Molecular cloning and functional expression of human deoxyhypusine synthase cDNA based on expressed sequence tag information

Deoxyhypusine synthase is an NAD(+)-dependent enzyme that catalyses the formation of a deoxyhypusine residue on the eukaryotic initiation factor 5A (eIF-5A) precursor by transferring an aminobutyl moiety from spermidine to the epsilon-amino group of a unique lysine residue. We have recently cloned and characterized the Neurospora crassa deoxyhypusine synthase cDNA using a reverse genetics approach. A GenBank search showed that a stretch of the deduced amino acid sequence (96 amino acids) of Neurospora deoxyhypusine synthase matches a short human expressed sequence tag (EST), Z25337, with greater than 70% amino acid identity. Gene-specific primers based on this EST were used together with universal primers to obtain 1219 bp and 1078 bp cDNAs from a human cDNA library. The 1219 bp and 1078 bp sequences, each containing an open reading frame, encode polypeptides of respectively 368 and 321 amino acids. The short sequence is identical to the long one except that it is missing a stretch of 47 amino acids spanning residues 261-307. The 368-amino-acid sequence of human deoxyhypusine synthase shares a high degree of identity ( > 50%) and similarity ( > 60%) with that of the Neurospora and yeast deoxyhypusine synthases. After cloning into an expression vector, the 368-amino-acid recombinant protein exhibits high deoxyhypusine synthase activity. In contrast, the 321-amino-acid recombinant protein shows no detectable activity.

Superscan in patients with nasopharyngeal carcinoma

Bone scintigraphy plays an important role in the early detection of bone metastases in patients with nasopharyngeal carcinoma and serial scans may aid the clinician to assess the therapeutic response. A superscan is a pattern described as abnormal bone scan, indicating extensive bony metastases associated with various neoplastic diseases. Bone scans from 407 patients with nasopharyngeal carcinoma were reviewed retrospectively. Only six superscans (1.5%) were found. The appearance of a superscan is frequently accompanied by an abnormal titer of serological markers IgG-VCA and IgA-VCA, liver metastases, and poor survival. Although a superscan rarely occurs in nasopharyngeal carcinoma, its appearance may represent a poor prognosis in these patients.

Determination of the appropriate fraction number and size of the HDR brachytherapy for cervical cancer

Based on the linear-quadratic model, we have made two isoeffect tables for transforming the traditional low dose rate (LDR) point A doses at 20, 30, 40, 50, 60, and 70 Gy to those of the high dose rate (HDR) dose per fraction. HDR fractions ranged from 1 to 12, with corresponding sizes for each fraction. We also propose the therapeutic gain ratio (TGR) method for determining the appropriate fraction number of HDR brachytherapy in cervical cancer. TGR is defined as addition of the calculated biological therapeutic difference with the supposed physical therapeutic difference of HDR brachytherapy. Through the TGR method, we predicted that after 2 to 3, 2 to 4, and 4 to 7 fractions of HDR treatments, the tumor control rate and complication rate would be equivalent to those of LDR point A doses of 30, 40, and 70 Gy, respectively. The TGR is affected by many factors, such as the equivalent total dose of LDR, dose rate of LDR, HDR fraction number, T1/2, and differences between LDR and HDR in the dose in critical organs. The TGR method might explain why a low fraction number of HDR can be used in clinical practice. We may use this principle to replace the traditional trial-and-error method for transcribing the relationship between LDR and HDR treatments.

The age-dependent binding of CBP/tk, a CCAAT binding protein, is deregulated in transformed and immortalized mammalian cells but absent in premature aging cells

CBP/tk, CCAAT Binding Protein for thymidine kinase, has been shown to bind to the distal and proximal CCAAT elements in human TK gene at G1/S boundary in normal human IMR-90 cells after serum stimulation (Pang and Chen, 1993). We now show that the serum-induced binding activity of CBP/tk was inversely related to the population doubling level (PDL) of the normal IMR-90 cells. However, little or almost no CBP/tk binding activity was observed in cells derived from patients with premature aging syndromes (e.g., Werner, Hutchinson-Gilford, and Cockayne syndrome). In contrast, CBP/tk binding activity in SV-40 virus-transformed human cells and in HeLa cells was overexpressed at levels 5- to 15-fold higher than that in normal cells and appeared to be deregulated. The half-life of CBP/tk binding activity in SV-40 transformed cells was at least 10 times longer than that in normal IMR-90 cells, suggesting that posttranslational control may contribute to the deregulation. CBP/tk binding activity detected in other mammalian cells such as murine NIH3T3, an immortal cell line, did not reveal any cell cycle dependence either. Further characterization of CBP/tk binding complex indicates that the binding complex may contain NF-YA and NF-YB and that the binding activity was sensitive to oxidizing reagents. Taken together, our data showed that the age- and cell cycle-dependent nature of CBP/tk is a function of cell types and that CBP/tk binding activity may be subjected to posttranslational and redox regulation.

Differential regulation of cyclin A, cyclin B and p21 concentrations in a growth-restricted human fibroblast cell line

When the culture temperature was shifted from 35 degrees C to 39 degrees C, human fibroblasts immortalized by the temperature-sensitive simian virus 40 T antigen became larger and acquired the morphological characteristics of senescent fibroblasts. After culture at 39 degrees C for 48 h, most cells had ceased to proliferate. A rapid depletion of cells with S-phase DNA content was observed after the temperature shift. To elucidate the mechanism governing this rapid arrest of proliferation, we studied the expression of genes involved in the regulation of cell cycle progression. Cyclin A, cyclin B and p34cdc2 concentrations were not changed during growth restriction, whereas p21 was rapidly induced in these growth-restricted cells. Transient expression of exogenous p21 in cells cultured at 35 degrees C led to growth restriction and morphological changes characteristic of senescence. Furthermore, we studied the reversibility of growth restriction induced by the temperature increase. The results showed that senescent morphology and growth arrest were not reversible. In these cells the p21 concentration remained high and p34cdc2 remained undetectable. This indicates that p21 accumulation might be responsible for the maintenance of senescence. Our findings provide information on the use of growth restriction of immortalized fibroblasts induced by a temperature shift as a model system to study senescence.

Elimination of dose limiting toxicities of cisplatin, 5-fluorouracil, and leucovorin using a weekly 24-hour infusion schedule for the treatment of patients with nasopharyngeal carcinoma

BACKGROUND

Cisplatin, 5-flourouracil (5-FU), and leucovorin (PFL) chemotherapy has been reported to be effective in the treatment of cancers but severe mucositis or neutropenia are dose limiting toxicities. This Phase II study evaluated the anticancer effect and the toxicities of a new weekly 24-hour infusional PFL chemotherapy in patients with nasopharyngeal carcinoma (NPC).

METHODS

Forty-two patients with stage IV NPC were studied. Cisplatin 25 mg/m2/d, 5-FU 2200 mg/m2/d, and leucovorin 120 mg/m2/d were adminstered weekly by 24-hour intravenous continuous infusion in an outpatient setting. Clinical response and toxicity were evaluated weekly.

RESULTS

The complete response rate (CR) was 30% and the partial response (PR) rate 60% in the localized previously untreated group. The CR rate was 22.7% and PR rate 45.5% in local recurrent/metastatic group. The overall response rate was 79%. Eighty-one percent of patients who had no previous chemotherapy and 67% of patients who had previous chemotherapy responded to weekly PFL. There were no dose limiting toxicities. No patient had grade 3 or 4 mucositis or neutropenia. Thirty-two patients (76%) had no oral mucositis. Seven patients (17%) had grade 1 mucositis and 3 patients (7%) had grade 2 mucositis.

CONCLUSIONS

Elimination of dose limiting toxicities is possible using a weekly 24-hour infusion schedule of PFL chemotherapy while retaining significant anticancer activity as demonstrated in these patients with advanced NPC. To discover whether this schedule is superior to cisplatin and 5-FU or other PFL chemotherapy regimens requires further investigation.

Molecular cloning and functional expression of Neurospora deoxyhypusine synthase cDNA and identification of yeast deoxyhypusine synthase cDNA

Deoxyhypusine synthase catalyzes the formation of deoxyhypusine residue on the eIF-5A precursor using spermidine as the substrate. We have purified deoxyhypusine synthase from Neurospora crassa to apparent homogeneity (Tao, Y., and Chen, K. Y. (1995) J. Biol. Chem. 270, 383-386). We have now cloned and characterized the deoxyhypusine synthase cDNA using a reverse genetic approach. Conceptual translation of the nucleotide sequence of the cloned 1258-base pair cDNA revealed an open reading frame containing 353 amino acids with a predicted M(r) of 38,985. The deoxyhypusine synthase cDNA was subcloned into the expression vector pQE60 to produce a 40,000-dalton recombinant protein on SDS-PAGE which exhibited deoxyhypusine synthase activity. A GenBank search showed that the Neurospora deoxyhypusine synthase cDNA possessed significant sequence homology to a previously uncharacterized yeast sequence (accession number U00061 (1994)). The yeast sequence encodes a protein of 387 amino acids that shows 69% of total amino acid identity and 80% of total amino acid similarity to the Neurospora enzyme. Sequence alignment and hydropathy analysis suggest that the yeast sequence represents deoxyhypusine synthase.

Effect of granulocyte-macrophage colony-stimulating factor on oral mucositis in head and neck cancer patients after cisplatin, fluorouracil, and leucovorin chemotherapy

PURPOSE

To evaluate prospectively the efficacy of granulocyte-macrophage colony-stimulating factor (GM-CSF) in the reduction of chemotherapy-induced oral mucositis.

PATIENTS AND METHODS

Twenty patients with stage IV squamous cell carcinoma of head and neck were studied. Two-cycles (periods) of identical doses of cisplatin, fluorouracil (5-FU), and leucovorin (PFL) chemotherapy with cisplatin 20 mg/m2/d, 5-FU 800 mg/m2/d, leucovorin 90 mg/m2/d by 96-hour continuous intravenous infusion every 3 weeks were given to each patient. After PFL chemotherapy, GM-CSF 4 micrograms/kg subcutaneously from days 5 to 14 or no therapy was given by a randomized self-controlled crossover study design. Oral mucositis was graded with modified Radiation Therapy Oncology Group criteria.

RESULTS

In the first cycle of PFL chemotherapy, GM-CSF significantly reduced the incidence, mean duration, and mean area under the curve (AUC) of severe oral gross mucositis (grade > or = 3) compared with no therapy. These beneficial effects continued into the second cycle of PFL chemotherapy after crossover to no GM-CSF. The incidence of severe mucositis was reduced when GM-CSF was given in the second cycle of PFL. Analysis of variance indicated significant direct GM-CSF treatment effects on the mean AUC of gross/functional scores and duration of moderate gross mucositis (grade > or = 2) over both periods. There was a significant period effect in favor of giving GM-CSF in the first cycle of chemotherapy.

CONCLUSION

GM-CSF can significantly reduce the severity and duration of chemotherapy-induced oral mucositis after PFL chemotherapy.

Hypertrophic pulmonary osteoarthropathy in nasopharyngeal carcinoma: an early sign of pulmonary metastasis

The aims of this study were to determine the incidence of hypertrophic pulmonary osteoarthropathy (HPO) in nasopharyngeal carcinoma (NPC) and assess its clinical significance. Altogether, 407 NPC patients were reviewed retrospectively. HPO was identified by 99Tcm-methylene diphosphonate bone scans and related clinical and radiographic evidence. Pulmonary metastases, bony metastases and titre of anti-Epstein Barr virus (EBV) immunoglobulin were assessed in patients with and without HPO. The patients had a mean (+/- S.D.) age of 50.4 +/- 12.4 (range 17-73) years. HPO was found in 27 of the 407 (6.6%) NPC patients, among whom 13 (48%) had pulmonary metastases. HPO preceded lung metastases by 7-22 months (14.4 +/- 6 months) in 7 (52%) patients. Six patients had overt lung metastases at the time of the bone scan. No significant difference was found in anti-EBV immunoglobulins between the patients with or without HPO, nor in the incidence of bony metastases between these two groups of patients. HPO should be regarded as an early sign of pulmonary metastases.

Varicella zoster virus infection after allogeneic or autologous hemopoietic stem cell transplantation

A retrospective study was carried out in 161 patients who underwent allogeneic or autologous hemopoietic stem cell transplants. The aim was to determine the frequency, outcome and risk-factors associated with varicella zoster virus (VZV) infection. Post-transplant VZV infection occurred in 29 patients. The median onset of infection was 6.5 months post-transplant, with 82% of cases occurring within the first year. Localized herpes zoster was seen in 27 patients, one patient had varicella, and one patient had simultaneous presentation of both herpes zoster and varicella. No cutaneous or visceral dissemination was noted in the series. Each patient was treated with intravenous acyclovir. Mild complications with postherpetic neuralgia were reported by three patients. There were no deaths from VZV infection. Two risk factors noted to be associated with VZV infection were the presence of graft-versus-host disease in allogeneic transplants and leukemia as the underlying disease in autologous transplants. The overall incidence of post-transplant VZV infection in the present series was relatively low compared with that of other reports involving either allogeneic or autologous bone marrow transplantation.

Analysis of sequence-specific binding activity of cis-elements in human thymidine kinase gene promoter during G1/S phase transition

Expression of thymidine kinase (TK) gene in normal human diploid, cells is both cell cycle and age dependent and appears to be transcriptionally regulated. Several studies have indicated that the G1/S control sequence may reside within the region of about 130 bp upstream of the transcription initiation site. We have previously shown that a trans-acting factor, CBP/tk (CCAAT binding protein for TK gene), binds to either one of the two inverted CCAAT boxes in a cell cycle- and age-dependent manner (Pang and Chen, 1993, J. Biol. Chem., 268:2909-2916). An upstream 25 bp fragment (-109/-84), containing both Yi-like and E2F-like binding sites, has recently been proposed to be essential for the G1/S regulation of human TK gene. To assess the contribution of various cis-elements in human TK promoter to the G1/S regulation, we have examined the binding activity of these cis-elements in the nuclear extracts derived from human IMR-90 cells at low passage number. Our results indicated that no binding activity could be detected using either the 25 bp fragment (-109/-94) or the authentic Yi sequence. However, Yi binding activity was observed in SV-40 transformed IMR-90 cells. In contrast, the 28 bp fragment (-91/-64) that contains the distal inverted CCAAT box exhibited a strong binding in serum-stimulated young IMR-90 cells. The binding of CBP/tk to the 28 bp fragment was abolished by a single base mutation in the CCAAT box. The CBP/tk binding of the 28 bp fragment could not be displaced by either the 25 bp fragment or the authentic Yi element. A deletion of the 5'-flanking region of the 28 bp fragment up to 5 bases also abolished the binding activity. The CBP/tk binding in IMR-90 cells was supershifted by antiserum against NF-Ya, but not by antiserum made against p107, pRb, cyclin A, p33cdk2, or p34cdc2. Taken together, our results suggest that the G1/S regulatory cis-element in human TK promoter may be confined only to CBP/tk binding sites.

Rapid activation of the heat shock transcription factor, HSF1, by hypo-osmotic stress in mammalian cells

Osmoregulation is important to living organisms for survival in responding to environmental changes of water and ionic strength. We demonstrated here for the first time that exposure of HeLa cells to a hypotonic medium (30% growth medium and 70% water) prominently induced the binding activity of the heat shock transcription factor (HSF). Pretreatment of cells with cycloheximide did not inhibit the induction of HSF-binding activity, indicating that the mechanisms of induction are independent of new protein synthesis. The magnitude of hypo-osmotic stress-induced HSF-binding activity was comparable with that induced by heat shock. The induction, as monitored by gel-mobility-shift assay, occurred within 5 min of hypo-osmotic stress and persisted at least up to 4 h in HeLa cells under the hypotonic conditions. Addition of sorbitol to the hypotonic medium abolished HSF activation. Hypo-osmotic stress-induced HSF binding could also be demonstrated in HeLa cells maintained in simple sorbitol solution by decreasing the sorbitol concentration from 300 mM to 200 mM or less. Competition analysis suggests that the effects of hypo-osmotic stress on HSF-binding activity was specific. Cross-linking experiments and Western-blot analysis demonstrated that hypo-osmotic stress induced trimerization of human heat shock factor 1 (HSF1) in intact HeLa cells, suggesting that trimer formation of HSF1 was responsible for inducing HSF-binding activity in hypo-osmotically stressed cells. However, unlike heat shock response, the activation of HSF by hypo-osmotic stress did not lead to accumulation of hsp70 mRNA in HeLa cells.

Purification of deoxyhypusine synthase from Neurospora crassa to homogeneity by substrate elution affinity chromatography

Deoxyhypusine synthase is an NAD(+)-dependent enzyme that catalyzes the formation of deoxyhypusine residue on the eIF-5A precursor by using spermidine as the substrate. Deoxyhypusine synthase bound tightly to 1,12-diaminododecane-agarose and could be eluted selectively by spermidine. This finding enabled us to develop a simple two-column procedure to purify deoxyhypusine synthase from Neurospora crassa to apparent homogeneity. The purified enzyme had a specific activity of 130,000 units/mg of protein, representing a 64,000-fold purification from cell extracts. Size exclusion chromatography indicated that the native enzyme had a molecular mass of 180 kDa. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the pure enzyme showed a single band at the 40-kDa position, suggesting that Neurospora deoxyhypusine synthase is a homotetramer. Deoxyhypusine synthase appeared to be hydrophobic and required non-ionic detergent such as Tween 20 to stabilize the activity. Treatment of the enzyme with sulfhydryl reagents resulted in a complete loss of activity. Inclusion of NAD+ reduced the inactivation rate by manyfold, indicating the presence of -SH groups at or near the active site. Partial amino acid sequences of four peptide fragments that cover about one quarter of the enzyme were obtained for cDNA and genomic cloning work.

Effects of field size on the survival of pig epidermal colony-forming in situ after electron irradiation

The survival of colony-forming cells in pig epidermis after irradiation was measured using different electron field sizes. The sensitivity of the colony-forming cells was characterized by D(o) = 2.5-3.0 Gy. There was an effect of field size, described approximately by: Dose (to give five colonies/cm2) (Gy) = (31 +/- 2) x Area-(0.048 +/- 0.015). The effect of field size was less than found previously using tolerance to skin reactions (area exponent = 0.16). This work indicates for the first time that the effects of different large field sizes in skin can be detected at the level of colony-forming cell survival.

Early irradiation effects observed on magnetic resonance imaging and angiography, and positron emission tomography for arteriovenous malformations treated by Gamma Knife radiosurgery

In 14 patients (7 males and 7 females, age 16-49, mean 29 years), medium-to-large arteriovenous malformations (AVMs; nidus volume 3.5-17.5 cm3, mean 9.4 cm3) were treated by Gamma Knife radiosurgery. Stereotactic MR and conventional angiography were included for targeting to improve targeting accuracy and tissue content in the irradiation volume. Maximum irradiation doses to the nidi were 36-40 Gy (mean 38.9 Gy) and minimum target doses were 18-24 Gy (mean 20 Gy). MR images and MR angiography demonstrated decreasing caliber of feeding vessels and AVM nidus volumes from an early stage, 3 months after radiosurgery, which indicated improvement in cerebral hemodynamics. The improvement correlated well with that observed on PET using [18F]fluorodeoxyglucose (FDG) and with the patients' clinical condition. MR creates an opportunity to monitor treatment effects in a completely noninvasive manner, while conventional angiography remains necessary for verifying complete obliteration of AVMs. More patients and longer follow-ups are needed for clarifying the role of MR techniques in radiosurgery for AVMs.

Expression of the Epstein-Barr virus DNA polymerase in Escherichia coli for use as antigen for the diagnosis of nasopharyngeal carcinoma

Epstein-Barr virus (EBV) encoded DNA polymerase (POL) was cloned and over-expressed in Escherichia coli. Western blot analysis confirmed the presence of antibody to this POL protein in sera from nasopharyngeal carcinoma (NPC) patients. By Western blot analysis, moderate to high concentration of IgG POL-specific antibodies were present in 43 of 48 NPC sera and only 4 of 48 healthy, seropositive controls. The POL-specific IgG antibodies appear as early as stage I of NPC, suggesting that the recombinant POL protein can be a useful diagnostic marker for early diagnosis of the disease. It was also found that human sera containing high titer of cytomegalovirus (CMV) antibodies or herpes simplex virus type 1 (HSV-1) antibodies did not cross-react with the recombinant EBV POL, despite the homology shared by DNA polymerase proteins of these viruses.

Asparagine markedly induces the expression of ornithine decarboxylase gene in transformed mammalian cells but not in their untransformed counterparts

We have previously shown that asparagine alone induces a 10-15-fold increase in ornithine decarboxylase (ODC) mRNA level in DF-40 mouse neuroblastoma cells. The induction is due to an accumulation of ODC mRNA through a post-transcriptional stabilization mechanism (Chen, Z.P. and Chen, K.Y. (1992) J. Biol. Chem., 267, 6946-6951). In the present study we showed that asparagine induced ODC gene expression in v-Ha-ras-transformed 3T3 (ras-3T3) cells but not in 3T3 cells. Other growth related genes including c-src, c-ras, and c-fos were not affected by asparagine in ras-3T3 cells. Southern blot analysis indicated that the pronounced asparagine effect was not due to ODC gene amplification in ras-3T3 cells. The effect of asparagine on the induction of ODC mRNA could account for the significant increases in the ODC activity in ras-3T3 cells. We also examined the effect of asparagine on ODC gene expression in human KD cells and their transformed counterparts. Our findings strongly suggest that the induction of ODC mRNA by asparagine may represent a component of an altered growth regulatory program associated most prominently with cell transformation.

Global change of gene expression at late G1/S boundary may occur in human IMR-90 diploid fibroblasts during senescence

The hallmark of cellular aging is the failure of senescent diploid cells to enter or to complete the S phase of the cell cycle. The cause for such failure may hold the key for our understanding of the molecular basis of cellular aging. We have previously shown that aging of IMR-90 human diploid fibroblasts in culture is accompanied by a five to sevenfold decrease in both thymidine kinase activity and thymidine kinase mRNA level (Chang and Chen, 1988, J. Biol. Chem., 263:11431-11435). To examine whether attenuation of gene expression at G1/S boundary is unique for thymidine kinase or it may involve most, if not all, of other G1/S genes, we compared the expressions of two classes of G1/S genes in young and in old IMR-90 cells following serum stimulation. We found that the expression of all these genes, including thymidylate synthase (TS), dihydrofolate reductase (DHFR), ribonucleotide reductase (PNR), proliferating cell nuclear antigen (PCNA), histone H1, histone H2A + 2B, histone H3, and histone H4, was induced to high levels in young IMR-90 cells but not in old IMR-90 cells. The mRNA levels of all G1/S genes in young cells were more than tenfold higher than that in old cells 12 hr after serum stimulation. The enzymes encoded by TS and DHFR genes and dUTPase also exhibited similar age-dependent attenuation in activities. In contrast, expression of growth-related genes such as eIF-5A, c-Ha-ras, and beta-actin did not show significant differences between young and old cells after serum stimulation. Computer analysis of the promoter region of these G1/S genes revealed an Sp-1 binding site as the most common cis-element. Taken together, our results suggest that the suppression of G1/S gene expressions during senescence may be a global phenomenon and that G1/S genes may be coordinately controlled.

PCR-based cloning of the full-length Neurospora eukaryotic initiation factor 5A cDNA: polyhistidine-tagging and overexpression for protein affinity binding

Eukaryotic initiation factor 5A (eIF-5A) is the only cellular protein known to contain a hypusine residue that is formed by transferring the aminobutyl moiety from spermidine to a specific lysine residue, followed by hydroxylation at the aminobutyl group. A simple PCR-based strategy was developed to obtain a full-length cDNA of Neurospora crassa eIF-5A. The strategy consists of (i) the design of a pair of key primers (21-mer) based on the highly conserved eIF-5A cDNA domains known in other species, (ii) PCR amplification of Neurospora cDNA using the two key primers to obtain the core sequence for the design of core primers, and (iii) combined use of the key primers, core primers and the universal primers, T3 and T7, to amplify the target sequence in a Neurospora cDNA library. The longest cDNA obtained was cloned into pBlueScript phagemid, and sequence analysis indicated that it encodes a polypeptide of 163 amino acid residues with a codon usage preference characteristic of abundant Neurospora genes. The Neurospora polypeptide showed 59% and 67% identity with human and yeast eIF-5A precursor protein respectively. We subcloned the Neurospora eIF-5A cDNA into pQE-30, which introduces six adjacent histidine residues to the N-terminus of the recombinant protein. The resulting plasmid, pQTy21, was overexpressed in Escherichia coli, and the soluble polyhistidine-tagged protein was purified by metal chelation chromatography. We obtained about 60 mg of purified eIF-5A precursor from 1 litre of culture in a single step using a Ni(II)-nitrilotriacetic acid (NTA)-agarose column. The histidine-tagged eIF-5A precursor protein could be recognized by anti-Neurospora crassa 21 kDa protein serum raised against wild-type eIF-5A precursor and could serve as the substrate protein for deoxyhypusine synthase. Using the histidine-tagged recombinant protein and the Ni(II)-NTA-agarose column, we constructed a protein affinity column and demonstrated an affinity binding between eIF-5A precursor and deoxyhypusine synthase in the presence of NAD+. One-step eIF-5A precursor affinity-column chromatography could lead to a 30-fold purification of deoxyhypusine synthase.

Deoxyhypusine synthase assay based on the use of polyhistidine-tagged substrate and metal chelate-affinity chromatography

Hypusine formation on the eukaryotic initiation factor 5A (eIF-5A) precursor is a unique spermidine-dependent post-translational modification that appears to be ubiquitous in eukaryotic cells. In this modification, a specific lysine residue of eIF-5A precursor protein is first converted to deoxyhypusine by an addition of a butylamino group derived from spermidine; the deoxyhypusine residue is then hydroxylated to form hypusine. Deoxyhypusine synthase, an NAD(+)-dependent enzyme, catalyzes the first step of hypusine formation on the eIF-5A precursor. Since deoxyhypusine formation represents one of the most specific polyamine-dependent reactions in eukaryotic cells, the reaction may play an important role in cellular growth regulation. To facilitate the study of the function and significance of deoxyhypusine formation, we have developed a rapid and sensitive assay for deoxyhypusine synthase. The assay relied on the use of hexahistidine-tagged recombinant Neurospora 21-kDa eIF-5A precursor protein as the substrate protein. The radiolabeled polyhistidine-tagged protein, once modified by [3H]spermidine, was separated from free [3H]spermidine by a microscale metal-affinity chromatography in a dot blot filtration apparatus and quantified by liquid scintillation counting. The assay procedure is quick and simple compared to other methods reported in the literature. The sensitivity is limited by the specific activity of [3H]-spermidine in the reaction mixture. The metal-affinity chromatographic assay for deoxyhypusine synthase should facilitate the purification, characterization, and functional studies of this enzyme.

The response of a Bacillus subtilis temperature-sensitive sigA mutant to heat stress

The mutant sigA allele of Bacillus subtilis DB1005 was confirmed to be temperature sensitive (ts) and transferable among strains of B. subtilis by chromosomal transformation and gene conversion. This ts sigA allele had a pleiotropic effect on gene expression of DB1005. The induction of certain heat shock proteins in DB1005 was markedly less significant than that observed in the wild-type strain (DB2) under heat stress. In contrast, some proteins required for coping with oxidative stress and glucose starvation were induced abruptly in DB1005 but not in DB2. Heat induction of the groEL gene in vivo at both transcription and translation levels was much lower in DB1005 than in DB2. Besides, the putative sigma A-type promoter from the groESL operon of B. subtilis was able to be transcribed by the reconstituted sigma A RNA polymerase in vitro at both 37 and 49 degrees C. These results strongly suggest that the expression of the groEL gene of B. subtilis under heat stress is regulated at least in part by sigma A at the level of transcription. Our results also showed that DB1005 did not respond too differently from the wild type to ethanol stress, except after a relatively long exposure.

A phase II study of outpatient chemotherapy with cisplatin, 5-fluorouracil, and leucovorin in nasopharyngeal carcinoma

BACKGROUND

Systemic disease progression occurs in the majority of patients with locally advanced nasopharyngeal carcinoma (NPC). Although a variety of chemotherapeutic drugs have had tumoricidal activity, the roles of chemotherapy and optimal regimens must be further defined. Based on high response rates of Cisplatin, 5-Fluororacil and Leucovorin (PFL) in patients with advanced squamous cell cancers of the head and neck, we tested a new outpatient PFL chemotherapy program in patients with advanced NPC.

METHODS

Patients with NPC and 1) previously untreated, locally advanced disease; 2) local regional recurrence (LR) after radiotherapy; or 3) metastatic disease were eligible for study. Cisplatin 20 mg/m2/d, 5-FU 800 mg/m2/d and Leucovorin 90 mg/m2/d were administered simultaneously by continuous 96-hour intravenous infusion every three weeks. Patients were evaluated for response, survival, and toxicity.

RESULTS

Thirty-five patients were studied. The response rates of PFL therapy were 100% (15% complete response [CR], 85% partial response [PR]) in 20 patients with locally advanced or locally recurrent disease, and 80% (13.3% CR, 67.7% PR) in 15 patients with metastatic disease. The overall median survival was 20 months after therapy (range, 2-21). The median survival rate for previously untreated, locally advanced patients was not reached. The median survival rate for previously treated, local recurrence was 34 months and for metastatic patients was 14 months. Mucositis and leukopenia were the dose-limiting toxicities (20-23%, grade III) and occurred more frequently in patients previously irradiated. No treatment-related deaths occurred.

CONCLUSIONS

Outpatient PFL chemotherapy is active, safe, and convenient for advanced stage nasopharyngeal carcinoma patients, and the overall toxicities are tolerable.

Effects of osmotic stress and growth stage on cellular pH and polyphosphate metabolism in Neurospora crassa as studied by 31P nuclear magnetic resonance spectroscopy

High-resolution 31P-NMR was employed to investigate the effects of growth stage and environmental osmolarity on changes of polyphosphate metabolism and intracellular pH in intact Neurospora crassa cells. Our study showed that changes of these parameters were growth-dependent. The ratio of polyphosphate to orthophosphate in vacuoles increased from 2.4 to 13.5 in N. crassa as cells grew from early log phase to stationary phase. Cytoplasmic pH and vacuolar pH changed, respectively, from 6.91 and 6.49 in early log phase cells to 7.25 and 6.84 in stationary phase cells. Hypoosmotic shock of N. crassa produced growth-dependent changes including: (i) a rapid hydrolysis of polyphosphate with a concomitant increase in the concentration of the cytoplasmic phosphate, (ii) an increase in cytoplasmic pH, and (iii) an increase in vacuolar pH. Early log phase cells produced the most dramatic response whereas the stationary phase cells appeared to be recalcitrant to the osmotic stress. Thus, 95% and 60% of polyphosphate in the early log phase and mid-log phase cells, respectively, disappeared in response to hypoosmotic shock, but little or no hydrolysis of polyphosphate occurred in stationary cells. The cytoplasmic pH and the vacuolar pH increased in response to hypoosmotic shock by 0.4 and 0.53 unit, respectively, in early log phase cells; and by 0.22 and 0.27 unit, respectively, in the mid-log phase cells. In contrast, hypoosmotic shock of the stationary phase cells did not cause any change in intracellular pH. The osmotic stress-induced polyphosphate hydrolysis and pH changes in early log and mid-log phase cells were reversible, suggesting that these changes were related environment osmolarity. Addition of polyamines or basic amino acids which are known to be sequestered in vacuoles did not effect polyphosphate metabolism.

Neurite outgrowth and protein phosphorylation in chick embryonic sensory ganglia induced by a brief exposure to 12-O-tetradecanoylphorbol 13-acetate

An exposure to 12-O-tetradecanoylphorbol 13-acetate (TPA) at 20 nM for as short as 30 min was sufficient to elicit neurite outgrowth from explanted chick embryonic sensory ganglia. Attachment of the ganglia to the collagen-coated substratum during exposure to TPA was essential for subsequent neurite outgrowth. Pulse-labeling with [35S]-methionine indicated no significant difference in protein synthesis between control and TPA-treated ganglia. In vitro phosphorylation assay revealed a prominent protein kinase C substrate with an apparent molecular mass of 66,000 dalton (66 kDa) in chick embryo ganglia extracts. Treatment of intact ganglia with TPA for 30 min also specifically stimulated the phosphorylation of the same protein. When staurosporine, a potent inhibitor of protein kinase C, was present during TPA treatment, both neurite outgrowth and the phosphorylation of the 66-kDa protein were blocked. Biochemical analysis of the phosphorylated 66-kDa protein indicated that (1) phosphorylation was only in serine residue, (2) the pI value was 4.5, (3) after V8 protease digestion, two phosphorylated peptide fragments, 6.0 and 7.5 kDa in size, were produced, and (4) it cross-reacted with an antiserum raised against a 66-kDa neurofilament subunit from rat spinal cord. These results suggest that early activation of protein kinase C and the phosphorylation of the 66-kDa protein may be involved in neuritogenesis.