Use of a recombinant parvovirus to facilitate screening for human melanoma cell clones expressing tetracycline-responsive transactivators

The tetracycline regulatory (TET) system provides a useful means of controlling foreign gene expression in mammalian cells. Exploiting this system in cultured cells requires the prior isolation, from the cells of interest, of transfectant clones expressing the necessary TET transactivator, tTA, or reverse transactivator, rtTA. We describe a simple screening procedure for identifying transfectant clones expressing a properly regulated transactivator, and the application of this method to isolating clones of human melanoma cells expressing either tTA or rtTA. Clones in multi-well plates are transduced by exposure to a recombinant parvovirus containing a luciferase reporter, under control of a promoter responsive to the TET system transactivators. Transactivation of reporter expression in the presence or absence of doxycycline (DOXY) is determined after one to two days, using a rapid luciferase assay. Screening is easier and more reproducible with this transduction method than with conventional transient transfection of analogous reporter plasmids. Clones of two human melanoma cell lines showing >100-200-fold transactivation after transfection with either tTA or rtTA were readily identified using this method.

Bystander killing of tumour cells by antibody-targeted enzymatic activation of a glucuronide prodrug

RHI-betaG-PEG, formed by linking poly(ethylene glycol)-modified beta-glucuronidase to Mab RH1, was employed to examine bystander killing of antigen-negative N1S1 rat hepatoma cells by activation of a glucuronide prodrug (BHAMG) of p-hydroxyaniline mustard (pHAM) at antigen-positive AS-30D rat hepatoma cells. Sequential treatment of cells with 10 microg ml(-1) RH1-betaG-PEG and 20 microM BHAMG was not toxic to N1S1 cells but killed 99% of AS-30D cells. Over 98% of N1S1 cells, however, were killed in mixed populations containing as few as 2% AS-30D cells after identical treatment, demonstrating an in vitro bystander effect. Subcutaneous injection of AS-30D and N1S1 cells in BALB/c nu/nu mice produced solid tumours containing both cells. Uptake of radiolabelled RH1-betaG-PEG in solid AS-30D and mixed AS-30D/N1S1 tumours was 11.6 and 9.3 times greater than a control antibody conjugate 120 h after i.v. injection. Intravenous treatment with RH1-betaG-PEG and BHAMG cured seven of seven nude mice bearing solid s.c. AS-30D tumours and significantly delayed, compared with control conjugate and prodrug treatment, the growth of mixed N1S1/AS-30D tumours with one cure, showing that targeted activation of BHAMG kills bystander tumour cells in vivo.

Neuronal degeneration in canine narcolepsy

Narcolepsy is a lifelong illness characterized by persistent sleepiness, hypnagogic hallucinations, and episodes of motor paralysis called cataplexy. We have tested the hypothesis that a transient neurodegenerative process is linked to symptom onset. Using the amino-cupric silver stain on brain sections from canine narcoleptics, we found elevated levels of axonal degeneration in the amygdala, basal forebrain (including the nucleus of the diagonal band, substantia innominata, and preoptic region), entopeduncular nucleus, and medial septal region. Reactive neuronal somata, an indicator of neuronal pathology, were found in the ventral amygdala. Axonal degeneration was maximal at 2-4 months of age. The number of reactive cells was maximal at 1 month of age. These degenerative changes precede or coincide with symptom onset. The forebrain degeneration that we have observed can explain the major symptoms of narcolepsy.

Ifosfamide-based chemotherapy for previously treated lung cancer patients

BACKGROUND

Ifosfamide-based chemotherapy has already been the basis of three separate clinical trials. In this study, ifosfamide was administered to lung cancer patients who had failed to respond to previous chemotherapy, to assess its response rate and toxicity.

METHODS

From January 1993 to December 1996, 21 patients were treated, including eight patients with small cell lung cancer (SCLC) and 13 with non-small cell lung cancer (NSCLC). Patients who had histocytologically confirmed lung cancer, were previously treated with chemotherapy, had a measurable lesion(s), were younger than 75 years of age, had an Eastern Cooperative Oncology Group performance status of 0-3 and adequate marrow, renal and liver function were eligible for inclusion in this study. For SCLC patients, ifosfamide 2.4 g/m2 intravenous (i.v.) infusion was given over 30 minutes on days 1-3 every four weeks. For NSCLC two regimens were used: IFL (ifosfamide 2 g/m2, 5-fluorouracil (FU) 600 mg/m2 and leucovorin 50 mg/m2 i.v. infusion on days 1-3 every four weeks) and LIFE (leucovorin 50 mg/m2, ifosfamide 1 g/m2, 5-FU 400 mg/m2 and epirubicin 12 mg/m2 i.v. infusion on days 1-3 every four weeks). For NSCLC patients, IFL was used for the first two years of treatment and LIFE was used in the last two treatment years. All patients were evaluated for treatment response and toxicity.

RESULTS

The major toxic effect, myelosuppression (grade 3 or 4 leukopenia), occurred in 62.5% of SCLC patients and 23.1% of NSCLC patients during treatment, and in 62.5% and 10% of SCLC and NSCLC patients, respectively, throughout the course. Only one SCLC and one NSCLC patient experienced febrile neutropenia. One toxic death, attributed to febrile neutropenia, was documented in a patient with SCLC. Alopecia was ubiquitous. Other toxicities were uncommon and mild. The overall response rate was 50% in SCLC and 7.7% in NSCLC. The median time to disease progression was 61 days in SCLC and 47 days in NSCLC. Median survival was 172 days in SCLC and 173 days in NSCLC.

CONCLUSIONS

The study results suggest that ifosfamide chemotherapy is active with an acceptable toxicity profile in previously treated SCLC patients. However, it lacks efficacy in NSCLC patients who have been previously treated.

Dehydroepiandrosterone induces the transforming growth factor-beta production by murine macrophages

Dehydroepiandrosterone(DHEA), a predominant androgen secreted by the adrenal cortex, and dehydroepiandrosterone sulfate (DHEAS). Its predominant form in serum, were investigated for their role in the regulation of transforming growth factor-beta (TGF beta) production by murine macrophages. Using a bioassay based on the growing inhibition to Mv-1-Lu cells and RT-PCR analysis, the effect of DHEA and DHEAS on the TGF-beta production and gene expression was studied. Results suggested that DHEA at relatively high concentration (10 microM) significantly induced TGF-beta secretion by both peritoneal cells and P388D1 macrophage-like cells. For the cells treated with DHEAS, no significant increase in TGF-beta secretion was found statistically. Result of RT-PCR confirmed the observation that cDNA from the cells pretreated with DHEA generated a significant amount of amplicons but cDNA samples obtained from both control cells and DHEAS-treated cells showed relatively weak signals. In a quantitative RT-PCR analysis, both DHEAS-treated cells and control cells failed to compete with internal standards and failed to produce any detectable amplicons. Dexamethasone, one of the commonly used glucocorticoids, induced an increase in TGF-beta secretion and in mRNA level. Dexamethasone and DHEA failed to show a synergistic effect on the DHEA-induced increase in TGF-beta secretion and gene expression. The biological significance for DHEA to act as a positive stimulator for TGF-beta production and its role in glucocorticoid-mediated immunoregulation needs to be further delineated.

Relationship between paxillin and myosin phosphorylation during muscarinic stimulation of smooth muscle

The tyrosine phosphorylation of paxillin increases in association with force development during tracheal smooth muscle contraction, suggesting that paxillin plays a role in the contractile activation of smooth muscle [Z. L. Wang, F. M. Pavalko, and S. J. Gunst. Am. J. Physiol. 271 (Cell Physiol. 40): C1594-C1602, 1996]. We compared the Ca2+ sensitivity of the tyrosine phosphorylation of paxillin and myosin light chain (MLC) phosphorylation in tracheal muscle and evaluated whether MLC phosphorylation is necessary to induce paxillin phosphorylation. Ca(2+)-depleted muscle strips were stimulated with 10(-7)-10(-4) M acetylcholine (ACh) in 0,0.05, 0.1, or 0.5 mM extracellular Ca2+. In the absence of extracellular Ca2+, 10(-4) M ACh induced a maximal increase in paxillin phosphorylation without increasing MLC phosphorylation or force. Increases in extracellular Ca2+ concentration did not further increase paxillin phosphorylation. However, during stimulation with 10(-6) M ACh, paxillin phosphorylation increased with increases in extracellular Ca2+ concentration. We conclude that the tyrosine phosphorylation of paxillin can be stimulated by signaling pathways that do not depend on Ca2+ mobilization and that the activation of contractile proteins is not required to elicit paxillin phosphorylation.

Phase II trial of intrapleural paclitaxel injection for non-small-cell lung cancer patients with malignant pleural effusions

A phase II clinical trial of intrapleural paclitaxel injection for malignant effusions of non-small-cell lung cancer (NSCLC) was conducted in order to evaluate the efficacy and toxicity profile of paclitaxel pleurodesis in patients with malignant effusions. From February to May of 1996, 15 NSCLC patients with malignant pleural effusions were enrolled on study. After adequate drainage and assurance of lung re-expansion, paclitaxel 125 mg m-2 diluted in normal saline was infused through a preinserted pig-tail catheter which was removed 2 h later. Chest radiography and sonography were scheduled 4 days later; depending on whether there remained a significant amount of pleural effusion, further drainage by needle thoracentesis or by a pig-tail catheter was performed. All patients were assessable for toxicity. Ipsilateral chest and/or shoulder pain, fever, facial flushing and nausea were the most frequent side-effects. Grade 4 neutropenia, grade 3 anaemia, and grade 3 renal impairment occurred in one patient each. Fourteen patients were evaluable for response at the end of the fourth week. Overall response rate of pleural effusion in evaluable patients was 92.9%, with a complete response rate of 28.6%. There was one out of 14 evaluable patients whose measurable tumour lesion decreased by more than 50% (partial response). No disease progression was noted among evaluable patients at the end of the fourth week. It is concluded that paclitaxel is a useful agent for the treatment of malignant pleural effusions. Because of its relatively low systemic toxicity, intrapleural paclitaxel injection in combination with systemic chemotherapy or radiotherapy can be considered in treating NSCLC patients with malignant pleural effusions.

Cure of malignant ascites and generation of protective immunity by monoclonal antibody-targeted activation of a glucuronide prodrug in rats

We examined the in vivo efficacy of targeting beta-glucuronidase (betaG) to activate a glucuronide prodrug (BHAMG) of p-hydroxyaniline mustard (pHAM) at hepatoma ascites in Sprague-Dawley rats. Injection i.p. of 500 microg RH1-betaG, a conjugate formed between recombinant betaG and monoclonal antibody RH1 with specificity for an antigen expressed on AS-30D rat hepatoma cells, into rats bearing AS-30D ascites resulted in the accumulation of 54 microg conjugate per 10(9) tumor cells after 2 hr. Ascites fluid and serum contained 0.53 and 0 microg/ml, respectively, RH1-betaG 2 hr after injection of the conjugate. Conjugate binding to AS-30D cells was heterogeneous and non-saturated, as determined by flow cytometry. BHAMG was less toxic than pHAM to SD rats based on measures of animal mortality, weight loss and hematological toxicity. Treatment of rats bearing established hepatoma ascites with 500 microg RH1-betaG followed 2 hr later with a single i.p. injection of 30 mg/kg BHAMG or 3 i.p. injections of 10 mg/kg BHAMG 2, 3 and 4 hr later resulted in the cure of 6/8 and 8/8 animals, respectively. Treatment with BHAMG or pHAM alone did not produce cures, whereas treatment with a control antibody-betaG conjugate and BHAMG produced significantly greater hematological toxicity compared to treatment with RH1-betaG and BHAMG. All cured rats were completely protected from rechallenge with 2 x 10(7) AS-30D cells, indicating that successful treatment of animals induced protective immunity.

Prolonged survival in a nasopharyngeal carcinoma patient with multiple metastases: a case report and review of the literature

Nasopharyngeal carcinoma is a common cancer in South East Asia. In the early stages, radiotherapy alone may achieve sustained control, but once metastasis occurs, it becomes an incurable disease with limited survival time. We report a case of nasopharyngeal carcinoma, initial stage T4N0M0, diagnosed in 1985 in a patient aged 36 years who received 70 Gy radiotherapy to the head and neck region. In 1988, relapse occurred with multiple lung metastases. The patient received many chemotherapy regimens with a very good response, including near complete remission with the first treatment regimen of cisplatin, 5-fluorouracil and leucovorin for lung metastases, and with the fifth chemotherapy regimen of ifosfamide as a single agent. After ifosfamide treatment, there was residual fibrotic change in the lung and complete disappearance, lasting for almost a year, of the liver and bone lesions. The patient eventually died in July 1995 due to progressive disease. Prolonged survival after mainly thoracic metastasis is possible in patients with nasopharyngeal carcinoma, especially if the tumor is chemo-responsive.

Mechanisms for the mechanical response of airway smooth muscle to length oscillation

Airway smooth muscle tone in vitro is profoundly affected by oscillations in muscle length, suggesting that the effects of lung volume changes on airway tone result from direct effects of stretch on the airway smooth muscle. We analyzed the effect of length oscillation on active force and length-force hysteresis in canine tracheal smooth muscle at different oscillation rates and amplitudes during contraction with acetylcholine. During the shortening phase of the length oscillation cycle, the active force generated by the smooth muscle decreased markedly below the isometric force but returned to isometric force as the muscle was lengthened. Results indicate that at rates comparable to those during tidal breathing, active shortening and yielding of contractile elements contributes to the modulation of force during length oscillation; however, the depression of force during shortening cannot be accounted for by cross-bridge properties, shortening-induced cross-bridge deactivation, or active relaxation. We conclude that the depression of contractility may be a function of the plasticity of the cellular organization of contractile filaments, which enables contractile element length to be reset in relation to smooth muscle cell length as a result of smooth muscle stretch.

Pharmacological modulation of the mechanical response of airway smooth muscle to length oscillation

Stretch and retraction of the airways caused by changes in lung volume may play an important role in regulating airway reactivity. We studied the effects of different pharmacological stimuli on airway smooth muscle to determine whether the muscle behavior during length oscillation can be modulated pharmacologically and to evaluate the role of different activation mechanisms in determining its behavior during the oscillation. Active force decreased below the static isometric force during the shortening phase of length oscillation, resulting in an overall depression of force during the length oscillation cycle. This pattern of response was unaffected by the contractile stimulus or level of activation, suggesting that it was caused by a mechanism that is independent of the level of activation of cross bridges. The normalized area of the length-force hysteresis loop (hysteresivity) differed depending on the stimulus used for contraction. Effects of different stimuli on hysteresivity were not correlated with their effects on isotonic shortening velocity or isometric force, suggesting that the pharmacological modulation of the behavior of airway smooth muscle during length oscillation at these amplitudes cannot be accounted for by the effects on the cross-bridge cycling rate.

Experience with ifosfamide and etoposide combination chemotherapy in extensive-disease small-cell lung cancer

BACKGROUND

Ifosfamide, an isomeric analogue of cyclophosphamide, has significant activity against many human tumors including lung cancer, testicular cancer, lymphoma and sarcoma, and may be superior to its analogue. Herein, we report our preliminary experience using ifosfamide and etoposide (IE) combination chemotherapy in previously untreated patients with extensive-disease (ED) small-cell lung cancer (SCLC).

METHODS

Patients with histologically or cytologically confirmed SCLC, measurable or assessable ED, no previous chemotherapy or thoracic irradiation, younger than 70 years of age, Eastern Cooperative Oncology Group (ECOG) performance status (PS) of 0-3, and adequate marrow, liver, and renal functions were eligible for treatment which consisted of ifosfamide 2.0 g/m2/d given intravenously (i.v.) for 3 days with mesna 400 mg/m2/dose i.v. administered 0, 4, and 8 hours after the daily administration of ifosfarnide, and etoposide 80 mg/m2/d i.v. given for 3 days in every 4 weeks for a maximum of 6 cycles.

RESULTS

Between January 1994 and February 1995, 10 patients were enrolled into the treatment. All were men with a mean age of 63 +/- 6 years. Five patients had an ECOG PS of 0 or 1, 4 patients of 2, and 1 patient of 3. A total of 45 cycles of IE were given. The mean number of cycles per patient was 4.5 +/- 2.1. Six patients completed 6 courses of therapy. Thirty-two of 45 cycles (71%) of IE were given at full doses, while the remaining 13 cycles (29%) were given at 75% of doses. Nine patients were assessable for response. Eight patients had a partial remission and one patient had stable disease. The overall response rate was 89%. The median survival was 8 months (range, 0 to 23 months) and the median failure-free survival duration was 5.5 months (range, 0 to 18 months). The 1- and 2-year survival rates were 30% and 0%, respectively. Myelotoxicity was the most important toxicity, particularly neutropenia, while thrombocytopenia and anemia were mild. Five of 10 patients (50%) experienced grade 4 neutropenia, which occurred in 2 patients during the first course of IE and resulted in one patient death from early sepsis. Other nonhematologic toxicities were mild.

CONCLUSIONS

Our preliminary experience demonstrates that ifosfamide is an active drug against SCLC and combination chemotherapy with IE results in similar response rate and median survival, but probably higher myelotoxicity than reported studies in patients with ED SCLC.

A phase I feasibility and pharmacokinetic study of intrapleural paclitaxel in patients with malignant pleural effusions

To evaluate the feasibility and pharmacology of intrapleural (IP(L)) administration of paclitaxel, 18 patients with malignant pleural effusions were entered onto a phase I clinical study, 13 were caused by lung cancer. Following an effusion drainage rate of less than 100 ml/24 h and full expansion of the lung, patients were treated with a single instillation of pacilitaxel administered IP(L) in 500 ml of normal saline and retained for a maximum of 96h when tolerated. No systemic chemotherapy or ipsilateral thoracic irradiation was given for 4 weeks before and after the IP(L) treatment. The starting dose was 82.5 mg/m2 with the dose escalation schedule of 125, 175, 225 and 300 mg/m2. There were minimal local or systemic toxicities, such as local chest pain or myelosuppression, even when the paclitaxel dose reached 225 mg/m2. The pharmacological advantages of the IP(L) administration of paclitaxel were demonstrated by the mean exposure of the pleural cavity (area under the concentration time curve) to paclitaxel after IP(L) delivery exceeding that of the plasma by approximately 370-fold (range 55-684) and by the extraordinarily slow IP(L) clearance of paclitaxel (mean +/- SE 0.49 +/- 0.07 l/m2/day; range 0.08-1.16 l/m2/day) with significant concentrations of paclitaxel persisting within the cavity for more than 48-96 h after a single IP(L) instillation. In patients with detectable plasma paclitaxel levels, the plasma levels achieved exceed the minimal concentrations that are required to induce cytotoxic effects in vitro. Four patients had progressive dyspnea during IP(L) retention of paclitaxel solution because of treatment failure and needed drainage of effusion. One of these patients who was at the dose level of 225 mg/m2 originally had severely chronic obstructive lung disease, developed acute respiratory failure, refused mechanical ventilation support and succumbed to respiratory failure. No further patients were included after this event. Antitumor effect was shown by four of the 15 evaluable patients having no recurrence of effusion on chest radiograph at 1 month. Most of these responders had a good performance status, normal pretreatment pleural pH and/or glucose compared with the non-responders. We conclude that paclitaxel at a dose level of 175 or 225 mg/m2 is feasible for use intrapleurally. It could be considered for incorporation into treatment programs for patients with less advanced thoracic tumors with carcinomatous pleuritis or with IP(L) tumors following surgical debulking.

Phase II study of ifosfamide and etoposide chemotherapy for extensive-disease small-cell lung cancer

We conducted a phase II study of ifosfamide and etoposide chemotherapy in patients with untreated extensive-disease small-cell lung cancer to assess response and toxicity. Between January 1994 and December 1995, 16 patients were treated. Ifosfamide and etoposide doses were ifosfamide 2 g/m2, with mesna, i.v. infusion over 30 minutes on days 1-3 and etoposide 80 mg/m2 i.v. over 120 minutes on days 1-3 every 4 weeks for up to six cycles. All patients were evaluable for toxicity profile and treatment response. As expected, the major toxicity was myelosuppression. With one exception, grade 3 or 4 leukopenia occurred in all patients during treatment, and 48.7% of the total courses had grade 3 or 4 leukopenia. Nine of 16 patients (56.3%) experienced episodes of febrile neutropenia. One toxic death due to febrile neutropenia with sepsis was documented. Toxicities other than leukopenia were few and mild in severity. After two cycles of treatment, the overall response rate was 81.3% (95% confidence interval 62.2-100) in this study. The median duration of response was 8 months and median survival was 11 months. In conclusion, ifosfamide and etoposide is an active combination regimen with acceptable toxicity profile in Chinese patients with extensive-disease small-cell lung cancer.

Class I-deficient hemopoietic cells and nonhemopoietic cells dominantly induce unresponsiveness of natural killer cells to class I-deficient bone marrow cell grafts

NK cells in normal mice reject bone marrow transplants from class I-deficient mice. In contrast, class I-deficient mice do not reject autologous cells, suggesting that NK cell tolerance is acquired. We employed fetal liver irradiation chimeras to assess two potential mechanisms that could account for the tolerance of NK cells in class I-deficient mice to class I-deficient cells: 1) a positive model, in which recognition of class I+ cells molecules by NK cells is necessary to induce functional NK cell maturation; and 2) a negative model, in which interactions of NK cells with class I-deficient cells induce tolerance. In class I+ chimeras reconstituted with mixtures of class I+ and class I-deficient fetal liver cells, the rejection of class I-deficient bone marrow cell grafts was significantly impaired, supporting the negative model. We further addressed whether nonhemopoietic cells are also able to induce NK cell tolerance. Class I- mice reconstituted with class I+ fetal liver cells were tolerant of class I-deficient cells, favoring this idea. Furthermore, class I-deficient mice reconstituted with a mixture of class I-deficient and class I+ fetal liver cells were more tolerant to class I-deficient cells than were class I+ mice reconstituted with the same fetal liver cell mixture. These results suggest that maximal tolerance induction requires the presence of class I-deficient nonhemopoietic cells.

Class I-deficient hemopoietic cells and nonhemopoietic cells dominantly induce unresponsiveness of natural killer cells to class I-deficient bone marrow cell grafts

NK cells in normal mice reject bone marrow transplants from class I-deficient mice. In contrast, class I-deficient mice do not reject autologous cells, suggesting that NK cell tolerance is acquired. We employed fetal liver irradiation chimeras to assess two potential mechanisms that could account for the tolerance of NK cells in class I-deficient mice to class I-deficient cells: 1) a positive model, in which recognition of class I+ cells molecules by NK cells is necessary to induce functional NK cell maturation; and 2) a negative model, in which interactions of NK cells with class I-deficient cells induce tolerance. In class I+ chimeras reconstituted with mixtures of class I+ and class I-deficient fetal liver cells, the rejection of class I-deficient bone marrow cell grafts was significantly impaired, supporting the negative model. We further addressed whether nonhemopoietic cells are also able to induce NK cell tolerance. Class I- mice reconstituted with class I+ fetal liver cells were tolerant of class I-deficient cells, favoring this idea. Furthermore, class I-deficient mice reconstituted with a mixture of class I-deficient and class I+ fetal liver cells were more tolerant to class I-deficient cells than were class I+ mice reconstituted with the same fetal liver cell mixture. These results suggest that maximal tolerance induction requires the presence of class I-deficient nonhemopoietic cells.

Specificity, tolerance and developmental regulation of natural killer cells defined by expression of class I-specific Ly49 receptors

Natural killer cells in the mouse express class I MHC-specific inhibitory receptors of the Ly49 protein family. The receptors mediate inhibition of the lysis of tumor cells and normal cells, and mediate the specificity of bone-marrow graft rejection by NK cells in vivo. The function of these receptors may be to confer upon NK cells the capacity to distinguish normal self cells from cells that have down-regulated expression of some or all self-class I molecules. Ly49 receptors discriminate between different class I molecules, and are distributed in expression to overlapping subsets of NK cells. The receptors appear to interact with class I-MHC residues and associated N-glycans, with little or no discrimination of the class I-bound peptide. The Ly49 receptor repertoire may be initially generated by a stochastic process that distributes receptors randomly to different cells and treats the two alleles of a given Ly49 gene independently. However, class I-MHC-dependent "education" processes shape the functional repertoire. The education processes silence potentially auto-aggressive NK cells, probably by ensuring that each NK cell expresses at least one self-specific Ly49 receptor. In addition, NK cell clones that express multiple self-specific Ly49 receptors are disfavored by the education processes, perhaps to confer greater discrimination on to individual NK cells.

Major histocompatibility complex class I-dependent skewing of the natural killer cell Ly49 receptor repertoire

Subsets of mouse natural killer (NK) cells express receptors encoded by the Ly49 gene family that recognize allelic determinants on major histocompatibility complex (MHC) class I molecules. Recognition of self class I molecules typically inhibits NK cell lytic function. The presence of NK cell subsets expressing receptors which are able to discriminate class I alleles raises the possibility that there exist mechanisms to coordinate the NK cell receptor repertoire with the class I molecules of the host. In the present study, we determined the effects of class I gene expression on the frequencies of NK cells expressing three different Ly49 receptors defined by monoclonal antibodies. We show here an MHC-dependent skewing of NK cell subsets expressing multiple Ly49 receptors with specificity for self MHC. The results provide the first evidence that the frequencies of NK cells expressing different Ly49 receptors are determined by the host's MHC molecules. The results also extend previous findings that MHC class I expression influences the cell surface levels of each Ly49 receptor, suggesting an additional mechanism by which MHC molecules may influence the effective specificity of NK cells. Models to account for self tolerance and MHC-controlled repertoire differences are discussed.

Role of contractile protein activation in the length-dependent modulation of tracheal smooth muscle force

The active isometric force developed by a muscle decreases at muscle lengths below an optimal length (Lo). However, when the length of an actively contracting muscle is abruptly decreased, a lower level of isometric force is reached during force redevelopment than when the contraction is initiated at the shorter length. This has been attributed to a deactivation of contractile proteins caused by shortening. In this study, intracellular Ca2+ and myosin light chain (MLC) phosphorylation were measured to assess the mechanisms for the modulation of isometric force caused by changing smooth muscle length before or during isometric contraction. The decline in isometric force between Lo and 0.5Lo was associated with decreases in MLC phosphorylation and intracellular Ca2+ during contractions elicited by acetylcholine or 60 mM KCl. Quick release of the muscle during contraction depressed force redevelopment at the shorter length but not MLC phosphorylation. We conclude that decreases in Ca(2+)-calmodulin-dependent MLC phosphorylation contribute significantly to the decline in isometric force at lengths below Lo, but the depression of contractility associated with the quick release of actively contracted smooth muscle is not caused by a shortening-induced deactivation of contractile proteins.

Mechanisms for the mechanical plasticity of tracheal smooth muscle

In smooth muscle tissues, the relationship between muscle or cell length and active force can be modulated by altering the cell or tissue length during stimulation. Mechanisms for this mechanical plasticity were investigated by measuring muscle stiffness during isometric contractions in which contractile force was graded by changing stimulus intensity or muscle length. Stiffness was significantly higher in contracted than in resting muscles at comparable forces; however, the relationship between stiffness and force during force development was curvilinear and independent of muscle length and stimulus intensity. This suggests that muscle stiffness during force development reflects properties of cellular components other than cross bridges which contribute to the series elasticity only during activation. During the tonic phase of isometric contraction, muscle stiffness increased while force remained constant. A step decrease in the length of a contracted muscle resulted in a high level of stiffness relative to force during isometric force redevelopment following the length step. We propose that the arrangement of the cytoskeleton can adjust to changes in the conformation of resting smooth muscle cells but that the organization of the cytoskeleton becomes more fixed upon contractile activation and is modulated very slowly during a sustained contraction. This may provide a mechanism for optimizing force development to the physical conformation of the cell at the time of activation.

Inhibitory effects of class I molecules on murine NK cells: speculations on function, specificity and self-tolerance

This review addresses the physiological role of class I-mediated inhibition of NK cell lysis. It is suggested that several distinct activating receptors can stimulate NK lysis, all of which can be inhibited by class I molecules on the target cell. Evidence that most or all peptides that bind a class I molecule can cause inhibition is discussed, supporting a model in which NK cells detect loss of class I molecules, rather than loss of specific peptide/class I complexes. Finally, the acquisition of self-tolerance among NK cells is addressed with respect to data suggesting that autoaggressive NK cells are not deleted but rather exhibit altered characteristics which may render them unable to lyse autologous cells.

Phosphorylation of dense-plaque proteins talin and paxillin during tracheal smooth muscle contraction

Reorganization of cytoskeletal-membrane interactions during contractile stimulation may contribute to the regulation of airway smooth muscle contraction. We investigated the effect of contractile stimulation on the phosphorylation of the actin-membrane attachment proteins talin, vinculin, and paxillin. Stimulation of 32P-labeled canine tracheal smooth muscle strips with acetylcholine (ACh; 10(-3) M) resulted in a rapid 2.6-fold increase in phosphorylation of serine and/or threonine residues, compared with resting levels of 0.22 mol PO4(3-)/mol talin. After stimulation with ACh, phosphorylation of tyrosine residues on paxillin increased approximately threefold. Two-dimensional phosphopeptide mapping of in vivo labeled talin and paxillin indicated phosphorylation on a limited number of sites. Vinculin phosphorylation was undetectable in either resting or ACh-stimulated muscle. We conclude that phosphorylation of talin and paxillin occurs during ACh-stimulated contraction of tracheal smooth muscle and that distinct signaling pathways activate a serine/threonine kinase that phosphorylates talin and a tyrosine kinase that phosphorylates paxillin. The pharmacological activation of airway smooth muscle cells might involve the anchoring of contractile filaments to the membrane.

Establishment and characterization of TSGH9201, a human gastric carcinoma cell line that is growth inhibited by epidermal growth factor

A human signet ring gastric carcinoma cell line TSGH9201 was established in vitro. The cells grew in vitro as a monolayer with polygonal morphology and had a population doubling time of 34 hours. The cells secreted tumor markers CEA and CA 125. They were, however, not tumorigenic in athymic nude mice. Karyotypic analysis demonstrated a near tetraploidy with a modal chromosome number of 98. Northern blotting and immunocytochemical analysis revealed the expression of both transforming growth factor alpha and high levels of epidermal growth factor receptor. Cell growth was inhibited by the epidermal growth factor in vitro. The cell line may be a useful tool to study autocrine growth regulation through the epidermal growth factor receptor.