Pharmacokinetics of 5-fluorouracil in patients heterozygous for the IVS14+1G > A mutation in the dihydropyrimidine dehydrogenase gene

5-Fluorouracil (5FU) and capecitabine are two of the most frequently prescribed chemotherapeutic drugs for the treatment of patients with cancer. Administration of test doses of 5FU to eight patients heterozygous for the IVS14+1G > A mutation and five control patients showed that the AUC and clearance were weak parameters with respect to the identification of patients with a DPD deficiency. However, highly significant differences were observed for the terminal half life of 5FU between DPD patients and controls. Thus, a DPD deficiency could be predicted from 5FU blood concentrations measured after the administration of a test dose of 5FU.

Final results of a prospective multicenter study on the prevalence and genotype/phenotype correlation of the dihydropyrimidine dehydrogenase (DPD) gene exon-14 skipping mutation in patients treated with 5-fluorouracil (5-FU) chemotherapy

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Background: DPD represents the initial and rate-limiting enzyme in the catabolism of 5-FU. Deficiency of DPD has been linked to toxic side effects of 5-FU. The most common mutation of the DPD gene resulting in severe DPD deficiency is a G to A mutation in the GT 5’-splice recognition site of intron 14 (exon 14 skipping mutation). The corresponding mRNA lacks exon 14 and the enzymatic activity of the translated DPD protein is virtually absent. In a clinical setting heterozygous and homozygous carriers are being observed. Methods: We developed an RT-PCR based assay suitable for routine identification of the exon 14 skipping mutation. From February 2001 to October 2004 we performed an open, uncontrolled, prospective multicenter study to evaluate the prevalence and genotype/phenotype correlation of the exon 14 skipping mutation in patients treated with 5-FU chemotherapy. 1455 patients from 70 clinical centers in Germany were included in the study. Results: We identified 15 heterozygous carriers confirming a prevalence of 1% in the Caucasian population. For the analysis of 5-FU related toxicity WHO grades were ranked with a toxicity index revealing a significant higher toxicity in heterozygous compared to wildtype patients (p<0.0001). 50% of the heterozygote patients subsequently were treated with reduced doses of 5-FU. Nonetheless the positive predictive value of the screening test was still 50% indicating a strong correlation between genotype and phenotype. To identify patients in risk of severe 5-FU related toxicity we performed 5-FU pharmacokinetics in 12 heterozygous patients and 8 wildtype patients. All heterozygous patients showed a pathological 5-FU half-life with broad variations after intravenous bolus application of 450 mg/m2 5-FU while 75% of the wildtype controls had physiological results. Conclusions: We conclude that routine testing for the exon 14 skipping mutation and additional 5-FU pharmacokinetics for heterozygous patients prior to 5-FU treatment is an important step towards individually tailored therapy in cancer patients.

[Table: see text]

Comparison of mRNA expression levels determined with TaqMan and competitive template RT-PCR

Two methods for measurement of thymidylate synthase (TS) and dihydropyrimidine dehydrogenase (DPD) mRNA expression were compared. Although the relative mRNA levels compared to beta-actin measured with competitive template RT-PCR were different from the data obtained with a TaqMan based PCR, a significant correlation between the two assays was found.

Circadian variation of dihydropyrimidine dehydrogenase mRNA expression in leukocytes and serum cortisol levels in patients with advanced gastrointestinal carcinomas compared to healthy controls

PURPOSE

The activity of dihydropyrimidine dehydrogenase (DPD) - the rate-limiting enzyme in fluorouracil (5-FU) catabolism - has been reported to vary according to the time of day. On the basis of this data, so-called chronomodulated chemotherapy regimens with variable-rate infusions of 5-FU have been investigated in the treatment of advanced colorectal cancer. Recent results suggest lower toxicity of 5-FU by chronomodulated application. However, the pattern of circadian DPD activity levels have been shown to vary considerably.

METHODS

We, therefore, studied the circadian changes in mRNA expression of DPD in leukocytes of ten patients with advanced gastrointestinal carcinomas prior to chronomodulated 5-FU-based salvage therapy and in 5five healthy controls. Simultaneously, we measured serum cortisol levels (SCL) to evaluate the endogenous circadian hormone rhythm.

RESULTS

SCL displayed a consistent circadian rhythm with the mean peak value of serum cortisol at 8 a.m. and the mean trough value at 11 p.m. both in patients and in controls. However, mean minimum-maximum serum cortisol differences of SCL were significantly lower in patients compared to controls. In the 5fivehealthy controls, a trend towards a circadian rhythm of DPD mRNA expression was observed with the peak of expression at 5 a.m. which was significantly different from the trough at 2 p.m. ( P<0.005 Mann-Whitney-Wilcoxon test). When each control was studied separately, only two individuals showed circadian variations that could be fitted to a cosine wave ( P=0.001, P=0.014, Cosinor analysis). In contrast, DPD mRNA expression in patients with advanced gastrointestinal carcinomas did not demonstrate any consistent circadian rhythm. Pairwise comparisons of groups of DPD mRNA levels at different times of the day did not show significant differences.

CONCLUSIONS

In conclusion, our analysis of DPD mRNA expression in leukocytes from healthy controls demonstrates first evidence for a circadian DPD mRNA expression periodicity. In patients with advanced gastrointestinal carcinomas, however, this rhythm seems to be disturbed although circadian endogenous cortisol secretion pattern is maintained.

Prevalence of a common point mutation in the dihydropyrimidine dehydrogenase (DPD) gene within the 5'-splice donor site of intron 14 in patients with severe 5-fluorouracil (5-FU)- related toxicity compared with controls

Deficiency of dihydropyrimidine dehydrogenase (DPD), the rate-limiting enzyme in 5-fluorouracil (5-FU) catabolism, has been linked to toxic side effects of 5-FU. The most prominent mutation of the DPD gene resulting in severe DPD deficiency is a G to A mutation in the GT 5'-splice recognition site of intron 14 (exon 14-skipping mutation). The corresponding mRNA lacks exon 14, and the enzymatic activity of the translated DPD protein is virtually absent. We developed a reverse transcription-PCR-based assay suitable for routine identification of the exon 14-skipping mutation and screened a control cohort of 851 Caucasian individuals as well as a cohort of 25 cancer patients reported by their physicians to have suffered from WHO grades 3-4 toxicity upon 5-FU chemotherapy. Within the control cohort, in total, eight heterozygotes were detected (0.94%): one heterozygote in 51 healthy donors, (1.96%); five heterozygotes in 572 hospital patients (0.87%); and two heterozygotes in 228 colorectal tumor patients (0.88%). Among the 25 patients with severe 5-FU-related toxicity, 5 (20%) were heterozygous and 1 (4%) was homozygous for the exon 14-skipping mutation. All six patients had experienced WHO grade 4 myelosuppression. Lethal outcome was seen in the homozygous and two of the heterozygous cases. We conclude that carriers of the DPD exon 14-skipping mutation are at significantly increased risk to experience life-threatening myelosuppression upon 5-FU treatment, even when the allelic status is heterozygous. These data lead us to suggest routine testing for the exon 14-skipping mutation before 5-FU treatment.

Bispecific antibody-mediated destruction of Hodgkin's lymphoma cells

CD30 is a molecule that is overexpressed on the surface of Hodgkin's lymphoma cells. Therefore, CD30 represents a potential candidate for immunotherapy. In this study, we report the in vitro results of two bispecific molecules (BSMs) that target CD30 to trigger molecules expressed on myeloid effector cells. The first BSM is composed of the Fab' fragment of a CD30-specific antibody, Ki-4, chemically linked to the Fab' fragment of the humanized CD64 (FcgammaRI)-specific antibody, H22 (H22xKi-4). In the second BSM, the H22 Fab' is replaced with the Fab' fragment of the CD89 (FcalphaR)-specific, antibody, A77 (A77xKi-4). Both BSMs were able to bind specifically to lymphoma cell lines expressing CD30. In addition, the H22xKi-4 and A77xKi-4 BSMs were shown to bind cells expressing CD64 and CD89, respectively. Both BSMs mediated potent, dose-dependent antibody dependent cell-mediated cytotoxicity (ADCC) of CD30-expressing tumor cell lines when human monocytes were used as effector cells. In addition, freshly prepared polymorphonuclear leukocytes (PMNs) and effector cells in whole blood were able to mediate the ADCC of targets in conjunction with the A77xKi-4 BSM in some, but not all, experiments. Furthermore, we examined the ability of monocyte-derived macrophages (MDMs) to phagocytose CD30-expressing tumor cell lines in conjunction with the BSM. MDM-mediated phagocytosis was significantly enhanced in the presence of both BSMs. These results demonstrate that targeting lymphoma cells via CD30 to the myeloid high affinity Fc receptor for IgG and to the Fc receptor for IgA results in potent in vitro anti-tumor activity.

Functional significance of NH2- and COOH-terminal regions of staphylokinase in plasminogen activation

Structure/function relationships in the activation of plasminogen with staphylokinase were studied using mutants of recombinant staphylokinase (Sak42D). Deletion of up to 10 NH2-terminal amino acids (Sak42D delta N10) did not affect plasminogen activation, but removal of 11 amino acids completely abolished the ability to activate plasminogen. Elimination of potential plasmin cleavage sites in the NH2-terminal region yielding mutants Sak42D(K8H,K10H,K11H) and Sak42D(K6H,K8H,K11H) did not alter the rate of the exposure of a proteolytically active site (amidolytic activity) in equimolar mixtures with plasminogen, but destroyed the plasminogen activator properties of these muteins. Deleting two residues following the preferred processing site at position 10 (Sak42 delta (K11,G12)) resulted in a mutein also inactive in plasminogen activation. Removal of the COOH-terminal Lys136, yielding Sak42D delta C1, or of Lys135 and Lys136 in Sak42D delta C2 resulted in proteins with strongly reduced plasminogen activation capacity. In contrast, substitution of Lys135 and Lys136 with Ala in Sak42D(K135A,K136A) did not affect activation. Cyanogen bromide cleavage of Sak42D(M26L,E61M,D82E) produced a 61 amino acid NH2-terminal and a 65 amino acid COOH-terminal fragment which did not activate plasminogen, but bound to plasminogen with affinity constants Ka of 4.0 x 10(5) M-1 and 1.4 x 10(7) M-1, respectively (as compared to a Ka of 1.1 x 10(8) M-1 for Sak42D). These results indicate that Lys11 and the COOH-terminal region of staphylokinase play a key role in the activation of plasminogen.

Stalling of Escherichia coli RNA polymerase in the +6 to +12 region in vivo is associated with tight binding to consensus promoter elements

Three synthetic promoters, PS1, PS2 and PS3, which differ in their core promoter elements, were studied in vivo and in vitro. Whereas an increased homology score correlates with higher rates of RNA polymerase binding, it does not correlate with activity in vivo. Permanganate probing in vivo reveals that PS1, which exhibits the lowest homology score, is rate-limited during the early phase of promoter-RNA polymerase interactions. By contrast, PS2 and PS3, with higher homology scores, are limited at a late step involving an open DNA region spanning from +6 to +12, indicating a stalling of RNA polymerase. These complexes disappear upon treatment of cells with rifampicin and are replaced by open complexes covering the start site. Because initiated complexes are selectively insensitive to rifampicin action, this confirms that RNA polymerase stalled at +6 to +12 has initiated RNA synthesis. Kinetic studies indicate that the enzyme is released slowly from this position and that this slow release appears to be responsible for the low promoter activity. For PS3, which exhibits the highest homology score and which binds RNA polymerase most efficiently, the release of the stalled complex is particularly slow. PS3 is found to be the weakest of the three promoters in vivo. These results support models in which promoter activity can be determined by various rate limiting steps, including those following the formation of open complexes and even the initiation of RNA synthesis.

Context-dependent effects of upstream A-tracts. Stimulation or inhibition of Escherichia coli promoter function

Phased A-tract sequences were inserted in the upstream region of three synthetic promoters known to encompass different rate-limiting steps within the pathway of RNA polymerase-promoter interaction (Ellinger et al., accompanying paper). Promoter PS1, which is rate-limited in complex formation, was stimulated by A-tracts in vivo. Permanganate probing showed that the stimulation is due to an enhanced ability to compete for limiting RNA polymerase in vivo, leading to the increased formation of open complexes. By contrast, promoters PS2 and PS3, which are rate-limited in steps following open complex formation, were inhibited in vivo by A-tracts. Permanganate probing showed that the inhibition was accompanied by an A-tract-dependent accumulation of stalled initial transcribing complexes. A single A-tract was as effective as three. The phasing of the A-tracts with respect to the core promoter sequence was found to be important for promoter function. The position that caused maximal activation at one promoter caused maximal inhibition at another. These results suggest that the same molecular interaction gives rise to both inhibition and activation. This is likely to be due to facilitated RNA polymerase binding in the presence of A-tracts, which stimulates binding-limited promoters but inhibits promoter function in which polymerase escape and promoter clearance is rate limiting.

Complete nucleotide sequence of plasmid pGB3631, a derivative of the Streptococcus agalactiae plasmid pIP501

The complete nucleotide (nt) sequence of plasmid pGB3631 (5842 nt), a deletion derivative of the Streptococcus agalactiae plasmid pIP501, was determined on both strands. Six open reading frames (ORFs) were found. Five ORFs were responsible for replication, copy-number control and resistance against MLS antibiotics.

High yield production and purification of recombinant staphylokinase for thrombolytic therapy

Recombinant plasmids were constructed in which the signal sequence of the sak42D and the sakSTAR staphylokinase genes were replaced by an ATG start codon and which express staphylokinase under the control of a tac promoter and two Shine-Dalgarno sequences in tandem. Induction of transfected E. coli TGl cells in a bacterial fermentor produced intracellular staphylokinase representing 10 to 15% of total cell protein. Gram quantities of highly purified recombinant staphylokinase were obtained from cytosol fractions by chromatography, at room temperature, on SP-Sepharose and on phenyl-Sepharose columns, with yields of 50 to 70 percent. The material, at a dose of 4 mg/kg, did not produce acute reactions or affect body weight in mice. Intravenous administration of 10 mg SakSTAR over 30 minutes in five patients with acute myocardial infarction induced complete coronary artery recanalization, without associated fibrinogen degradation. However, neutralizing antibodies appeared in the plasma of all patients within 12 to 20 days. Thus, the present expression and purification method for recombinant staphylokinase yields large amounts of highly purified mature protein (approximately 200 mg per liter fermentation broth) suitable for a more detailed clinical investigation of its potential as a thrombolytic agent.

Modulation of the spc operon affects growth and protein secretion in Bacillus subtilis

A proximal segment of B. subtilis secY gene was placed under the control of the inducible spac promoter/Lac repressor system. This fusion was integrated into the chromosomal spc operon of B. subtilis via Campbell-like reciprocal recombination. The growth of the resulting strain was strongly IPTG dependent. With staphylokinase and alpha-amylase as reporter proteins it was found, that the protein secretion capacity of this strain was correlated to the conditions of repression or induction of the chromosomal spac promoter.

RepR protein expression on plasmid pIP501 is controlled by an antisense RNA-mediated transcription attenuation mechanism

Expression of the rate-limiting initiator protein RepR of plasmid pIP501 is controlled by the antisense RNAIII. Mutational alteration of individual G residues within the single-stranded loops of RNAIII led to an increase in copy number. In contrast to the G-rich single-stranded loops, two smaller AT-rich loops of RNAIII were found to be dispensable for its inhibitory function. Reciprocal mutations in the same loop compensated for each other's effect, and a destabilization of the major stem structure of RNAIII also resulted in an increased copy number. These data were consistent with the idea that the interaction of RNAIII with its target starts with the formation of a kissing complex between the single-stranded loops of both molecules. The repR mRNA leader sequence, which includes the target of RNAIII, is able to assume two alternative structures due to the presence of two inverted repeats the individual sequences of which are mutually complementary. In the presence of the antisense RNAIII, one of these inverted repeats (IR2) is forced to fold into a transcriptional terminator structure that prevents transcription of the repR gene. In the absence of RNAIII, formation of the transcriptional terminator is prevented and expression of the essential repR gene can proceed normally. This antisense RNA-driven transcriptional attenuation mechanism was supported by extensive deletional analysis and direct evidence that IR2 functions as a transcriptional terminator.

On the mechanism of the activation of human plasminogen by recombinant staphylokinase

The mechanism of activation of human plasminogen by recombinant staphylokinase (STAR) was studied using the active site titrant p-nitrophenyl-p'-guanidinobenzoate (NPGB). NPGB prevented active site exposure in equimolar mixtures of plasminogen and STAR but reacted stoichiometrically with mixtures preincubated in the absence of titrant. Active site generation occurred progressively, with a marked initial lag phase followed by an exponential growth phase, and was associated with the conversion of single-chain plasminogen to two-chain plasmin. Incubation of mixtures of plasminogen and STAR with catalytic amounts (< 0.2% molar ratio) of preformed plasmin.STAR complex or of urokinase shortened the lag hase, whereas catalytic amounts (5% molar ratio) of the plasmin inhibitor alpha 2-antiplasmin delayed active site generation. The following kinetic model for the activation of plasminogen (P) by STAR (S) fits the experimental data, [formula: see text] and is described by [formula: see text] or [formula: see text] In this model, plasminogen and STAR produce an inactive complex (P.S), in which active plasmin.STAR (p.S) is generated in a rate limiting step, which is accelerated by plasminogen activators and delayed by plasmin inhibitors. At room temperature in a 0.1 M Veronal buffer, pH 8.3, containing 0.1 M arginine, the data are adequately fitted by the integrated equation with k1 = 4.0 x 10(-7) s-1 and k2 = 1.3 x 10(-2) microM-1 s-1. The k1 value could be explained by contamination of the plasminogen preparation with 3 ppm plasmin, converted by S to p.S. It is concluded that STAR activates plasminogen via a mechanism which differs in several essential aspects from that of streptokinase.

Physical and conformational properties of staphylokinase in solution

The structure of staphylokinase has been analyzed by solution X-ray scattering, dynamic light scattering, ultracentrifugation and ultraviolet circular dichroism spectroscopy. Staphylokinase has a radius of gyration of 2.3 nm, a Stokes radius of 2.12 nm and a maximum dimension of 10 nm. The sedimentation coefficient is 1.71 S. These physical parameters indicate that the shape of staphylokinase is very elongated. The protein molecule consists of two folded domains of similar size. The mean distance of the centres of gravity of the domains is 3.7 nm. The mutual positions of the two domains are variable in solution. Thus, the molecule is shaped like a flexible dumbbell. About 18% of the amino acids of staphylokinase are organized in helical structures, 30% are incorporated in beta-sheets and 20% form turns.

Characterization of the minimal origin required for replication of the streptococcal plasmid pIP501 in Bacillus subtilis

By using deletional analysis the origin of replication, oriR, of the streptococcal plasmid pIP501 in Bacillus subtilis has been mapped at a position immediately downstream of the repR gene. Determination of both the right and left border of oriR allowed the definition of a sequence of a maximum of 52 nucleotides which theoretically constitutes the minimal origin of replication. Recently, the start point of leading-strand synthesis of the closely related plasmid pAM beta 1 has been mapped at a position which is located exactly in the middle of this sequence (Bruand et al., 1991). The function of oriR did not depend on its location downstream of the repR gene. Translocation of oriR-containing fragments to other regions of the plasmid proved to be possible. The smallest translocated fragment that still reconstituted autonomous replication was 72bp in size. This fragment was also active in directing the replication of an Escherichia coli plasmid in B. subtilis when the RepR protein was supplied in trans from a repR gene integrated into the host chromosome. The transformation efficiency of plasmids carrying translocated oriR fragments showed a certain dependence on the fragment length and orientation. The DNA sequence of oriR included an inverted repeat, both branches of which appeared to be essential for oriR function. The repeats of oriR shared sequence similarity with a repeat located upstream of promoter pII, which has been suggested to be involved in autoregulation of repR expression.

Suppression of the growth and export defects of an Escherichia coli secA(Ts) mutant by a gene cloned from Bacillus subtilis

A gene library of Bacillus subtilis chromosomal DNA was screened for genes capable of reverting the growth defects of the Escherichia coli secA51(Ts) mutant at 42 degrees C. A B. subtilis gene, designated csaA, was found to phenotypically suppress not only the growth defects of the E. coli mutant, but also to relieve the detrimental accumulation of precursors of exported proteins. The csaA gene encoded a protein of 15 kDa (137 amino acids) and was likely to be the distalmost member of an operon. No similarity to csaA was found among DNA or protein sequences deposited in databases. In contrast to other homologous or heterologous suppressors of the E. coli secA51(Ts) mutation, the csaA gene did not exert pleiotropic effects on either the E. coli secY24(Ts) or lep9(Ts) mutations. However, it restored the ability of a SecB-deficient mutant to grow on complex medium. It is proposed that CsaA serves as a molecular chaperone for exported proteins or alternatively acts by stabilizing the SecA protein.

The amount of RepR protein determines the copy number of plasmid pIP501 in Bacillus subtilis

To prove the hypothesis that the amount of RepR protein is the rate-limiting factor for replication of plasmid pIP501 in Bacillus subtilis, the repR gene was placed under control of the inducible promoter pspac. The plasmid copy number of the pIP501 derivative pRS9 could be deliberately adjusted between approximately 1 and 50 to 100 molecules per cell by varying the concentration of the inducer isopropyl-beta-D-thiogalactopyranoside. Construction of a repR-lacZ fusion proved that the increase in copy number was due to a proportional increase in the amount of RepR protein.

In vitro and in vivo analysis of transcription within the replication region of plasmid pIP501

Derivatives of the conjugative streptococcal plasmid pIP501 replicate stably in Bacillus subtilis. The region essential for replication of pIP501 has been narrowed down to a 2.2 kb DNA segment, the sequence of which has been determined. This region comprises two genes, copR and repR, proposed to be involved in copy control and replication. By in vitro and in vivo transcriptional analysis we characterized three active promoters, pI, pII and pIII within this region. A putative fourth promoter (pIV) was neither active in vitro nor in vivo. We showed that copR is transcribed from promoter pI while the repR gene is transcribed from promoter pII located just downstream of copR. The pII transcript encompasses a 329 nucleotide (nt) long leader sequence. A counter transcript that was complementary to a major part of this leader was found to originate from a third promoter pIII. The secondary structure of the counter transcript revealed several stem-loop regions. A regulatory function for this antisense RNA in the control of repR expression is proposed. Comparative analysis of the replication regions of pAM beta 1 and pSM19035 suggested a similar organization of transcriptional units, suggesting that an antisense RNA is produced by these plasmids also.

Biological activity of mutants of human tumour necrosis factor-alpha

Point mutations in different regions of the tumour necrosis factor-alpha (TNF-alpha) molecule influence anti-tumour cytotoxic/cytostatic activities as well as haemorrhagic tumour necrosis, tumour regression and lethal toxicity in mice. Mutations in the C-terminal region in positions 150 and 155 markedly decrease cytotoxicity for murine L929 fibroblasts and human MCF7 mammary carcinoma cells. Competitive binding experiments with 125I-labelled TNF-alpha revealed that the loss of cytotoxicity is caused by a loss of target cell binding. In contrast to the reduced activity against L929 and MCF7 cells, neither binding to nor cytostatic activity against the human myeloid leukaemia cell lines HL60 and U937 are affected. This target cell type-dependent behaviour is probably due to the fact that L929 and MCF7 cells express different types of TNF receptor compared with myeloid leukaemia cells. While a mutation in position 127 decreases the overall activity of TNF-alpha, a deletion of four N-terminal amino acids does not reduce biological activity. In vivo the TNF mutants differed in their anti-tumour effects and lethal toxicity, but a segregation of anti-tumour activity and toxicity was not observed.

Copy number control of the streptococcal plasmid pIP501 occurs at three levels

Transcriptional analysis of the replication region of plasmid pIP501 has revealed three active promoters. The repR gene which is essential for pIP501 replication was transcribed from promoter pII. A small antisense RNA (136 nt, RNAIII) generated from promoter pIII was complementary to the leader region of the repR mRNA. Introduction of either point mutations or deletions into promoter pIII or RNAIII resulted in a 5-20fold increased plasmid copy number suggesting a negative regulatory function for RNAIII. The copR gene, the complete DNA and amino acid sequence of which is reported, was dispensable for pIP501 replication. However, deletion of the copR promoter pI and/or the copR coding sequence led to a 10-20fold increase in plasmid copy number. This effect was also observed when a -1 frameshift mutation was introduced into the CopR coding region. Mutations in copR and pIII/RNAIII were not additive. It is, therefore, proposed that both components act at the same level of copy number control most likely in a sequential way. A second level of copy number control was found to involve an inverted repeat structure upstream of and overlapping with promoter pII. Destruction of this repeat sequence by deletion caused an increase in copy number 2-3fold higher than that observed for either RNAIII or copR mutations. A working model is proposed how different components of pIP501 interact to regulate its copy number.

Expression and subcellular location of native and mutant hTNF alpha proteins in Escherichia coli

Several mutant hTNF alpha genes were constructed by deletion and stepwise reconstitution of regions coding for C-terminal sequences. The mutant hTNF alpha proteins behaved differently from native hTNF alpha when expressed in Escherichia coli. They were either sensitive to proteolytic degradation or formed insoluble aggregates depending on the strains and conditions used for expression. By contrast, native hTNF alpha was always present in a soluble form and had a tendency to associate with the cytoplasmic membrane. It was even transported to the periplasmic space in E. coli as shown by both cell fractionation and immunoelectron microscopy. The different behaviour of mutant hTNF alpha proteins probably results from a disturbance of protein folding.

Synergistic cytotoxicity of human recombinant tumour necrosis factor alpha combined with microtubule effectors

Combinations of human recombinant tumour necrosis factor alpha (rhTNF alpha) with each of four different agents disturbing the microtubule system of the cellular cytoskeleton were tested for synergistic cytotoxic action against murine melanoma B16K and L-M(S) cells. In addition to the known microtubule effectors colchicine, vincristine, and taxol, the influence of the fluorenone-azo-methine derivative alpha-diphenylene-N-(p-[bis-(beta-hydroxyethyl-amino]-phenyl)- nitrone (DHPN) on the rhTNF alpha cytotoxicity was studied. Applying a novel computer-based isobole method [Suehnel J (1990) Antiviral Res 13:23-40] concentration ranges of synergistic, zero, and antagonistic interaction were found after in vitro combination of rhTNF alpha with each of the drugs tested in a 72-h cytotoxicity assay. In contrast, a 24-h exposure of B16K cells to these combinations still did not inhibit in vitro colony formation to a greater extent than either drug alone. A preliminary in vivo experiment revealed an increased antitumour effect after treatment of established subcutaneous melanoma B16 tumours with a combination of rhTNF alpha and DHPN.

Stabilization of thermally labile alkylcobalamins by a haptocorrin from chicken serum

Binding of neopentylcobalamin and benzylcobalamin to the apoprotein of a haptocorrin from chicken serum has been demonstrated spectrophotometrically. The spectra of the protein-bound cobalamins strongly resemble those of base-on alkylcobalamins and show that when unbound these sterically hindered alkylcobalamins are only approximately 75% (benzyl) and 40% (neopentyl) base-on, at neutral pH and at 5 degrees C. The haptocorrin was found to stabilize the spontaneous thermal decomposition of the neutral species of benzylcobalamin and neopentylcobalamin by 470-fold (3.6 kcal) and 166-fold (3.0 kcal), respectively, relative to the protein-free species. After correction of the activation parameters for the thermal decomposition of the protein-free, neutral alkylcobalamins for the relative proportions of base-on and base-off species, the haptocorrin was found to stabilize the base-on species of both alkylcobalamins by 275- to 1400-fold (approximately 3.3 to 4.3 kcal). From the temperature dependence of the decomposition reactions, the enthalpies of activation are found to be essentially identical for the protein-free and protein-bound species of either cobalamin. Thus, stabilization of the thermal decomposition of these sterically hindered alkylcobalamins by haptocorrin is entirely due to entropic factors.

Immunogold labelling of human IFN alpha 2 and an IFN alpha 1/ alpha 2 hybrid produced by recombinant Escherichia coli

In recombinant Escherichia coli strains the subcellular location of human interferon (IFN) alpha 2 and a hybrid IFN alpha 1/alpha 2 was investigated by immunogold labelling techniques. The gold label was scattered throughout the cytoplasm in cells containing the gene for mature IFN alpha 2 under the control of heterologous staphylokinase sak42D transcription and translation initiation signals. In contrast, in cells containing in addition the sak42D signal peptide coding region in front of the IFN gene, the gold label was found mainly near the cell membrane and in the periplasmic space. Inclusion bodies were identified in cells accumulating IFN in the cytoplasm.

Synergistic cytotoxic effect of human recombinant tumor necrosis factor alpha combined with dihydroambazone

Dihydroambazone (DHA) is a water-soluble derivative of the experimental anticancer drug ambazone. In vitro, a combination of DHA and human recombinant tumor necrosis factor alpha (TNF) exerted a strong synergism of cytotoxicity against both mouse melanoma B16K cells and the TNF-sensitive mouse fibroblast line L-M (S). Furthermore, in a colony-forming assay with B16K cells a combination of TNF and DHA inhibited colony-formation much more severely than either drug alone. An increased antiproliferative efficiency was also confirmed in vivo against established subcutaneous melanoma B16 tumors of C57BL/6 mice.

Temperature-inducible gene expression in Bacillus subtilis mediated by the cI857-encoded repressor of bacteriophage lambda

An efficient system to control the expression of cloned genes in Bacillus subtilis was established by introducing the Escherichia coli bacteriophage lambda cI857 repressor-pR promoter system into this host. A staphylokinase reporter gene (sak42D), which was fused to the lambda pR promoter was constitutively expressed in B. subtilis even when the cI857 gene was present on the same plasmid. S1 nuclease mapping of the transcription start point confirmed that the pR promoter was active in B. subtilis. Constitutive expression under pR-control in B. subtilis was, therefore, likely to result from a lack of repressor formation caused by the inefficiency of cI857 expression signals in the Gram+ host. This lack of repressor synthesis was overcome by fusing the cI857 gene to sak42D transcription and translation signals which have previously been shown to function efficiently in B. subtilis. Plasmids carrying the cI857 gene together with an alpha-amylase-encoding gene (amy) under pR-control mediated temperature-inducible amy expression at 37 degrees C and 42 degrees C. The high repression factor (greater than or equal to 1400) was comparable to the OR efficiencies reported in E. coli.

Molecular analysis of the replication region of the conjugative Streptococcus agalactiae plasmid pIP501 in Bacillus subtilis. Comparison with plasmids pAM beta 1 and pSM19035

The large conjugative plasmid pIP501 was originally isolated from Streptococcus agalactiae. To study the molecular basis of pIP501 replication we determined the nucleotide sequence of a 2.2 kb DNA segment which is essential and sufficient for autonomous replication of pIP501 derived plasmids, in Bacillus subtilis cells. This region can be divided into two functionally discrete segments: a 496 bp region (oriR) that acts as an origin of replication, and a 1488 bp segment coding for an essential replication protein (RepR). The RepR protein, which has a molecular mass of 57.4 kDa, could complement in trans a thermosensitive replicon bearing the pIP501 origin. Chimeric Rep proteins and replicons were obtained by domain swapping between rep genes of closely related streptococcal plasmids belonging to the inc18 group (pIP501, pAM beta 1 and pSM19035). The chimeras were functional in B. subtilis.

Transcriptional start sites of the staphylokinase 42D promoter in E. coli and B. subtilis

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Intracellular expression of hIFN alpha genes in Escherichia coli and Bacillus subtilis directed by staphylokinase signals

Portable expression units for intracellular formation of heterologous proteins in Escherichia coli and Bacillus subtilis were constructed by inserting the transcription and translation initiation signals of the staphylokinase sak42D gene into the polylinker of plasmid pUC18. Fusions with ATG-gene cassettes coding for mature human interferons (hIFN) alpha 1 and alpha 2 resulted in intracellular expression of both proteins in E. coli. The 20 fold lower yield of hIFN alpha 2 was not due to unfavorable mRNA secondary structure formation as ruled out by constructing a hybrid hIFN alpha 1/alpha 2 gene. Intracellular expression of IFN alpha 1 in B. subtilis reached 6 x 10(4) IU/ml. Nuclease S1 mapping of transcriptional start sites revealed differential promoter usage in E. coli and B. subtilis. In E. coli transcription from the sak42D promoter was drastically reduced by by transcription initiating from upstream lac and tet promoters. In contrast, in B. subtilis transcription proceeded exclusively from the sak42D promoter.

Immunoelectron microscopy of Bacillus subtilis cells secreting human interferon alpha 1 or staphylokinase

Post-embedding labelling techniques with colloidal gold-IgG or -protein A complexes were used to determine the subcellular location of IFN alpha 1 and staphylokinase secreted from Bacillus subtilis GB500 cells. Both proteins were present in the cytoplasma and the cell envelope pointing to a posttranslational mode of translocation across the cytoplasmic membrane. 5- to 10-fold higher concentrations of gold particles per 0.1 micron 2 were found on the cell envelope and clustering was observed suggesting preferential regions for secretion sites. Several control experiments ensured the specificity of the labelling data.

Secretory expression in Escherichia coli and Bacillus subtilis of human interferon alpha genes directed by staphylokinase signals

A DNA segment covering the signal sequence coding region, the ribosome binding site, and the promoter of the staphylokinase (sak) 42D gene (Behnke and Gerlach 1987) was cloned into pUC19 to form a portable expression-secretion unit (ESU). Fusion of human interferon alpha 1 (hIFN alpha 1) and hybrid hIFN alpha 1/2 genes to this sak ESU resulted in secretory expression of the two gene products in both Escherichia coli and Bacillus subtilis. While most of the IFN alpha was exported to the periplasmic space of E. coli, about 99% was secreted to the culture medium by recombinant B. subtilis strains. The total yield in E. coli was 1.2 x 10(5) IU/ml. This level of expression and export led to instability of the recombinant strains that was spontaneously relieved in vivo by inactivation of the sak ESU through insertion of an IS1 element. No such instability was observed with B. subtilis although expression and secretion levels reached even 3 x 10(6) IU/ml. Proteolytic degradation of IFN alpha by extracellular proteases was avoided by a combination of constitutive expression and secretion during the logarithmic growth phase and the use of exoprotease-reduced host strains. The IFN alpha 1 protein purified from B. subtilis culture supernatant was correctly processed, carried the expected 11 amino acid N-terminal elongation that resulted from DNA manipulations and proved to be homogenous in Western blotting experiments. The same recombinant plasmid that directed efficient secretion of hIFN alpha 1 in B. subtilis gave poor yields when introduced into Streptococcus sanguis.

[The use of phage lambda promotors for expressing genes of secreted proteins in Bacillus subtilis cells]

At was shown with the help of promoterless alpha-amylase and staphylokinase genes that lambda PR and lambda PL promoters could be used in Bacillus subtilis. Promoters strength was compared to promoter of alpha-amylase gene, this enabled to order the promoters in a row: PAA greater than lambda PR greater than lambda PL. The lambda PR promoter region was controlled by temperature in E. coli cells only, but not in B. subtilis, therefore, the active lambda C1857 gene product was not produced in B. subtilis cells. The lambda PR promoter is used by B. subtilis at a later growth stage than PAA and the lambda PL promoter at a still later stage than lambda PR. The data enables lambda PR to be considered as quite useful for Bacilli.

Purification and characterization of the bacterial plasminogen activator staphylokinase secreted by a recombinant Bacillus subtilis

A gene coding for the bacterial plasminogen activator staphylokinase (SAK) was cloned from Staphylococcus aureus bacteriophage 42D into an exoprotease reduced mutant strain of Bacillus subtilis (1). Yields of up to 50 mg SAK per litre of culture supernatant were obtained depending on the medium used. SAK purified by ion exchange chromatography and gel filtration had a specific activity of 16,000 units/mg protein. Isoelectric focusing of the purified SAK revealed heterogeneity with respect to the isoelectric points. Four different SAK proteins were identified among which the majority fraction had an IEP of 6.3 and a N-terminal amino acid sequence of NH2-Lys-Gly-Asp ... This N-terminus was 10 amino acids downstream of the expected signal peptide cleavage site beyond AA 27. It resulted most likely from a postsecretory proteolytic modification of the transiently appearing and correct processing product. In contrast to other plasminogen activators SAK was found to be resistant to proteolytic inactivation by plasmin.

Expression and secretion of interferon-alpha 1 by Streptomyces lividans: use of staphylokinase signals and amplification of a neo gene

A gene coding for mature human interferon, IFN-alpha 1, fused to the expression and secretion signals of a staphylokinase gene (sak) derived from Staphylococcus aureus phage 42D, was inserted into the Streptomyces promoter probe vector pIJ487. Streptomyces lividans transformed with the recombinant plasmid (pMG341) secreted biologically active IFN-alpha 1 into the culture medium. Expression of the IFN-alpha 1 gene was at least on the translational level directed by the sak signals since numerous upstream stop codons would have prevented the formation of a fusion protein. Long-term continuous chemostat cultivation under various limitation conditions was used to select clones with an IFN-alpha 1 yield increased about 60-100-fold (1-2 x 10(5) IU/ml). The increase in IFN-alpha 1 formation was accompanied by spontaneous amplification of the adjacent neo gene, but not of the remaining plasmid DNA. Examination of the DNA sequence around the endpoints of the amplified region revealed almost identical stem-loop structures followed by an octanucleotide direct repeat.

Cloning and expression in Escherichia coli, Bacillus subtilis, and Streptococcus sanguis of a gene for staphylokinase--a bacterial plasminogen activator

The gene coding for the bacterial plasminogen activator staphylokinase was cloned from the Staphylococcus aureus phage 42D, a serogroup F phage used for lysotyping, onto the standard Escherichia coli plasmid vector pACYC184. The coding and flanking sequences of the sak42D gene were largely identical to those of a sak gene cloned from the serologically different S. aureus phage SøC (Sako and Tsuchida 1983). Subcloning of a 2.5 kb phage 42D DNA fragment onto plasmid pGB3631 allowed the sak42D gene to be introduced into the gram-positive hosts Bacillus subtilis and Streptococcus sanguis. The sak42D gene was expressed and secreted most efficiently by B. subtilis cells (25 micrograms/ml of culture supernatant) reduced in exoprotease production. In this host expression and secretion of Sak was initiated at the early growth phase and continued through the logarithmic phase. Formation of Sak was, however, also observed with the other cloning hosts. The Sak elaborated by the heterologous hosts was serologically identical with authentic Sak derived from S. aureus.

[Vector plasmids and the strategy of molecular cloning for streptococci]

The experiments on elaboration of gene engineering methodology for streptococci are described. Two vectors were constructed for DNA cloning in streptococci on the basis of plasmids pSM19035 and pIP2501. Some of the plasmids occurred to be valuable vectors for molecular cloning in bacilli. Peculiarities of the transformation mechanism in streptococci were found to impede the molecular cloning. The recombination technique of cloning was successfully used in the streptococcal system.

Isolation of a putative nicotinic acetylcholine receptor from the central nervous system of Locusta migratoria

The alpha-bungarotoxin binding component from locust central nervous tissue was solubilized and purified by affinity chromatography on alpha-bungarotoxin Sepharose 4B. On sucrose density gradients containing Triton X-100, the toxin binding site sedimented with an apparent sedimentation coefficient of about 10 S. As revealed by sodium dodecylsulfate polyacrylamide gel electrophoresis, the purified receptor protein was composed predominantly of 65,000 molecular weight polypeptides.

Broad geographical distribution of a cytotoxin gene mediating beta-hemolysis and bacteriocin activity among Streptococcus faecalis strains

Conjugative hemolysin-bacteriocin plasmids were isolated from Streptococcus faecalis var. zymogenes strains of diverse geographical origins. Cloned DNA fragments containing the hemolysin-bacteriocin gene(s) from one of these plasmids (pAD1) hybridized to two EcoRI fragments of identical size from each of the five plasmids examined. Results of hybridization experiments in which total plasmid DNA was used suggested that the plasmids shared extensive homology. Two of the plasmids, pAD1 from strain DS16 (Ann Arbor, Mich.) and pAM gamma 1 from strain DS5 (Miami, Fla.), were 100% homologous and had identical EcoRI restriction patterns (eight fragments each). There was no detectable homology between the plasmid-mediated hemolysin determinants of S. faecalis and DNA from other beta-hemolytic streptococci (Lancefield groups A, B, F, or H).