Lactacystin-induced apoptosis of cultured mouse cortical neurons is associated with accumulation of PTEN in the detergent-resistant membrane fraction

The tumor suppressor function of PTEN is attributed to its phospholipid phosphatase activity that dephosphorylates the plasma membrane phosphatidylinositol-(3,4,5)-triphosphate [PtdIns(3,4,5)P3]. Implicit in this notion is that PTEN needs to be targeted to the plasma membrane to dephosphorylate PtdIns(3,4,5)P3. However, the recruitment of PTEN to the plasma membrane is not fully understood. Here, we demonstrate PTEN accumulation in the detergent-insoluble fraction of neuronal cells in response to treatment by the proteasome inhibitor lactacystin. First, lactacystin induces apoptosis and the activation of caspase-3 in cultured cortical neurons. Second, PTEN undergoes proteolysis to form a truncated 50-kDa form that lacks parts of its C-terminal tail. Third, the truncated PTEN is stably associated with the detergent-insoluble fraction in which the plasma membrane marker protein flotillin-1 resides. Taken together, our results suggest that truncation and accumulation of PTEN to the detergent-insoluble membrane fraction are two events associated with the apoptotic signals of the proteasome inhibitor in cortical neurons.

Resolution of adefovir-related nephrotoxicity by adefovir dose-reduction in patients with chronic hepatitis B

BACKGROUND

Chronic hepatitis B patients (CHB) treated with adefovir were followed up to evaluate nephrotoxicity and its outcome.

AIM

To assess the incidence of renal dysfunction during adefovir therapy in Asian patients and factors associated with it, and evaluate strategies to improve adefovir-related renal dysfunction and their impact on viral suppression.

METHODS

Chronic hepatitis B clinic patients from a tertiary hospital on adefovir treatment, with their clinical and laboratory parameters were extracted from the hospital electronic clinical database in an observational study design. Patients were excluded if they had liver/renal transplant, baseline renal impairment or were on dialysis. Adefovir-related renal dysfunction was defined as adefovir-related abnormal serum creatinine (ARASC) > 125 μmol/L (males), >90 μmol/L (females); adefovir-related abnormal GFR <60 mL/min; and adefovir-related increased serum creatinine >0.5 mg/dL, without other known causes of nephrotoxicity.

RESULTS

A total of 271/383 adefovir-treated patients were suitable for analysis and 33(12%) patients developed abnormal serum creatinine. Cumulative increase in proportion of patients with ARASC was 33.8% and GFR ≤60 mL/min was 38.3% by 6 years, while serum creatinine increase ≥0.5 mg/dL was 21.48% by 5 years. Using multivariate analysis, the only independent baseline predictor of ARASC was GFR ≤76.1 mL/min. Patients who had ARASC had similar levels of viral suppression to those who did not have ARASC. Those who had ARASC either continued adefovir (24%), switched therapy (24%) or had adefovir dose reduction (52%). ARASC resolved and GFR normalised in almost all patients after either switching therapy or reducing adefovir dose, with no difference between the two strategies (P = 0.737). Those with adefovir dose reduction had no significant increase in HBV DNA (P = 0.170).

CONCLUSIONS

Adefovir-related renal dysfunction occurred in a significant number of adefovir-treated patients, but reduction of the dose led to renal improvement without compromising treatment efficacy.

Germ line MLH1 and MSH2 mutations in Taiwanese Lynch syndrome families: characterization of a founder genomic mutation in the MLH1 gene

This multicenter study evaluated the mutation spectrum and frequencies of the MLH1 and MSH2 genes and determined the occurrence of large genomic deletions in 93 unrelated Taiwanese families that fulfilled the Amsterdam criteria II by denaturing high-performance liquid chromatography analysis, DNA sequencing for aberrant chromatograms, and multiplex ligation-dependent probe amplification analysis. In total, 38 pathogenic mutations (10 large deletions and 28 point mutations or small deletion/insertions) in the MSH2 or MLH1 gene were identified in 61 of the 93 families (66%). Three of the 10 large deletions and 14 of the 28 point mutations or small insertions/deletions have not been reported elsewhere. Three mutations in the MLH1 gene, the MLH1c.1846_1848delAAG (5 families), deletion exons 11-15 (4 unrelated families), and MLH1c.793C>T (13 unrelated families), accounted for 35% of all cases with pathogenic mutations. Haplotype analysis indicated that mutant c.793C>T alleles were derived from two distinct common founders that might be inherited from a single ancestor of presumably Chinese origin. As a mutation detection strategy for Taiwanese Lynch syndrome patients, we recommend that diagnosis starts with screening for large genomic deletions and continues by screening for common mutations in exons 10 and 16 of the MLH1 gene prior to searching for small mutations in the remaining exons.

Sequence confirmation of theEWS-WT1 fusion gene transcript in the peritoneal effusion of a patient with desmoplastic small round cell tumor

Desmoplastic small round cell tumor (DSRCT) is a rare undifferentiated neoplasm. The prognosis is poor, even if therapy is instituted promptly, and thus it is important to differentiate it from other histologically and cytologically similar-looking malignancies of the young adult. We present a case of DSRCT in a 17-yr-old male with disseminated peritoneal disease and peritoneal effusion. The cytology sample showed a malignant small round cell tumor, the classical cytological features of DSRCT, and immunohistochemistry performed in the prepared cell block exhibited an antibody expression profile in keeping with DSRCT. Further material from the effusion was prepared for RNA extraction, following which a reverse-transcriptase polymerase chain reaction (RT-PCR) and sequencing of the t(11;22)(p13;q11 or q12) were carried out. The result showed the presence of the reciprocal translocation and thus confirmed the diagnosis of DSRCT. This case shows how molecular techniques (including sequencing) can be applied to cytology in clarifying and confirming certain difficult diagnosis of undifferentiated neoplasms, DSRCT in this particular case.

Immunocytochemistry versus molecular fingerprinting of metastases

Examination of cytological samples of cancer to suggest a possible primary site of origin is one of the commonest and most difficult tasks of diagnostic cytopathologists. Currently, both cytomorphology and immunocytochemistry are the main approaches to this diagnostic dilemma. We report the application of microsatellite analysis in cytological samples in a patient with a primary colonic tumour and two subsequent lung nodules, which were suspected on CT scans of the chest, and compared the findings with those obtained with conventional immunocytochemistry. The molecular results were in agreement with the radiological impression and conflicted with the immunocytochemistry. We conclude that immunocytochemical and molecular biology approaches to the diagnosis of tumours may give rise to contradictory results.

Glutathione S-transferase (GST) M1 and GST T1 genotypes and hematopoietic effects of benzene exposure

This study investigated whether or not the genotypes glutathione S-transferase theta (GST T1) and mu (GST M1) correlated with low white blood cell (WBC) count found in benzene exposed workers. We found that individuals with genotypes positive for both GST T1 and GST M1 showed the highest prevalence of low WBC [odds ratio (OR) = 4.67, P = 0.046, 95% confidence interval (CI) = 1.02-24.15] when the benzene exposure was high. Multiple logistic regression showed that benzene exposure (OR = 2.81, P = 0.062, 95% CI = 0.96-8.30) was associated with increased OR on low WBC and interactions between the benzene exposure and the genotype of GST T1 were also observed. These observations suggest that GST T1 and GST M1 may play important roles in the biotransformation of benzene, the effect which leads to its hematotoxicity.

Detection of low numbers of neuroblastoma cells in vitro

Neuroblastoma is a tumour derived from the sympathoadrenal progenitors of the neural crest. It is one of the most malignant solid tumours in childhood with an annual incidence of 9.4 per 10(6) children under 15 years of age. Recent studies suggest that immunocytological detection of neuroblastoma cells in bone marrow and circulating neuroblasts during treatment may predict clinical outcome and correlate with tumour relapse. The present methods of diagnosing metastasis in neuroblastoma include histological, biochemical and immunohistological analysis. Morphological distinction between tumour cells and primitive lymphoblasts in bone marrow is often difficult, and these methods may also not always be sensitive enough for early detection of the residual and minimally circulating tumor cells. A sensitive assay for detection of such residual cells using two tissue-specific markers, NFM and SYN, by reverse transcriptase-polymerase chain reaction (RT-PCR) is reported here. Analysis of the specificity of this assay in three neuroblastoma cell lines, namely IMR 32, SK-N-SH and SY5Y showed positive expression while control peripheral blood mononuclear cells (HL 60) were negative. In reconstituted cell spiking tests, this method has the ability to detect 1-10(3) neuroblastoma cell in 10(7) normal peripheral blood mononuclear cells (PBMC), as shown by serial dilution and limiting dilution. The NFM marker was found to be a more sensitive marker. The specificity and sensitivity of this technique makes it suitable for future application in detection of minimally disseminated tumour cells in neuroblastoma patients.

Molecular studies of loss of heterozygosity in retinoblastoma

Retinoblastoma (Rb) is a paediatric intraocular tumour in which predisposition can be inherited. Cases of Rb tumours can be divided into three types: familial cases, sporadic bilateral cases and sporadic unilateral cases. Familial and sporadic bilateral cases are usually categorised as hereditary while sporadic unilateral cases as non-hereditary. In both familial and non-familial forms of Rb, loss of heterozygosity of the Rb locus has been reported although its frequency in tumours has not so far been accurately determined. The cloning of the gene responsible for retinoblastoma (Rb1) has facilitated DNA studies and genetic counselling of patients. We have examined forty-five cases of retinoblastoma at five intragenic sites of the Rb1 locus, namely intron 1/BamH1, intron 17/Xba1, intron 24/TthIII1, intron 25/Dra1 and Rb1.20 VNTR. Thirty-six out of the forty-five cases (80%) were informative for these markers. Comparison of results between genomic DNA from peripheral blood and from tumours revealed that loss of heterozygosity of alleles could be detected in 50% of cases studied in which tumour samples were available. Investigation of parental origin of retained alleles showed that in all these cases, the paternal alleles were preferentially retained. The analysis of the genetic origin of mutations predisposing to retinoblastoma can facilitate new approaches for identifying recessive mutant genes that lead to cancer as well as to provide a conceptual basis for accurate prenatal predictions of cancer predisposition.

p53 gene mutation in cerebral primitive neuroectodermal tumor in Taiwan

p53 mutation has been rarely reported in cerebral primitive neuroectodermal tumors (PNET). To determine the significance of p53 mutations in the development of cerebral PNET, we studied cerebral PNET samples from 14 patients, 8 females and 6 males with a mean age of 38 years (range 10 months to 77 years) who had total or subtotal surgical resection. Histological typing of PNET with neuronal (N) and non-neuronal (NN) differentiation groups revealed 8 and 6 cases, respectively. Six (43%) of the 14 patients had p53 mutation. The p53(+) and p53(-) groups had an age range of 19-77 with a mean of 49 years and 10 months to 57 years with a mean of 30 years, respectively. p53 expression between the PNET-N and PNET-NN groups was 5 of 8 (62.5%) and 1 of 6 (16.7%), respectively. The mutations contained 3 transitions, 2 transversions and 1 frameshift; none of them occurred at the site of 'hot-spot' residues (codons 175, 248, 273). The results suggest that: (1) p53 mutation in cerebral PNET tends to show a higher incidence of neuronal differentiation and occurs in the older age group in Taiwan, (2) there was no difference in survival time between the PNET-N and PNET-NN groups (7 months and 6 months) (P = 0.54), and between p53(+) and p53(-) groups (6 months and 7 months) (P = 0.57), and (3) PNET may be an entity of a heterogenous group of tumors with different genetic mechanisms controlling their trends of differential lineage. Further studies are needed to determine the significance of p53 mutations in PNET development, especially the role of carcinogens in the genesis of PNET in Taiwan.

Occurrence of genetic segregation in a putative haploid strain of Endomyces fibuliger met by spontaneous sectoring of protoplast fusants

Detailed genetic analysis of Endomyces fibuliger, an amylolytic yeast which is homothallic and exists predominantly in the diploid state, has not been performed. From a naturally occurring strain, E. fibuliger 8014 met, a morphological mutant, 193 met, was obtained by u.v. mutagenesis. To obtain a haploid strain suitable for genetic analysis, an intergeneric hybrid between E. fibuliger 193 met and a strain of a closely related dimorphic heterothallic lipolytic yeast, Yarrowia lipolytica, A his1, was produced by mass mating. The intergeneric hybrid was highly unstable in vegetative culture on yeast extract/phosphate/soluble starch/agar media and produced numerous mitotic sectors. Most of the sectors were mitotically unstable. However, one mitotically stable sector, N14i60 met, was obtained which also differed from the strain 193 as gauged by the appearance of DNA bands on pulsed-field gel electrophoresis. The putative haploid strain, N14i60 met, had six bands whilst the mutant 193 met had seven. Ultra-violet treatment of cells of N14i60 met produced 19 auxotrophic mutants. Protoplast fusion between pairs of different mutants showed complementation and the fusants were unstable mitotically and gave unstable aneuploid and stable haploid sectors of parental and non-parental combinations of markers. It is postulated that complementary diploid fusants, which were obtained by protoplast fusion, produced sectors by mitotic non-disjunction. Such a mechanism provides a means to establish a genetic analysis system for E. fibuliger via the parasexual cycle.

Inhibition of platelet-aggregating activity in thrombotic thrombocytopenic purpura plasma by normal adult immunoglobulin G

Plasma from patients with thrombotic thrombocytopenic purpura (TTP) caused the aggregation of autologous and homologous platelets, and effect which was inhibited by normal plasma. IgG purified from seven normal adults at a concentration of 0.7 mg/ml completely inhibited the platelet aggregation induced by plasma obtained from two TTP patients with active disease. The inhibition of platelet aggregation by human adult IgG was concentration dependent, and the inhibitory activity of human IgG was neutralized by rabbit antihuman IgG. Fab fragments inhibited the TTP plasma-induced platelet aggregation as well as intact IgG, whereas Fc fragments had no effect. Platelet aggregation caused by ADP, collagen, epinephrine, or thrombin was not affected by purified human IgG. The prior incubation of IgG with TTP plasma caused a significantly greater reduction of platelet aggregation by TTP plasma than that of IgG and platelet suspension, suggesting that the IgG inhibits TTP plasma-induced platelet aggregation through direct interaction with platelet aggregating factor in TTP plasma. IgG obtained initially from five infants and young children under the age of 4 yr did not possess any inhibitory activity. When one of the children reached 3 yr of age, his IgG inhibited the aggregation induced by one TTP plasma, but not that caused by another plasma. The IgG procured from the same boy at 4 yr of age inhibited the aggregation induced by both TTP plasmas. The IgG purified from the TTP plasma during active disease failed to inhibit the aggregation caused by the same plasma. After recovery, however, the IgG effectively inhibited aggregation. These observations suggest that platelet-aggregating factors present in the TTP plasma are heterogeneous in nature and that the IgG present in the normal adult plasma, which inhibits the TTP plasma-induced platelet aggregation, may be partially responsible for the success of plasma infusion therapy in TTP.

Purification and some properties of a protein obtained from normal human plasma which inhibits the platelet aggregation induced by thrombotic thrombocytopenic purpura plasma

Plasma from patients with thrombotic thrombocytopenic purpura (TTP) caused the aggregation of washed human platelets, which was inhibited by preincubation with normal plasma. Using salt fractionation, ion exchange chromatography, and preparative agarose gel electrophoresis, we purified a protein from normal plasma which inhibited the platelet aggregation caused by TTP plasma. On SDS polyacrylamide gel, the purified inhibitor gave a single band with a M.W. of 150,000. The antiserum against the purified protein neutralized the activity of the inhibitor and formed an identical precipitin line against normal and TTP plasma.