuss why we believe "APACHE" to be a misnomer and support "papular angiolymphoid hyperplasia" as a more accurate and encompassing term. In addition, we illustrate a case with significant overlapping features with lymphoplasmacytic plaque in children, suggesting that both entities may exist on a clinical andhistological spectrum.

Quality of life in people with mental illness in non-residential community mental health services in Hong Kong

OBJECTIVE

To identify the subjective quality of life in people with chronic mental health problems who were in non-residential community mental health services, and to investigate factors affecting their quality of life after the illness.

METHODS

People with mental illness (n = 105) were recruited. They were assessed with the self-rated Hong Kong Chinese version of the World Health Organization Quality of Life Brief questionnaire.

RESULTS

The participants had lower total quality-of-life and the 4 domain scores of the questionnaire than the general population. They were particularly dissatisfied with their financial situation. Duration of illness was positively correlated with subjective quality-of-life variables while age at onset of the mental illness was negatively correlated with subjective quality of life, in particular the physical health, psychological health, and environmental domains.

CONCLUSION

This study highlighted the significance of duration and age at onset of illness in subjective quality of life of people with mental illness. A longitudinal study to test the causal relationships between these factors and the quality of life in people with mental illness is recommended.

Obstacles and solutions to screening psoriasis patients for cardiovascular risk factors

BACKGROUND

Psoriasis has been linked with cardiovascular risk factors (CVRFs), including the metabolic syndrome, yet many patients with psoriasis remain unscreened.

OBJECTIVE

To assess the reasons for lack of screening for CVRFs in psoriasis patients, and the impact of an education programme targeting these deficiencies.

METHODS

All patients with psoriasis, regardless of severity, and all dermatologists working at the National Skin Centre (NSC) in Singapore were surveyed over a 2-month period on their attitudes and knowledge regarding psoriasis and cardiovascular risk. This was followed by a targeted programme which was implemented over 2 months to address these identified deficiencies. Patients and doctors were surveyed a second time to assess the effects of the intervention.

RESULTS

Obstacles to screening included lack of patient knowledge, patients not considering screening important, and lack of time during the clinic consultation. After the intervention, there was a significant increase in the proportion of patients who were aware of increased cardiovascular risk in psoriasis (33.0% to 62%), with more patients attending screening (39.1% to 63.2%). While the level of doctors' knowledge did not significantly increase, there was an increase in the proportion of patients who were screened post-intervention (37.1% to 66.2%), and more doctors reported that they were more likely to screen psoriatic patients from an earlier age (30.2% to 58.1%).

CONCLUSIONS

The obstacles in implementing universal screening for CVRFs in psoriasis patients stem from patient, doctor and system factors. A comprehensive programme targeting all aspects of this ecosystem helps to achieve holistic care for patients with psoriasis.

The hedgehog signaling pathway, a new therapeutic target for treatment of ischemic heart disease

The hedgehog (Hh) protein is involved in angiogenesis and cardiovascular development via activation of the classical ligand-dependent signaling transduction. So its potential therapeutic meaning of Hh signaling proteins to the ischemic heart diseases has been greatly explored. Recent studies show that up-regulated expression of hypoxia-induced factor-1 (HIF-1) and inflamemation in ischemic tissues activate the Hh signaling cascade in a GLI-dependent or independent way, resulting in elevated expression levels of pro-angiogenic and agiogenic factors to facilitate angiogenesis. In addition, Hh signaling pathway activation can promote residual myocardial progenitors, endogenous EPCs and MSCs differentiating into cardiomyocytes, inhibit cardiomyocyte apoptosis; thirdly, high level of exogenous Hh signaling can reduce myocardial ischemic/reperfusion injuries(I/R). In conclusion, three kinds of mechanisms induced by Hh signaling pathway participate in the heart repair after myocardial ischemia. Therefore, Hh agonists including Hh protein, Hh gene transfer and small molecule agonist could be part of a potential therapeutic strategy for acute or chronic ischemic heart disease.

Clinics in diagnostic imaging (116). Ruptured hepatocellular carcinoma

A 37-year-old Chinese man with chronic hepatitis B, who frequently defaulted past follow-up appointments, was admitted for acute abdomen and shock. Computed tomography of the abdomen revealed a ruptured hepatocellular carcinoma involving the left lobe. After fluid resuscitation, gelfoam embolisation was performed to arrest the bleeding, followed by segmental resection of the hepatic lesion. There was aggressive recurrence following left segmental hepatectomy, and despite two courses of transarterial chemoembolisation, the patient died of local and pulmonary recurrences five months after his initial presentation. The management of hepatocellular carcinoma rupture is discussed.

Effects of environmental enrichment on spatial memory and neurochemistry in middle-aged mice

The present study compared the effects of environmental enrichment on spatial memory, glutamic acid decarboxylase (GAD) activity, and synaptophysin levels in middle-aged male and female mice. Prior to testing, a subset of 18-month-old male and female C57BL/6 mice was housed with two to three toys and a running wheel in the home cage for up to 29 d. Adult mice (7 mo) of both sexes and the remaining middle-aged mice were group (social) housed, but not exposed to enriching objects. After the enrichment period, all mice were tested in a 1-day version of the Morris water maze, in which both spatial and nonspatial memory were assessed. Immediately after testing, the hippocampus and frontoparietal cortex were dissected, and GAD activity and synaptophysin levels were measured. Environmental enrichment reduced the age-related impairment in spatial acquisition and retention; relative to adult social controls, middle-aged enriched mice were unimpaired, whereas middle-aged social controls were impaired. This reduction was similar in middle-aged males and females. Enrichment did not affect cued memory in either sex. Although hippocampal GAD activity was increased by enrichment in males, all other neurochemical measurements were unaffected by enrichment or aging in either sex. These data suggest that environmental enrichment initiated at middle age can reduce age-related impairments in spatial memory in males and females, although the underlying neurobiological mechanisms of this effect remain unknown.

[Down-regulation of ETA receptor of vascular smooth muscle cells by 17 beta-estradiol]

In the present study, the effects of 17 beta-estradiol on vascular reactivity of ovariectomized rats and proliferation of cultured rat aortic smooth muscle cells were studied. The vascular reactivity was significantly increased in ovariectomized rats compared with the sham-operated animals. The selective ETA receptor antagonist BQ123 inhibited the increase in [3H]-TdR incorporation in response to ET-1 on vascular smooth muscle cells (VSMCs). 17 beta-estradiol also attenuated the ET-1 effects in a dose-dependent manner. The results of RT-PCR and Western blot show that expression of ETA receptor was decreased after treatment with 17 beta-estradiol. The effect of 17 beta-estradiol was partially inhibited by estrogen receptor antagonist tamoxifen. The above results demonstrate that proliferation of VSMCs stimulated by ET-1 was mainly mediated through ETA receptor. Due to the down-regulation of ETA receptor and mediation of estrogen receptor, 17 beta-estradiol inhibits the ET-1-induced proliferation of VSMCs and decreases the vascular reactivity of ovariectomized rats.

[Effect of microinjection of L-arginine into the caudal pressor area of medulla oblongata on cardiovascular responses in rats]

AIM

To study the effect of microinjection L-arginine, a precursor for the synthesis of nitric oxide into the functionally identified caudal pressor area (CPA) in ventral surface of medulla oblongata.

METHODS

Artery pressure (AP), renal perfusion pressure (RPP) and heart rate were recorded to study the effects of microinjection of NO related drugs into CPA.

RESULTS

(1) Unilateral microinjection of L-arginine (60 - 100 nmol) into CPA produced prominent dose-related depressor and bradycardic effects and reduced renal perfusion pressure. (2) Unilateral microinjection of L-arginine (100 nmol) 3 min after microinjection of methylene blue (10 nmol) into CPA did not significantly change AP and RPP. (3) Unilateral microinjection of L-glutamate (350 nmol) into CPA elicited pressor effect which was significantly dose-related attenuated by prior microinjection of L-arginine (60-100 nmol) into the same area.

CONCLUSION

Theses results suggest that L-arginine-NO pathway in the CPA participates in the central regulation of arterial pressure and may have a key role in the inhibiting of glutamatergic neurotransmission in the anesthetized rats.

[Effects of microinjection of L-arginine into the depressor area of ventral surface of medulla oblongata on cardiovascular responses]

AIM

To study the effects of L-arginine, a precursor for the synthesis of nitric oxide, when it was microinjected into the functionally identified depressor area in ventral surface of medulla oblongata (VSMd) on cardiovascular responses.

METHODS

Artery pressure (AP), perfusion pressure of the kidney (PPK) and heart rate were recorded to study the effects of microinjection of NO related drugs into VSMd.

RESULTS

(1) Unilateral microinjection of L-arginine (60 - 100 nmol) into VSMd produced prominent dose-related pressor effect and increased PPK but without significant changes in heart rate. (2) Microinjection of L-Arg (100 nmol) 3 min after microinjection of methylene blue (10 nmol) into VSMd did not significantly change AP and PPK. (3) Unilateral microinjection L-glutamate (350 nmol) into VSMd elicited depressor effect (-34.97% +/- 4.33%). The depressor effect was significantly dosed related attenuated by prior microinjection L-arginine (60 - 100 nmol) into the same area.

CONCLUSION

These results suggest that the L-arginine - NO pathway in the VSMd participate in the central regulation of artery pressure and the pathway may have a key role in inhibiting glutamatergic neurotransmission in the anesthetized rats.

Which depressed patients respond to nefazodone and when?

BACKGROUND

Retrospective data analyses were conducted of a single-blind trial of 993 outpatients with nonpsychotic major depression (DSM-III-R) treated for 12 weeks with nefazodone to provide a more specific picture of the nature and timing of response or remission to acute-phase treatment.

METHOD

All patients participated in a single-blind, 16-week lead-in to obtain responders eligible for a subsequent double-blind, randomized continuation phase trial. Outcomes were defined by the 17-item Hamilton Rating Scale for Depression (HAM-D). A > or = 50% reduction from baseline defined response, and a total HAM-D exit score of < or =8 defined remission.

RESULTS

Of all patients who entered the trial, 41.8% (last observation carried forward) responded at or before week 4 (early responders), and an additional 25.2% responded thereafter; 18.3% achieved remission at or before week 4; 33.6% achieved remission after week 4. Thus, 77.3% of those responding ultimately remitted. On average, remission followed response by 2 weeks. The average end-of-treatment dose was 376 mg/day at exit (last observation carried forward). Responders or remitters (as opposed to nonresponders or nonremitters) had lower baseline depressive symptomatology and were more likely to be married or cohabiting.

CONCLUSION

The full symptomatic benefit of antidepressant medication may not be apparent until completion of an 8- to 10-week trial. A high number of responders ultimately attained remission. Baseline demographic and clinical features were not highly predictive of who would or would not benefit from nefazodone. For routine care, a minimal acute-phase trial, using a 50% reduction in baseline symptom severity to define response, should be 8 weeks. Whether ultimate nonresponders can be identified earlier than 8 weeks deserves further study.

[Effect of aldosterone on the secretion of endothelin by ventricular fibroblasts]

Using cell culture, radioimmunoassay for endothelin and RT-PCR, the effect of aldosterone on the endothelin secretion of ventricular fibroblasts was studied. The results showed that aldosterone (1 x 10(-7) mol/L) promoted the expression of ppET-1 mRNA, which began to increase in 2 hours and attained the highest level in 4 hours, thereafter decreased; aldosterone increased the endothelin level in ventricular fibroblasts and fibroblast conditioned growth medium (FCGM) as well, which was blocked by spironolactone (1 x 10(-6) mol/L), an aldosterone receptor antagonist. The results suggest that aldosterone can increase endothelin secretion by ventricular fibroblasts, which can be inhibited by its receptor antagonist spironolactone.

[Role of mitogen-activated protein kinase in the inhibition of myocardial hypertrophy by nitric oxide in renovascular hypertensive rats]

The aim of this study was to examine the effects of L-arginine, a nitric oxide (NO) precursor, on protein expression of endothelial nitric oxide (eNOS), nitrite/nitrate content, protein expression of mitogen-activated protein kinase phosphatase-1 (MKP-1) and the activity of mitogen-activated protein kinase (MAPK) in cardiac tissues in renovascular hypertensive rats (RHR). The Goldblatt renovascular hypertensive model was established by two-kidney one clip method. The rats were divided into four groups, respectively treated with 50, 150 and 450 mg/kg L-arginine and 150 mg/kg L-arginine plus 10 mg/kg L-NAME (an eNOS inhibitor) (i.p.). Another group did not receive specific treatment from the 5th week after renal artery constriction. Control group was sham-operated. Mean arterial blood pressure (MABP) and the ratio of left ventricular weight to body weight (LVW/BW) were measured 8 weeks after treatment. eNOS protein expression, nitrite/nitrate content, MKP-1 protein expression and MAPK activity in cardiac tissues were detected using Western blot analysis, enzyme-reduction method and substrate in-gel kinase assay, respectively. It was found that L-arginine significantly inhibited the increase of MABP and LVW/BW, attenuated the activity of MAPK, increased protein expression of eNOS and MKP-1 and potentiated production of NO in cardiac tissue with the most effective dosage of 150 mg/kg, and these effects of L-arginine could be inhibited by L-NAME. These results suggest that MKP-1 may play an important role in the NO-induced inhibition of myocardial hypertrophy. The anti-hypertrophic effects of L-arginine may involve increase of eNOS protein expression and NO production, potentiation of MKP-1 protein expression, and inhibition of MAPK activity in the cardiac tissue of RHR.

[Role of conditioned growth medium for ventricular fibroblasts in promoting fibroblast collagen synthesis and proliferation]

Ventricular fibroblasts were cultured using conditioned growth medium for ventricular fibroblasts (FCGM). The rate of the total collagen synthesis of ventricular fibroblasts was measured by assaying the incorporation rate of [3H]-proline, whereas the proliferation of ventricular fibroblasts was assessed by determining the incorporation rate of [3H]-TdR and the expression of c-fos genes. FCGM significantly increased the [3H]-proline incorporation rate and [3H]-TdR incorporation rate of fibroblasts in a dose-dependent manner. Furthermore, FCGM promoted the c-fos gene expression of fibroblasts, which attained its maximum in 1 h. BQ123, an ETA receptor antagonist, partially blocked the above effects of FCGM, but AT1 receptor antagonist CV11974 and alpha-adrenergic receptor antagonist regitin did not. It is suggested that the ventricular fibroblast has an autorine function in promotion of collagen synthesis and proliferation of fibroblasts by secreting endothelin and other bioactive substances.

[The effect of aldosterone of promotion on proliferation of ventricular fibroblasts]

AIM

To study the effect of promoting aldosterone on proliferation of ventricular fibroblasts.

METHODS

Assay of [3H]-TdR incorporation rate and RT-PCR were used.

RESULTS

Aldosterone could promote [3H]-TdR incorporation of ventricular fibroblasts, the effective dose of aldosterone was among (1 x 10(-9)-1 x 10(-6))mol/L, and had dose-dependent manner, the c-fos gene was expressed after stimulated by aldosterone for 15 min, and studied the highest in 1 h, then reduced later. Spironolactone, aldosterone receptor antagonist could block the effect of aldosterone.

CONCLUSION

Aldosterone promotes the proliferation of ventricular fibroblasts, mediated by aldosterone receptor.

Nitric oxide inhibits the expression of proto-oncogene c-fos induced by angiotensin II and endothelin-1 in cardiomyocytes

The effect of nitric oxide (NO) on the hypertrophic response and the proto-oncogene c-fos expression induced by angiotensin II (AII) or endothelin-1 (ET-1) was investigated in the primary culture of neonatal rat cardiomyocytes. Total protein content of cardiomyocytes (used as the index of cardiac myocyte hypertrophy) was determined by the Bradford method. The proto-oncogene c-fos expression was assessed using reverse transcription-polymerase chain reaction (RT-PCR) standardized with glyceraldehyde-3-phosphate dehydrogenase (GAPDH). RT-PCR was performed in a single tube using gene-specific primers and the SuperScript One-Step RT-PCR System. Total protein content of cardiomyocytes increased significantly on day 5 after A II treatment or on day 3 after ET-1 treatment and the increased protein content was inhibited by SNP (NO donor). A II, ET-1 and PMA (protein kinase C activator) induced the c-fos gene expression of cardiomyocytes, while L-arginine inhibited it. The L-arginine effect was blocked by L-NAME (NOS inhibitor). SNP inhibited the c-fos gene expression of cardiomyocytes induced by A II,ET-1 or PMA as well. These results suggest that NO can inhibit the hypertrophic response and the proto-oncogene c-fos expression of cardiomyocytes induced by A II or ET-1 and the cross-link may be located at the site of protein kinase C.

[17beta -estradiol induced nitric oxide release in vascular endothelial cells]

Bovine aortic endothelial cells (BAECs) were used to study the effect of 17beta -estradiol (E(2)) on nitric oxide (NO) release, nitric oxide synthase (eNOS) mRNA expression and intracellular free calcium con~cen~tration ([Ca(2+)](I)) and modulation of the effect of E(2) by estrogen receptor (ER) antagonist tamoxifen and NOS inhibitor L-NAME. E(2) (10(-12) 10(-8) mol/L) induced NO release of BAECs in a concentration-dependent manner and the abundant expression of eNOS mRNA in BAECs increased obviously after treatment with E(2) (10(-8)mol/L) for 48 h. These effects were evidently inhibited by tamoxifen (10(-7)mol/L) and L-NAME (10(-6) mol/L). Furthermore treatment with E(2) (10(-8) mol/L) for 48 h significantly increased the resting [Ca(2+)](I) and the rise of [Ca(2+)](I) induced by ATP in BAECs. These results suggest that E(2)-induced NO release and eNOS mRNA expression in BAECs may be mediated by ER and related to calcium mobilization.

[MKP-1 regulates the cardiomyocyte hypertrophic responses induced by angiotensin II]

The aim of this study was to determine the regulation by MKP-1 of MAPK activity and protein expression in cardiomyocyte hypertrophic response induced by Ang II. Neonatal rat cardiomyocyte hypertrophic response was assayed by cell surface area, protein synthesis rate and protein content. MAPK activity was determined by an in-gel kinase assay. Protein expression of MAPK and MKP-1 were detected by Western blotting. The results are as follows. (1) Ang II induced promotion of (3)H-leucine incorporation and increase in cell protein content and cell surface area in a dose-dependent manner. Pretreatment with a selective AT(1) receptor antagonist CV11974 or a specific MEK inhibitor PD098059, cardiomyocyte hypertrophic response induced by Ang II was inhibited by 85% and 32.5%, respectively. (2) After pretreatment with PD098059 or CV11974, AngII-induced increases in p44MAPK and p42MAPK protein expression and enzyme activity (expressed by gamma-(32)P-ATP incorporation) were all inhibited obviously. (3) With treatment of myocytes by Ang II for 5 min, MAPK activity determined by p44MAPK and p42MAPK protein expression began to increase, while MKP-1 protein expression was detected within 30 min and lasted more than 2 h following treatment with Ang II. (4) Pretreatment of cardiomyocytes with actinomycin D (3 microgram/ml) for 30 min inhibited MKP-1 protein expression, while p44MAPK and p42MAPK protein expression was still detected 120 min after Ang II treatment. The above results demonstrate that activation of MAPK plays an important role in Ang II-induced cardiomyocyte hypertrophic response in neonatal rat cardiomyocytes through MKP-1 mediated inactivation of p44MAPK and p42MAPK.cardiomyocyte hypertrophic response in neonatal rat cardiomyocytes through MKP-1 mediated inactivation of p44MAPK and p42MAPK.

[Effect of protein kinase C on inhibition of nitric oxide synthesis in cultured neonatal rat cardiomyocytes by angiotensin II]

The purpose of the present study was to investigate the effect of angiotensin II (Ang II) on nitric oxide (NO) concentration and its signal transduction pathway in cultured neonatal rat cardioymocytes. NO content was measured in cultured neonatal rat cardiomyoctes using a nitrite/nitrate colormetric method kit. NO content was represented by measured nitrite (NO(2)) and nitrate (NO(3)) level (NO(2)/NO(3)). The results are as follows. NO production was decreased by Ang II in a dose dependent manner but increased by L Arg. The Saralasin, an antagonist of Ang II receptor, inhibited the effect of Ang II on NO production. The effect of Ang II on NO production was inhibited by NOS blocker N(G)-nitro-L-arginine methyl ester L-NAME but not by L-Arg. Pretreatment of Phorbol 12-myristate 13-acetate PMA , a PKC activator, decreased NO concentration significantly. This effect was strengthened by L-NAME. Staurosporine, a PKC inhibitor, abolished the inhibiting effect of Ang II on production of NO. The above results suggest that Ang II could decrease NO content in cultured neonatal rat cardiomyocytes significantly. Activity of NOS may be inhibited by Ang II. Ang II receptor was involved in the inhibitory effect of Ang II on NO production. Activation of protein kinase C (PKC) decreased significantly NO production in cultured neonatal rat cardiomyoctes, which appears to be associated with PKC in the signal transduction pathway.

[Nitric oxide changes aortic function in rats with renal hypertension]

This work was undertaken to investigate the effect of nitric oxide (NO) on aortic function of two-kidney and one-clip (2K1C) rats with renal hypertension. Animals were divided into 5 groups: the sham operation, 2K1C, captopril, L-arginine and L-NAME groups. The results are as follows. At the 4th week after constriction of the left renal artery, the mean arterial pressure was significantly elevated. In isolated aortic rings, acetylcholine-induced dilation was attenuated, and phenylephrine induced contractile response was markedly enhanced. The level of aorta cGMP content was significantly lowered. These changes were abolished in 2K1C rats treated with captopril. L-arginine partially reversed the aortic vascular reactivity of 2K1C rats, and elevated aortic cGMP content. In 2K1C rats treated with nitric oxide synthase inhibitor, L-NAME, blood pressure was increased further, acetylcholine-induced aorta diastolic response was attenuated further and cGMP content reduced, while phenylephrine-induced contractile response was unaffected. These results suggest that deficiency of nitric oxide production and increase in renin-angiotensin system activity may contribute to vascular endothelial dysfunction of 2K1C rats, and these factors may be involved in development and maintenance of 2K1C renal hypertension.

[Cardiocyte hypertrophy induced by cultured neonatal rat ventricular fibroblast conditioned growth medium]

The present work demonstrated that cultured neonatal rat ventricular fibroblast conditioned growth medium (FCGM) could significantly increase cell surface area and protein content and promote (3)H -Leucine incorporation on neonatal rat cardiomyocyte. The above effect was strongest on the third day, and was dose-dependent. BQ(123), an ET-A receptor antagonist, significantly blocked the effect, while CV11974, an Ang II I-type receptor antagonist, and regitin, an alpha-adrenergic receptor antagonist, did not. These results suggest that there are some substances promoting hypertrophy of cardiomyocytes in FCGM, which may be ET-1. The FCGM-induced increases in cardiomyocyte protein synthesis and cell surface area were inhibited partially by pertusis toxin (PTX) and PKC inhibitor staurosporine (ST), suggesting that the hypertrophic effect is related with PTX sensitive G protein and PKC.

[The role of nitric oxide in the angiotensin II-induced hypertrophy of cardiac myocytes]

The purpose of this study was to determine the role of nitric oxide (NO) in the angiotensin II-induced hypertrophic response in cultured neonatal rat cardiac myocytes. Angiotensin II induced significant increase of protein content, decrease of NOS activity in cultured neonatal rat cardiomyocytes and decrease of NO concentration in the culture medium. Angiotensin II decreased significantly the eNOS mRNA level of cardiomyocytes. Saralasin and PTX inhibited significantly the increased protein content, the decreased NOS activity and the decreaseed NO production of cardiomyocytes induced by angiotensin II. Sodium nitroprusside increased significantly NO concentration in the culture medium and inhibited significantly the increased protein content of cardiomyocytes induced by angiotensin II. The results suggest that angiotensin II may induce hypertrophy of cultured neonatal rat cardiomyocytes. The effect of angiotensin II is mediated by receptors which are coupled with PTX-sensitive G protein and may be related to the decreased eNOS gene expression, NOS activity and NO production. Exogenous NO can prevent the hypertrophy of cardiomyocytes induced by angiotensin II.

[Effect of angiotensin II on c-fos expression and protein synthesis in cultured rat myocardial cells]

The present study was to investigate the effects of angiotensin II on c-fos mRNA expression and protein synthesis in cultured neonatal rat myocardial cells. The results showed that angiotensin II induced c-fos mRNA expression, increased protein content in a dose-dependent manner and stimulated 3H-leucine incorporation rate. All these effects were blocked by angiotensin II receptor antagonist saralasin. The angiotensin II-induced expression of c-fos gene was also blocked by Ca2+ channel antagonist nicardipine.

[Effect of ET-1 on intracellular free calcium in cultured neonatal myocardial cells]

In this present study, the effects of ET-1 on intracellular free calcium concentration ([Ca2+]i) and the underlying mechanisms were investigated in cultured neonatal rat myocardial cells loaded with fura-2/AM. The results are as follows. ET-1 induced an increase of [Ca2+]i in a dose-dependent manner, which consisted of a transient and sustained phase. BQ123, a selective ETA receptor antagonist, blocked the ET-1 induced [Ca2+]i responses, suggesting that these responses were mediated by ETA receptors. After removal of extracellular Ca2+, ET-1 induced the transient increase of [Ca2+]i without the sustained change. Protein kinase C (PKC) agonist PMA attenuated the ET-1 induced transient [Ca2+]i increase. Amiloride and nifedipine did not block the [Ca2+]i change induced by ET-1. After pretreatment of myocardial cells with pertussis toxin, ET-1 also induced the transient increase of [Ca2+]i but did not affect the sustained increase. These results suggest that the transient [Ca2+]i increase may involve pertussis toxin-insensitive G protein and the sustained one may be caused by extracellular calcium influx, in which pertussis toxin sensitive G protein is involved. Furthermore, PKC, but not Na+/H+ exchange, plays an important role in these effects.

[ET-1 induces the expression of prooncogene c-fos in cultured neonatal rat myocardial cells]

In the present study, the effect of endothelin-1 (ET-1) on the expression of proto-oncogene c-fos in cultured neonatal rat myocardial cells was investigated. The results are as follows: ET-1 induced c-fos expression in a dose-dependent manner. Selective ET(A) receptor antagonist blocked ET-1-induced responses. Protein kinase C(PKC) agonist PMA induced c-fos expression.PKC inhibitor staurosporine blocked ET-1 induced c-fos expression. Calcium channel blocker, nifedipine did not significantly affect the expression of c-fos induced by ET-1. These results suggest that in cultured neonatal cardiomyocytes, ET-1 induced c-fos gene expression is mediated by ET(A) receptor with the participation of protein kinase C, while the voltage-dependent L-type Ca(2+) channel is not involved.

GEF-mediated GDP/GTP exchange by monomeric GTPases: a regulatory role for Mg2+?

GTPases share highly conserved guanine nucleotide-binding domains and fulfill diverse functions through a common molecular switch. An inactive GDP-bound protein is turned on by a guanine nucleotide exchange factor (GEF) that catalyzes exchange of GTP for GDP, but unfortunately little is known about the mechanism of GEF action. A common mechanism for GDP/GTP exchange can be envisioned wherein GEFs activate monomeric GTPases through transient disruption of Mg2+ coordination in the nucleotide-binding pocket while stabilizing a nucleotide-free (and cation-free) conformation. After guanine nucleotide exchange, Mg2+ coordination is restored to complete the conformational switch to the active GTP-bound state. Evidence in the literature highlighting an important regulatory role for Mg2+ in the mechanism of GEF-mediated GDP/GTP exchange by monomeric GTPases is summarized.

[The role of G protein, protein kinase C and Na(+)-H+ exchanger in endothelin-1-induced cardiomyocyte hypertrophic responses]

Endothelin-1 (ET-1) has been shown to be a potent growth factor and to induce cardiac hypertrophy. In the present study, we examined the role of G protein, protein kinase C (PKC) and Na(+)-H+ exchanger in ET-1-induced cardiac hypertrophy in cultured neonatal rat cardiac myocytes. ET-1 (10(-10)-10(-7) mol/L) induced promotion of 3H-leucine incorporation, increase in cell protein content and cell surface area in a dose-dependent manner with EC50 value of 5.2 x 10(-10), 5.2 x 10(-10) and 7.3 x 10(-10) mol/L respectively. All of these ET-1-induced cardiomyocyte hypertrophic responses were completely blocked by pretreatment with staurosporine (2 nmol/L), a protein kinase C inhibitor, and stimulated by 4-phorbol, 12-myristate, 13-acetate (PMA) (10(-8)-10(-6) mol/L), a protein kinase C activator, in a dose-dependent manner. Pretreatment of amiloride (10(-4) mol/L), a Na(+)-H+ exchange inhibitor completely inhibited the ET-1-induced, but not PMA-induced cardiomyocyte hypertrophic responses. The ET-1-induced increase in cardiomyocyte protein synthesis and cell surface area was significantly inhibited by pretreatment with pertussis toxin (150 ng/ml). These results suggest that ET-1-induced cardiomyocyte hypertrophy was linked with pertussis toxin sensitive G protein, and PKC and Na(+)-H+ exchange may be an important intracellular signaling transduction pathway during ET-1-induced cardiac hypertrophy in cultured neonatal rat cardiac myocytes.

[Changes in the expression of alpha- and beta-myosin heavy chain gene during the development of renal hypertension in rats]

The changes in the expression of cardiac alpha- and beta-myosin heavy chain (MHC) gene of the left ventricle were investigated in two-kidney, one-clip (2K1C) renal hypertensive rats. The results were as follows: (1) When blood pressure was increased, the left ventricle became hypertrophic, alpha-MHC gene expression was reduced and beta-MHC gene expression was increased in 2K1C renal hypertensive rats. (2) When the animal was treated with captopril, angiotensin converting enzyme inhibitor 4 W after operation and then 8 W with removal of the ischemic kidney, the blood pressure was decreased with attendant regression of left ventricular hypertrophy, while the increase in beta-MHC mRNA level was attenuated and the inhibition of alpha-MHC mRNA level was reduced. The above results suggest that the rise in arteral pressure is an important factor in the left ventricular hypertrophy and the MHC gene switch. Renin angiotension system may be involved in the cardiac hypertrophic and MHC gene switch during the development and maintenance of 2K1C renal hypertension.

Synthesis and effect of nonhydrolyzable xanthosine triphosphate derivatives on prenylation of Rab5D136N

A novel and convenient method for nucleoside triphosphate synthesis was applied to the preparation of potentially nonhydrolyzable xanthosine triphosphate derivatives. The N-methylimidazolide of xanthosine 5'-monophosphate reacted rapidly with methylenediphosphonic acid and imidodiphosphonic acid to give xanthosine 5'-(beta, gamma-methylene)triphosphate and xanthosine 5'-(beta, gamma-imido)triphosphate, respectively, in good yields. Both compounds inhibited the xanthosine-diphosphate-dependent prenylation of a mutant of Rab5, Rab5D136N, the nucleotide specificity of which had been converted from GTP to xanthosine triphosphate. The results indicate that xanthosine 5'-(beta, gamma-methylene)triphosphate and xanthosine 5'-(beta, gamma-imido)triphosphate bound to the mutant protein with similar affinities and were not hydrolyzed under the assay conditions. These novel derivatives may be useful tools for the study of the role of individual GTPases mutated to xanthosine triphosphate specificity in the background of other GTP-binding proteins.

[Expression of c-fos mRNA induced by pressure overload in the left ventricle]

In the present study the effect of pressure overload on the expression of protooncogene c-fos in the left ventricle was investigated in rats with abdominal aorta constriction. It was found that a remarkable expression of c-fos was induced by pressure overload and the expression was greatly attenuated by angiotensin converting enzyme inhibitor captopril. In the pressure overload group the angiotensinogen mRNA level was found increased. The above results suggest that angiotensin II is involved in the expression of c-fos due to pressure overload.

Influence of Mg2+ on the structure and function of Rab5

Mg2+ inhibits GDP release from Rab5WT but not from Rab5S34N, a mutant lacking Ser34 critical for Mg2+ coordination in the nucleotide binding pocket. Thus, inhibition of GDP release is apparently exerted via coordination of Mg2+ between Rab5 and GDP. Mg2+ also induces conformational changes in Rab5WT, demonstrated by increased tryptophan fluorescence intensity and a red shift in lambda max for the GDP-bound protein. Mg(2+)-induced fluorescence changes are not observed for Rab5S34N. The correlation between Mg2+ effects on nucleotide exchange and the fluorescence properties of Rab5 suggests that a conformation promoted through Mg2+ coordination with Ser34 also contributes to inhibition of GDP release. The role of structural changes in GDP release was investigated using C- and N-terminal truncation mutants. Similar to Rab5WT, Mg2+ inhibits GDP release and alters the fluorescence of Rab5(1-198) but only partially inhibits release from Rab5(23-198) and fails to induce changes in the latter's fluorescence properties. Since Rab5(23-198) maintains Ser34 necessary for Mg2+ coordination, the lack of Mg(2+)-induced fluorescence changes suggests a requirement for the N-terminal domain to promote a conformation blocking GDP release. A model for mechanisms of interaction between Ras-like proteins and their exchange factors is proposed.

[Reduction of incidence of ischemia-reperfusion induced ventricular fibrillation by captopril]

To investigate the role of catecholamine and prostacyclin in ischemia reperfusion-induced ventricular fibrillation, experiments were performed in rat hearts using methods of radioimmunoassay and fluorohistochemistry. Regional myocardial ischemia was induced by ligation of the left coronary artery followed by reperfusion. In the ischemia reperfusion group, ventricular fibrillation during reperfusion took place in 78% of the hearts. In the group pretreated with captopril, the incidence of ventricular fibrillation decreased significantly (65.5%). In comparison with the ischemia reperfusion group, myocardial catecholamine content and 6-keto-PGF1 alpha of the captopril group were significantly increased (P < 0.01) while thromboxane B2 (TxB2) and TxB2/6-keto-PGF1 alpha were decreased (P < 0.01). In Ang II group, infusion of angiotensin II reversed the protective effect of captopril and restored the incidence of ventricular fibrillation (85%), while myocardial catecholamine content was not different from the ischemia reperfusion group (P > 0.05). Above results suggest that reduction of the incidence of ischemia reperfusion-induced ventricular fibrillation by captopril may be due to its inhibition on angiotensin II production with consequent reduction of the release of myocardial catecholamine, suppression of TxB2 and promotion of PGI2 synthesis.

GDP dissociation inhibitor serves as a cytosolic acceptor for newly synthesized and prenylated Rab5

In vitro synthesis and post-translational prenylation of Rab5 is accomplished using reticulocyte lysate supplemented with prenyl precursors (Sanford, J. C., Pan, Y., and Wessling-Resnick, M. (1993) J. Biol. Chem. 268, 23773-23776). When Rab5 is translated in the presence of biotin-lysine-tRNA, it incorporates biotin-lysine into its peptide backbone and is efficiently prenylated; since this modification is dependent on guanine nucleotide binding, biotin-Rab5's functional integrity must be maintained. Prenylated biotin-Rab5 associates with a 45-kDa reticulocyte GDP dissociation inhibitor (GDI), sedimenting as a approximately 70-kDa particle on 5-20% sucrose density gradients. The GDI-Rab5 complex can be captured using streptavidin-linked agarose beads. Only Rab5 peptides that are substrates for prenylation are found to cosediment with the lysate GDI on sucrose gradients. Post-translational association of Rab5 and GDI is a novel finding, since previous reports suggested Rab5 remains associated with Rab escort protein (REP) after prenylation (Alexandrov, K., Horiuchi, H., Steele-Mortimer, O., Seabra, M. C., and Zerial, M. (1994) EMBO J. 13, 5262-5273). Since post-translational prenylation is catalytically mediated by REP, our study suggests that a complex between Rab5 and this factor is transient in nature. Thus, newly synthesized and prenylated Rab5 is most likely escorted to its target membrane by a GDI acceptor molecule. Biotin-Rab5 provides a novel tool for future efforts to capture and characterize additional accessory factors required for Rab protein function in vesicle transport.

Effect of guanine nucleotide binding on the intrinsic tryptophan fluorescence properties of Rab5

To gain further insight into structural elements involved in Rab5 function, differences in the intrinsic tryptophan fluorescence of the GDP- and guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S)-bound forms of the protein were examined. When excited at 290 nm, Rab5 displays emission maxima at 339.7 nm for the GDP-bound and 336.7 nm for the GTP gamma S-bound forms. The tryptophan fluorescence intensity is quenched by approximately 25% in the GTP gamma S-bound form relative to the GDP-bound conformation. Variant Rab5 molecules were created by site-directed mutagenesis to convert the protein's two tryptophans to phenylalanine residues. Fluorescence studies reveal that the observed changes upon GDP/GTP gamma S exchange are due to a blue shift in the emission spectra for both Trp74 (342.0 to 339.5 nm) and Trp114 (335.3 to 333.7 nm) and fluorescence quenching of Trp114. Consistent with the blue shift in the emission spectra, both tryptophans are more resistant to oxidation by N-bromosuccinimide in the GTP gamma S-bound state. These data indicate that both of Rab5's tryptophans are brought into a more sequestered, hydrophobic environment upon conformational changes promoted by guanine nucleotide exchange. Since Trp74 lies adjacent to Rab5's cognate switch II domain, local conformational changes would be predicted based on the known structure of Ras. However, Trp114 lies within a region of Rab5 potentially related to the switch III domain unique to heterotrimeric G alpha t. Thus, changes in the fluorescence properties of Trp114 upon guanine nucleotide exchange suggest that Rab proteins may have structure-function relationships similar to those described for heterotrimeric GTP-binding proteins.