SCH 51344 inhibits ras transformation by a novel mechanism

A pyrazolo-quinoline compound, 6-methoxy-4-[2-[(2-hydroxyethoxyl)-ethyl]amino]-3-methyl-1M-pyrazo lo [3,4-b]quinoline (SCH 51344), was identified based on its ability to derepress human smooth muscle alpha-actin promoter activity in ras-transformed cells. In this study, we show that SCH 51344 reverts several key aspects of ras transformation, such as morphological changes, actin filament organization, and anchorage-independent growth, and also inhibits Val-12 Ras-induced maturation of Xenopus oocytes. SCH 51344 is also a potent inhibitor of the anchorage-independent growth of human tumor lines known to contain multiple genetic alterations in addition to activated ras genes. We have sought to determine whether SCH 51344 disrupts the signaling pathway that activates mitogen-activated protein (MAP) kinase or extracellular signal-regulated kinase (ERK) in normal and ras-transformed fibroblast cells. NIH 3T3 cells transformed by different oncogenes, which have products that participate at different steps of the Ras signaling pathway, were tested in a soft-agar colony formation assay to determine which step of the pathway is inhibited by SCH 51344. Our results indicate that SCH 51344 inhibits the ability of v-abl, v-mos, H-ras, v-raf, and mutant active MAP kinase kinase-transformed NIH 3T3 cells to grow in soft agar. Only v-fos-transformed cells were found to be resistant to the treatment of SCH 51344. SCH 51344 treatment had very little effect, if any, on the activation of MAP kinase kinase, MAP kinase, and p90RSK activity in response to growth factor stimulation. Treatment of ras-transformed cells with SCH 51344 led to stimulation of serum response factor DNA binding activity and activation of serum response element-dependent gene transcription, accounting for its ability to activate alpha-actin promoter activity in ras-transformed cells. Our results indicate that SCH 51344 inhibits ras transformation by a novel mechanism and acts at a point either downstream or parallel to extracellular signal-regulated kinase-dependent Ras signaling pathway.

Neu differentiation factor is a neuron-glia signal and regulates survival, proliferation, and maturation of rat Schwann cell precursors

We show that beta forms of Neu differentiation factor (NDF), homologous to acetylcholine receptor-inducing activity, glial growth factor, and heregulin, prevent apoptotic death and stimulate DNA synthesis of the E14 Schwann cell precursor, an early cell in the rat Schwann cell lineage. When precursors are exposed to NDF in defined medium, they generate Schwann cells without the requirement for DNA synthesis and with a time course that is similar to that with which Schwann cells appear in embryonic nerves in vivo. Furthermore, a neuronal signal that also mediates precursor survival and maturation is blocked by the extracellular domain of the ErbB4 NDF receptor, a protein that specifically blocks the action of NDFs. These observations provide important evidence that NDF is one of the hitherto elusive neuron-glia signaling molecules long proposed to regulate development in the Schwann cell lineage.

Structural and thermotropic properties of synthetic C16:0 (palmitoyl) ceramide: effect of hydration

Differential scanning calorimetry (DSC) and X-ray diffraction techniques have been used to investigate the structure and thermotropic properties of synthetic, non-hydroxy fatty acid (16:0) ceramide (NFA(C16)CER) as a function of hydration. Anhydrous NFA(C16)CER shows a single, broad endothermic transition at 95.4 degrees C (delta H = 10.4 kcal/mol). On hydration, a broad exothermic transition appears at approximately 50-70 degrees C while the main endothermic transition decreases to 90.0 degrees C (delta H = 13.8 kcal/mol). The enthalpy of the exothermic transition increases with hydration to a maximum value, delta H = 4.8 kcal/mol. This polymorphic phase behavior depends on the low temperature incubation time and prior cooling rate. X-ray diffraction of fully hydrated NFA(C16)CER at 26 degrees C, shows a well-ordered lamellar phase with a bilayer periodicity d = 46.9 A. At 68 degrees C, above the first exothermic transition, X-ray diffraction shows again a lamellar phase with reduced bilayer periodicity d = 41.8 A and an increased number of both lamellar and wide-angle reflections indicative of enhanced layer and chain packing order, respectively. At 90.0 degrees C, above the main transition, the diffraction pattern shows a broad, intense reflection at 29.9 A and a diffuse reflection at 4.6 A, indicative of a melted chain phase. On cooling, NFA(C16)CER exhibits polymorphic phase behavior involving the conversion of the melted chain phase to a metastable bilayer phase. On heating, this metastable phase undergoes an exothermic transition to a stable bilayer phase; on further heating, NFA(C16)CER converts endothermically to the melted-chain phase.(ABSTRACT TRUNCATED AT 250 WORDS)

Kinetic analysis of the interactions of recombinant human VpreB and Ig V domains

The surrogate light chain, composed of VpreB and lambda 5/14.1 proteins, is selectively expressed on B cell precursors, and is important for B cell development. The surrogate light chain associates with cell surface mu-chains on preB cells, but little is known about the ligand specificity and affinity of VpreB binding. To analyze its interactions with Igs, we made recombinant human VpreB protein and measured its affinity for H and L chain V domains using surface plasmon resonance. The recombinant VpreB protein existed as a homodimer in solution. VpreB chains associated with each other with an apparent Kd = 5 x 10(-7) M, and bound to a human VH domain, a mouse VH domain, and a human VL domain with a similar affinity. VpreB protein also bound to human Fab fragments of IgG with an apparent Kd = 6 x 10(-7) M, but showed a very low affinity for human Fc fragments of IgG. VpreB-Fab complex formation was reproduced by the formation of a trimolecular VpreB-VH-VL complex. Thus, VpreB proteins can associate with each other and also form complexes with Ig at sites different from those involved in VH-VL interaction. By flow cytometry, biotinylated VpreB protein bound to surface Ig-positive B cells but not T cells. Receptors that contain VpreB could be cross-linked by either Ig or by self-association.

Kinetic analysis of the interactions of recombinant human VpreB and Ig V domains

The surrogate light chain, composed of VpreB and lambda 5/14.1 proteins, is selectively expressed on B cell precursors, and is important for B cell development. The surrogate light chain associates with cell surface mu-chains on preB cells, but little is known about the ligand specificity and affinity of VpreB binding. To analyze its interactions with Igs, we made recombinant human VpreB protein and measured its affinity for H and L chain V domains using surface plasmon resonance. The recombinant VpreB protein existed as a homodimer in solution. VpreB chains associated with each other with an apparent Kd = 5 x 10(-7) M, and bound to a human VH domain, a mouse VH domain, and a human VL domain with a similar affinity. VpreB protein also bound to human Fab fragments of IgG with an apparent Kd = 6 x 10(-7) M, but showed a very low affinity for human Fc fragments of IgG. VpreB-Fab complex formation was reproduced by the formation of a trimolecular VpreB-VH-VL complex. Thus, VpreB proteins can associate with each other and also form complexes with Ig at sites different from those involved in VH-VL interaction. By flow cytometry, biotinylated VpreB protein bound to surface Ig-positive B cells but not T cells. Receptors that contain VpreB could be cross-linked by either Ig or by self-association.

Direct correlation between expression of endogenous inducible nitric oxide synthase and regression of M5076 reticulum cell sarcoma hepatic metastases in mice treated with liposomes containing lipopeptide CGP 31362

The purpose of this study was to determine whether the activation of inducible nitric oxide synthase (iNOS) can serve as a target for immunotherapeutic agents for treatment of murine reticulum cell sarcoma metastases. Liver metastases were established by the i.v. injection of M5076 cells into syngeneic C57BL/6 mice. Multiple systemic administrations of multilamellar vesicle-liposomes (MLV) containing the lipopeptide CGP 31362 (MLV-31362) or MLV-31362 combined with murine IFN-gamma eradicated the metastases. Tumor regression correlated with iNOS expression within the tumor lesions detected by Northern blot and immunohistochemistry techniques and with increased production of nitric oxide (NO). The administration of a specific iNOS inhibitor, NG-methyl-L-arginine, significantly decreased NO production and diminished the antitumor activities of the immunomodulators. Consistent with the regression of hepatic metastases, the combination of MLV-31362 and IFN-gamma synergistically induced iNOS gene expression, NO production, and apoptosis in the tumor cells under in vitro and in vivo conditions. The addition of NMA prevented the production of NO and apoptosis. These data imply that multiple systemic administrations of MLV-31362 plus IFN-gamma activate endogenous iNOS in sarcoma cells, which then undergo apoptosis, leading in turn to the regression of M5076 sarcoma hepatic metastases.

Molecular mechanism and classification of von Willebrand disease

The characterization of mutations in von Willebrand disease provides useful insight into the synthesis, structure, and function of von Willebrand factor. This growing body of information has prompted a reclassification of vWD types that is intended to reflect distinct pathophysiologic mechanisms. Despite this apparent progress, many aspects of vWF biology and pathophysiology remain poorly understood. These include the mechanism by which binding of vWF to platelets is induced at sites of vascular injury, and the factors that influence the likelihood of bleeding symptoms in patients with vWD type 1.

Ultraviolet radiation reduces phagocytosis and intracellular killing of mycobacteria and inhibits nitric oxide production by macrophages in mice

Exposure of mice to a single or multiple low doses of ultraviolet radiation (UVR) decreases the induction of the delayed-type hypersensitivity (DTH) response to Mycobacterium bovis BCG and Mycobacterium lepraemurium (MLM) and impairs the clearance of bacteria from the lymphoid organs. This study is an attempt to address the mechanism by which UV radiation impairs the clearance of bacteria from the lymphoid organs by determining whether alterations in macrophage function such as ingestion and intracellular killing of mycobacteria or production of reactive nitrogen intermediates might be responsible for these effects. BALB/c or C3H/HeN mice were exposed to a single dose of UVB (280-320 nm) radiation ranging from 0.35 to 45 kJ/m2, and at regular intervals after irradiation, the peritoneal and splenic macrophages were collected, cultured, and infected with live BCG or MLM. Phagocytosis was assessed at 6 h by counting the number of acid-fast bacteria per macrophage after Ziehl-Neelsen staining. The rate of intracellular killing was assessed by lysing the macrophages at 6, 12, 24, and 48 h after BCG infection, plating the suspension on 7H11 agar, and counting the number of colony-forming units 21 days later. Similarly, the nitric oxide production, as measured by nitrite, by macrophages obtained from UVB-irradiated and nonirradiated mice in response to BCG was assessed. There was a significant reduction in the uptake of organisms by both peritoneal and splenic macrophages collected from UV-irradiated mice. The intracellular killing of organisms was also significantly reduced, as was the production of nitric oxide by peritoneal macrophages infected with BCG in vitro. These results indicate that UVR affects macrophage functions and are consistent with our hypothesis that impaired clearance of bacteria in vivo results from an alteration in macrophage function.

Further Evidence that the N(inf2)-Fixing Endophytic Bacterium from the Intercellular Spaces of Sugarcane Stems Is Acetobacter diazotrophicus

Nitrogen-fixing bacteria, isolated from the sugar solution in intercellular spaces of sugarcane stems, were compared with the type strain of Acetobacter diazotrophicus (PAL-5) and found to be congruent with it in all characters studied. These characters were 37 morphological and biochemical tests, cellular fatty acid composition, and nitrogenase activity. The nitrogenase activity was measured by acetylene reduction and H(inf2) evolution and found to be unusual in that the H(inf2) evolution was suppressed much less than expected by high concentrations of acetylene.

Transformation reversion induced in JB6 RT101 cells by AP-1 inhibitors

The present study was directed to characterizing the reversion of neoplastic epidermal JB6 RT101 cells by AP-1 inhibiting drugs. Treatment of tumorigenic JB6 RT101 cells with retinoic acid (RA), fluocinolone acetonide (FA) or forskolin (FN) induced drug dependent (reversible) reversion of transformation. A synergistic effect on reversion was found with the three drugs in combination. Cells reverted by these three drugs also showed reduced levels of AP-1 transcription factor activity. After long term exposure of RT101 cells to FA, enrichment of flat revertants occurred in the population while a few unreverted cells formed foci. These unreverted cells appeared to be FA-resistant. Cloning of cells following RA treatment revealed stable reversion at least 2 months after drug withdrawal. Stable revertants showed lower basal AP-1 activity than RT101 cells (P < 0.01) and unstable revertants returned to transformed phenotype and elevated AP-1 activity within days following drug withdrawal. To our knowledge this is the first demonstration that drug induced reversion co-selects for reduced AP-1 activity. These data suggest that the JB6 RT101 cell line is a useful cell model for studying reversion of transformation and that inhibition of AP-1 activity may be one molecular mechanism of reversion. Considering the development of resistance with FA alone and the relative inefficiency of RA or FN alone, combinations of the three AP-1 activity inhibitors RA, FA and FN may be useful for further animal and clinical studies.

[Protective effect of total flavonoids of radix Astragali on mammalian cell damage caused by hydroxyl radical]

The protective effect of total flavonoids of Radix Astragali (TFA) on V79 cell damage caused by H2O2-Fe2+ system has been studied. The results show that total flavonoids of Radix Astragali inhibit lipid peroxides and increase SOD activity. It has also been found that TFA has different protective effect against various damages of V79 cells caused by hydroxyl radical.

Transfection with the inducible nitric oxide synthase gene suppresses tumorigenicity and abrogates metastasis by K-1735 murine melanoma cells

Previous studies from our laboratory demonstrated an inverse relationship between the expression level of inducible nitric oxide synthase (iNOS) and the metastatic potential of murine K-1735 melanoma cells. The purpose of this study was to provide direct evidence that the expression of iNOS suppresses metastatic potential of melanoma cells. Highly metastatic K-1735 clone 4 cells (C4.P), which express low levels of iNOS, were transfected with a functional iNOS (C4.L8), inactive-mutated iNOS (C4.S2), or neomycin-resistance (C4.Neo) genes in medium containing 3 mM NG-methyl-L-arginine (NMA). Positive transfectants were identified by Southern and Northern blot analyses and homogeneous staining with a specific anti-iNOS monoclonal antibody. Semiconfluent cultures of C4.P (parental), C4.Neo.3 (control transfection), C4.S2.3 (inactive iNOS), and C4.L8.5 (functional iNOS) were harvested, and viable cells were injected intravenously into syngeneic C3H/HeN mice and allogeneic BALB/c nude mice. C4.P, C4.Neo.3, and C4.S2.3 cells were highly metastatic whereas C4.L8.5 cells were not metastatic. Experiments with [125I]dUrd-labeled tumor cells demonstrated that the initial arrest in the lung microvasculature did not differ among the lines, but that C4.L8.5 cells died by 48-72 h after injection. Enhanced survival of all K-1735 C4 cells (including C4.L8.5) was found in mice given twice daily injections of 20 mg NMA. The C4.L8.5 cells produced slow growing subcutaneous tumors in nude mice, whereas the other three lines produced fast growing tumors. In vitro studies confirmed that in the absence of NMA the expression of iNOS in C4.L8.5 cells induced apoptosis. Collectively, these data demonstrate that the expression of recombinant iNOS in melanoma cells is associated with apoptosis, suppression of tumorigenicity, and abrogation of metastasis.

3,4-Diaminopyridine induced hydrolysis of phosphoinositide in cultured neurons from embryo chick forebrain

The effect of 3,4-diaminopyridine (DAP) on phosphoinositide hydrolysis in cultured neurons from embryo chick forebrain has been studied. DAP produced a dose- and time-dependent accumulation of inositol phosphates. At 1 mM DAP a maximal effect was obtained. In Ca2+ free medium, DAP-activated turnover of phosphoinositide was reduced, but was still significant. Blocking Ca2+ entry with 200 microM Cd2+ also did not abolish the DAP-induced accumulation of inositol phosphates. As a comparison the effect of high K+ exposure was investigated. High K+ enhanced phosphoinositide hydrolysis, and this effect was also reduced by excluding Ca2+ influx. Moreover, DAP had no additional effect on the high K(+)-induced hydrolysis of phosphoinositide. Using oxonol-V, a depolarization of the membrane potential was seen in the neurons bathed in DAP containing medium. It is suggested that the depolarization may play a role in DAP-activated phosphoinositide turnover in cultured neurons of the embryo chick forebrain, but that Ca2+ entry is not necessary for this effect.

Activation and cytotoxicity of 2-alpha-aminoacyl prodrugs of methotrexate

In an effort to improve the selectivity of the anticancer drug methotrexate (MTX), a series of potential prodrugs in which the 2-amino group was acylated with various alpha-amino acids (as well as L-pyroglutamic acid) was synthesized. Such derivatives are anticipated to be hydrolysed to MTX by appropriate aminopeptidases localized (over-expressed naturally or targeted as anti-tumor antibody conjugates) in the vicinity of the tumor. The L-leucyl, L-valyl, L-isoleucyl, D-alanyl and L-pyroglutamyl derivatives were assessed as to their suitability as prodrugs. Except for the L-pyroglutamyl compound, all derivatives decomposed slowly when incubated in phosphate buffer, pH 7.3; the formation of MTX was minimal. No major differences were observed when serum was included in the incubation medium, except for the L-leucyl compound, which was hydrolysed to MTX. The L-leucyl, L-valyl and L-isoleucyl derivatives were hydrolysed readily to MTX by aminopeptidase M (EC 3.4.11.2), while the L-pyroglutamyl and D-alanyl compounds were activated by pyroglutamate aminopeptidase (EC 3.4.19.3) (from Bacillus amyloliquefaciens) and D-aminopeptidase (from Ochrobactrum anthropi), respectively. When tested for inhibition of the target enzyme dihydrofolate reductase (DHFR; EC 1.5.1.3), 2-L-valyl-MTX showed inhibition two orders of magnitude poorer than that given by MTX, in agreement with the expectation that acylation of the 2-amino group reduces binding to DHFR. After treatment of this derivative with aminopeptidase M, the extent of inhibition correlated with the amount of MTX formed. MTX derivatives alone or in combination with the complementary peptidase were tested for cytotoxicity on murine L1210 cells in culture. The above-listed derivatives were considerably less cytotoxic than MTX, except for the L-leucyl derivative which showed considerable cytotoxicity. When the appropriate exogenous peptidase was included, the cytotoxicity of the activated prodrugs approached that of MTX. These results indicate that 2-L-leucyl-MTX is unsuitable as a prodrug since it is activated prematurely by serum enzymes. Although the L-valyl and L-isoleucyl derivatives do not hydrolyse to MTX in serum and are readily activated, they are not ideal prodrugs since they decompose under physiological conditions; the properties of the decomposition product will have a bearing on the ultimate suitability of these compounds. 2-L-Pyroglutamyl-MTX is the best candidate prodrug, showing stability and ready activation by the appropriate aminopeptidase.

Level and function of epidermal growth factor receptor predict the metastatic potential of human colon carcinoma cells

The purpose of this study was to determine whether production of liver metastasis by human colon carcinoma (HCC) cells depends on the response of tumor cells to organ-derived growth factors. HCC cells were isolated from several surgical specimens whose malignant potential differed (Dukes' stage B or D tumors), adapted to grow in culture, and assessed for expression of the epidermal growth factor receptor (EGF-R). Northern blot analyses revealed that highly metastatic HCC cells expressed >5-fold the number of EGF-R mRNA transcripts as low metastatic cells. The level of mRNA correlated with the amount of EGF-R protein as detected by Western blotting, immunohistochemistry, and Scatchard analyses. HCC growth response in vitro to picograms of transforming growth factor alpha was associated with functional cell surface EGF-Rs as determined by receptor tyrosine kinase activity assays. The EGF-R gene was not amplified or rearranged in highly metastatic cells. However, fluorescence in situ hybridization analysis showed that the copy number of chromosome 7 was higher in the highly metastatic cells. HCC cells were selected in vitro for low or high expression of EGF-R. Subsequent to injection into nude mice, only cells with high expression of EGF-R produced a high incidence of liver metastasis. These data demonstrate that expression of EGF-R by HCC cells directly correlates with their ability to produce hepatic metastasis.

von Willebrand's factor and von Willebrand's disease

von Willebrand's factor is required for platelet adhesion to subendothelium, and for normal factor VIII survival in the circulation. These functions require the assembly of von Willebrand's factor into multimers that exhibit properly regulated binding to platelet glycoprotein lb. Recent studies suggest that the propeptide of von Willebrand's factor may catalyze multimer assembly and have identified new segments of von Willebrand's factor that appear to regulate its affinity for glycoprotein lb. Two segments of von Willebrand's factor have been found to interact with collagen type VI, which is a candidate binding site for von Willebrand's factor in the subendothelium. Advances in the identification of mutations have prompted a reclassification of von Willebrand's disease. ABO antigens on von Willebrand's factor may impair the efficacy of plasma or recombinant von Willebrand's factor when administered to patients with incompatible ABO blood type.

[Effect of verapamil on Ca2+ and Ca(2+) Mg(2+)-ATPase activity in rat brain synaptosomes]

To elicit the correlation between the adrenergic transmitter release and calmodulin (CaM), the effect of verapamil on the free Ca2+ concentration was measured with fluorescence analysis and Ca(2+) Mg(2+)-ATPase activity in rat synaptosomes were studied. When stimulated with high-K+ or norepinephrine, the concentration of free Ca2+ in rat synaptosome was increased by verapamil 10, 50, and 100 mumol.L-1. But the free Ca2+ concentration in the resting synaptosome was reduced by verapamil. The activity of Ca(2+) Mg(2+)-ATPase in synaptosome was remarkably inhibited by verapamil in a dose-dependent manner. These results support our hypothesis that CaM not only acts directly on the vesicles to enhance the transmitter release, but also acts on the activity of Ca(2+) Mg(2+)-ATPase to reduce the free Ca2+ in the cytosol, and indirectly inhibited the transmitter release.

Function of bone marrow stromal cell lines derived from nude mice

We previously reported that in double deficient nude.xid mice B cells failed to develop and their bone marrow did not produce mature B cells in vitro. However, when progenitors from nude.xid bone marrow were placed on a preestablished normal stromal cell line (AC6) they differentiated into surface IgM+ cells. This raised the possibility of a deficiency of nude and nude.xid stromal cells such that they were incapable of supporting the maturation of X-linked immune deficiency (xid) B cells. Here we ask whether bone marrow stromal cells from nude and nude.xid mice have the ability to support xid B cell lymphopoiesis. A primary stromal cell layer derived from nude mice supported xid B cell differentiation in vitro. We derived panels of stromal cell lines by transfection of primary stromal cell layers with a retrovirus encoding SV40 large T Ag. Several bone marrow stromal cell lines derived from nude and nude.xid mice supported xid B cell differentiation from CD43+/CD45 (B220-) to CD45 (B220+) and from CD45 (B220+)/surface IgM- to surface IgM+. Supporting cell lines expressed both IL-7 and insulin-like growth factor I. The frequencies of bone marrow stromal cells capable of supporting xid B cell differentiation were similar in normal, xid, nude, and nude.xid mice. These results demonstrate that nude and nude.xid mice have bone marrow stromal cells with normal abilities to support B cell maturation.

Function of bone marrow stromal cell lines derived from nude mice

We previously reported that in double deficient nude.xid mice B cells failed to develop and their bone marrow did not produce mature B cells in vitro. However, when progenitors from nude.xid bone marrow were placed on a preestablished normal stromal cell line (AC6) they differentiated into surface IgM+ cells. This raised the possibility of a deficiency of nude and nude.xid stromal cells such that they were incapable of supporting the maturation of X-linked immune deficiency (xid) B cells. Here we ask whether bone marrow stromal cells from nude and nude.xid mice have the ability to support xid B cell lymphopoiesis. A primary stromal cell layer derived from nude mice supported xid B cell differentiation in vitro. We derived panels of stromal cell lines by transfection of primary stromal cell layers with a retrovirus encoding SV40 large T Ag. Several bone marrow stromal cell lines derived from nude and nude.xid mice supported xid B cell differentiation from CD43+/CD45 (B220-) to CD45 (B220+) and from CD45 (B220+)/surface IgM- to surface IgM+. Supporting cell lines expressed both IL-7 and insulin-like growth factor I. The frequencies of bone marrow stromal cells capable of supporting xid B cell differentiation were similar in normal, xid, nude, and nude.xid mice. These results demonstrate that nude and nude.xid mice have bone marrow stromal cells with normal abilities to support B cell maturation.

A Nitrogen-Fixing Endophyte of Sugarcane Stems (A New Role for the Apoplast)

The intercellular spaces of sugarcane (Saccharum officinarum L.) stem parenchyma are filled with solution (determined by cryoscanning microscopy), which can be removed aseptically by centrifugation. It contained 12% sucrose (Suc; pH 5.5.) and yielded pure cultures of an acid-producing bacterium (approximately 104 bacteria/mL extracted fluid) on N-poor medium containing 10% Suc (pH 5.5). This bacterium was identical with the type culture of Acetobacter diazotrophicus, a recently discovered N2-fixing bacterium specific to sugarcane, with respect to nine biochemical and morphological characteristics, including acetylene reduction in air. Similar bacteria were observed in situ in the intercellular spaces. This demonstrates the presence of an N2-fixing endophyte living in apoplastic fluid of plant tissue and also that the fluid approximates the composition of the endophytes's optimal culture medium. The apoplastic fluid occupied 3% of the stem volume; this approximates 3 tons of fluid/ha of the crop. This endogenous culture broth consisting of substrate and N2-fixing bacteria may be enough volume to account for earlier reports that some cultivars of sugarcane are independent of N fertilizers. It is suggested that genetic manipulation of apoplastic fluid composition may facilitate the establishment of similar symbioses with endophytic bacteria in other crop plants.

Organ-specific modulation of steady-state mdr gene expression and drug resistance in murine colon cancer cells

BACKGROUND

The major cause of death from cancer is metastases that are resistant to conventional therapies. The resistance of metastatic tumor cells to chemotherapy can be caused by their intrinsic properties, such as increased expression of the mdr genes.

PURPOSE

The purpose of our present study was to determine some of the mechanisms by which the organ microenvironment influences the response of tumor cells to chemotherapy.

METHODS

Murine CT-26 colon cancer cells growing in continuous culture (parental cells) were harvested and injected subcutaneously into the lateral flank (to produce subcutaneous tumors) or the lateral tail vein (to produce experimental lung metastases) of 10 8-week-old syngeneic male BALB/c mice. Seven days after tumor-cell injection, the mice were given intravenous injections of either doxorubicin (10 mg/kg) or 0.9% NaCl (controls). This in vivo injection was repeated 7 days later. Mice with subcutaneous tumors and lung metastases were killed by cervical dislocation on day 21, and tumor samples from control mice were harvested and adapted to culture. The sensitivity of the cultured cells to doxorubicin and fluorouracil (5-FU) was determined at multiple time points. Levels of mdr-1 DNA were measured by slot-blot and Southern-blot analyses. mdr mRNA expression levels were measured by Northern-blot analysis using mdr-1- and mdr-3-specific hybridization probes, and P-glycoprotein level was determined by fluorescence-activated cell sorting using different monoclonal antibodies.

RESULTS

Treatment with doxorubicin produced 80% growth inhibition of CT-26 subcutaneous tumors but had little effect on the number (and size) of experimental lung metastases. Collectively, the results suggest that the multidrug-resistant phenotype developed in CT-26 cells growing in the lung environment. Cultures established from lung metastases were initially resistant to doxorubicin (but not to 5-FU) and showed elevated expression of mdr-1 mRNA transcripts and P-glycoprotein. This resistance could be overcome by verapamil and disappeared after 21 days in culture. No mdr gene amplification was detected. The expression level of mdr-specific mRNA (predominance of mdr-1) and P-glycoprotein was directly associated with resistance to doxorubicin.

CONCLUSIONS

Results of this study have demonstrated that the in vivo sensitivity of murine CT-26 colon carcinoma cells to doxorubicin depends on the organ environment. The organ environment can influence the P-glycoprotein-mediated multidrug-resistant phenotype in tumor cells, and the increased expression of P-glycoprotein is transient; once removed from the environment (lung), the cell's resistance reverts to that of the sensitive parent cells.

Modulation of tumor cell response to chemotherapy by the organ environment

The outcome of cancer metastasis depends on the interaction of metastatic cells with various host factors. The implantation of human cancer cells into anatomically correct (orthotopic) sites in nude mice can be used to ascertain their metastatic potential. While it is clear that vascularity and local immunity can retard or facilitate tumor growth, we have found that the organ environment also influences tumor cell functions such as production of degradative enzymes. The organ microenvironment can also influence the response of metastases to chemotherapy. It is not uncommon to observe the regression of cancer metastases in one organ and their continued growth in other sites after systemic chemotherapy. We demonstrated this effect in a series of experiments using a murine fibrosarcoma, a murine colon carcinoma, and a human colon carcinoma. The tumor cells were implanted subcutaneously or into different visceral organs. Subcutaneous tumors were sensitive to doxorubicin (DXR), whereas lung or liver metastases were not. In contrast, sensitivity to 5-FU did not differ between these sites of growth. The differences in response to DXR between s.c. tumors (sensitive) and lung or liver tumors (resistant) were not due to variations in DXR potency or DXR distribution. The expression of the multidrug resistance-associated P-glycoprotein as determined by flow cytometric analysis of tumor cells harvested from lesions in different organs correlated inversely with their sensitivity to DXR: increased P-glycoprotein was associated with overexpression of mdr1 mRNA. However, the organ-specific mechanism for upregulating mdr1 and P-glycoprotein has yet to be elucidated.

New Production Cost-Tolerance Models for Tolerance Synthesis

Several new production cost-tolerance models and a hybrid-model tolerance optimization formulation for tolerance synthesis are presented. These new models are introduced based upon the empirical cost-tolerance data of typical production processes, including hole producing, turning, milling, grinding and casting. The introduced models fit empirical cost-tolerance data with considerably less errors, and provide more reliable results for tolerance synthesis. In addition, the hybrid-model tolerance optimization formulation provides further modeling error reduction. The systematic evaluation of various cost-tolerance models provides model selection guidelines for tolerance synthesis. A typical tolerance design example is used to illustrate the method.

Differential transformation efficiency but not AP-1 induction under anchorage-dependent and -independent conditions

The JB6 mouse epidermal cell system has been extensively used as an in vitro model for the study of tumor promotion. The present study aimed to assess the relevance of monolayer measurements to the process of transformation, which is induced more efficiently under anchorage-independent (AI) conditions. Although it would be ideal to use identical conditions for studying tumor promoter-induced transformation and biochemical and molecular events that may cause the process, it is not feasible in the case of soft agar conditions because cells cannot be readily recovered. In the present report, we used liquid medium over agar as an AI condition that permitted efficient recovery of cells. Responses to tumor promoter have been compared with those in monolayer and semisolid agar. Results indicate that 12-O-tetradecanoyl-phorbol-13-acetate (TPA) induced similar magnitude concentration-dependent transformation of JB6 cells under both of the AI conditions, namely soft agar and over-agar. Under anchorage-dependent (AD) conditions of exposure to TPA, the transformation efficiency was much lower than that seen under AI conditions. Mechanical detachment of monolayer cells after 5-10 days TPA exposure enriched the transformed phenotype. Activator protein 1 transcriptional activity measured at 12 h was induced equally under AD and AI conditions, and thus is not an early limiting event that could explain the lower transformation efficiency seen under AD conditions. To summarize, the over-agar and monolayer assays described in this study can be considered valid for the study of early biochemical and molecular events relevant to the promotion of transformation measured in soft agar.

Chromate-mediated free radical generation from cysteine, penicillamine, hydrogen peroxide, and lipid hydroperoxides

The Cr(VI)-mediated free radical generation from cysteine, penicillamine, hydrogen peroxide, and model lipid hydroperoxides was investigated utilizing the electron spin resonance (ESR) spin trapping technique. Incubation of Cr(VI) with cysteine (Cys) generated cysteinyl radical. Radical yield depended on the relative concentrations of Cr(VI) and Cys. The radical generation became detectable at a cysteine:Cr(VI) ratio of about 5, reached its highest level at a ratio of 30, and declined thereafter. Cr(VI) or Cys alone did not generate a detectable amount of free radicals. Similar results were obtained with penicillamine. Incubation of Cr(VI), Cys or penicillamine and H2O2 led to hydroxyl (.OH) radical generation, which was verified by quantitative competition experiments utilizing ethanol. The mechanism for .OH radical generation is considered to be a Cr(VI)-mediated Fenton-like reaction. When model lipid hydroperoxides such as t-butyl hydroperoxide and cumene hydroperoxide were used in place of H2O2, hydroperoxide-derived free radicals were produced. Since thiols, such as Cys, exist in cellular systems at relatively high concentrations, Cr(VI)-mediated free radical generation in the presence of thiols may participate in the mechanisms of Cr(VI)-induced toxicity and carcinogenesis.

Regulatory mechanisms for the expression of type IV collagenases/gelatinases in murine macrophages

The purpose of this study was to determine the regulation of type IV collagenase expression in murine peritoneal macrophages (PEM) after they are incubated with LPS. LPS stimulated the production of the latent forms of 92-kDa (MMP-9) and 72-kDa (MMP-2) type IV gelatinases in a dose-dependent (> 10 ng/ml) and serum-dependent manner. Time course analyses revealed that LPS regulated the expression of MMP-9 and MMP-2 via discordant kinetics. Prolonged treatment of PEM with LPS decreased MMP-9 but not MMP-2 activities. IFN-gamma decreased the production of both gelatinases by PEM responding to LPS. TGF-beta stimulated production of both matrix metalloproteinases but blocked the LPS-mediated secretion of MMP-9. LPS-stimulated MMP-9 production was suppressed by genistein and tyrphostin, two specific tyrosine kinase inhibitors, as well as H-7, a serine/threonine protein kinase inhibitor, but not by HA1004, a relatively selective inhibitor for PKA and PKG. Our data demonstrate that the secretion of MMP-2 and MMP-9 by murine PEM is differentially regulated, suggesting a distinct in vivo role for these two otherwise analogous type IV gelatinases in macrophage-mediated connective tissue destruction at sites of immunologic challenges.

Regulatory mechanisms for the expression of type IV collagenases/gelatinases in murine macrophages

The purpose of this study was to determine the regulation of type IV collagenase expression in murine peritoneal macrophages (PEM) after they are incubated with LPS. LPS stimulated the production of the latent forms of 92-kDa (MMP-9) and 72-kDa (MMP-2) type IV gelatinases in a dose-dependent (&gt; 10 ng/ml) and serum-dependent manner. Time course analyses revealed that LPS regulated the expression of MMP-9 and MMP-2 via discordant kinetics. Prolonged treatment of PEM with LPS decreased MMP-9 but not MMP-2 activities. IFN-gamma decreased the production of both gelatinases by PEM responding to LPS. TGF-beta stimulated production of both matrix metalloproteinases but blocked the LPS-mediated secretion of MMP-9. LPS-stimulated MMP-9 production was suppressed by genistein and tyrphostin, two specific tyrosine kinase inhibitors, as well as H-7, a serine/threonine protein kinase inhibitor, but not by HA1004, a relatively selective inhibitor for PKA and PKG. Our data demonstrate that the secretion of MMP-2 and MMP-9 by murine PEM is differentially regulated, suggesting a distinct in vivo role for these two otherwise analogous type IV gelatinases in macrophage-mediated connective tissue destruction at sites of immunologic challenges.

[Immunochemical identification of kinesin in Physarum polycephalum]

Physarum polycephalum, a low eukaryote ameba provides an attractive system for studying contractile proteins. In this work, we have identified a kinesin-like protein in the plasmodium of Physarum polycephalum by western blotting, using monoclonal antibody against kinesin (bovine brain). The molecular weight of the polypeptide which immunologically cross-reacts with kinesin from bovine brain is about 137kd. It suggests that the 137kd polypeptide is the heavy chain of the kinesin in Physarum polycephalum.

Circumvention of multidrug-resistance in murine fibrosarcoma and colon-carcinoma cells by treatment with the alpha-adrenoceptor antagonist furobenzazepine

The purpose of this study was to determine whether agonists and antagonists of alpha-adrenoceptors that affect calcium fluxes and protein kinase C signal transduction alter the chemosensitivity of cancer cells that exhibit multidrug resistance (MDR). The effects of nine alpha-adrenoceptor antagonists or antagonists on the in vitro chemosensitivity of the UV-2237 murine fibrosarcoma and its doxorubicin-selected MDR variants (UV-2237-R1 and UV-2237-R10) were examined. Noncytotoxic concentrations of the alpha-adrenoceptor antagonist furobenzazepine enhanced the antitumor activity of doxorubicin, actinomycin D, vinblastine and vincristine, but not 5-fluorouracil. Similar effects of furobenzazepine were also observed in recently established doxorubicin-resistant MDR variants of the CT-26 murine colon carcinoma. The chemosensitizing effect of furobenzazepine was associated with an increase in intracellular accumulation of anticancer drugs. Furobenzazepine did not compete with [H-3]azidopine for photoaffinity labeling of P-glycoprotein, but it did produce a transient 30% reduction of P-glycoprotein in the MDR cells. These data indicate that furobenzazepine can reverse a P-glycoprotein-mediated experimental MDR phenotype.

Disulfide bonds required to assemble functional von Willebrand factor multimers

The hemostatic functions of human von Willebrand Factor (vWF) depend on the normal assembly of disulfide-linked multimers from approximately 250-kDa subunits. Subunits initially form dimers through disulfide bonds near the COOH terminus. Dimers then form multimers through disulfide bonds near the NH2 terminus of each subunit. Previous studies of plasma vWF and recombinant vWF fragments indicate that 1 or more of the Cys residues at position 459, 462, and 464 form intersubunit disulfide bonds. No evidence has been reported that vWF multimer formation involves additional intersubunit bonds. To probe the disulfide bond requirements for multimer formation, mutant vWF proteins were expressed in which all 3 Cys residues at positions 459, 462, and 464 were changed to either Gly or Ala. Surprisingly, none of these cysteines appears to be necessary for efficient multimer assembly. Furthermore, recombinant vWF with Gly or Ala at all three positions induces platelet aggregation in the presence of ristocetin and binds to platelet glycoprotein Ib, factor VIII, and collagen in a manner similar to wild-type recombinant vWF. These results suggest that other intersubunit disulfide bonds must exist. Direct evidence for such a bond was obtained by characterization of tryptic fragments of vWF. By Edman degradation, amino acid composition, and mass spectrometry, a disulfide bond was demonstrated between Cys379 residues of adjacent vWF subunits. Thus, intersubunit disulfide bonds involving Cys379 and 1 or more of the Cys residues at positions 459, 462, and 464 connect the NH2-terminal ends of the vWF subunits in a parallel orientation.

Effects of 3,4-diaminopyridine on myoplasmic calcium and phosphoinositide hydrolysis in frog sartorius muscle fibers

Using Ca(2+)-selective microelectrodes, the effects of 3,4-diaminopyridine (DAP) on myoplasmic calcium ([Ca2+]i) were studied in frog satorius muscle fibers. DAP induced an increase of [Ca2+]i in a concentration-dependent manner. DAP 1 mmol.L-1 increased the [Ca2+]i from control 166 +/- 41 nmol.L-1 to 416 +/- 69 nmol.L-1 (n = 10). In the absence of external calcium, DAP still enhanced [Ca2+]i. [Ca2+]i of the fibers bathed in Ca(2+)-free Ringer's solution containing DAP 1 mmol.L-1 was 152 +/- 43 nmol.L-1, which was significantly higher than 77 +/- 35 nmol.L-1 of [Ca2+]i of the fibers in Ca(2+)-free Ringer's solution. In addition, DAP promoted the hydrolysis of phosphoinositides, and DAP-induced hydrolysis was more in the presence of external calcium. It is suggested that, through enhancing the hydrolysis of phosphoinositides, DAP released Ca2+ from intracellular Ca2+ store in frog sartorius muscle fibers.

Radioimmunoguided surgery in gastric cancer using 131-I labeled monoclonal antibody 3H11

A clinical trial of radioimmunoguided surgery (RIGS) using 131-I labeled monoclonal antibody (MAb) 3H11 was performed on 25 cases with gastric cancer in this study. The results showed that the route of the administration of radiolabeled MAb is the key point of successful RIGS for gastric cancer. The RIGS in 19 cases in the group of submucosal injection via endoscope was very satisfying. For the detection of metastatic lymph nodes, the sensitivity rate of RIGS was 99.2% (118/119), the specificity, 97.7% (43/44), and the accuracy 98.8% (161/163). The accuracy rate in detecting tumor infiltration of the gastric wall was 95.9% (94/98), the sensitivity 94.6% (35/37), and the specificity 96.7% (59/61). Thus, the use of RIGS may improve the radical resectability rate and possibly the overall survival rate in patients with gastric cancer.

Inverse correlation between expression of inducible nitric oxide synthase activity and production of metastasis in K-1735 murine melanoma cells

The purpose of these studies was to determine whether the induction of NO synthase activity in murine K-1735 melanoma cells correlated with their metastatic potential. Nonmetastatic, metastatic, and somatic cell hybrids (produced by fusion of nonmetastatic and metastatic cells) were injected i.v. into syngeneic C3H/HeN mice. Metastatic cells survived to produce experimental lung metastases, whereas nonmetastatic cells did not. The various clones and somatic cell hybrids were incubated in vitro with combinations of tumor necrosis factor, interleukin 1, gamma-interferon, and lipopolysaccharide. Nonmetastatic cells exhibited high levels of inducible NO synthase activity and NO, whereas metastatic cells did not. Both the cytotoxic effects of the cytokines and NO production were inhibited by the addition of NG-monomethyl-L-arginine, a specific inhibitor of NO synthase. These data demonstrate an inverse correlation between production of endogenous NO and the ability of K-1735 cells to survive in syngeneic mice to produce lung metastases.

Blocking of tumor promoter-induced AP-1 activity inhibits induced transformation in JB6 mouse epidermal cells

AP-1 transcriptional activity is stimulated by the transformation promoters phorbol 12-myristate 13-acetate ("12-O-tetradecanoylphorbol 13-acetate," TPA) and epidermal growth factor (EGF) in promotion-sensitive (P+) but not in promotion-resistant (P-) JB6 mouse epidermal cell lines. Although TPA stimulates expression of the jun and fos family genes, only c-jun expression shows higher elevation in P+ cells than in P- cells. The present study tests the hypothesis that induced AP-1 activity is required for tumor promoter-induced transformation in JB6 P+ cells. Both retinoic acid and the glucocorticoid fluocinolone acetonide inhibited basal and TPA-induced AP-1 activities that were tested with a stromelysin promoter-chloramphenicol acetyltransferase reporter gene in P+ cells. Since both retinoic acid and fluocinolone acetonide are active in inhibiting TPA-induced anchorage-independent transformation of P+ cells in the dose range that blocks TPA-induced AP-1 activity, their antipromoting effects may occur through inhibition of AP-1 activity. To test the hypothesis with a more specific inhibitor, stable clonal transfectants of P+ cells expressing dominant negative c-jun mutant encoding a transcriptionally inactive product were analyzed. All transfectants showed a block in TPA and EGF induction of AP-1 activity. All transfectants also showed inhibition of TPA-induced transformation, and most transfectants showed a block in EGF-induced transformation. These results indicate that AP-1 activity is required for TPA- or EGF-induced transformation. This work demonstrates that a specific block in induced AP-1 activity inhibits tumor promoter-induced transformation.

An efficient route to N-palmitoyl-D-erythro-sphingomyelin and its 13C-labeled derivatives

We describe here a practical and efficient route to a homogeneous N-palmitoyl-D-erythro-sphingomyelin and its 13C-labeled derivatives. (2S,3R,4E)-2-Azido-3-(tert-butyldimethylsilyloxy)-4-octad ecene-1-ol 1 was converted to the sphingosine equivalent 2 by treatment with triphenylphosphine and water. Amine 2 was then coupled with palmitic acid, affording the ceramide derivative 3a. In the following two reactions the phosphorylcholine functional group was generated by using 2-chloro-2-oxo-1,3,2-dioxaphospholane and trimethylamine, respectively. The final deprotection of the secondary hydroxyl group in 5a produced the desired N-palmitoyl-D-erythro-sphingomyelin 6a. The overall yield of this five-step synthesis is 43%. The melting point, 213-215 degrees C, the specific rotation, [alpha]20D = +6.8 (c = 1.3, CH2Cl2/MeOH 1:1) and 1H- and 13C-NMR data indicate that the synthetic sphingomyelin is enantiomerically pure. The 13C-labeled derivatives 6b, 6c and 6d were synthesized by employing the same scheme.

Optimal Rough Machining of Sculptured Parts on a CNC Milling Machine

An optimal approach to the rough machining of sculptured parts with least machining time is presented. The contour map cutting method is used to generate CNC tool paths based on the CAD model of sculptured parts. The part and stock geometry related parameters, including the number of cutting layers and the distributions of cutting depth, and the process parameters of feed rate and depth of cut, are optimized. The method can automate CNC programming for sculptured part rough machining, considerably improve productivity, and lower production costs. Two examples are used to illustrate the approach and its advantages.

Protein tyrosine kinase inhibitors decrease induction of nitric oxide synthase activity in lipopolysaccharide-responsive and lipopolysaccharide-nonresponsive murine macrophages

We investigated tumoricidal activation and induction of nitric oxide synthase (NOS) activity in macrophages from LPS-responsive (C3H/HeN) and -unresponsive mice (C3H/HeJ). Macrophages were incubated in vitro with a synthetic lipopeptide or with LPS and IFN-gamma. LPS and IFN-gamma activated C3H/HeN but not C3H/HeJ macrophages to lyse B16 melanoma cells. In contrast, lipopeptide and IFN-gamma activated macrophages from both strains of mice. Genistein, a specific inhibitor of protein tyrosine kinase, significantly blocked tumoricidal activation of macrophages from both strains of mice. Genistein did not affect tumor cell binding but significantly inhibited the production of nitric oxide. Genistein, herbimycin A, and tyrphostin inhibited the induction of NOS activity in macrophages from both strains of mice. These data suggest that protein tyrosine kinase activity is involved in the signal transduction pathway of LPS and other synthetic bacterial-related immunomodulators at a point preceding triggering of macrophage tumoricidal activation and expression of inducible NOS activity.

Protein tyrosine kinase inhibitors decrease induction of nitric oxide synthase activity in lipopolysaccharide-responsive and lipopolysaccharide-nonresponsive murine macrophages

We investigated tumoricidal activation and induction of nitric oxide synthase (NOS) activity in macrophages from LPS-responsive (C3H/HeN) and -unresponsive mice (C3H/HeJ). Macrophages were incubated in vitro with a synthetic lipopeptide or with LPS and IFN-gamma. LPS and IFN-gamma activated C3H/HeN but not C3H/HeJ macrophages to lyse B16 melanoma cells. In contrast, lipopeptide and IFN-gamma activated macrophages from both strains of mice. Genistein, a specific inhibitor of protein tyrosine kinase, significantly blocked tumoricidal activation of macrophages from both strains of mice. Genistein did not affect tumor cell binding but significantly inhibited the production of nitric oxide. Genistein, herbimycin A, and tyrphostin inhibited the induction of NOS activity in macrophages from both strains of mice. These data suggest that protein tyrosine kinase activity is involved in the signal transduction pathway of LPS and other synthetic bacterial-related immunomodulators at a point preceding triggering of macrophage tumoricidal activation and expression of inducible NOS activity.

Dosage-dependent dominance over wild-type p53 of a mutant p53 isolated from nasopharyngeal carcinoma

Mutational inactivation of p53, a tumor suppressor gene, is the most common genetic alteration found in human cancer. Most mutated p53s either lose tumor suppressor function or gain oncogenic activity. We recently reported the detection of a heterozygous point mutation of p53 at codon 280 in nasopharyngeal carcinoma (NPC) (1), a high-incidence malignancy in southern China and southeast Asia. Given its heterozygous state, in which both wild-type and mutated p53 gene were expressed, p53-thr280 should function dominantly in the presence of the wild-type form if it is to play a role in nasopharynx carcinogenesis. We tested this dominance hypothesis in the cells of two model systems: 1) human Saos-2 cells lacking endogenous p53, and 2) mouse JB6 tumor promotion-resistant cells (P-) expressing endogenous wild-type p53. The results showed dosage-dependent dominance of p53-thr280 in controlling WT p53-driven transcriptional activity; in governing cell growth; and in progressing P- phenotype to tumor promotion-sensitive (P+) phenotype. This dominant negative effect was seen at a 1:1 (WT:MU) ratio and was more striking at a ratio of 1:3. A model is proposed to explain the dominant negative effect of mutant p53. We conclude from this study that p53-thr280 is likely to be dominant in the heterozygous state found in NPC and that this dominant-negative mutated p53 may contribute to the genesis of NPC or of other carcinomas in which both mutant and wild-type p53 are expressed.

DNA polymerase III accessory proteins. IV. Characterization of chi and psi

The gamma complex (gamma delta delta' chi psi) subassembly of the Escherichia coli replicase initiates processive replication upon assembling the ring-shaped beta subunit around DNA. The beta ring acts as a clamp to hold the replicase down to DNA for highly processive synthesis. In this report we characterize the chi and psi subunits of the gamma complex. Both chi and psi are monomeric, and they associate to form a 1:1 complex. The chi subunit does not form a complex with gamma, but psi binds gamma tightly thereby acting as a bridge to assimilate chi into the gamma complex structure. The psi subunit stimulated the ATPase and replication activities of gamma. The chi subunit only stimulated the activities of gamma when the psi subunit was also present thus reflecting the structure where psi bridges the interaction of chi with gamma.

DNA polymerase III accessory proteins. I. holA and holB encoding delta and delta'

The genes encoding the delta and delta' subunits of the 10-subunit Escherichia coli replicase, DNA polymerase III holoenzyme, have been identified and sequenced. The holA gene encoding delta is located downstream of rlpB at 15.2 min and predicts a 38.7 kda protein. The holB gene encoding delta' is located at 24.3 min and predicts a 36.9-kDa protein. Hence the delta and delta' subunits are unrelated proteins encoded by separate genes. The genes have been used to express and purify delta and delta' in quantity. The predicted amino acid sequence of delta' is homologous to the sequences of the tau and gamma subunits revealing a large amount of structural redundancy within the holoenzyme.

DNA polymerase III accessory proteins. III. holC and holD encoding chi and psi

Genes encoding the chi and psi accessory proteins of the DNA polymerase III holoenzyme replicase of Escherichia coli have been identified, sequenced, and used to express and purify both chi and psi in quantity. The holC gene encoding chi is located between the xerB and valS genes at 96.5 min on the chromosome; it encodes a 147-amino acid protein of 16.6 kDa. holD encoding psi lies upstream of rimI at 99.3 min and encodes a 137-amino acid protein of 15.2 kDa. The genes have been cloned into expression vectors, and both chi and psi have been purified in quantity. The accompanying report characterizes the function and physical interactions of chi and psi with other holenzyme subunits (Xiao, H., Dong, Z., and O'Donnell, M. (1993) J. Biol. Chem. 268, 11779-11784).

The immunogenic properties of drug-resistant murine tumor cells do not correlate with expression of the MDR phenotype

Alterations in the immunogenic properties of tumor cells frequently accompany selection for multiple-drug-resistant (MDR) variants. Therefore, studies were performed to examine the hypothesis that overexpression of membrane P-glycoprotein, commonly observed in MDR tumor cells, is associated with enhanced immunogenic properties. Immunogenicity was determined by (a) the ability of drug-sensitive parental UV2237M fibrosarcoma cells and drug-resistant UV2237M variant cells to immunize normal mice against rechallenge with parental tumor cells and (b) the ability of normal syngeneic mice to reject cell inocula that caused progressive tumor growth in immunocompromised mice. Variant UV2237M cell lines included subpopulations selected for a six- to ten-fold increase in mRNA for P-glycoprotein and expression of the MDR phenotype (resistance to doxorubicin) and cells sensitive to doxorubicin (and no expression of MDR properties) but resistant to ouabain. All UV2237M drug-resistant cells were highly immunogenic in immunocompetent mice, regardless of their MDR phenotype. Additional studies showed that CT-26 murine adenocarcinoma cells, sensitive or resistant to doxorubicin (expressing high levels of P-glycoprotein), injected into normal syngeneic Balb/c mice produced rapidly growing tumors. The data do not demonstrate a correlation between the immunogenic properties of drug-resistant tumor cells and the expression of P-glycoprotein.