Selective inhibitors of mTORC1 activate 4EBP1 and suppress tumor growth

The clinical benefits of pan-mTOR active-site inhibitors are limited by toxicity and relief of feedback inhibition of receptor expression. To address these limitations, we designed a series of compounds that selectively inhibit mTORC1 and not mTORC2. These 'bi-steric inhibitors' comprise a rapamycin-like core moiety covalently linked to an mTOR active-site inhibitor. Structural modification of these components modulated their affinities for their binding sites on mTOR and the selectivity of the bi-steric compound. mTORC1-selective compounds potently inhibited 4EBP1 phosphorylation and caused regressions of breast cancer xenografts. Inhibition of 4EBP1 phosphorylation was sufficient to block cancer cell growth and was necessary for maximal antitumor activity. At mTORC1-selective doses, these compounds do not alter glucose tolerance, nor do they relieve AKT-dependent feedback inhibition of HER3. Thus, in preclinical models, selective inhibitors of mTORC1 potently inhibit tumor growth while causing less toxicity and receptor reactivation as compared to pan-mTOR inhibitors.

RAS nucleotide cycling underlies the SHP2 phosphatase dependence of mutant BRAF-, NF1- and RAS-driven cancers

Oncogenic alterations in the RAS/RAF/MEK/ERK pathway drive the growth of a wide spectrum of cancers. While BRAF and MEK inhibitors are efficacious against BRAFV600E-driven cancers, effective targeted therapies are lacking for most cancers driven by other pathway alterations, including non-V600E oncogenic BRAF, RAS GTPase-activating protein (GAP) NF1 (neurofibromin 1) loss and oncogenic KRAS. Here, we show that targeting the SHP2 phosphatase (encoded by PTPN11) with RMC-4550, a small-molecule allosteric inhibitor, is effective in human cancer models bearing RAS-GTP-dependent oncogenic BRAF (for example, class 3 BRAF mutants), NF1 loss or nucleotide-cycling oncogenic RAS (for example, KRASG12C). SHP2 inhibitor treatment decreases oncogenic RAS/RAF/MEK/ERK signalling and cancer growth by disrupting SOS1-mediated RAS-GTP loading. Our findings illuminate a critical function for SHP2 in promoting oncogenic RAS/MAPK pathway activation in cancers with RAS-GTP-dependent oncogenic BRAF, NF1 loss and nucleotide-cycling oncogenic KRAS. SHP2 inhibition is a promising molecular therapeutic strategy for patients with cancers bearing these oncogenic drivers.

Developmental changes in BDNF protein levels in the hamster retina and superior colliculus

Quantitative studies of ontogenetic changes in the levels of brain-derived neurotrophic factor (BDNF) mRNA and its effector, BDNF protein, are not available for the retinal projection system. We used an electrochemiluminescence immunoassay to measure developmental changes in the tissue concentration of BDNF within the hamster retina and superior colliculus (SC). In the SC, we first detected BDNF (about 9 pg/mg tissue) on embryonic day 14 (E14). BDNF protein concentration in the SC rises about fourfold between (E14) and postnatal day 4 (P4), remains at a plateau through P15, then declines by about one-third to attain its adult level by P18. By contrast, BDNF protein concentration in the retina remains low (about 1 pg/mg tissue) through P12, then increases 4.5-fold to attain its adult level on P18. The developmental changes in retinal and collicular BDNF protein concentrations are temporally correlated with multiple events in the structural and functional maturation of the hamster retinal projection system. Our data suggest roles for BDNF in the cellular mechanisms underlying some of these events and are crucial to the design of experiments to examine those roles.

Effects of early visual experience and diurnal rhythms on BDNF mRNA and protein levels in the visual system, hippocampus, and cerebellum

The expression of brain-derived neurotrophic factor (BDNF) mRNA and the secretion of BDNF protein are tightly regulated by neuronal activity. Thus, BDNF has been proposed as a mediator of activity-dependent neural plasticity. Previous studies showed that dark rearing (DR) reduces BDNF mRNA levels in the primary visual cortex (V1), but the effects of visual experience on BDNF protein levels are unknown. We report that rearing in constant light or DR alters BDNF mRNA and protein levels in the retina, superior colliculus (SC), V1, hippocampus (HIPP), and cerebellum (CBL), although the changes in mRNA and protein are not always correlated. Most notably, DR increases BDNF protein levels in V1 although BDNF mRNA is decreased. BDNF protein levels also undergo diurnal changes. In the retina, V1, and SC, BDNF protein levels are higher during the light phase of the circadian cycle than during the dark phase. By contrast, in HIPP and CBL, the tissue concentration of BDNF protein is higher during the dark phase. The discrepancies between the experience-dependent changes in BDNF mRNA and protein suggest that via its effects on neuronal activity, early sensory experience alters the trafficking, as well as the synthesis, of BDNF protein. The circadian changes in BDNF protein suggest that BDNF could cause the diurnal modulation of synaptic efficacy in some neural circuits. The fluctuations in BDNF levels in nonvisual structures suggest a potential role of BDNF in mediating plasticity induced by hormones or motor activity.

Effect of sandblasting on the bond strength of the bondable molar tube bracket

This study examined the effect of surface treatment with sandblasting on bracket bonding strength. Extracted human tooth, base metal alloy and porcelain surfaces were treated with sandblasting. The bracket bonding strengths of sandblasted surfaces were evaluated and compared with the controls and etched enamel surfaces. Morphological observation of the treatment surfaces and the failure sites was conducted. Statistical analysis included one-way analysis of variance (ANOVA) and a Scheffe's F-test at the 95% confidence level was performed. The results indicated that mean bond strength values ranged from 3.6 MPa (the untreated control) to 20.4 MPa for the etched enamel surface. No statistically significant differences were determined among the etched enamel, sandblasted metal and sandblasted porcelain surfaces (P > 0.05). Most debonding specimens failed at either the resin-tooth interface or within the adhesive. In conclusion, sandblasting the metal and porcelain surfaces obtained a bracket bond strength comparable with that with the etched enamel surface.

Identification of estrogen-induced genes downregulated by AhR agonists in MCF-7 breast cancer cells using suppression subtractive hybridization

Aryl hydrocarbon receptor (AhR) agonists inhibit 17beta-estradiol (E2) induced growth of MCF-7 human breast cancer cells in vitro and rodent mammary tumor growth in vivo. Genes associated with inhibitory AhR-estrogen receptor (ER) crosstalk were investigated in MCF-7 human breast cancer cells using poly(A)(+)RNA from cells treated with either 1 nM E2 (target) or E2 plus 1 nM 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) (reference) or 25 microM diindolylmethane (DIM) as AhR agonists in MCF-7 cells. Suppression subtractive hybridization (SSH) was subsequently used to identify 33 genes with sequence homology to known human genes that are induced by E2 and inhibited by AhR agonists in MCF-7 cells; two unknown genes were also identified. Many of these genes are involved in cell proliferation and these include cell cycle regulators (cdc28/cdc2-associated protein), nucleotide synthases (thymidylate synthase), early intermediate genes (early growth response alpha, EGRalpha) and other proteins involved in signaling pathways (calmodulin, ATP synthase alpha subunit). Thus SSH has identified a diverse spectrum of new genes that are affected by inhibitory AhR-ER crosstalk and among this group are a subset of genes that may be critical for the in vivo antitumorigenic effects of AhR agonists.

Regulation of CREB by moderate hypoxia in PC12 cells

The mechanisms by which excitable cells adapt and respond to changes in O2 levels remain largely unknown. We have investigated the effect of hypoxia on the cyclic AMP response element binding protein (CREB) transcription factor. PC12 cells were exposed to moderate levels of hypoxia (5% O2) for various times between 20 min and 6 hr. We found that hypoxia rapidly and persistently induced ser133 phosphorylation of CREB. This effect was more robust than that produced by exposing PC12 cells to either forskolin, KCl, or NGF. This effect was not due to activation of any of the previously known CREB kinases, including PKA, CaMK, PKC, p70s6k, or MAPKAP kinase-2. Thus, hypoxia may induce activation of a novel CREB kinase. To test whether phosphorylation of CREB was associated with an activation of CRE-dependent gene expression, cells were transfected with wild type and mutated regions of the 5'-flanking region of the tyrosine hydroxylase (TH) gene fused to a CAT reporter gene. Mutation of the CRE element in a TH reporter gene reduced, but did not abolish, the effects of hypoxia on TH gene expression. However, hypoxia did not induce transactivation of a GAL4-luciferase reporter by a GAL4-CREB fusion protein. Thus, the mechanism by which hypoxia regulates CREB is distinct, and more complex, than that induced by forskolin, depolarization, or nerve growth factor.

Apoptosis and restriction of G(1)/S cell cycle by fenretinide in Burkitt's lymphoma mutu I cell line accessed with bcl-6 down-regulation

Fenretinide (4-HPR) is a synthetic retinoid with cancer chemopreventative potential and clinically manageable side effects, compared to the prototype retinoid, all-trans retinoic acid (RA). 4-HPR has been shown to modulate cell proliferation and induce apoptosis in a variety of human tumor cell types, but its effects on B-cell non-Hodgkin's lymphomas (NHL-B) have not been explored. Treatment of Burkitt's lymphoma Mutu I cells with 3 microM 4-HPR is accompanied by growth arrest, induction of apoptosis, and restricted progression of the cell cycle at the G(1)/S checkpoint. We also observed that 4-HPR elicited a reduced expression of bcl-6 in these cells, which supports the proposed role of bcl-6 as an anti-apoptotic gene. While 4-HPR treatment had no effect on total Rb gene expression, it significantly reduced the state of hyperphosphorylation of Rb, resulting in the predominant existence of Rb in the underphosphorylated state.

Necrotizing fasciitis in children in eastern Ontario: a case-control study

BACKGROUND

Early recognition and treatment are important factors that can help improve survival following necrotizing fasciitis. However, early recognition is complicated by the difficulty in distinguishing the infection from other, less serious soft-tissue infections such as cellulitis. We reviewed the charts of children presenting with necrotizing fasciitis at a tertiary care pediatric hospital in Ontario to document potential increases in the frequency of cases and to identify clinical and laboratory features that could help distinguish between necrotizing fasciitis and cellulitis.

METHODS

Necrotizing fasciitis was defined as a soft-tissue infection characterized by necrosis of subcutaneous tissue and confirmed at surgery or on pathological examination. A retrospective chart review was conducted to identify cases of necrotizing fasciitis that occurred between June 1, 1983, and May 31, 1999. The characteristics of the identified cases, their clinical manifestations and the laboratory features at presentation were compared with those of matched controls admitted to the hospital with cellulitis.

RESULTS

In total, 8 cases of necrotizing fasciitis were identified during the study period. There were no cases from 1983 to 1987, 1 from 1988 to 1991, 1 from 1992 to 1995, and 6 cases from 1996 to 1999. Compared with the children who had cellulitis, those who had necrotizing fasciitis were more likely to present with a generalized erythematous rash (odds ratio [OR] 11.0; 95% confidence interval [CI] 1.5-81.6) and a toxic appearance (OR 23.0; 95% CI 2.0-262.5). They were also more likely than the children with cellulitis to have a history of fever (8/8 v. 10/24, p = 0.004), a higher temperature (mean 38.7 degrees C v. 37.8 degrees C, p = 0.006), a higher respiratory rate (mean 31.5 v. 25.4 breaths/min, p = 0.02) and a lower platelet count on presentation (mean 194.0 v. 299.3 x 10(9)/L, p = 0.03).

INTERPRETATION

On presentation, factors that may help distinguish necrotizing fasciitis from cellulitis include a generalized erythematous rash, toxic appearance, fever and low platelet count.

Cloning and characterization of Drosophila topoisomerase IIIbeta. Relaxation of hypernegatively supercoiled DNA

We cloned cDNA encoding Drosophila DNA topoisomerase III. The top3 cDNA encodes an 875-amino acid protein, which is nearly 60% identical to mammalian topoisomerase IIIbeta enzymes. Similarity between the Drosophila protein and the topoisomerase IIIbetas is particularly striking in the carboxyl-terminal region, where all contain eight highly conserved CXXC motifs not found in other topoisomerase III enzymes. We therefore propose the Drosophila protein is a member of the beta-subfamily of topoisomerase III enzymes. The top3beta gene is a single-copy gene located at 5 E-F on the X chromosome. P-element insertion into the 5'-untranslated region of this gene affects topoisomerase IIIbeta protein levels, but not the overall fertility and viability of the fly. We purified topoisomerase IIIbeta to near homogeneity and observed relaxation activity only with a hypernegatively supercoiled substrate, but not with plasmid DNA directly isolated from bacterial cells. Despite this difference in substrate preference, the degree of relaxation of the hypernegatively supercoiled substrate is comparable to relaxation of plasmid DNA by other type I enzymes. Drosophila topoisomerase IIIbeta forms a covalent linkage to 5' DNA phosphoryl groups, and the DNA cleavage reaction prefers single-stranded substrate over double-stranded, suggesting an affinity of this enzyme for DNA with non-double-helical structure.

Phosphatidylinositol 3-kinase is required for insulin-like growth factor-I-induced vascular smooth muscle cell proliferation and migration

Insulin-like growth factor-I (IGF-I) plays an important role in regulating vascular smooth muscle cell (VSMC) proliferation and directed migration. The mitogenic and chemotactic actions of IGF-I are mediated through the IGF-I receptor, but how the activation of the IGF-I receptor leads to these biological responses is poorly understood. In this study, we examined the role of phosphatidylinositol 3-kinase (PI3 kinase) in mediating the mitogenic and chemotactic signals of IGF-I. IGF-I treatment resulted in a significant increase in phosphotyrosine-associated PI3 kinase activity in cultured primary VSMCs. To determine whether insulin receptor substrate (IRS)-1, -2, or both are involved in IGF-I signaling in VSMCs, cell lysates were immunoprecipitated with either an anti-IRS-1 or an anti-IRS-2 antibody, and the associated PI3 kinase activity was determined. IGF-I stimulation resulted in a significant increase in IRS-1- but not IRS-2-associated PI3 kinase activity, suggesting that IGF-I primarily utilizes IRS-1 to transmit its signal in VSMCs. The IGF-I-induced increase in IRS-I-associated PI3 kinase activity was concentration dependent. At the maximum concentration (50 ng/mL), IGF-I induced a 60-fold increase. This activation occurred within 5 minutes and was sustained at high levels for at least 6 hours. IGF-I also caused a concentration-dependent and long-lasting activation of protein kinase B (PKB/Akt). Inhibition of PI3 kinase activation by LY294002 or wortmannin abolished IGF-I-stimulated VSMC proliferation and reduced IGF-I-directed VSMC migration by approximately 60%. These results indicate that activation of PI3 kinase is required for both IGF-I-induced VSMC proliferation and migration.

MEK inhibitors block BDNF-dependent and -independent expression of GABA(A) receptor subunit mRNAs in cultured mouse cerebellar granule neurons

Brain-derived neurotrophic factor (BDNF) can regulate the maturation of developing cerebellar granule neurons. Within 1-2 days of culture, BDNF induces the expression of granule neuron terminal differentiation markers, particularly GABA(A) receptor alpha6 subunit (GABA(A)alpha6) mRNA. Other trophic factors including insulin-like growth factor, the neurotrophin NT-3, pituitary adenylate cyclase-activating polypeptide (PACAP), and fetal bovine serum failed to induce this early expression. The expression of other GABA(A) receptor subunits, including alpha1 and gamma2, was also enhanced by exposure of developing granule neurons to BDNF. This BDNF-dependent expression of GABA(A) receptor subunit mRNAs could be effectively blocked by treatment with the mitogen-activated protein kinase kinase (MEK) inhibitors, PD98059 or U0126. In the absence of BDNF, GABA(A)alpha6 expression occurs but not until 3-4 days of culture. This BDNF-independent expression of GABA(A)alpha6 was also inhibited by PD98059. Further studies showed that the BDNF-dependent expression GABA(A)alpha6 could also be reduced by LY294002, an inhibitor of the phosphatidylinositol 3-kinase, or depolarizing concentrations of KCl. These results thus suggest that both BDNF-dependent and -independent expressions of GABA(A) receptor subunits require the activation of MEK and the mitogen-activated protein kinase (MAPK) pathway. However, it is also likely that other signaling pathways modulate this maturation process.

Changes in expression of the 44-kilodalton outer surface membrane antigen (p44 kD) for monitoring progression of infection and antimicrobial susceptibility of the human granulocytic ehrlichiosis (HGE) agent in HL-60 cells

Changes in human granulocytic ehrlichiosis (HGE)-specific major outer membrane protein (p44 kD) were assayed by Western blot analysis in HL-60 cells in vitro infected by the HGE agent. Time course study demonstrated that the expression of p44 preceded the rise in cell infection as determined by the presence of intracellular morulae. To test whether the expression of p44 may be suitable for evaluating the effects of antibiotics in vitro, three recent isolates of the HGE agent were exposed to doxycycline and ampicillin during culture with HL-60 cells. Loss of infection concurrent with disappearance of the 44 kD protein was found with doxycycline treatment. In contrast, ampicillin treatment had no discernible effects on infection or 44 kD expression. There was excellent agreement between infection, as measured by morulae, and 44 kD expression (coefficient of correlation r = 0.97, p < 0.01). Following treatment with doxycycline, the 44 kD protein disappeared with an estimated t1/2 of approximately 24-30 h, which was considerably shorter than a t1/2 of >60 h calculated for loss of morulae. Measurement of p44 expression may be a more rapid and simple assay to determine antibiotic susceptibility of the HGE agent in cell culture. Furthermore, it may be used to indicate the presence of infection before morulae are apparent.

Activation of caspase 3 in HL-60 cells exposed to hydrogen peroxide

Recent studies have suggested that hydrogen peroxide (H2O2), a reactive compound formed endogenously in the breakdown of superoxide, may mediate the induction of apoptosis in various cell types in response to external stimuli. However, the role of H2O2 in the apoptotic pathway has not been clearly established. The purpose of this study was to determine if H2O2 treatment could induce apoptosis through the activation of caspases. Doses of H2O2 ranging from 10 microM to 100 microM, when added to HL-60 cells, resulted in the cleavage of poly(ADP-ribose) polymerase (PARP) from its native 113 Kd form to a processed 89 Kd fragment, indicative of cells undergoing apoptosis. PARP was predominantly in the fragmented form when doses of 20 microM and greater were used. A time course study of changes in PARP processing in H2O2-treated cells revealed that 10 and 50 microM H2O2 required 6 and 3 h, respectively, to specifically degrade PARP, suggesting that the H2O2-induced PARP cleavage is both time and concentration dependent. Since PARP is cleaved by CPP32 (caspase-3), we next determined if H2O2 was capable of effecting changes in CPP32 activity. The caspase activity was assayed using a colorimetric substrate, DEVD-pNa. Results of these experiments showed that H2O2 increased caspase activity at 3 h, corresponding to the time of appearance of fragmented PARP. Also, CPP32 activity and PARP processing were both significantly suppressed by caspase-3 inhibitors. Taken together, these results suggest that H2O2 mediates specific cleavage of PARP and possibly apoptosis by activating caspase 3.

Identifying Lys359 as a critical residue for the ATP-dependent reactions of Drosophila DNA topoisomerase II

Substituting Lys359 with either Gln or Glu in the highly conserved QTK-loop in the DNA gyrase B protein homologous domain of Drosophila topoisomerase II inactivates its catalytic activities. Although strand passage and DNA-dependent ATPase activities are affected in these mutant proteins, their DNA cleavage activity is comparable with the wild-type enzyme and can be stimulated to the same level by topoisomerase-targeting anticancer drugs. The sequence specificity in the DNA cleavage reaction remains unaltered for the mutant proteins. We have used both glass fiber filter binding assay and CsCl density gradient ultracentrifugation to monitor the formation of a salt-stable, protein-clamp complex. Both Gln and Glu mutant proteins can form a clamp complex in the presence of 5'-adenylyl-beta,gamma-imidodiphosphate, albeit with a lower efficiency than the wild-type enzyme. However, the mutant proteins can form a stable complex either in the presence of ATP or in the absence of any cofactors. These results are in an interesting contrast with the wild-type enzyme, which cannot form a stable complex under similar conditions. Our data suggest that Lys359 is critical for the catalytic activity of topoisomerase II and may have an important function in the ATP signaling process.

BDNF injected into the superior colliculus reduces developmental retinal ganglion cell death

The role of neurotrophins as survival factors for developing CNS neurons, including retinal ganglion cells (RGCs), is uncertain. Null mutations for brain-derived neurotrophic factor (BDNF) or neurotrophin 4 (NT4), individually or together, are without apparent effect on the number of RGCs that survive beyond the period of normal, developmental RGC death. This contrasts with the BDNF dependence of RGCs in vitro and the effectiveness of BDNF in reducing RGC loss after axotomy. To investigate the effect of target-derived neurotrophins on the survival of developing RGCs, we injected BDNF into the superior colliculus (SC) of neonatal hamsters. At the age when the rate of developmental RGC death is greatest, BDNF produces, 20 hr after injection, a 13-15-fold reduction in the rate of RGC pyknosis compared with the rates in vehicle-injected and untreated hamsters. There is no effect 8 hr after injection. Electrochemiluminescence immunoassay measurements of BDNF protein in the retinae and SC of normal and BDNF-treated hamsters demonstrate that the time course of BDNF transport to RGCs supports a role for target-derived BDNF in promoting RGC survival. The effectiveness of pharmacological doses of BDNF in reducing developmental RGC death may be useful in further studies of the mechanisms of stabilization and elimination of immature central neurons.

Control of cell cycle regulatory protein expression by 1,25-dihydroxyvitamin D-3 in human promyelocytic HL-60 leukemic cells cultured in serum-free medium

1,25-Dihydroxyvitamin D-3 (herein referred to as vitamin D-3), the natural vitamin D-3 formed by successive hydroxylation of cholecalciferol at the 25 and 1 alpha position, and numerous vitamin D-3 analogs, have been reported to decrease proliferation and promote terminal differentiation from several types of human malignant cells, including the human promyelocytic HL-60 leukemic cells. The purpose of this study was to determine if and to what extent the cell culture conditions affect the sensitivity of the HL-60 cells to vitamin D-3, both in terms of cell growth, differentiation, and changes in expression of specific proteins. Addition of 10 nM and 100 nM vitamin D-3 to HL-60 cells cultured in the serum-free, chemically defined medium of insulin/transferrin/selenium (ITS) effected cell growth differently than cells maintained in a fetal bovine serum-supplemented medium. In addition to the greater degree of growth suppression by 100 nM vitamin D-3, cells maintained in serum-free medium also displayed significantly higher levels of monocytic differentiation. Furthermore, Western blot analysis showed that a pronounced arrest of cell cycling at the G(1)-to-S-phase transition, concomitant with a corresponding 36% down-regulation of cyclin D1 and, in parallel, a similar decreased hyperphosphorylation of pRb, was elicited by 100 nM vitamin D-3. These results indicate that the sensitivity of HL-60 cells to vitamin D-3 is dependent on the availability of serum.

Regulation of androgen receptor (AR) and prostate specific antigen (PSA) expression in the androgen-responsive human prostate LNCaP cells by ethanolic extracts of the Chinese herbal preparation, PC-SPES

As part of the study on the potential use of natural product-based combination therapy for treating prostate cancer, we have investigated the effects of a "HPLC standardized" herbal preparation, PC-SPES, on the prostate LNCaP cell line. Proliferation of the LNCaP cells was inhibited by a 4-6 day incubation with ethanolic extracts of PC-SPES. Decrease of cell growth was accompanied by a 60-70% down-regulation of the proliferating cell nuclear antigen (PCNA) and level of secreted PSA. A smaller and more variable decrease (20-40%) in the level of intracellular PSA was also observed. The PC-SPES-modulated PSA changes occurred concurrently with the decrease of AR expression, based on Western blot analysis and binding to the radioactive ligand [3H]R1881. A 60% decrease in R1881 binding occurred after a 24 h incubation with PC-SPES. These results suggest that PC-SPES negatively affects cell growth in part through its ability to modulate changes in PCNA, and may decrease PSA levels indirectly by suppressing AR expression.

Induction of apoptosis and altered nuclear/cytoplasmic distribution of the androgen receptor and prostate-specific antigen by 1alpha,25-dihydroxyvitamin D3 in androgen-responsive LNCaP cells

In addition to suppressing prostate cell growth, vitamin D also up-regulates the expression of androgen receptor (AR) and prostate-specific antigen (PSA). To study the mechanism involved in the control of these proteins, LNCaP cells were treated with 10 nM 1alpha,25-dihydroxyvitamin D3 and separated into cytosol and nuclear fractions. AR and PSA were analyzed by western blot analysis. A second approach involved incubating control and treated cells with [3H]R1881, fractionating the cells into the cytosolic and nuclear components, and quantifying the amount of radioactivity associated with the respective fractions. Alternatively, immunohistochemical assays were performed by staining cells with cognate antibodies for AR and PSA. Both biochemical and immunohistochemical analyses show proportionately greater increased presence of AR in the nucleus, accompanied by relatively reduced AR in the cytosol, following treatment of LNCaP cells with vitamin D3. Surprisingly, PSA was found to be present in the nuclear fraction in both control and treated cells. These results suggest that vitamin D3 promotes the translocation of AR from the cytosol to the nucleus. The presence of PSA in the nucleus of LNCaP cells raises the possibility of an autogenous mode of control of PSA gene expression.

Differential expression and regulation of p53 in human prostatic cells

Although genetic analysis has convincingly shown the association possibly existing between alterations in p53 tumor suppressor gene and a broad spectrum of human tumors including prostate cancer, surprisingly little is known about ways in which p53 at the protein level is controlled. To determine factors that may play a role in its regulation and expression, changes in p53 protein was investigated by using the androgen-insensitive JCA-1, DU-145, PC-3 and the androgen-responsive LNCaP cells. With the exception of PC-3 cells in which p53 is missing, multiple distinct forms of p53 were found in the other 3 prostate cell lines. A single p53 band was detected in the JCA-1 cell extracts, whereas two and three p53 immunoreactive bands were correspondingly observed in the DU-145 and LNCaP cells. The relative abundance and distribution of the different forms of p53 in the latter two cell types varied with proliferation of cells in culture. In the presence of charcoal-stripped fetal bovine serum (cFBS), LNCaP took on the morphology of neuroendocrine cells, a phenotypic change which was accompanied by a greater than 80% reduction in p53 expression, concurrent with elimination of the two slow migrating forms of p53. Induction of apoptosis in JCA-1 cells by treatment with the retinoid 4-HPR caused the virtual disappearance of p53, which coincided with specific processing of p53 into lower molecular weight 28 kD fragments. We propose that rapid and dynamic posttranslational changes in p53 may actively participate in determining mutually exclusive functional cellular events such as proliferation, differentiation, and apoptosis.

Postirradiation laryngeal osteosarcoma: case report and literature review

BACKGROUND

Laryngeal sarcoma is a rare disease entity. In review of the literature, chondrosarcoma is the most common sarcoma, followed by fibrosarcoma. Osteosarcoma is very rare; there are only seven cases reported in the literature. Postirradiation sarcoma is a late complication of radiotherapy. Osteosarcoma is the most common type in this group. The larynx is often involved in the radiation field of treatment for head and neck malignancies. However, postirradiation laryngeal osteosarcoma has not yet been reported.

METHODS

We present a 56-year-old man who under went radiotherapy for nasopharyngeal carcinoma 32 years ago and later developed a laryngeal osteosarcoma.

RESULTS

The patient underwent total laryngectomy but died 1 year and 9 months later with locally extensive disease.

CONCLUSIONS

We report the first case of postirradiation laryngeal osteosarcoma. In addition to surgical treatment, adjunctive therapies should be considered for this group of patients.

Isolation and characterization of a Drosophila gene essential for early embryonic development and formation of cortical cleavage furrows

We have isolated a new female sterile mutant from Drosophila melanogaster, which arrests the embryonic development during the transition from syncytial to cellular blastoderm. Cytological analysis of the mutant embryos indicates that pseudocleavage furrows in the syncytial blastoderm are abnormal but not completely disrupted. However, cleavage furrows during cellularization are totally disorganized, and no embryos can develop beyond this stage. Consistent with this observation, the expression of this gene peaks around the cellular blastoderm and not in any later developmental stages. Based on immunofluorescence experiments, the protein product of this gene is localized in both pseudocleavage furrows at the syncytial blastoderm and in the cleavage furrows during the cellularization stage. Sequence homology analysis demonstrates a modest, but statistically significant, similarity of this protein with the carboxyl-terminal domains of dystrophin and a family of proteins collectively known as apodystrophins. It is possible that this protein may play an essential role in organizing and maintaining a specialized cytoskeletal structure, a function also suggested for dystrophin and apodystrophins.

Glycoconjugates in normal and abnormal secondary neurulation

In chick embryos, the anterior greater portion of the neural tube develops by the folding, apposition, and fusion of the neuroectoderm. The smaller caudal portion that forms the secondary neural tube (lumbosacral and coccygeal regions) is derived from the tail bud, an aggregate of mesenchymal cells located at the caudal limit of the body. Tail bud mesenchyme, arranged in a solid cord, undergoes mesenchymal-epithelial transformation to form the secondary neural tube. Previous evidence suggests that this transformation is accompanied by modulation of cell surface glycoconjugates in the differentiating tissues. In this study, we show by lectin histochemistry and lectin blotting of proteins isolated by SDS-PAGE, that Datura stramonium agglutinin (DSA) binds preferentially to differentiating tail bud cells. This lectin is specific for beta 1-4-linked N-acetylglucosamine oligomers, such as the oligosaccharides of the poly-N-acetyllactosamine series that have been previously implicated in cell differentiation. Ultrastructural lectin cytochemistry indicates that at least some of the proteins binding DSA are localized extracellularly. The use of DSA as a teratogen resulted in embryos showing a variety of neural tube and notochord defects. We have also examined the binding of DSA to embryos that were treated with teratogenic doses of retinoic acid by sub-blastodermal injection, and find that the DSA-binding patterns are perturbed. Analysis of DSA-treated embryos using the TUNEL technique indicated that cell death was not a factor in DSA teratogenesis. This strongly suggests that the glycoconjugates of the cell surface have a role in the normal differentiation of tail bud mesenchyme into the neuroepithelium of the secondary neural tube. Perturbations of glycoconjugate activity results in defects of the secondary neural tube and associated tail bud derivatives.

Modulation of proliferation and cellular-changes of human prostatic-cancer cells by activated lymphocytes

The effect of immune cells on the growth and development of human prostatic cancer cells was investigated. Cell proliferation of androgen-independent human prostatic cancer cells JCA-1 was reduced 30-40% with the supplementation of a growth modulating activity present in lymphocyte conditioned medium. The slower growing cells had a longer doubling time revealing a blocking for G(1) cells entering into S phase. The clonogenicity of the cells was also reduced. Displayed in parallel was altered phenotypes including the development of dendrite-like processes with less intercellular contact. Immunocytochemical staining showed significantly increased: expression of actin, vimentin and cytokeratin 8, suggesting a differentiated cell type. Activated lymphocytes were shown to require RNA synthesis for providing the modulating activity which was estimated to be 18,500-27,500 Da. The role of immune cells in growth regulation of prostatic cells is discussed.

Chronic mastoiditis mimicking recurrence of nasopharyngeal carcinoma: report of a case

A nasopharyngeal mass with cranial neuropathies usually indicates an advanced neoplastic process. We present a case of nasopharyngeal carcinoma diagnosed and treated 38 years ago. A nasopharyngeal mass recurred with cranial neuropathies and concurrent otologic infection in June, 1990. Repeated nasopharyngeal biopsies were negative with respect to tumors. Suspecting direct extension of the otologic infection, modified radical mastoidectomy was performed. The nasopharyngeal mass resolved after the surgical intervention. Spread of otologic infection from the temporal bone to the nasopharynx may be more common than was previously thought. Clinicians should modify diagnostic approaches in patients with a nasopharyngeal mass and concurrent otologic disease.

Function of the hydrophilic carboxyl terminus of type II DNA topoisomerase from Drosophila melanogaster. II. In vivo studies

Genetic complementation, protein distribution, and in vivo enzymatic activity by carboxyl-terminal truncation mutations of the Drosophila enzyme were examined. Removal of more than 273 of the 1447 amino acids composing the full-length topoisomerase inactivates the enzyme in vivo and in vitro; removal of 227 amino acids or less has no apparent effect on the ability of the enzyme to substitute for a conditional lethal, or null mutation, of the Saccharomyces cerevisiae top2 gene. Four catalytically active mutants, from which 227 or 240 amino acids are deleted, define an intervening, critical region. Each mutant in this critical region displays different in vivo complementation activity ranging from complete complementation to noncomplementation. Deletion analysis revealed a potent nuclear localization signal within the most distal 60 amino acids, although this is apparently not the only functional signal sequence encoded in the enzyme. Subcellular fractionation and indirect immunofluorescence demonstrate that the truncated enzymes localize to the nucleus, albeit with reduced efficiency compared to wild type. The ability of these mutants, including a mutant in the critical region which does not complement, to catalyze the decatenation of replicated plasmids and the segregation of replicated chromosomes was also examined.

Function of the hydrophilic carboxyl terminus of type II DNA topoisomerase from Drosophila melanogaster. I. In vitro studies

The function of the hydrophilic carboxyl-terminal region of Drosophila DNA topoisomerase II was examined by constructing a series of deletion mutants at the 3'-end of the Drosophila Top2 cDNA. The truncated enzymes were then expressed in Saccharomyces cerevisiae. Deletion of up to 240 out of 1447 total amino acids had no apparent effect on the enzyme's ability to catalyze topisomerization reactions. When 273, or more, amino acids were deleted, the enzyme was no longer active. Examples were found where deletion of less than 240 amino acids inactivated the enzyme. Based on the hydrodynamic properties determined for one of these mutants, the lack of activity was most likely due to misfolding of the polypeptides. The active mutants have similar hydrodynamic properties and heat inactivation profiles as the intact enzyme, suggesting that they are dimeric and stably folded. The carboxyl-terminal 240 amino acids also were not required for interaction with the drug VM26. The only difference noted between the shortest, active mutant and the full-length enzyme was a decrease in the stability of the interaction of the truncated enzyme with DNA as evidenced by a decrease in the ionic strength at which catalysis was optimal and at which the transition between a processive and distributive mode of supercoil relaxation occurred.

Incomplete reversion of double stranded DNA cleavage mediated by Drosophila topoisomerase II: formation of single stranded DNA cleavage complex in the presence of an anti-tumor drug VM26

Anti-tumor drug VM26 greatly stimulates topoisomerase II mediated DNA cleavage by stabilizing the cleavable complex. Addition of a strong detergent such as SDS to the cleavable complex induces the double stranded DNA cleavage. We demonstrate here that heat treatment can reverse the double stranded DNA cleavage; however, topoisomerase II remains bound to DNA even in the presence of SDS. This reversed complex has been shown to contain single strand DNA breaks with topoisomerase II covalently linked to the nicked DNA. Chelation of Mg++ by EDTA and the addition of salt to a high concentration also reverse the double strand DNA cleavage, and like heat reversion, topoisomerase II remains bound to DNA through single strand DNA break. The reversion complex can be analyzed and isolated by CsCl density gradient centrifugation. We have detected multiple discrete bands from such a gradient, corresponding to protein/DNA complexes with 1, 2, 3, ..... topoisomerase II molecules bound per DNA molecule. Analysis of topoisomerase II/DNA complexes isolated from the CsCl gradient indicates that there are single stranded DNA breaks associated with the CsCl stable complexes. Therefore, topoisomerase II/DNA complex formed in the presence of VM26 cannot be completely reversed to yield free DNA and enzyme. We discuss the possible significance of this finding to the mechanism of action of VM26 in the topoisomerase II reactions.

Eustachian tube dysfunction in patients with nasopharyngeal carcinoma, pre- and post-irradiation

Eustachian tube function tests were performed in 34 patients with nasopharyngeal carcinoma before and after irradiation. Tubal dysfunction prior to irradiation in these patients was due to functional impairment. However, tubal dysfunction after irradiation was due to both organic obstruction and functional impairment. Organic obstruction of the tube was found to be severe with higher dosages of irradiation (to 80 Gy) resulting in subsequent otitis media. In our experience, higher doses of irradiation should be avoided if possible, but insertion of a ventilation tube should be done if a high dose of irradiation is planned.

Multiple risk factors of nasopharyngeal carcinoma: Epstein-Barr virus, malarial infection, cigarette smoking and familial tendency

A community-based case-control study was carried out to assess multiple risk factors and familial aggregation of nasopharyngeal carcinoma (NPC). All of the 347 pathologically-confirmed NPC new cases were serially recruited from the National Taiwan University Hospital, and healthy community controls one-to-one matched with cases on age, sex and residence were selected from household registration offices. NPC risk factors were obtained from the study subjects through standardized interviews according to a structured questionnaire. Levels of antibody to EBV-specific DNase (anti-EBV DNase) and IgA antibody to EBV viral capsid antigen (anti-EBV VCA) were determined by standard methods blindly. Multiple logistic regression analysis for matched data showed significant associations of NPC with high levels of anti-EBV DNase and anti-EBV VCA independently. The effect of cigarette smoking on NPC was modified by age. The older the age, the more striking the dose-response relation between cigarette smoking and NPC. There was no significant association between alcohol consumption and NPC. Malarial infection history was associated with NPC with an odds ratio of 2.2, but the association was significant in males only. First-degree relatives of NPC cases had a greater NPC-affected rate than those of matched healthy controls with a relative risk of 19.2, and the heritability of NPC was estimated as 0.60 (95% confidence interval = 0.55-0.64) based on the multifactorial inheritance model. Familial NPC cases were younger than sporadic cases, but environmental risk factors were similar in the two groups.

Nuclease protection by Drosophila DNA topoisomerase II. Enzyme/DNA contacts at the strong topoisomerase II cleavage sites

A DNA consensus sequence for topoisomerase II cleavage sites was derived previously based on a statistical analysis of the nucleotide sequences around 16 sites that can be efficiently cleaved by Drosophila topoisomerase II (Sander, M., and Hsieh, T. (1985) Nucleic Acids Res. 13, 1057-1072). A synthetic 21-mer DNA sequence containing this cleavage consensus sequence was cloned into a plasmid vector, and DNA topoisomerase II can cleave this sequence at the position predicted by the cleavage consensus sequence. DNase I footprint analysis showed that topoisomerase II can protect a region of approximately 25 nucleotides in both strands of the duplex DNA, with the cleavage site located near the center of the protected region. Similar correlation between the DNase I footprints and strong topoisomerase II cleavage sites has been observed in the intergenic region of the divergent HSP70 genes. This analysis therefore suggests that the strong DNA cleavage sites of Drosophila topoisomerase II likely correspond to specific DNA-binding sites of this enzyme. Furthermore, the extent of DNA contacts made by this enzyme suggests that eucaryotic topoisomerase II, in contrast to bacterial DNA bacterial DNA gyrase, cannot form a complex with extensive DNA wrapping around the enzyme. The absence of DNA wrapping is probably the mechanistic basis for the lack of DNA supercoiling action for eucaryotic topoisomerase II.