A novel conditional Akt 'survival switch' reversibly protects cells from apoptosis

The anti-apoptotic Akt kinase is commonly activated by survival factors following plasma membrane relocalization attributable to the interaction of its pleckstrin homology (PH) domain with phosphatidylinositol 3-kinase (PI3K)-generated PI3,4-P(2) and PI3,4,5-P(3). Once activated, Akt can prevent or delay apoptosis by phosphorylation-dependent inhibition or activation of multiple signaling molecules involved in apoptosis, such as BAD, caspase-9, GSK3, and NF-kappaB and forkhead family transcription factors. Here, we describe and characterize a novel, conditional Akt controlled by chemically induced dimerization (CID). In this approach, the Akt PH domain has been replaced with the rapamycin (and FK506)-binding domain, FKBP12, to make F3-DeltaPH.Akt. To effect membrane recruitment, a myristoylated rapamycin-binding domain from FRAP/mTOR, called M-FRB, binds to lipid permeable rapamycin (and non-bioactive synthetic 'rapalogs'), leading to reversible heterodimerization of M-FRB with FKBP-DeltaPH.Akt. Like endogenous c-Akt, we show that the kinase activity of membrane-localized F3-DeltaPH.Akt correlates strongly with phosphorylation at T308 and S473; however, unlike c-Akt, phosphorylation and activation of inducible Akt (iAkt) is largely PI3K independent. CID-mediated activation of iAkt results in phosphorylation of GSK3, and contributes to NF-kappaB activation in vivo in a dose-sensitive manner. Finally, in Jurkat T cells stably expressing iAkt, CID-induced Akt activation rescued cells from apoptosis triggered by multiple apoptotic stimuli, including staurosporine, anti-Fas antibodies, PI3K inhibitors and the DNA damaging agent, etoposide. This novel inducible Akt should be useful for identifying new Akt substrates and for reversibly protecting tissue from apoptosis due to ischemic injury or immunological attack.

Assessment of dynamic cerebral autoregulation based on spontaneous fluctuations in arterial blood pressure and intracranial pressure

Assessments of dynamic cerebral autoregulation usually measure the cerebral blood flow velocity (CBFV) response to changes in arterial blood pressure (ABP). We studied the effect of substituting ABP by cerebral perfusion pressure (CPP), expressed as the difference between ABP and intracranial pressure (ICP), in estimates of dynamic autoregulation obtained by transfer function analysis. CBFV, ABP and ICP were recorded during periods of physiological stability in 30 patients with severe head injury. Transfer function analysis was performed using the following combinations of input-output variables: ABP-CBFV, CPP-CBFV and CBFV-ICP. Frequency and time-domain (step response) functions were averaged for recordings with mean ICP < 20 mmHg (group A) and mean ICP > or = 20 mmHg (group B). The ABP-CBFV transfer function parameters and step response for group A were similar to previous studies in normal subjects, but group B showed deterioration of dynamic autoregulation. Radically different step responses were obtained from both groups for the CPP-CBFV transfer function and the coherence was not significantly improved. The CBFV-ICP transfer function had the highest values of coherence and indicates that changes in CBFV are the cause of spontaneous fluctuations in ICP. Furthermore, the ICP step response plateau was significantly higher for group B than for group A. An alternative calculation of the CBFV step response to changes in CPP resembled the corresponding responses for the ABP input. For spontaneous fluctuations in ABP, ICP and CBFV, it is not possible to calculate the CPP-CBFV transfer function directly due to the high positive correlation between ICP and CBFV, but an alternative estimate can be obtained by using the CBFV-ICP transfer function. The latter could also be useful as a method to assess intracranial compliance in head injury patients.

A p53 homologue and a novel serine proteinase inhibitor are over-expressed in lung squamous cell carcinoma

LSCC is a common type of lung cancer and accounts for approximately 30% of all lung cancers. We have used a combination of subtraction and cDNA microarray technology to identify genes preferentially over-expressed in LSCC. Here we report extensive molecular characterization of two novel full-length cDNA sequences, L530S and L531S. Although L530S and L531S were found to be differentially over-expressed in LSCC, the expression profiles for these two genes were not identical. L530S expression was specifically elevated in LSCC whereas L531S transcript was up regulated in both LSCC and head and neck squamous cell carcinoma samples. L530S is a homologue of p53, and L531S belongs to a new member of serine proteinase inhibitors with significant homology to SCCA1 and SCCA2. Furthermore, L531S protein was found to be expressed in lung cancers by IHC analysis. The distinct as well as similar expression profiles exhibited by L530S and L531S suggest that each gene may play a unique role for tumorgenesis of LSCC. Identification of these genes not only allows us to further explore their diagnostic and therapeutic potentials for LSCC, but also provides us with additional tools and reagents for understanding the biology behind LSCC, and differentiating LSCC from other types of lung cancer at the molecular level.

[Analysis on HLA-E polymorphism in Shanghai Han population]

OBJECTIVE

To investigate the distribution of HLA-E alleles in Chinese Han in Shanghai area.

METHODS

HLA-E alleles were assigned by using a PCR/SSO method in 201 random healthy individuals from Shanghai region. HLA-A,-B antigens typing was carried out with NIH standard microlymphocytoxicy method.

RESULTS

Three alleles of HLA-E could be detected in this population. The E*0101 is the most common allele with a frequency of 42.29%, followed by E*01032 and E*01031 with 32.84% and 24.88% respectively. No E*0102 and E*0104 could be detected in all of the individuals. The analysis of linkage on two loci between HLA-E and HLA-A or -B showed that no significant difference could be found between expected frequencies and observed frequencies excepting B15/E*01032 and A2/E*01032.

CONCLUSION

The allele frequencies of HLA-E are 42.29% for E*0101, 24.88% and 32.84% for E*01031 and E*01032 respectively in Shanghai Chinese. No extensive linkage disequilibrium was found between HLA-E and HLA-A or -B locus.

Influence of the characteristics of natural organic matter on the fouling of microfiltration membranes

Natural organic matter (NOM) plays a significant role in fouling microfiltration membranes in drinking water treatment processes even though the NOM is retained only to a small extent. The aim of this study was to obtain a better understanding of the interactions between the fractional components of NOM and microfiltration membranes. Filtration experiments were performed using 0.22 microm hydrophobic and hydrophilic polyvinylidene fluoride (PVDF) membranes in a stirred-cell system on the NOM isolated from three Australian surface waters. As expected, the fouling rate for the hydrophobic membrane was considerably greater than for the hydrophilic membrane. Focusing on the hydrophobic membrane, it was shown that the high molecular weight fraction of NOM ( > 30 kDa) was responsible for the major flux decline. Filtration tests on the four fractions of NOM isolated on the basis of hydrophobicity and charge using non-functionalised and anionic resins revealed that the fouling potential for the three waters was hydrophilic neutral > hydrophobic acids > transphilic acids > hydrophilic charged. The low-aromatic hydrophilic neutral compounds were the main determinant of the rate and extent of flux decline. This was linked to the colloidal size fraction ( > 30 kDa) and to the selective concentration of calcium in the fraction leading to organics-Ca2+ bridging. It was also shown that the higher the aromaticity of the NOM the greater the flux decline, and the aromatics mainly resided in the hydrophobic acids fraction. Overall, the fouling mechanism controlling the flux decline involved the combined effects of adsorptive and colloidal fouling by the hydrophilic neutral fraction in the internal pore structure of the membrane.

[A cephalometric investigation on Shanghainese with normal occlusion using Ricketts analysis]

OBJECTIVE

To provide a database for orthodontic diagnosis, treatment planning and treatment evaluation.

METHODS

Cephalograms taken from 121 Shanghainese (57 adolescents and 64 adults) with normal occlusion were traced and examined using Ricketts analysis.

RESULTS

(1) In adolescent group, the angle of mandibular arc and facial contour were larger in male than in female. (2)In adults group, the angle of mandibular arc and genial angle were larger in male than in female, whilst the lower facial height and the convexity of lower incisor were smaller in male than in female. (3) The angle of mandibular arc, the convexity of lower incisor and the position of upper first molar were larger in adults than in adolescents,whilst the convexity of A was smaller in adults than in adolescents.

CONCLUSION

In adolescents, the ramus and maxilla grow more in male than in female. In adults, chin and ramus grow more in male than those in female.

L552S, an alternatively spliced isoform of XAGE-1, is over-expressed in lung adenocarcinoma

Using a combination of cDNA subtraction and microarray analysis, we report here the identification and characterization of L552S, an over-expressed, alternatively spliced isoform of XAGE-1 in lung adenocarcinoma. Real-time RT-PCR analysis shows that L552S is expressed at levels greater than 10-fold in 12 of 25 lung adenocarcinoma tumors compared with the highest expression level found in all normal tissues tested. L552S is expressed in both early and late stages of lung adenocarcinoma, but it was not detected in large cell carcinoma, small cell carcinoma, or atypical lung neuroendocrine carcinoid. The full-length cDNA for L552S comprises 770 bp and encodes a polypeptide of 160 amino acids. C-terminal 94 amino acids of L552S are identical to a cancer testis antigen, XAGE-1, found in Ewing's sarcoma. Genomic sequence analysis has revealed that L552S and XAGE-1 are alternatively spliced isoforms, and expression of both L552S and XAGE-1 isoforms are present in lung adenocarcinoma. Immunohistochemistry analysis using affinity purified L552S polyclonal antibodies demonstrated specific nuclear staining in 10 of 12 lung adenocarcinoma samples. Furthermore, antibody responses to recombinant L552S protein were observed in seven of 17 lung pleural effusion fluids of lung cancer patients. These results strongly imply that L552S protein is immunogenic and suggest that it might have use as a vaccine target for lung cancer.

Brachial flow-mediated vasodilator responses in population-based research: methods, reproducibility and effects of age, gender and baseline diameter

BACKGROUND

Brachial artery ultrasound has been proposed as an inexpensive, accurate way to assess cardiovascular risk in populations. However, analysis and interpretation of these data are not uniform.

METHODS

We analysed the relationship between relative and absolute changes in brachial artery diameter in response to flow-mediated dilation and age, gender and baseline diameter among 4,040 ultrasound examinations from subjects aged 14 to 98 years.

RESULTS

Reproducibility studies demonstrated intra- and interreader and intrasubject correlations from 0.67 to 0.84 for repeated measures of per cent change in diameter. Per cent change in diameter after flow stimulus was 3.58 +/- 0.10% (mean +/- standard deviation). Corresponding values for baseline diameter and absolute change in diameter were 4.43 +/- 0.87 mm and 0.15 +/- 0.01 mm, respectively. Baseline diameter and its variance were inversely related to per cent change in diameter (P< 0.001). In contrast, absolute change in diameter was more uniform throughout the range of baseline diameters. Baseline diameter was directly related, and per cent change in diameter inversely related, to age (P < 0.001 for all three measures). Time to maximum vasodilator response increased with age (P < 0.001). Women (n=2,315) had significantly larger per cent change in diameter than men (n=1,725) (P < 0.001). However, after adjustment for age and baseline diameter, per cent and absolute change were 5% smaller in women than men (P < 0.05 for both). In multivariate analysis, age was overwhelmingly the most important determinant of absolute change in diameter (P < 0.001).

CONCLUSIONS

Automated analysis of brachial flow-mediated vasodilator responses is both feasible and reproducible in large-scale clinical and population-based research.

The inhibition and selectivity of bacterial topoisomerases by BMS-284756 and its analogues

Analogues of BMS-284756, a novel des-F(6)-quinolone, were synthesized and evaluated in order to determine the effects of modification of substituents on in vitro target inhibition. BMS-340281 (stereoisomer of BMS-284756), BMS-340280 (C-6 fluorinated analogue of BMS-284756), BMS-340278 (C-8-H derivative), BMS-433366 (C-8 methoxy analogue) and fluoroquinolone comparators were evaluated for antibacterial activity. The MICs of BMS-284756 were generally found to be within two-fold of the MICs of BMS-284756 analogues against a panel of Gram-positive and -negative organisms. BMS-284756 had MICs of 0.03-0.125 mg/L against Streptococcus pneumoniae strains with GyrA and ParC mutations, and was the most active quinolone. BMS-284756 and its analogues had similar activity compared with ciprofloxacin and moxifloxacin against topoisomerase IV decatenation, but were three times more active than levofloxacin. The IC(50) of BMS-284756 for human topoisomerase II (hTopo II) was 3000 times higher than its IC(50) for DNA gyrase, and no whole-cell cytotoxicity was noted. Two analogues, BMS-340280 and BMS-340278, demonstrated moderate inhibition against hTopo II and cytotoxicity in the cellular assay. BMS-284756 demonstrated greater Gram-positive antibacterial activity and similar inhibition of targets compared with other fluoroquinolones, and more favourable selectivity compared with the other BMS-284756 analogues.

[Correction of occipito-posterior by maternal postures during the process of labor]

OBJECTIVE

To investigate the effect on correction of occipito-posterior (OP) by changing maternal posture during labor.

METHODS

One hundred normal primigravida with head OP position in the latent phase of labor were randomly divided into 2 groups: Group A (n = 50), women were instructed to lay on the same lateral posture with the fetal spine during labor in order to correct the fetal position from OP to occipito anterior (OA); Group B (n = 50) lay on the opposite side to the fetal spine. The OP position was diagnosed by vaginal examination or B ultrasound, and the course of labor and mode of delivery were observed.

RESULTS

Thirty-four women delivered vaginally (68%) in group A, with 27 of them turned to OA position (54%); spontaneously while they were 22 (44%) and 12 (24%) in group B respectively, a significant difference was shown (P < 0.005). The average time interval for the 1st stage was (13.5 +/- 6.5) hour and (17.1 +/- 7.2) hour for group A and B respectively, also a significant difference was noted (P < 0.01).

CONCLUSION

To instruct women in labor to take the lateral recumbent position with the same side of fetal spine for correcting OP to OA is an effective method. It may increase vaginal deliveries and shorten the first stage of labor, thus reduce dystocia due to OP position. This method is simple and effective, and maybe adopted in most obstetric units.

[Gene dispersal risk of transgenic plants]

Gene flow is a key problem and top topic in risk assessment and management of transgenic plants. Five major study areas of gene dispersal in transgenic plants were reviewed in this paper, which include gene flow from transgenic plant to its wild species, characteristics of gene flow based on pollen, methods of doing experiment and risk assessment for gene flow, safety standards of risk assessment of transgenic plants, and long-term ecological impact of gene flow in the future. Some areas needed to be studied further were also proposed.

Automated embolus identification using a rule-based expert system

Transcranial Doppler ultrasound (US) can be used to detect microemboli in the cerebral circulation, but is still limited because it usually relies on "human experts" (HEs) to identify signals corresponding to embolic events. The purpose of this study was to develop an automatic system that could replace the HE and, thus, make the technique more widely applicable and, potentially, more reliable. An expert system, based around a digital signal-processing board, analysed Doppler signal patterns in both the time domain and frequency domain. The system was trained and tested on Doppler signals recorded during the dissection and recovery phases of carotid endarterectomy. It was tested with 74 separate 2.5-min recordings that contained at least 575 artefacts in addition to 253 s of diathermy interference. The results were compared with the results obtained by three HEs. Using a "gold-standard" that classified any event detected by the majority of HEs as an embolus, the automatic system displayed a sensitivity of 94.7% and a specificity of 95.1% for 1151 candidate events 7 dB or more above the clutter (signal-to-clutter ratio, SCR, > or = 7 dB), and 89.6% and 95.3%, respectively, for 2098 candidate events with SCR > or = 5 dB. The system had a very similar performance to individual HEs for SCR > or = 7dB, and was only marginally worse for SCR > or = 5 dB.

Dopamine acutely stimulates Na+/H+ exchanger (NHE3) endocytosis via clathrin-coated vesicles: dependence on protein kinase A-mediated NHE3 phosphorylation

Dopamine (DA) is a key hormone in mammalian sodium homeostasis. DA induces natriuresis via acute inhibition of the renal proximal tubule apical membrane Na(+)/H(+) exchanger NHE3. We examined the mechanism by which DA inhibits NHE3 in a renal cell line. DA acutely decreases surface NHE3 antigen in dose- and time-dependent fashion without altering total cellular NHE3. Although DA(1) receptor agonist alone decreases surface NHE3, simultaneous DA(2) agonist synergistically enhances the effect of DA(1). Decreased surface NHE3 antigen, caused by stimulation of NHE3 endocytosis, is dependent on intact functioning of the GTPase dynamin and involves increased binding of NHE3 to the adaptor protein AP2. DA-stimulated NHE3 endocytosis can be blocked by pharmacologic or genetic protein kinase A inhibition or by mutation of two protein kinase A target serines (Ser-560 and Ser-613) on NHE3. We conclude that one mechanism by which DA induces natriuresis is via protein kinase A-mediated phosphorylation of proximal tubule NHE3 leading to endocytosis of NHE3 via clathrin-coated vesicles.

Simulation of contact line dynamics in a two-dimensional capillary tube by the lattice Boltzmann model

During immiscible-fluid displacement, the contact angle between the interface and the wall of a tube, as well as the velocity V of the contact line where a fluid interface intersects the wall of a tube, depends on the applied capillary pressure Pcap. In this paper, the contact line dynamics of immiscible-fluid displacement is simulated by using the lattice Boltzmann model in a two-dimensional capillary channel with an ideally smooth wall. The V dependence of the contact angle is studied for two different wetting cases. Our simulational results are in good agreement with those based on theoretical computations and with molecular dynamics simulations. In particular, the power-law behavior Pcap approximately Vx is found with an exponent x very close to 1. The simulations suggest that the lattice Boltzmann model may serve as an alternative reliable quantitative approach to study the contact line dynamics, and also may be a promising tool for investigating some other immiscible displacement related subjects.

Multiple regions of subunit interaction in Drosophila mitochondrial DNA polymerase: three functional domains in the accessory subunit

Drosophila mitochondrial DNA polymerase, pol gamma, is a heterodimeric complex of catalytic subunit and accessory subunits. Physical interactions between the two subunits were investigated by deletion mutagenesis in both in vivo reconstitution and in vitro protein overlay analyses. Our results suggest that the accessory subunit may consist of three domains, designated the N, M, and C domains. The M and C regions comprise the major contacts involved in subunit interaction, likely with multiple sites in the exonuclease (exo) region and part of the spacer between the exo and DNA polymerase (pol) regions in the catalytic subunit. Furthermore, the N region in the accessory subunit may modulate subunit assembly and/or conformation through weak interaction with the pol region in the catalytic subunit. Sequence comparisons identify a significant similarity between the M region of the accessory subunit and the RNase H domain of HIV-1 reverse transcriptase. On the basis of these results, the proposed function of the C-terminus of the accessory subunit in RNA primer recognition, and previous observations that mitochondrial DNA polymerase is itself a reverse transcriptase, we propose that the overall conformation and arrangement of functional regions in the Drosophila pol gamma complex resemble those of HIV-1 reverse transcriptase.

[Mechanical ventilation therapy for aged patients with severe acute left heart failure combined with respiratory failure]

OBJECTIVE

To sum up the clinical experience of mechanical ventilation in treatment of aged patients with severe left heart failure (ALVF) combined with acute respiratory failure (ARF).

METHODS

A retrospective analysis was carried out of the pattern, improvement rate, mortality, and complication of medical ventilation applied on 102 aged patients (82.0 9.9 yrs) with severe ALVF and ARF in the past 10 years. The data of the patients with ARF type I (42 cases) and the data of the patients with ARF type II (60 cases) were compared.

RESULTS

The route of mechanical ventilation in 102 patients (115 times) included administration of oxygen via nasal mask (18 times), nasal intubation (69 times) and oral intubation (29 times). The ventilation pattern included volume control (115 times), pressure control (25 times), CPAP (26 times), and PEEP (45 times). The improvement rates in the patients as a whole, group ARF-I, and group ARF-II were 60.8%, 69.0%, and 55.0% respectively (P < 0.05 between each two groups). The mortality rates in the patients as a whole, group ARF-I, and group ARF-II were 39.2%, 30.9%, and 45.0% respectively (P < 0.05). The complications ever found in all of the patients included arrhythmia (37.3%). Hypotension (35.3%), pulmonary infection (34.3%), bleeding of gastrointestinal tract (31.4%), acid0base unbalance (20.6), and pressure pneumothorax (2.9%). The clinical condition (severity, mortality, and complication rate) was more critical in group ARF-II than in group ARF-I.

CONCLUSION

Mechanical ventilation is conducted with more difficulty and higher risk for aged patients with severe ALVF. However, while operated appropriately, it will be effective.

An adaptive template-matching method and its application to the boundary detection of brachial artery ultrasound scans

We developed an adaptive template-matching method for vessel wall boundary detection in brachial artery ultrasound (US) scans. The computer-aided identification of lumen-intima and media-adventitia boundaries of the brachial artery US scan is a critical step for flow-mediated vasodilator response measurement, which has become an increasingly important tool in both clinical and research applications. The adaptive template we propose in this paper is a combination of two parameterized Gaussian envelopes that approximates the US pulse envelope. The algorithm for template matching is cast as a constrained nonlinear least squares problem. A best match between the template and the observed US scan line signal results in a set of optimum parameters of the adaptive template, and the location of the boundaries is directly computed from these parameters. We present the results of applying our method to synthetic and clinical data, showing that the adaptive template-matching method provides superior accuracy in detecting the media-adventitia boundaries of both the near wall and the far wall of the vessel to that of conventional edge-detection methods.

Molecular cloning and characterization of hNP22: a gene up-regulated in human alcoholic brain

An improved differential display technique was used to search for changes in gene expression in the superior frontal cortex of alcoholics. A cDNA fragment was retrieved and cloned. Further sequence of the cDNA was determined from 5' RACE and screening of a human brain cDNA library. The gene was named hNP22 (human neuronal protein 22). The deduced protein sequence of hNP22 has an estimated molecular mass of 22.4 kDa with a putative calcium-binding site, and phosphorylation sites for casein kinase II and protein kinase C. The deduced amino acid sequence of hNP22 shares homology (from 67% to 42%) with four other proteins, SM22alpha, calponin, myophilin and mp20. Sequence homology suggests a potential interaction of hNP22 with cytoskeletal elements. hNP22 mRNA was expressed in various brain regions but in alcoholics, greater mRNA expression occurred in the superior frontal cortex, but not in the primary motor cortex or cerebellum. The results suggest that hNP22 may have a role in alcohol-related adaptations and may mediate regulatory signal transduction pathways in neurones.

Production of zebrafish germ-line chimeras from embryo cell cultures

Although the zebrafish possesses many characteristics that make it a valuable model for genetic studies of vertebrate development, one deficiency of this model system is the absence of methods for cell-mediated gene transfer and targeted gene inactivation. In mice, embryonic stem cell cultures are routinely used for gene transfer and provide the advantage of in vitro selection for rare events such as homologous recombination and targeted mutation. Transgenic animals possessing a mutated copy of the targeted gene are generated when the selected cells contribute to the germ line of a chimeric embryo. Although zebrafish embryo cell cultures that exhibit characteristics of embryonic stem cells have been described, successful contribution of the cells to the germ-cell lineage of a host embryo has not been reported. In this study, we demonstrate that short-term zebrafish embryo cell cultures maintained in the presence of cells from a rainbow trout spleen cell line (RTS34st) are able to produce germ-line chimeras when introduced into a host embryo. Messenger RNA encoding the primordial germ-cell marker, vasa, was present for more than 30 days in embryo cells cocultured with RTS34st cells or their conditioned medium and disappeared by 5 days in the absence of the spleen cells. The RTS34st cells also inhibited melanocyte and neuronal cell differentiation in the embryo cell cultures. These results suggest that the RTS34st splenic-stromal cell line will be a valuable tool in the development of a cell-based gene transfer approach to targeted gene inactivation in zebrafish.

[Malformed macrocephalous sperm with polytails and chromosomal aberrance]

OBJECTIVE

To investigate the relationship between sperm anomalies and chromosomal aberrance and to further understand the pathological changes of anomalous spermatozoa.

METHODS

Light and electronic (SEM or TEM) microscopes were used for morphological analysis. Fluorescence in situ hybridization(FISH) with chromosome X-, Y-specific probes were used for aneuploidy detection in sperms of the patient.

RESULTS

Ninety eight point seven five per cent of the Papanicolaou stained sperms were observed to be abnormal; 100% of the sperm heads were abnormal, measured under oil objective (1000 times); 60.25% of the sperms had two or more tails (the maximum being eight tails). SEM and TEM demonstrated that the heads contained a large amount of cytoplasmic structure, the surfaces of heads were uneven, the nuclei were of much irregular shape; besides aberrance in quantity, anomalies occurred with centromeres, mitochondria and flagella in the tails. The results of FISH showed that the aneuploidy rate of sex chromosomes was 61.41% which was parallel to the rate of polytails.

CONCLUSION

Even though the chromosomes in somatic cells are normal, the chromosomes in anomalous sperms may be abnormal.

Inhibition of N-myc expression and induction of apoptosis by iron chelation in human neuroblastoma cells

Neuroblastoma is the second most common solid malignancy of childhood. Enhanced expression of the amplified N-myc gene in the tumor cells may be associated with poor patient prognosis and may contribute to tumor development and progression. The use of deferoxamine mesylate (DFO), an iron chelator, to treat neuroblastoma is being investigated in national clinical studies. We show here by TUNEL assay and DNA laddering that DFO induces apoptosis in cultured human neuroblastoma cells, which is preceded by a decrease in the expression of N-myc and the altered expression of some other oncogenes (up-regulating c-fos and down-regulating c-myb) but not housekeeping genes. The decrease in N-myc expression is iron-specific but does not result from inhibition of ribonucleotide reductase, because specific inhibition of this iron-containing enzyme by hydroxyurea does not affect N-myc protein levels. Nuclear run-on and transient reporter gene expression experiments show that the decrease in N-myc expression occurs at the level of initiation of transcription and by inhibiting N-myc promoter activity. Comparison across neuroblastoma cell lines of the amount of residual cellular N-myc protein with the extent of apoptosis measured as pan-caspase activity after 48 h of iron chelation reveals no correlation, suggesting that the decrease in N-myc expression is unlikely to mediate apoptosis. In conclusion, chelation of cellular iron by DFO may alter the expression of multiple genes affecting the malignant phenotype by multiple pathways. Given the clinical importance of N-myc overexpression in neuroblastoma malignancy, decreasing N-myc expression by DFO might be useful as an adjunct to current