Cytoplasmically sequestered wild-type p53 protein in neuroblastoma is relocated to the nucleus by a C-terminal peptide

Cytoplasmic sequestration of wild-type p53 protein occurs in a subset of primary human tumors including breast cancer, colon cancer, and neuroblastoma (NB). The sequestered p53 localizes to punctate cytoplasmic structures that represent large protein aggregates. One functional consequence of this blocked nuclear access is impairment of the p53-mediated G1 checkpoint after DNA damage. Here we show that cytoplasmic p53 from NB cells is incompetent for specific DNA binding, probably due to its sequestration. Importantly, the C-terminal domain of sequestered p53 is masked, as indicated by the failure of a C-terminally directed antibody to detect p53 in these structures. To determine (i) which domain of p53 is involved in the aggregation and (ii) whether this phenotype is potentially reversible, we generated stable NB sublines that coexpress the soluble C-terminal mouse p53 peptide DD1 (amino acids 302-390). A dramatic phenotypic reversion occurred in five of five lines. The presence of DD1 blocked the sequestration of wild-type p53 and relocated it to the nucleus, where it accumulated. The nuclear translocation is due to shuttling of wild-type p53 by heteroligomerization to DD1, as shown by coimmunoprecipitation. As expected, the nuclear heterocomplexes were functionally inactive, since DD1 is a dominant negative inhibitor of wild-type p53. In summary, we show that nuclear access of p53 can be restored in NB cells.

RNA polymerase signals UvrAB landing sites

Transcription when coupled to nucleotide excision repair specifies the location in active genes where preferential DNA repair is to take place. During DNA damage-induced recruitment of RNA polymerase (RNAP), there is a physical association of the beta subunit of Escherichia coli RNAP and the UvrA component of the repair apparatus (G. C. Lin and L. Grossman, submitted for publication). This molecular affinity is reflected in the ability of the RNAP to increase, in a promoter-dependent manner, DNA supercoiling by the UvrAB complex. In the presence of the RNAP, the UvrAB complex is able to bind to promoter regions and to translocate in a 5' to 3' direction along the non-transcribed strand. As a consequence of this helicase-catalyzed translocation, preferential incision of DNA damaged sites occurs downstream on the transcribed strand. Because of the helicase directionality, the initial binding of the UvrAB complex to the transcribed strand would inevitably lead to its collision with the RNAP. These results imply that the RNAP-induced DNA structure in the vicinity of the transcription start site signals a landing or entry site for the UvrAB complex on DNA.

The binding of UvrAB proteins to bubble and loop regions in duplex DNA

Based on the binding of the UvrAB complex to a promoter region in transcription open complexes (Ahn, B., and Grossman, L. (1996) J. Biol. Chem. 271, 21453-21461) and the requirement of a single-stranded region for UvrAB helicase activity, we examined the binding of UvrAB proteins to synthetic bubble or loop regions in duplex DNA and the role of these regions in translocation of the UvrAB complex as well as incision of DNA damage. We found that the UvrAB complex was able to bind to bubble and loop regions with an affinity similar to that for damaged DNA in the absence of RNAP. The preferential recognition and incision of damaged sites by the UvrAB complex was observed downstream of the bubble or loop region in the strand complementary to the strand along which the UvrAB complex translocates. These results imply that the bubble region generated in duplex DNA by RNAP serves as a preferred entry site for the translocation of the UvrAB complex, and that preferential binding and unidirectional translocation of the UvrAB complex predetermine where incision is to occur.

Promotion potential of tamoxifen on hepatocarcinogenesis in female SD or F344 rats initiated with diethylnitrosamine

The liver promotion potential of tamoxifen (TAM), which has been widely used in the treatment of hormone-dependent breast cancers, was investigated using female SD or F344 rat initiated with diethylnitrosamine (DEN). In Experiment 1, 45 newborn female SD rats were administered DEN (100 mg/kg, i.p.) (Groups 1 and 2) or saline (Group 3) 24 h after birth. After weaning at week 3, Groups 1 and 3 were subcutaneously injected with TAM citrate (1 mg/rat per day), suspended in corn oil, in the subscapular region, while Group 2 was given the vehicle alone (s.c.) daily for 9 weeks, and killed at week 12. In Experiment 2, 70 female F344 rats at 7 weeks of age were divided into five groups. All animals were initially given DEN (200 mg/kg i.p.) for initiation. Two weeks later Groups 1-4 were given diets containing 100, 250, 500 ppm TAM, or 500 ppm PB for 6 weeks, respectively, while Group 5 was administered basal diet as a control for the same period. The rats were subjected to two-thirds partial hepatectomy (PH) at week 3 and were killed at week 8. The enhanced development of glutathione S-transferase-placental form (GST-P)-positive liver cell foci after DEN exposure in both newborn SD and adult F344 rat medium-term liver bioassay models (Experiments 1 and 2). This suggests that TAM exerts promotion potential for hepatocarcinogenesis in female rats.

Biphasic modifying effect of indole-3-carbinol on diethylnitrosamine-induced preneoplastic glutathione S-transferase placental form-positive liver cell foci in Sprague-Dawley rats

The biphasic modifying effects of indole-3-carbinol (I3C), a naturally occurring constituent of edible cruciferous vegetables, on the development of glutathione S-transferase placental form (GST-P)-positive liver cell foci were investigated by using a medium-term liver bioassay system and a newborn rat hepatocarcinogenesis system. In Experiment 1, a total of 65 male Sprague-Dawley (SD) rats were divided into 5 groups. Animals were given a single intraperitoneal (i.p.) injection of 200 mg/kg diethylnitrosamine (DEN) dissolved in saline for groups 1, 2, and 3 or a single i.p. injection of saline for groups 4 and 5. Group 1 was given the diet containing 0.25% I3C for 2 weeks prior to DEN initiation and then basal diet for 8 weeks. Group 2 was given basal diet for 4 weeks prior to and after DEN initiation and then the diet containing 0.25% I3C for 6 weeks. The rats of group 3 were placed on basal diet during the experiment. Animals of groups 4 and 5 were treated in the same manner as those of groups 1 and 2 except for injection with saline instead of DEN solution. All rats were subjected to two-thirds partial hepatectomy at week 3 and were killed at week 8 after DEN or saline injection. In Experiment 2, a total of 45 female SD rats were dosed with DEN (100 mg/kg, i.p.) or saline at 24 h after birth. After weaning at week 3, the rats were fed diet containing 0.25% I3C for 9 weeks and then were killed at week 12. In Experiment 1, preinitiation exposure to 0.25% I3C caused a significant decrease in numbers of GST-P-positive liver cell foci (P < 0.05), while postinitiation exposure to 0.25% I3C caused significant increases in both number (No./cm2) and area (mm2/cm2) of GST-P-positive liver cell foci (P < 0.05 or 0.01). In Experiment 2, the relative liver weight in the DEN + I3C group was significantly increased (P < 0.001). The numbers and areas of GST-P-positive liver cell foci in the DEN + I3C group were significantly increased as compared to the values of the DEN-alone group (P < 0.001). These results clearly demonstrated that I3C exerts a promoting effect on the postinitiation stage as well as an inhibitory effect on the preinitiation stage in the medium-term liver bioassay.

Dependence of biphasic heart rate response to sustained hypoxia on magnitude of ventilation in man

We studied the dynamic profile of respiratory and circulatory activities during sustained isocapnic hypoxia in healthy males. In response to end-tidal PO2 depression to about 55 Torr, minute ventilation first increased briskly and then depressed. Such biphasic response to hypoxia was also observed in the heart rate. A significantly positive correlation was found between the magnitudes of ventilatory and heart rate responses. No significant increases were found in arterial noradrenaline and potassium, but adrenaline significantly increased gradually with time. Furthermore, when VT and f were intentionally maintained constant so as to prevent the biphasic ventilatory change, the biphasic heart rate response previously seen in spontaneous hypoxic breathing disappeared. We suggest that the heart rate is mainly determined by the pulmonary vagal inflation reflex. Putative neurochemicals to elicit hypoxic ventilatory depression, and arterial catecholamine and potassium concentrations may not be directly related to the specific profile of the biphasic heart rate response during moderate hypoxia.

Effect of verapamil on ventilatory and circulatory responses to hypoxia and hypercapnia in normal subjects

Recent investigations have shown that the calcium channel blocker verapamil attenuated the hypoxic ventilatory chemosensitivity of carotid body in animals. To determine whether this is also the case in humans, transient physiological chemodenervation by O2 breaths (withdrawal test) during sustained hypoxia (N = 7), and ventilatory and circulatory responses to progressive hypoxia and hypercapnia (N = 8) were examined after oral administration of verapamil. During sustained hypoxia after verpamil, there was a significant reduction of withdrawal response from 5th to 25th min value (p < 0.01), but not after placebo. On the other hand, no significant difference in ventilatory responses to progressive hypoxia and hypercapnia was observed after verapamil. Verapamil run reveals similar features with placebo run in circulatory parameters except blood pressure response, which tended to be suppressed by verapamil. We conclude that verapamil attenuates peripheral chemoreceptor activity with time during sustained mild hypoxia in normal adult humans and this may be explained by delayed depletion in intracellular Ca2+ for chemotransduction of the peripheral chemoreceptors.

Construction of deletion mutants of the Escherichia coli UvrA protein and their purification from inclusion bodies

The functions of each of the three subunits of the damage-specific UvrABC endonuclease is currently being studied by systematically mutagenizing the corresponding genes to generate mutant proteins for characterization in vitro. In this communication, we describe the construction of C-terminal deletion mutants of the UvrA protein and a procedure to purify the mutant and wild-type UvrA proteins from inclusion bodies in cells overexpressing the recombinant proteins. The method yields highly purified proteins with between 10 and 50% of the specific activity of wild-type UvrA purified by conventional techniques from the soluble fraction. The wild-type UvrA protein purified by this method had the properties of significant and selective loss of activity in assays of incision of damaged DNA, while still retaining high levels of the other unique molecular phenotypic properties associated with intact UvrA. Furthermore, the demonstration of the absolute requirement for zinc during refolding for recovery of activity is the first evidence that the zinc previously shown to be associated with the UvrA protein is in fact a necessary component for its function.

Dynamic profile of cardiovascular activity in relation to augmented ventilation and humoral agents during hypercapnic hypoxia

A time course of cardiovascular activity in 8 healthy males in relation to augmented ventilatory activity and humoral factors was observed during step CO2 elevation with constant hypoxia. During the first step increase, by 3 Torr in end-tidal PCO2 (PETCO2), the heart rate (HR) initially tended to decrease, then slowly increased to slightly below that of the previous eucapnic level, whereas ventilation maintained a gradual rise throughout this period. On the other hand, during second step PETCO2 elevation, by a further 3 Torr, both HR and ventilation progressively increased. The plasma catecholamine (CA) concentration was also significantly elevated during this period, suggesting a concomitant enhancement in sympathetic activity. Blood pressure (Bp) was progressively augmented throughout the entire hypoxic challenge. We conclude that 1) the characteristic profile of HR change may be explained by the observation that initial HR depression by peripheral chemoreceptor stimulation is gradually overridden by delayed hyperventilation, CA elevation, and enhanced sympathetic activity; 2) Bp augmentation may be elicited by increased CA release and sympathetic activity; and 3) plasma K+ concentration does not change so as to affect cardiovascular and respiratory activity.

Ventilatory responses to chemosensory stimuli in quadriplegic subjects

We tested the hypothesis that interruption of motor traffic running down the spinal cord to respiratory muscle motoneurons suppresses the ventilatory response to increased chemical drive. We compared the hypoxic (HVR) and hypercapnic (HCVR) ventilatory responses, based on the rebreathing technique, before and during inspiratory flow-resistive loading in 17 quadriplegic patients with low cervical spinal cord transection and in 17 normal subjects. The ventilatory response was evaluated from minute ventilation (VE) and mouth occlusion pressure (P0.2) slopes on arterial oxygen saturation (SaO2) or on end-tidal PCO2 (PACO2), and from absolute VE values at SaO2 80% or at PACO2 55 mmHg. We found no difference in the unloaded HVR or HCVR between the quadriplegic and normal subjects. In the loaded HVR, the delta VE/delta SaO2 slope tended to decrease similarly in both groups of subjects. The delta P0.2/delta SaO2 slope was shifted upwards in normal subjects, yielding a significantly higher P0.2 at a given SaO2. In contrast, this rise in the P0.2 level during loaded HVR was absent in quadriplegics. Loaded HCVR yielded qualitatively similar results in both groups of subjects; delta VE/delta PACO2 decreased and delta P0.2/delta PACO2 increased significantly. The results show that the ventilatory chemosensory responses were unsuppressed in quadriplegics, although they displayed a disturbance in load-compensation, as reflected by occlusion pressure, in hypoxia. We conclude that the descending drive to respiratory muscle motoneurons is not germane to the operation of the chemosensory reflexes.

Ventilatory responses to chemosensory stimuli in quadriplegic subjects

We tested the hypothesis that interruption of motor traffic running down the spinal cord to respiratory muscle motoneurons suppresses the ventilatory response to increased chemical drive. We compared the hypoxic (HVR) and hypercapnic (HCVR) ventilatory responses, based on the rebreathing technique, before and during inspiratory flow-resistive loading in 17 quadriplegic patients with low cervical spinal cord transection and in 17 normal subjects. The ventilatory response was evaluated from minute ventilation (VE) and mouth occlusion pressure (P0.2) slopes on arterial oxygen saturation (SaO2) or on end-tidal PCO2 (PACO2), and from absolute VE values at SaO2 80% or at PACO2 55 mmHg. We found no difference in the unloaded HVR or HCVR between the quadriplegic and normal subjects. In the loaded HVR, the delta VE/delta SaO2 slope tended to decrease similarly in both groups of subjects. The delta P0.2/delta SaO2 slope was shifted upwards in normal subjects, yielding a significantly higher P0.2 at a given SaO2. In contrast, this rise in the P0.2 level during loaded HVR was absent in quadriplegics. Loaded HCVR yielded qualitatively similar results in both groups of subjects; delta VE/delta PACO2 decreased and delta P0.2/delta PACO2 increased significantly. The results show that the ventilatory chemosensory responses were unsuppressed in quadriplegics, although they displayed a disturbance in load-compensation, as reflected by occlusion pressure, in hypoxia. We conclude that the descending drive to respiratory muscle motoneurons is not germane to the operation of the chemosensory reflexes.

Ventilatory and cardiovascular responses to hypoxic and hyperoxic static handgrip exercise in man

The purpose of this study was to evaluate the ventilatory and cardiovascular responses to static handgrip exercise at different levels of arterial chemoreceptor activation. The study was done on 10 healthy subjects. They performed handgrip of 50% of maximal voluntary contraction on a background of either hypoxia (PE'O2 approximately 47 mm Hg) or hyperoxia (PE'O2 approximately 216 mm Hg), i.e., enhanced or suppressed chemoreceptor activity. The subjects were able to sustain the handgrip for 50-60 sec, during which time no steady-state responses were attainable. Minute ventilation (VI), cardiac output (Q), heart rate (HR), and a number of other variables were recorded. Handgrip exercise resulted in a rapid initial VI rise followed by a subsequent slow increase. Hyperoxia diminished the VI response over the exercise range. The ventilatory response was associated with an HR acceleration, increased arterial pressure and peripheral vascular resistance. No appreciable changes in Q were noted, nor was there any particular relationship between ventilatory and circulatory changes. These results provide no support for the Q mediated ventilatory stimulus during static handgrip exercise in man. It is concluded that the ventilatory and cardiovascular responses are of independent nature.

Cardiac responses to hypoxia and hypercapnia in spinal man

The purpose of this study was to evaluate the effect of interruption of the descending supraspinal sympathetic outflow on heart rate control during exposures to chemical stimuli. We investigated the heart rate responses to progressive isocapnic hypoxia and hyperoxic hypercapnia using the rebreathing technique and quantified the relationship between heart rate (HR), oxygen saturation (SaO2), alveolar PCO2 (PACO2), and minute ventilation (VE) in 16 chronic tetraplegic subjects with low cervical spinal cord transection. The HR responses were determined from the linear slopes of HR on SaO2 and HR on PACO2. We found that mean resting heart rate was within normal range; 66 +/- 3 (SEM) beats min-1. HR increased as oxygenation fell or CO2 tension rose. The mean tetraplegic delta HR/delta SaO2 was 0.83 +/- 0.14 beats min-1 per 1% fall in SaO2 and that of delta HR/delta PACO2 was 0.30 +/- 0.13 beats min-1 per mmHG rise in PACO2. The HR and VE responses to either hypoxia or hypercapnia were related in the tetraplegic subjects. We conclude that the stimulatory HR responses to chemical stimuli are not suppressed by cervical spinal cord transection. Thus, the descending sympathetic activity does not underlie the HR acceleration by chemical stimuli.

Contribution of chemical and non-chemical drives to breath-holding determined by visual analog scale (VAS)

Chemical and non-chemical contributions to breath-holding time (BHT) were directly determined by using a visual analog scale (VAS). These values were compared with those indirectly calculated from the method proposed by Godfrey and Campbell (1968). The magnitude of non-chemical factor at low PCO2 in our study was substantially less than the one obtained by the above investigators. We conclude that Godfrey and Campbell's model postulating linear augmentation of non-chemical sensation is inappropriate to explain dyspnea profile during breath-holding.

Facial cold receptors and the survival reflex "diving bradycardia" in man

We measured heart rate (HR), stroke volume (SV), systemic arterial blood pressure (BP), and mean arterial pressure (MAP) in 7 healthy volunteers in response to face immersion in water with concomitant breath-holding at different lung volumes. The subjects were at rest in the prone position. During breath-holding at total lung capacity (TLC), baseline HR (70 to 75 beats/min) fell by 10% within fractions of a second, both in the control preimmersion state when the head was surrounded by room air, and when it was immersed in water of 33 degrees C. This response was associated with rises in MAP and in SV. Immersion of the face in 10 degrees C water while breath-holding, was associated with a strong, negative chronotropic effect (22% fall in HR), which developed within 10 s. Breath-holding at functional residual capacity (FRC) reduced HR substantially only in 10 degrees C water, and in contrast to that at TLC, the response was slowly developing with a latency of 10-15 s. All these reductions in HR were significant and accompanied by increases in BP and MAP. The strong, negative chronotropic effect of cold water was typically linked to a rise in SV. The study identified two temporal components of HR reduction to face immersion: a fast parasympathetic response dependent on the input from the high pressure baroreceptors, and a late response mediated, in all likelihood, by sympathetic efferent activity. Facial receptors sensitive to cold seem to be vital in the largest responses observed. The fast response to breath-holding with the face in water of neutral temperature was equal to that in air. Thus "diving bradycardia" is in fact a basic survival response independent of water.

Effect of unilateral pulmonary vagotomy on respiratory control in man

We studied the breathing pattern and pulmonary function at rest, and ventilatory responses to progressive hypoxia and hypercapnia in 7 awake patients who had undergone esophageal-carcinoma resection with sectioning of the right pulmonary vagal branch by lymphadenectomy. Twelve control patients, who had received the same surgery without vagotomy, were also studied by the same protocol. Two months after the operation, both patient groups demonstrated substantial depressions in FVC and FEV1.0, and slight augmentations in breathing frequency, minute ventilation, and occlusion pressure at 0.2s (P0.2) at rest. In the vagotomized group, the occlusion pressure responses to hypercapnia (delta P0.2/delta PaCO2) and hypoxia (delta P0.2/delta SaO2) in terms of response curve slope increased from 1.3 +/- 1.2 to 1.9 +/- 1.1 cm H2O/Torr and from 0.29 +/- 0.19 to 0.88 +/- 0.53 cm H2O/% (p less than 0.05), respectively. Contrary to the vagotomized patients, the nonvagotomized control group exhibited no significant changes in ventilatory chemosensitivities. Furthermore, when comparing the control and vagotomized groups, postoperative ventilatory chemosensitivity responses in terms of both hypercapnic and hypoxic occlusion pressure responses were significantly higher in the latter. We suggest that (1) due to the development of the substantial mechanical limitation in pulmonary functions, the Hering-Breuer inflation reflex became activated after surgery, and (2) a diminished Hering-Breuer reflex effect to inhibit the respiratory centers by unilateral vagotomy may have resulted in augmented ventilatory chemosensitivities.

Heart rate response to breath-holding during supramaximal exercise

The cardiovascular responses to breath-holding (BH) during short-lasting supramaximal exercise (415 W) on a cycle ergometer were investigated in 15 healthy male subjects. The arterial oxygen saturation, heart rate (HR), endtidal PO2 and PCO2 were continuously monitored. Firstly, 15 subjects performed exercise during BH, preceded by air breathing (air-BH test), and secondly, exercise without BH. Then 9 of the subjects performed the same procedure as in the air-BH test, except that all subjects breathed 100% O2 for 1 min before apnoea (O2-BH test). In 2 of these subjects, the systemic arterial blood pressure was continuously measured via a catheter in the radial artery and plasma catecholamine concentration [CA] was also measured both during the air-BH and the O2-BH tests. In the later period of the air-BH test, the high HR level became progressively depressed. This response, however, was absent in the O2-BH test. There was a late increase in the arterial blood pressure in both tests, and both tests produced hypercapnia. Only the air-BH test resulted in hypoxia, substantial hypertension and HR-depression. The increase in plasma CA was similar in both tests. The marked HR-depression demonstrated here is ascribed mainly to activation of the peripheral arterial chemoreceptors by asphyxia, and partially to baroreceptor activity due to elevated blood pressure.

Circulatory and respiratory responses to lower body negative pressure in man

Circulatory and ventilatory responses to lower body negative pressure (LBNP) were simultaneously investigated in 8 healthy men before, during, and after the application of -20, -40, and -60 mmHg pressure. Minute ventilation (VE) decreased during LBNP due to a fall in respiratory frequency with sustained tidal volume. The cardiac output (Q) was reduced in proportion to the applied LBNP exposure, while VE decreased to almost the same level at all LBNP applications. In spite of decreased VE, end-tidal PO2 and PCO2 were increased and decreased, respectively, indicating a relative alveolar hyperventilation. The ventilation equivalent for O2 (VE/VO2) increased, while the cardiac output equivalent for O2 (Q/VO2) decreased. The relation between VE/VO2 and Q/VO2 showed a significant negative correlation (r = -0.93, p less than 0.01). The veno-arterial CO2 concentration difference (CvCO2--CaCO2) increased with LBNP, due to a fall in CaCO2 with constant CvCO2. The constant CvCO2 indicated a constant tissue acid-base balance. These observations suggest the existence of a ventilatory mechanism improving the efficiency of respiration in order to compensate for the sustained LBNP depression of Q at a given gas exchange.

Estimation of peripheral chemoreceptor contribution to exercise hyperpnea in man

Nine normal male subjects were studied at three levels of exercise (0, 40, and 80 W). Single vital capacity breath test was applied at rest and during exercise (phases 2 and 3). Minimum minute ventilation found within 4 breaths following the test was compared to the control value. Significant depression in minute ventilation was invariably observed. The minute ventilation was depressed more and more with increasing intensity of exercise. A significant difference was found between exercise and rest. However, the relative contribution of chemoreceptor activity remained the same 10-20% at all exercise levels. The magnitude of ventilatory depression (delta V resp) in phase 2 was larger than that in phase 3, when work rate increased to 80 W, both relative and absolute. A significant part of the exercise hyperpnea is due to peripheral chemoreceptor activity. The peripheral chemoreceptor activity is greater in phase 2 than in phase 3 at work rates of light to moderate intensity.

Use of fluorescein hydrazide and fluorescein thiosemicarbazide reagents for the fluorometric determination of protein carbonyl groups and for the detection of oxidized protein on polyacrylamide gels

Highly fluorescent thiosemicarbazide and hydrazide prepared by reaction of fluorescein isothiocyanate with hydrazine or adipic acid dihydrazide have been used to monitor the presence of carbonyl groups in oxidatively modified proteins. After oxidation, proteins react with these reagents under anaerobic conditions in the dark to yield fluorescent protein conjugates (presumably thiosemicarbazones or hydrazones) which can be visualized as fluorescent bands following electrophoresis (0-4 degrees C) on lithium dodecyl sulfate-polyacrylamide gels. These reagents do not react with unoxidized proteins. The conjugates formed dissociate readily at room temperature but are fairly stable at pH 6-9, 0 degrees C. Current data suggest that these reagents will be useful in the detection and quantitation of oxidatively modified proteins in biological systems.