Mechanisms of ventricular fibrillation induction by 60-Hz alternating current in isolated swine right ventricle

BACKGROUND

The mechanisms by which 60-Hz alternating current (AC) can induce ventricular fibrillation (VF) are unknown.

METHODS AND RESULTS

We studied 7 isolated perfused swine right ventricles in vitro. The action potential duration restitution curve was determined. Optical mapping techniques were used to determine the patterns of activation on the epicardium during 5-second 60-Hz AC stimulation (10 to 999 microA). AC captured the right ventricles at 100+/-65 microA, which is significantly lower than the direct current pacing threshold (0.77+/-0.45 mA, P:<0.05). AC induced ventricular tachycardia or VF at 477+/-266 microA, when the stimulated responses to AC had (1) short activation CLs (128+/-14 ms), (2) short diastolic intervals (16+/-9 ms), and (3) short diastolic intervals associated with a steep action potential duration restitution curve. Optical mapping studies showed that during rapid ventricular stimulation by AC, a wave front might encounter the refractory tail of an earlier wave front, resulting in the formation of a wave break and VF. Computer simulations reproduced these results.

CONCLUSIONS

AC at strengths less than the regular pacing threshold can capture the ventricle at fast rates. Accidental AC leak to the ventricles could precipitate VF and sudden death if AC results in a fast ventricular rate coupled with a steep restitution curve and a nonuniform recovery of excitability of the myocardium.

Safety and efficacy of cefpirome in comparison with ceftazidime in Chinese patients with sepsis due to bacterial infections

BACKGROUND

The safety and efficacy of cefpirome (CPM), a fourth-generation cephalosporin, has not yet been studied in an Asian population.

METHODS

Sixty-nine adult Chinese patients with sepsis due to bacterial infections were enrolled in the study and randomly assigned to receive CPM (2 g i.v. every 12 h) or ceftazidime (2 g i.v. every 8 h).

RESULTS

Both groups were comparable in terms of demographic, clinical and microbiological features. The causative pathogen was Escherichia coli or Klebsiella pneumoniae in the majority of microbiologically documented cases. The rates of clinical response (94 vs. 94%) and bacteriological response (65 vs. 68%) were similar in both groups. Similar adverse events, including rashes, gastrointestinal upset and asymptomatic elevation of hepatic enzymes, occurred in a minority of patients in both groups. All events were self-limited after discontinuation of the drugs.

CONCLUSION

CPM is as safe and effective as ceftazidime in the treatment of sepsis due to bacterial infections in Chinese patients.

Mutation analysis of PTEN/MMAC1 in acute myeloid leukemia

Recently, a putative tumor suppressor gene, PTEN/MMAC1, has been identified at chromosome 10q23.3, which encodes a 403 amino acid dual-specificity phosphatase containing a region of homology to tensin and auxillin. Somatic mutations of the PTEN/MMAC1 gene have been identified in a number of cancer cell lines and primary cancers. Mutations in PTEN/MMAC1 are most frequently found in advanced cancers. To evaluate the role of the PTEN/MMAC1 gene in leukemia, bone marrow and/or peripheral blood from 62 acute myeloid leukemia (AML) patients, 5 hemopoietic cell lines (HL60, U937, Raji, KG-1, K562), and 30 normal controls were analyzed. The results showed aberrant PTEN/MMAC1 transcripts in 15 of the 62 (24%) AML patients, 4 of the 5 cell lines (80%), and 4 of the 30 (13%) normal controls. As in our previous study of TSG101, the abnormal transcripts may result from aberrant RNA splicing as evidenced by the presence of both these aberrant transcripts and normal full length transcripts in all specimens examined. Loss of heterozygosity (LOH) analysis and PCR-SSCP of the entire coding region showed that none of the AML cases had LOH or mutation. Only one frameshift mutation at codon 130 (insertion of CCCG) with premature termination of coding sequence was observed in the U937 cell line. Our results indicate that the PTEN/MMAC1 gene may play a role in a small percentage of AML, but its significance needs to be further evaluated.

Dihydrofolate reductase from Kaposi's sarcoma-associated herpesvirus

Kaposi's sarcoma-associated herpesvirus (KSHV) is the first human virus known to encode dihydrofolate reductase (DHFR), an enzyme required for nucleotide and methionine biosynthesis. We have studied the purified KSHV-DHFR enzyme in vitro and analyzed its expression in cultured B-cell lines derived from primary effusion lymphoma (PEL), an AIDS-associated malignancy. The amino acid sequence of KSHV-DHFR is most similar to human DHFR (hDHFR), but the viral enzyme contains an additional 23 amino acids at the carboxyl-terminus. The viral DHFR, overexpressed and purified from E. coli, was catalytically active in vitro. The K(m) of KSHV-DHFR for dihydrofolate (FH(2)) was 2.4 microM, which is significantly higher than the K(m) of recombinant hDHFR (rhDHFR) for FH(2) (390 nM). K(m) values for NADPH were similar for the two enzymes, about 1 microM. KSHV-DHFR was inhibited by folate antagonists such as methotrexate (K(i): 200 pM), aminopterin (K(i): 610 pM), pyrimethamine (K(i): 29 nM), trimethoprim (K(i): 2.3 microM), and piritrexim (K(i): 3.9 nM). In all cases, K(i) values for these folate antagonists were higher for KSHV-DHFR than for rhDHFR. The viral enzyme was expressed at levels two- to tenfold higher than hDHFR in PEL cell lines as an early lytic cycle gene. KSHV-DHFR mRNA and protein appeared from 6 to 24 h after chemical induction of the KSHV lytic cycle. Epitope-tagged KSHV-DHFR and rhDHFR both localized to the nucleus of transfected cells, while other KSHV nucleotide metabolism genes localized to the cytoplasm. DHFR activity was not essential for viral replication in cultured PEL cells. Since hDHFR was not detectable in peripheral blood mononuclear cells (PBMCs), KSHV-DHFR may function to provide increased DHFR activity in vivo in infected cells that have little or none of their own enzyme.

[Analysis of imidacloprid and damanlin by high performance liquid chromatography]

A new method for determination of imidacloprid and damanlin by using HPLC was established. It was carried out on a mu Bondapak C18 column (3.9 mm i.d. x 300 mm) with ACN-MeOH-H2O (60:10:30, V/V) as eluent and detected at 240 nm using photodiode array detector. The results of imidacloprid and damanlin were 3.71% and 15.65% respectively. The standard deviations for imidacloprid and damanlin were 0.88% and 0.76% respectively.

Clinical implications of aberrant TSG101 transcripts in acute myeloblastic leukemia

Tsg101 is a mouse tumor suppressor gene whose homozygous deletion produces transformation of NIH3T3 cells and leads to metastases in nude mice. The human homologue of the gene, TSG101, is localized in chromosome 11p15.1-p15.2. Reduced TSG101 expression may cause the defect of the cell cycle checkpoint that leads to genetic instability and consequently to the progression of neoplasia. Aberrant TSG101 transcript have been identified in many types of cancers, and the relaxation of RNA splicing fidelity may be an onco-developmental marker in cancers and could play a general role in tumorigenesis. In our previous study, smaller TSG101 transcripts were found in AML specimens, hematopoietic cell lines and normal controls. The aberrant transcripts occurred more frequently in the AML cases and cell lines. The patients with aberrant TSG101 transcripts had higher initial white cell count, lower LDH level, and lower complete remission rate after induction chemotherapy. However, further multivariate analysis of clinical data revealed that there was no relationship to the TSG101 aberrant transcripts. The clinical significance of TSG101 aberrant transcript in AML needs further evaluation.

Mutation analysis of PTEN/MMAC 1 in sporadic thyroid tumors

Recently, a putative tumor suppressor gene, PTEN/MMAC1, has been identified at chromosome 10q23.3. This gene encodes a 403 amino acid dual specificity phosphatase containing a region of homology to tensin and auxillin. Somatic mutations of the PTEN/MMAC1 gene have been found in a number of cancer cell lines and primary cancers. Cowden disease, an autosomal dominant harmartoma syndrome associated with thyroid and breast tumors, has been found to be associated with mutations of PTEN/MMAC1 gene. To evaluate the role of the PTEN/MMAC1 gene in sporadic thyroid tumors, we studied 17 sporadic thyroid tumors, of which 12 were papillary thyroid carcinomas, 1 was follicular thyroid carcinoma, 1 was medullary thyroid carcinoma and 3 were thyroid adenomas. Direct sequencing of PCR-amplified products was performed for all nine exons of PTEN/MMAC1. No mutations of PTEN/MMAC1 gene were observed in any of the sporadic thyroid tumors. Our results indicate that the PTEN/MMAC1 gene may not play a major role in sporadic thyroid tumors.

Aberrant transcripts of FHIT, TSG101 and PTEN/MMAC1 genes in normal peripheral mononuclear cells

Aberrant transcripts of FHIT and TSG101 using nested RT-PCR were reported in many human tumours. The role of these aberrant transcripts in tumourigenesis is not clear. We, therefore, analyzed the aberrant transcripts of FHIT, TSG101 and PTEN/MMAC1 in peripheral mononuclear cells of normal individuals using nested RT-PCR to explore the role of these genes in cancer development. The results showed that there are at least five types of aberrant transcripts: type I is the deletion at junction located in-between normal exon and intron; type II has deletion of some bases and subsequent insertion of several bases in the deletion area; type III accommodates splicing donor or acceptor site-like sequence; type IV has homologous sequences near the deleted junction; and type V comprises the homologous sequences at the deletion junction. A normal healthy person can have more than one aberrant transcripts of FHIT, TSG101 and PTEN/MMAC1 genes. The size and the number of the transcripts vary and the diversity is unconstrained. It is not depended on the time, condition of the reaction, or the isolation method. From these results, we suggested that the aberrant transcripts of FHIT, TSG101 and PTEN/MMAC1 genes may be the imperfect products of splicesome which occur one in every thousands, ten thousands or more. As a result, these data implied no direct association between the aberrant transcripts and tumourigenesis.

Molecular characterization of secretor type alpha(1, 2)-fucosyltransferase gene deficiency in the Philippine population

We analyzed the seven mutations which are responsible for the deficiency of the secretor type alpha(1,2)-fucosyltransferase gene product, Se enzyme, in the Philippine population. One hundred and one unrelated Filipinos in Taiwan were studied. A new mutation, a 3-base pair deletion from nt 688 through 690, was found in two (0. 1%) of 202 chromosomes. The frequencies of six other mutated alleles were as follows: 71/202 (35.2%) were cDNA 385 A-->T missensed mutation (se2), 28/202 (13.9%) were C571T nonsense mutation (se3), 16/202 (7.9%) were G849A nonsense mutation (se4), 4/202 (1.9%) were G428A nonsense mutation (se1), and 81/202 (40.1%) were wild-type allele (Se). No C628T nonsense mutations (se5) or fusion genes of pseudogene and FUT2 gene (se 6) were found in this population. For the molecular basis of phenotype Le(a+ b-): eight cases had se2/se2, six cases had se2/se3, two cases had se3/se4, one case was homozygous of se4, one case was se3/se1, and two cases were se2/se7. For the Le(a+ b+) phenotype: four cases had se2/se2, two cases had se2/se3, one case was se3/se3, and one case was se2/se4. For the Le(a- b+) phenotype: 16 cases were Se/Se, 21 cases were Se/se2, six cases were Se/se3, five cases were Se/se4, and two cases had Se/se1. Our results suggest that the genotypes of the alpha(1, 2)-fucosyltransferase gene in phenotypes Le(a+ b+) and Le(a+ b-) are the same. Other factors that play important roles may cause the differences between these two phenotypes. Several hotspot mutations in the alpha(1,2)-fucosyltransferase gene are responsible for the nonsecretor phenotype.

MEQ and V-IL8: cellular genes in disguise?

One of the hallmarks of oncogenic viruses is their ability to subvert the growth regulation and evade immune response of the host. There are a number of tricks devised by various virus families. Oncogenic herpesviruses often accomplish this by encoding homologs of cellular genes involved in these functions. These viral homologs sometimes are hyperactive forms of their cellular counterparts, which function to overtake the cellular pathways, other times serve as decoys to mask the cellular functions. Marek's disease virus (MDV) carries at least two genes in that category. We have previously described Meq protein (MEQ gene product), a transcriptional factor with homology to proto-oncogenes Jun and Fos in the bZIP domain. Meq dimerizes with Jun or Fos and the Meq/Jun heterodimer is able to transactivate promoters with AP-1 site. We show here that Meq and Jun colocalize in living cells, adding to the physiological significance of the dimer formation. In addition, we present data to show that Meq and Jun can functionally complement each other in cis and in trans, using transformation and transactivation assays. Finally we describe the discovery of an IL8 chemokine homolog, designated as v-IL8 (viral IL8) in the MDV genome and discuss its possible function in MDV infection.

Kimura's disease of bilateral upper eyelids: a case report

We present a rare case of Kimura's disease of bilateral upper eyelids. A 41-year-old Chinese male had multiple masses over retroauricular, submandibular regions and bilateral upper eyelids since 13 years previously. Tumor recurred after each surgical excision, chemotherapy and Co 60 radiotherapy. Eosinophilia and elevation of blood immunoglobulin E (IgE) were noted in this admission. We operated on left upper eyelid to relieve the blocking of vision. A diffuse infiltration with numerous fibrotic bands was noted. Histological section showed a lymphoid hyperplasia, remarkable infiltration of eosinophils and proliferation of capillaries. Oral prednisolone 60 mg was given postoperatively. The patient had a satisfactory appearance and a relief of visual block.

Quatrefoil reentry in myocardium: an optical imaging study of the induction mechanism

INTRODUCTION

The "critical point hypothesis" for induction of ventricular fibrillation has previously been extended to infer the coexistence of four critical points, and hence four simultaneous spiral reentries or a quatrefoil reentry, resulting from only one premature stimulus delivered to the same location as the pacing stimulus. An optical imaging technique was used to explore its existence and to study the induction mechanism of this peculiar reentry pattern.

METHODS AND RESULTS

In 16 isolated, Langendorff-perfused rabbit hearts, high-speed optical imaging at 133 or 267 frames/sec was performed to observe the induced response with a unipolar point electrode. A novel quatrefoil-shaped reentry pattern consisting of two pairs of opposing rotors was created by delivering long stimuli during the vulnerable phase. Successful induction occurred in a narrow range of coupling intervals. A dogbone pattern of virtual electrodes was established during the premature stimulus. Propagating wavefronts launched from the virtual anodes immediately after the termination of S2. The alternating blocking and conducting effects of the virtual electrodes, as well as the boundary between virtual cathode and virtual anode, provided the necessary pathways for quatrefoil reentry. Propagation directions of the reentrant spiral wavefronts reversed with a reversal in S2 polarity. Quatrefoil reentries were not sustained and lasted 1 to 4 complete cycles.

CONCLUSION

The initiation of quatrefoil reentry followed anodal- or cathodal-break stimulation as a result of local symmetrical enhancement of the dispersion of tissue excitability. The "critical point hypothesis" provides the minimum topology required for this type of reentry; the "graded response hypothesis" can be viewed as providing a more detailed explanation of how this topology is actually realized. Triggering mechanisms due to the "break" mode of stimulation also posits a new mechanism for defibrillation.

Panoramic optical imaging of electrical propagation in isolated heart

Optical imaging of cardiac transmembrane potential in dye-stained tissue is an emerging technique in cardiac electrophysiology. Despite its widespread application to studies of isolated hearts, it has been applied traditionally to recording only a single view that presents the potential distribution of a fraction of the cardiac surface. This poses a significant limitation in studying whole heart electrophysiology, particularly when large-scale phenomena such as fibrillation and defibrillation are of interest. We have developed a panoramic imaging system based on a high-speed charge-coupled device camera with a maximum imaging speed of 335 frames/s at 128×64 pixels/frame. Our system provides one front view and two back mirror views of isolated hearts, thus extending optical imaging capabilities to record from the entire three dimensional heart surface with only one camera. © 1999 Society of Photo-Optical Instrumentation Engineers.

Allogeneic bone marrow transplantation of chronic myeloid leukemia from an HLA-matched unrelated donor with the beta-thalassemic trait

We report a chronic myeloid leukemia patient who underwent allogeneic bone marrow transplantation from an HLA-matched unrelated donor with the beta-thalassemic trait. The donor was a heterozygote for the -28 A-->G mutation. We examined the recipient's bone marrow and peripheral blood using the polymerase chain reaction (PCR) method to detect the -28 G-->A mutation of the donor type and monitored the sustained engraftment. This case suggests that a donor with the thalassemic trait can be a candidate for matched unrelated bone marrow transplantation for hematological malignancies and that PCR based genetic examination of the thalassemic mutation is a useful tool to detect early engraftment.

Kaposi's sarcoma-associated herpesvirus encodes a bZIP protein with homology to BZLF1 of Epstein-Barr virus

Kaposi's sarcoma-associated herpesvirus (KSHV) is a recently discovered human gamma herpesvirus strongly implicated in AIDS-related neoplasms. We report here the identification in the KSHV genome of a gene for a protein designated K-bZIP and belonging to the basic-leucine zipper (bZIP) family of transcription factors. K-bZIP shows significant homology to BZLF1, which plays a key role in the replication and reactivation of Epstein-Barr virus. K-bZIP is a homodimerizing protein of 237 amino acids with a prototypic bZIP domain at the C terminus. The N-terminal portion of K-bZIP is derived from the K8 open reading frame which, through in-frame splicing, adjoins the ZIP domain. This structure was revealed by rapid analysis of cDNA ends, followed by cloning of the entire cDNA. A 1.35-kb transcript encoding K-bZIP was detected in BCBL-1 cells treated with 12-O-tetradecanoylphorbol-13-acetate. The synthesis of this transcript was blocked by the protein synthesis inhibitor cycloheximide but not by the viral DNA synthesis inhibitor phosphonoacetate, a result which classifies it as an early lytic gene. RNase protection analysis further mapped the major transcription start site for the 1.35-kb K-bZIP mRNA and identified two other splice variants which encode proteins with the N-terminal portion of K-bZIP but lacking the C-terminal ZIP domain. Full-length K-bZIP forms dimers with itself, and the C terminus encompassing the ZIP domain is required for this process. Our studies set the stage for understanding the role of K-bZIP in the replication and reactivation of the KSHV genome.

Excavatolides F-M, new briarane diterpenes from the gorgonian Briareum excavatum

Eight new briarane-type diterpenes, excavatolides F-M (1-8), have been isolated from the gorgonian Briareum excavatum. The structures and relative stereochemistry of these compounds were established by spectral analysis and chemical methods. The cytotoxicity of these compounds toward various cancer cell lines has also been determined.

Kinetics of Kaposi's sarcoma-associated herpesvirus gene expression

Herpesvirus gene expression can be classified into four distinct kinetic stages: latent, immediate early, early, and late. Here we characterize the kinetic class of a group of 16 Kaposi's sarcoma-associated herpesvirus (KSHV)/human herpesvirus 8 genes in a cultured primary effusion cell line and examine the expression of a subset of these genes in KS biopsies. Expression of two latent genes, LANA and vFLIP, was constitutive and was not induced by chemicals that induce the lytic cycle in primary effusion lymphoma (PEL) cell lines. An immediate-early gene, Rta (open reading frame 50 [ORF50]), was induced within 4 h of the addition of n-butyrate, and its 3.6-kb mRNA was resistant to inhibition by cycloheximide. Early genes, including K3 and K5 that are homologues of the "immediate-early" gene of bovine herpesvirus 4, K8 that is a positional homologue of Epstein-Barr virus BZLF1, vMIP II, vIL-6, and polyadenylated nuclear (PAN) RNA, appeared 8 to 13 h after chemical induction. A second group of early genes that were slightly delayed in their appearance included viral DHFR, thymidylate synthase, vMIP I, G protein-coupled receptor, K12, vBcl2, and a lytic transcript that overlapped LANA. The transcript of sVCA (ORF65), a late gene whose expression was abolished by Phosphonoacetic acid, an inhibitor of KSHV DNA replication, did not appear until 30 h after induction. Single-cell assays indicated that the induction of lytic cycle transcripts resulted from the recruitment of additional cells into the lytic cycle. In situ hybridization of KS biopsies showed that about 3% of spindle-shaped tumor cells expressed Rta, ORF K8, vIL-6, vMIP I, vBcl-2, PAN RNA, and sVCA. Our study shows that several KSHV-encoded homologues of cellular cytokines, chemokines, and antiapoptotic factors are expressed during the viral lytic cycle in PEL cell lines and in KS biopsies. The lytic cycle of KSHV, probably under the initial control of the KSHV/Rta gene, may directly contribute to tumor pathogenesis.

A viral gene that activates lytic cycle expression of Kaposi's sarcoma-associated herpesvirus

Herpesviruses exist in two states, latency and a lytic productive cycle. Here we identify an immediate-early gene encoded by Kaposi's sarcoma-associated herpesvirus (KSHV)/human herpesvirus eight (HHV8) that activates lytic cycle gene expression from the latent viral genome. The gene is a homologue of Rta, a transcriptional activator encoded by Epstein-Barr virus (EBV). KSHV/Rta activated KSHV early lytic genes, including virus-encoded interleukin 6 and polyadenylated nuclear RNA, and a late gene, small viral capsid antigen. In cells dually infected with Epstein-Barr virus and KSHV, each Rta activated only autologous lytic cycle genes. Expression of viral cytokines under control of the KSHV/Rta gene is likely to contribute to the pathogenesis of KSHV-associated diseases.

Aberrant TSG101 transcripts in acute myeloid leukaemia

Recently, a tumour susceptibility gene, TSG101, has been identified at chromosome 11p15. A large intragenic deletion of this gene has been demonstrated in primary breast tumours. To evaluate the role of the TSG101 gene in leukaemia, bone marrow and/or peripheral blood from 68 acute myeloid leukaemia patients, five haemopoietic cell lines (HL60, U937. Raji, KG-1, K562) and 30 normal controls were analysed by reverse transcription of the TSG101 mRNA, followed by PCR amplification and sequencing of the products. The results showed aberrant TSG101 transcripts in 24/68 (35%) acute myeloid leukaemia (AML) patients, all of the cell lines (100%) and 3/30 (10%) normal controls. Our study indicated that the abnormal transcripts may have resulted from aberrant RNA splicing as evidenced by these aberrant transcripts. Also, normal full-length transcripts were present in all specimens examined. The aberrant transcript occurred more frequently in the AML and cell lines. However, because aberrant transcripts of TSG101 were also found in the normal controls, the role of TSG101 as a tumour suppressor gene should be evaluated carefully.

Identification of Bacillus cereus by Fourier transform infrared spectroscopy (FTIR)

The objective of this study was to evaluate the potential of Fourier transform infrared spectroscopy (FTIR) for rapid identification of Bacillus cereus isolates. Ten B. cereus group isolates (comprising B. cereus, Bacillus mycoides, and Bacillus thuringiensis strains), five other Bacillus spp., and five non-Bacillus spp. were used. Two types of media, brain heart infusion (BHI) and Trypticase soy agar (TSA), were tested. The results indicated that all B. cereus group isolates produced characteristic absorbance peaks at wave numbers between 1738 and 1740 cm-1. These peaks were not affected by the growth medium. None of the other bacteria tested showed a similar peak after growth on BHI or TSA. Absorbance peaks between 1800 and 1500 cm-1 of members of the B. cereus group had different shapes and sizes, suggesting that FTIR may be useful for rapid identification of species within the B. cereus group.

High prevalence of antibodies to human herpesvirus 8 in relatives of patients with classic Kaposi's sarcoma from Sardinia

A survey for antibodies to a recombinant small viral capsid antigen (sVCA) of human herpesvirus type 8 (HHV-8) was conducted in Sardinia, one of the world's highest incidence areas for classic Kaposi's sarcoma (KS). Prevalence of antibodies to HHV-8 sVCA was greatest in patients with KS (95%), followed by family members (39%) and a Sardinian control population age- and sex-matched to the relatives (11%). Within families, prevalence of antibodies was about equal among spouses, children, and siblings of KS patients, a finding that raises the possibilities of intrafamilial person-to-person or vertical transmission. Antibodies were detected 2-3 times more frequently in males than in females. The data show that prevalence of antibodies to HHV-8 sVCA correlates with the distribution of classic KS in a high- incidence area. Clustering of seroprevalence within some families suggests the presence of familial risk factors for active HHV-8 infection.

Distinct regions of EBV DNase are required for nuclease and DNA binding activities

Epstein-Barr virus (EBV) DNase possesses both endonuclease and exonuclease activities and accepts both double-stranded DNA (dsDNA) and single-stranded DNA (ssDNA) as substrates. To map regions of EBV DNase responsible for nuclease and DNA binding activities, a series of mutant DNase polypeptides was expressed using a bacterial system for the nuclease assay and in an in vitro transcription/translation system to assay binding activity to dsDNA or ssDNA cellulose. The results indicated that the C-terminus of EBV DNase, residues 450-460, is essential for nuclease activity but dispensable for DNA binding. However, deletion of residues 441-470 resulted in the loss of both nuclease and DNA binding activities. Substitution of Phe452 and Val458 led to inactive enzymes. In the N-terminus, deletion of residues 23-28 and residues 7-61 resulted in the loss of nuclease activity but the DNA binding activities of the deleted enzymes were intermediate and low, respectively. Mutation of Leu23 to Gly showed drastically reduced nuclease activity but its DNA binding ability was not affected. Based on the amino acid sequence alignment of various herpesvirus DNases, we chose four highly conserved and two less well conserved regions as controls for mutagenesis studies. These six internal deletion (ID) mutants were prepared using a recombinant PCR method. Each of the polypeptides was expressed in a bacterial system for the nuclease assay and using an in vitro transcription/translation system for the DNA binding assay. DNA binding and nuclease activities of all six internal deletion mutants were abolished, except that mutant ID2, with deletion of residues 138-152, retained an intermediate ability to bind DNA. These data indicate that since mutations at distinct regions within EBV DNase resulted in the loss of nuclease and/or DNA binding activities, it is suggested that these distinct regions are required for maintenance of an intact and highly ordered structure(s) for both activities.

Serologic association of human herpesvirus eight with posttransplant Kaposi's sarcoma in Saudi Arabia

BACKGROUND

This study investigates the association between human herpesvirus eight (HHV8) and Kaposi's sarcoma (KS), the most common cancer occurring in renal transplant recipients in Saudi Arabia.

METHODS

A cross-sectional study of seroreactivity to HHV8 antigens in posttransplant KS patients from a tertiary care hospital in Riyadh, Saudi Arabia, and in control subjects without KS was conducted. Seroreactivity rates were determined using immunoblotting assays to detect antibodies to two lytic cycle HHV8 antigens: p40, an antigen found in infected cells, and sVCA, an HHV8-encoded small viral capsid antigen expressed in Escherichia coli.

RESULTS

Antibodies to HHV8 p40 and sVCA were present in a significantly higher proportion of renal transplant patients with KS (13 of 14 patients) compared to renal transplant patients without KS (5 of 18; P<0.001) and compared to other control individuals (6 of 44; P<0.001). HHV8 seroreactivity was more common among patients with renal failure (28%) than among other control groups (7%).

CONCLUSIONS

The serologic results provide evidence of a strong association between HHV8 and posttransplant KS in Saudi Arabia.