[Comparative studies on the time course of proliferating cell nuclear antigen and bromodeoxyuridine staining pattern in regenerating rat liver cells]

Immunohistochemical staining pattern of proliferating cell nuclear antigen (PCNA) was examined in regenerating rat liver specimens fixed under the various conditions (10% buffered formalin for 6hr, 1% paraformaldehyde for 6hr, 100% methanol for 4hr, 70% ethanol for 6hr). Time course of PCNA staining pattern after hepatectomy in the specimens fixed with 100% methanol or 70% ethanol coincided closely with that of bromodeoxyuridine (BrdU) staining pattern, which is known to be standard marker of cell proliferation. Similar result was obtained in fixation with 10% buffered formalin (10% BF) or 1% paraformaldehyde (1% PFA) when only granular staining pattern of PCNA was evaluated. These findings suggest that granular immunostaining of PCNA in tissue specimens fixed with 100% methanol, 70% ethanol, 10% BF or 1% PFA is useful for evaluating the extent of cell proliferation.

Degradation process of ligand-stimulated platelet-derived growth factor beta-receptor involves ubiquitin-proteasome proteolytic pathway

The platelet-derived growth factor beta-receptor undergoes polyubiquitination as a consequence of ligand binding. We have previously reported that ligand-induced ubiquitination of the receptor plays a negative regulatory role in its mitogenic signaling possibly by promoting the efficient degradation of the ligand-activated receptor (Mori, S., Heldin, C.-H., and Claesson-Welsh, L. (1993) J. Biol. Chem. 268, 577-583). In the present study, we have examined effects of different kinds of cell-penetrating proteasome inhibitors, including substrate-related peptidyl aldehydes, Cbz-Ile-Glu(O-t-Bu)-Ala-leucinal (where Bu is butyl and Cbz is benzyloxycarbonyl) (PSI) and Cbz-Leu-Leu-norvalinal (MG115), and a Streptomyces metabolite lactacystin, on degradation of the receptor in intact cells with the aim of evaluating the role of the receptor ubiquitination in the proteasome-dependent proteolytic process. These proteasome inhibitors were found to considerably inhibit ligand-stimulated degradation of the wild-type beta-receptor; however, their inhibitory effect was not observed when the cells expressing the ubiquitination-deficient mutant beta-receptor were analyzed. These data suggest that the degradation process of the ligand-stimulated beta-receptor involves the ubiquitin-proteasome proteolytic pathway.

Ligand-activated platelet-derived growth factor beta-receptor is degraded through proteasome-dependent proteolytic pathway

The platelet-derived growth factor beta-receptor undergoes polyubiquitination as a consequence of ligand binding. Ubiquitin conjugation to protein is implicated in proteasome-dependent proteolytic pathway for short-lived proteins. In the present study, we have examined effects of different kinds of cell-penetrating proteasome inhibitors, including N-benzyloxycarbonyl-L-isoleucyl-gamma-t-butyl-L-glutamyl-L-alanyl-L-l eucinal (PSI) and a Streptomyces metabolite lactacystin, on ligand-stimulated degradation of the beta-receptor. These proteasome inhibitors were found to considerably inhibit the degradation of autophosphorylated and polyubiquitinated receptors, suggesting the possible involvement of proteasomes in the degradation process of the ligand-activated beta-receptor.

Histochemical properties of intrinsic laryngeal muscles in cats

As one means in elucidating the contractile properties of the intrinsic laryngeal muscles, we examined the histochemical properties of the posterior cricoarytenoid (PCA), thyroarytenoid (TA), lateral cricoarytenoid (LCA), arytenoid (A) and cricothyroid (CT) muscles in cats using the reaction for myosin ATPase following acid and alkali preincubation. The muscle fiber compositions of the intrinsic laryngeal muscles differed not only across the muscles but also across the muscle fascicles within a single muscle. The relative frequency of type-1 fibers was the smallest (9%) in the TA and the largest (45%) in the CT, and that of type-2A fibers was 39-48% in each muscle. The relative frequency of type-2B fibers was the smallest (9%) in the CT and the largest (42-45%) in the TA, LCA and A, and that of type-2C fibers was less than 1.0% in each muscle. Across the muscle fascicles, the TA was the most heterogeneous in muscle fiber distribution. The mediocaudal part of the TA was mainly composed of the muscle fascicles with type-1 fibers, while the laterocaudal and rostral parts of the TA were mostly composed of the muscle fascicles without type-1 fibers. The PCA was the most homogeneous in muscle fiber distribution. Our results demonstrate that the contractile properties of the intrinsic laryngeal muscles differ across the muscles and across the muscle fascicles within a single muscle and suggest that the delicate laryngeal movements are established by the coordinated activities of the intrinsic laryngeal muscle fibers with different contractile properties.

A colorimetric LDH assay for the titration of infectivity and the evaluation of anti-viral activity against ortho- and paramyxoviruses

A rapid and precise screening assay was developed for in vitro evaluation of anti-orthomyxo- and anti-paramyxovirus agents. The procedure is spectrophotometrical assessment for viability of cells via extracellular leakage of lactic dehydrogenase (LDH). HMV-II cells, a human melanoma cell line was found to be suitable for the titration of virus infectivity and screening of anti-viral agents for orthomyxo- and paramyxoviruses. Comparative titration of infectivity of stock viruses by the LDH and the MTT in site reduction of 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) methods with HMV-II cells as well as plaque titration with MDCK, Vero and HeLa cells was carried out. The LDH method was comparable or more sensitive for influenza viruses (FLUV)-A, B, C, parainfluenza viruses (PFLUV)-1, 2 and less sensitive for PFLUV-3, mumps virus (MPSV), measles viruses (MLSV) and respiratory syncytial virus (RSV) than the plaque titration. The 50% effective concentration (EC50) of 1-beta-D-ribofuranosyl-1, 2, 4-triazol-3-carboxamide (ribavirin) and 5-ethynyl-1-beta-D-ribofuranosyl-imidazole-4-carboxamide (EICAR) against orthomyxo- and paramyxoviruses were examined comparatively by the LDH, MTT and plaque reduction (PR) methods. The EC50 values of FLUV-C and PFLUV-1 were able to be evaluated only by the LDH but not by the MTT and PR methods. The LDH method with HMV-II cells simplifies the assay procedure and permits the evaluation of a large number of compounds for anti-orthomyxo- and anti-paramyxoviruses activity in vitro.

The relationships of onset and exacerbation of pustulosis palmaris et plantaris to smoking and focal infections

Clinical data, including focal infection and habitual cigarette smoking, were obtained from 203 male patients with pustulosis palmaris et plantaris (PPP) (age: 43.3 +/- 13.4) and 266 female patients (age: 44.0 +/- 13.7) for the 20 years from 1975 through 1994 to evaluate the relationship between the onset or severity of PPP and smoking. Seasonal incidences of onset were also studied. The incidence of onset of PPP symptoms was highest in June, when it is the most humid in Japan, and lowest in December. The most common infectious disease associated with PPP was tonsillitis. The percentages of heavy smoking (more than 20 cigarettes per day) were 74.7% and 32.9% for male and female patients, while those in the normal control population in Japan were 37.2% and 9.8% for males and females. These results suggest that heavy smoking, tonsillitis, and seasonal factors such as high humidity and high temperature may be related to the onset and exacerbation of PPP.

Inhibition of Ras/Raf interaction by anti-oncogenic mutants of neurofibromin, the neurofibromatosis type 1 (NF1) gene product, in cell-free systems

The neurofibromatosis type 1 (NF1) gene encodes a protein, neurofibromin, containing GTPase-activating protein-related domain (GRD) that stimulates intrinsic GTPase activity of Ras protein. By screening a randomly mutagenized NF1-GRD library in Saccharomyces cerevisiae, we isolated two NF1-GRD mutants (NF201 and NF204) with single amino acid substitutions, which suppress the heat shock-sensitive phenotype of the RAS2(G19V) mutant. The NF1-GRD mutants also suppress the oncogenic Ras-induced transformation of NIH 3T3 mouse fibroblasts (Nakafuku, M., Nagamine, M., Ohtoshi, A., Tanaka, K., Toh-e, A., and Kaziro, Y. (1993) Proc. Natl. Acad. Sci. U.S.A. 90, 6706-6710). In this paper, we investigated the molecular mechanism of inhibition of the transforming Ras-specific function by the NF1-GRD mutants in mammalian cells. In human embryonic kidney (HEK) 293 cells, the mutant NF1-GRDs attenuated the stimulation of mitogen-activated protein kinase by Ras(G12V), but not by platelet-derived growth factor. In cell-free systems, purified recombinant NF1-GRD mutants showed an inhibitory effect on the association of Ras.guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) with Raf at several times lower concentrations than the wild type. Furthermore, it was revealed that the binding affinity of the mutant NF1-GRDs toward Ras.GTP gamma S is approximately 5-10 times higher than the wild type. These results suggest that the mutant NF1-GRDs tightly bind to an oncogenic Ras in its GTP-bound active conformation and block the interaction between Ras and its effector, Raf.

Angioimmunoblastic T-cell lymphoma (angioimmunoblastic lymphadenopathy with dysproteinemia [AILD]-type T-cell lymphoma) followed by Hodgkin's disease associated with Epstein-Barr virus

A patient is described with angioimmunoblastic T-cell lymphoma (AIL) (angioimmunoblastic lymphadenopathy with dysproteinemia [AILD]-type T-cell lymphoma), which was later followed by Hodgkin's disease. At the time of the initial diagnosis, histological examination of a cervical lymph node showed a typical picture of AIL with abundant clear cells which were CD45RO+, CD43+, and CD20-, and there was no evidence of a monoclonal B-cell proliferation by immunohistochemical analysis. In situ hybridization for Epstein-Barr virus (EBV) was negative. Interposed by a bout of recurrence, the patient developed, 16 years later, a left subparotid mass which showed histologic features of Hodgkin's disease, mixed cellularity type. Diagnostic Reed-Sternberg cells and their variants were CD30+, CD15- and CD20+. Neither rearrangement of TCR beta and gamma chain genes nor of immunoglobulin heavy chain and kappa light chain genes was detected in DNA extract from fresh material. In situ hybridization showed the presence of EBV within the Reed-Sternberg cells. The data show that EBV was not etiologically related to AIL in this case. Further, the deficit in cellular immunity that accompanied AIL conceivably permit primary EBV infection or reactivation of latent infection, which eventuated in development of Hodgkin's disease, but the exact pathogenesis remains uncertain.

Ki-1 (CD30) positive anaplastic large cell lymphoma of T-cell phenotype developing in association with long-standing tuberculous pyothorax: report of a case with detection of Epstein-Barr virus genome in the tumor cells

We report a case of CD30 positive anaplastic large cell lymphoma of T-cell phenotype developing in association with long-standing tuberculous pyothorax. Phenotypic analysis showed CD1a-, CD2+, CD3+, CD4+, CD5-, CD8-, CD10-, CD19-, CD20 +/-, CD21-, CD25-, CD56-, T-cell receptor (TCR) alpha/beta antigens-, and HLA-DR+ phenotype. Neither rearrangement of TCR beta and gamma chain genes or of immunoglobulin heavy chain gene was detected in DNA extract from fresh material. The lymphoma cells were also shown to express the latent membrane protein-1 and the Epstein-Barr virus (EBV)-encoded nuclear antigen-2 by immunohistochemistry and EBV-encoded small RNAs by in situ hybridization.

Disorientation of animals in microgravity

Disorientation responses of animals exposed to microgravity produced by parabolic aircraft flights and also in-space experiments were reviewed. Disoriented postures in floating are largely species-dependent. Reflexive lowered tone of gravity-bearing extensor muscles by labyrinthectomy is not seen in mammals (hamster and monkey) and frog, though dorsiflexion of the neck and the trunk is not so remarkable in hamster and monkey as in frog. In weightlessness, fundamental vestibular reflexes may be affected (righting reflex in cat), but coordinated performance can be easily compensated by visual function (mouse, monkey and turtle). In normal birds and fish who can move three-dimensionally in their environments, exposure to parabolic flight microgravity induces irregular tumbling with the eyes open and regular looping with the eyes closed, although the loop direction is the opposite in these two animals; backward (inside) in pigeon and forward (outside) in fish. Most recently, however, it was found that normal fish (goldfish) tumbled backward when observed in prolonged microgravity in space, suggesting that microgravity effects on fish in aircraft-flight parabolas would differ from those in space. Sensory conflicts in normal fish diminish remarkably during 3-4 days of space microgravity, and the cerebellum may be involved in the recovery, lending support to the sensory conflict theory for the genesis of space motion sickness.

Cold preservation-induced changes in oxygen radical generation between parenchymal and nonparenchymal cells in rat liver

Many of the reports implicating the contribution of oxygen radicals to preservation-reperfusion injury have been based largely on indirect experiments demonstrating the effects or the consumption of various antioxidants. Investigations based on the direct measurement of the amounts of oxygen radicals that are actually formed during reoxygenation after preservation have not given satisfactory results. In this study, we attempted direct measurement of H2O2 from hepatocellular mitochondria and superoxide (O2-) from Kupffer cells, using the HRP method and cytochrome c perfusion method, respectively, for quantitative comparison of the cold preservation-induced changes in radical generation activity between these sources. H2O2 generation in mitochondria isolated after 24 h cold preservation decreased to 8% of non-preserved liver, but in the mitochondria isolated from the livers that were reperfused for 30 min after 24 h preservation H2O2 generation recovered to 60%. The respiratory control ratio also decreased significantly after 24 h preservation, and similarly recovered after an additional 30 min reperfusion. By contrast, O2- from Kupffer cells increased in time-dependent fashion until 12 h preservation and decreased after 24 h preservation. Although 12 h preservation did not cause an increase in LDH release, the lipid peroxide in the perfusate significantly increased after 12 h preservation, which indicated the occurrence of lipid peroxidation in the sinusoidal area. These results suggested that mitochondrial H2O2 was dependent upon the activity of respiratory function and so did not cause hepatocellular injury and that O2- from Kupffer cells contributed to oxidative injury to the sinusoidal lining cells. Our data support reports demonstrating the vulnerability of nonparenchymal cells.

Kinetic analysis of impaired work-cost performance in jaundiced rabbit liver

Impairment of energy metabolism was studied in jaundiced rabbit liver by kinetic analysis of energy transfer function. Free cytosolic ADP (ADPf), as calculated from the measured components of the glyceraldehyde-3-phosphate dehydrogenase and 3-phosphoglycerate kinase/lactate dehydrogenase reactions, decreased from the control value of 48.1 to 37.0 microM at 24 h after bile duct ligation. The maximal velocity (Vmax) of ATP synthesis, as measured by state 3 respiration of isolated mitochondria, decreased from the control value of 62.1 to 38.3 nmol ATP synthesized per min per mg mitochondrial protein, while the Michaelis constant for ADP (Km) decreased from the control value of 19.2 to 12.8 microM. ATP synthesis velocity in vivo }v: Vmax/[1 + (Km/[ADPf])], as calculated by Vmax, Km and ADPf, decreased from the control value of 44.4 to 28.5 nmol ATP synthesized per min per mg mitochondrial protein. Delta v/delta ADPf(delta v/delta ADPf: Vmax.Km/(Km + [ADPf])2), which indicates work-cost performance of the liver, decreased from the control value of 0.263 to 0.198. Biochemical output of the liver, as measured by hippurate synthesis from benzoate, decreased from the control value of 98.4 to 32.7 mg/h. These results indicate that synergistic decreases in ADPf, Vmax, v and delta v/delta ADPf take place in the course of deterioration of mitochondrial ATP synthesis and work output in jaundiced liver.

Differences in the interleukin-2 (IL-2) receptor system in human and mouse: alpha chain is required for formation of the functional mouse IL-2 receptor

Reconstitution with mouse interleukin-2 (IL-2) receptor subunits demonstrated that the mouse IL-2 receptor complex was different from the human complex in the alpha chain requirement for the functional mouse receptor complex. The heterotrimeric complex of the mouse exogenous alpha and beta chains and the endogenous gamma chain on mouse lymphoid BW5147 cells showed the ability to bind IL-2 with high affinity, resulting in IL-2-induced tyrosine phosphorylation of a cytosolic tyrosine kinase, JAK3, which is involved in IL-2-dependent signals. Exogenous introduction of the beta chain with the endogenous gamma chain, however, could neither confer appreciable IL-2 binding nor IL-2-induced signal transduction on BW5147 cells, unlike the human beta gamma heterodimer. Mouse spleen CD8+ cells, not having the alpha chain initially, showed IL-2-dependent cell proliferation only when expression of the alpha chain was induced. Collectively, these results illustrate that the functional mouse IL-2 receptor complex necessarily includes the alpha chain, and that the regulation of CD8+ T cell growth during immune reaction depends upon alpha chain expression.

Colocalization of vascular endothelial growth factor (vascular permeability factor) and insulin in pancreatic islet cells

Previously, we found that the islet of pancreas stained with a antibody against the vascular permeability factor (VPF; also known as vascular endothelial growth factor, VEGF) protein. To determine how common this reaction was and whether it was a specific reaction for the islet, we examined its expression and specific cellular localization. Two different antibodies directed against VPF/VEGF peptide revealed an intense reaction for beta-cells in the human islets of Langerhans, and several human beta-cell tumors (insulinomas), but no reaction, were detectable in the vascular endothelium. In the fetal pancreas (second and third trimesters), the VPF/VEGF peptide was detected in immature islets. Northern blot analysis of cell lines derived from rodent insulinomas revealed expression of VPF/VEGF messenger ribonucleic acid. Western blot analysis of conditioned medium from one of these cell lines showed the presence of the released VPF/VEGF protein. These findings indicate that beta-cells have a specific role other than endocrine function in the pancreas. VPF/VEGF in beta-cells may be involved in the maintenance and control of permeability within the islet capillary system.

Impaired proliferation of peripheral B cells and indication of autoimmune disease in lyn-deficient mice

The Src family protein-tyrosine kinase Lyn associates physically with the BCR and has been suggested to play an important role in BCR-mediated signaling. Studies with lyn-/- mice showed that the number of B cells decreased by half in their peripheral tissues. In addition, these B cells do not respond normally to a number of stimuli, including BCR cross-linking and CD40 ligand. Induction of tyrosine phosphorylation on a variety of cellular proteins, such as Vav, Cbl, and HS1, upon BCR cross-linking was also abolished in these B cells. Despite the impaired BCR-mediated signaling, concentrations of IgM and IgA in sera were remarkably elevated, and production of autoantibodies was detected in lyn-/- mice. Histological study showed splenomegaly and enlargement of lymph nodes that became evident with age in the mutant mice. The spleen contained significant number of plasma cells as well as unusual lymphoblast-like cells carrying Mac1 antigen and cytoplasmic IgM. These cells spontaneously secreted a large amount of IgM in vitro. Finally, significant number of lyn-/- mice show glomerulonephritis, an indication of autoimmune disease. From these data, we conclude that Lyn plays a role in signal transduction for not only clonal expansion and terminal differentiation of peripheral B cells but also elimination of autoreactive B cells.

Chimeric TLS/FUS-CHOP gene expression and the heterogeneity of its junction in human myxoid and round cell liposarcoma

Myxoid liposarcomas have a unique and specific t(12;16)q13;p11) chromosomal translocation. The breakpoint has recently been identified and shown to involve the TLS/FUS gene on chromosome 16 and the CHOP gene on chromosome 12. This translocation causes fusion of these genes resulting in the expression of a novel chimeric TLS/FUS-CHOP message. Using the polymerase chain reaction with primer sets derived from sequences of TLS/FUS and CHOP cDNAs, we could amplify three types of the fusion transcripts from seven of seven samples of myxoid and round cell liposarcomas. In six of the seven positive samples, two kinds of chimeric messenger RNAs were found that have been reported previously. However, the last sample had a novel chimeric message that had an extra sequence of 33 bp derived from the TLS/FUS gene. Thus, it was shown that these fusion transcripts had a varying extent of the sequence of TLS/FUS gene incorporated at the site of the fusion. However, the TLS/FUS-CHOP fusion transcripts were not detected in two pleomorphic liposarcomas or in three myxoid variants of malignant fibrous histiocytomas. Our findings indicate that in liposarcomas TLS/FUS-CHOP fusion transcripts have variations at the junction of chimeric messages, which was the case for Ewing's sarcoma. Detection of the chimeric message by reverse transcription polymerase chain reaction was also suggested to be a useful approach for the diagnosis of myxoid and round cell liposarcomas that have (12;16) translocation, and for distinguishing them from pleomorphic liposarcoma and myxoid variant of malignant fibrous histiocytomas.

Constitutive overexpression of the L-selectin gene in fresh leukemic cells of adult T-cell leukemia that can be transactivated by human T-cell lymphotropic virus type 1 Tax

L-selectin is an adhesion molecule of the selectin family that mediates the initial step of leukocyte adhesion to vascular endothelium. Upon cellular activation, expression of the L-selectin gene is downregulated at both the protein and mRNA levels. To understand the mechanism of leukemic cell infiltration into organs, we studied the expression and regulation of L-selectin mRNA in fresh leukemic cells of adult T-cell leukemia (ATL) patients and investigated the response of the L-selectin promoter to human T-cell lymphotropic virus type 1 (HTLV-1) Tax, which is a viral transcriptional transactivator. Flow cytometry showed that L-selectin was expressed on fresh ATL cells along with other activation antigens. Northern blot analysis showed that ATL cells overexpressed that L-selectin mRNA and that the level was aberrantly upregulated after PMA stimulation. Studies using in situ hybridization showed expression of the L-selectin mRNA in the infiltrating leukemic cells in the liver of two ATL patients. Intravenous injection of a rat T-cell line that overexpresses L-selectin showed increased organ infiltration. The induction of Tax expression in JPX9 cells resulted in about a twofold increase in the mRNA expression levels compared with the basal level. Chloramphenicol acetyltransferase (CAT) assay after transient cotransfection showed about a fivefold transactivation of the L-selectin promoter by Tax. The serum level of the shed form of L-selectin was significantly increased in ATL patients (mean +/- SD, 4,215.4 +/- 4,111 ng/mL) compared with those of asymptomatic carriers and healthy blood donors (mean +/- SD, 1,148.0 +/- 269.0 ng/mL and 991.9 +/- 224 ng/mL, respectively). These results indicated that ATL cells constitutively overexpress the L-selectin gene that can be transactivated by HTLV-1 Tax. The overexpression of L-selectin, as well as of inflammatory cytokines, by ATL cells may provide a basis for ATL cells to attach the vascular endothelium, leading to transmigration and organ infitration.

Ribozymes cleave the AML1/MTG8 fusion transcript and inhibit proliferation of leukemic cells with t(8;21)

The AML1/MTG8 fusion gene is thought to have a critical role in the leukemogenesis of AML with t(8;21)(q22;q22). To specifically inhibit the proliferation of leukemic cells having the AML1/MTG8 fusion gene, we constructed two hammerhead ribozymes against AML1/MTG8. Two cleavage sites were targeted as follows: site 1 for ribozyme 1(Rz1), a CUC located 3 bases upstream from the fusion site; site 2 for ribozyme 2(Rz2), an AUC located 3 bases downstream from the fusion site. In a cell-free system, Rz1 and Rz2 specifically cleaved AML1/MTG8 substrate, dependent on the concentration of ribozymes. When these ribozymes were transfected to Kasumi-1 cells, an AML cell line with AML1/MTG8, they were able to inhibit the cell growth. These data suggest that Rz1 and Rz2 may be applied as a new therapeutic agent in the treatment of AML with t(8;21).

Separation of protein factors that correct the defects in the seven complementation groups of xeroderma pigmentosum cells

We fractionated HeLa cell extracts by gel filtration and then micro-injected them into cells derived from the seven complementation groups (A-G) of xeroderma pigmentosum (XP). Distinct fractions that corrected the unscheduled DNA synthesis (UDS) of the complementation group XP cells were identified. The apparent molecular weights corresponding to complementation groups A, B, C, D, E, F, and G were estimated to be 80, 600, 600, 240, 100, 240, and 280 kDa, respectively. These factors were stable in the respective cell lines, the shortest half life being 16 h for the XP-A and XP-G complementing factors. The fraction (80 kDa) that corrected the UDS in XP-A cells also complemented the defect of the XP-A cell extract in the incision of DNA containing a pyrimidine dimer in a cell-free system. The separated fractions will be useful for understanding the molecular nature of these factors and for assigning complementation groups of cells derived from suspected XP patients.

Low incidence of a nucleotide sequence alteration of the neurofibromatosis 2 gene in human breast cancers

We investigated aberrations of the neurofibromatosis type 2 (NF2) gene in breast tumors of 60 patients by single-strand conformation polymorphism analysis of polymerase chain reaction products followed by nucleotide sequencing. We detected a tumor-specific single-base substitution in codon 398 in exon 12 of the gene, resulting in an alteration of a single amino acid, in DNA from a breast cancer sample. The results indicated possible but infrequent involvement of mutations of the tumor suppressor NF2 gene in human breast cancers.

Frequent mutations of the p53 gene and infrequent H- and K-ras mutations in urinary bladder carcinomas of NON/Shi mice treated with N-butyl-N-(4-hydroxybutyl)nitrosamine

To elucidate whether common genetic events in human urinary bladder carcinogenesis also occur in rodent models, we investigated the presence of p53, H- and K-ras mutations in 18 urinary bladder carcinomas induced by various concentrations of N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN) in male NON/Shi mice. Histopathologically, all were invasive, 11 being squamous cell carcinomas (SCCs) and the remaining seven being transitional cell carcinomas (TCCs). Using polymerase chain reaction single-strand conformation polymorphism (PCR-SSCP) analysis followed by DNA sequencing, p53, H- and K-ras mutations were observed in 14 (78%; exons 5-7), two (11%; one each on exons 1 and 2) and one (5.6%; exon 1) animals respectively. The frequencies of mutations in p53 exons 5, 6 and 7 were 7 (39%), 4 (22%), and 9 (50%) respectively, and no mutation was found in exon 8. All mutations involved one base-pair substitution with or without amino acid changes and the types of base-pair substitution were random. No evident association was observed between mutation sites and the histological phenotypes. In conclusion, p53 mutations are frequent in BBN-induced mouse invasive urinary bladder tumors, at similar levels to those observed for human high-grade invasive carcinomas, and this plus their distribution suggests their possible participation in this model of urinary bladder carcinogenesis.