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Biomedical subjects

Y Kubo

Publications and source records attributed to Y Kubo.

At least 37 records · Page 2Linked to original sources
PubMed2002

Graded response of heart rate variability, associated with an alteration of geomagnetic activity in a subarctic area.

It is becoming recognized that geomagnetic activity may influence biological processes, including the incidence of various human diseases. There is evidence that heart rate variability (HRV) may serve not only as an index of autonomic coordination of the circulation, but also as a powerful predictor of risk in apparently healthy subjects. This study focuses on the effects of geomagnetic disturbance on HRV, by comparing different indices of HRV of young, healthy men living in a subarctic area on days of low (Ap; 0-7), middle (Ap; 7-20), and high (Ap; 20-45) geomagnetic activity. The effect of geomagnetic disturbance on HRV is examined on the basis of 7-day records by Holter ECG, obtained longitudinally on 5 clinically healthy men, 21-31 years of age, in Alta, Norway (70 degree N). Frequency- and time-domain measures of HRV were analyzed for each subject on separate 24-hour spans. A graded alteration of HRV endpoints was found in association with increased geomagnetic activity. As time-domain measures of HRV, SDNNIDX and the 90% length of the Lorenz plot decreased statistically significantly on days with increased geomagnetic disturbance (p = 0.0144 and p = 0.0102, respectively). A graded decrease in frequency-domain HRV measures was also validated statistically for the total spectral power (decrease of 18.1% and 31.6% on days when 7 < Ap < 20 and 20 < Ap < 45 versus days when Ap < 7; p = 0.0013). The decrease in spectral power was mainly found at frequencies below 0.04 Hz, in the "ultra-low-frequency" (0.0001-0.003 Hz; 18.1% and 27.5% decrease, respectively; p = 0.0102) and "very-low-frequency" (0.003-0.04 Hz; 12.9% and 28.6% decrease, respectively; p = 0.0209) regions of the spectrum. The decrease in spectral power was much less pronounced around 10.5 sec ("low frequency"; N.S.) and around 3.6 sec ("high frequency"; N.S.). Evidence is provided here that HRV decreases on magnetically disturbed days, and that it does so in a dose-dependent fashion, HRV being depressed more on days when 20 < Ap < 45 than on days when 7 < Ap < 20, by comparison with days when Ap < 7. This graded response of HRV to geomagnetic activity should encourage us to search for human magnetoreceptors and for a better understanding of putative mechanisms of magnetoreception.

Adult↗
PubMed2002

Effect of H2 blockers on the circadian rhythm of intragastric acidity.

Most patients with peptic ulcer or gastro-oesophageal reflux disease develop nocturnal pain (epigastric and retrosternal pain from midnight to early morning), which often disappears before breakfast. Such pain may be related to a disturbance of the circadian rhythm of gastric acid secretion. Helicobacter pylori is a known aetiological agent of peptic ulcer disease and patients with gastritis or ulcers now undergo infection eradication therapy. However, this can result in the onset or exacerbation of gastro-oesophageal reflux disease. There has been a marked increase in the number of patients with oesophagitis rather than peptic ulcer and because most are negative for H. pylori, attention has centred on the status of their gastric acid secretion. Some patients with oesophagitis complain of nocturnal pain despite treatment with a proton pump inhibitor, and in those cases a short course of an H2 blocker can be very effective. We used a portable pH meter to study, in a cross-over fashion, the changes in the circadian rhythm of gastric acid secretion caused by two H2 blockers, laftidine and famotidine, in 10 H. pylori-negative subjects. There was a significant difference in the rhythm between baseline (no treatment) and when laftidine or famotidine were administered, with mean values for amplitude of 28.1, 13.80 and 10.82, respectively; for the midline estimating statistic of rhythm (MESOR), 22.7, 10.80, and 11.54; and for acrophase, 324.0. 312.3, and 274.5 (p < 0.001). The H2 blockers suppressed the normal circadian rhythm of intragastric acidity, which rises in the evening until the middle of the night and then drops in the morning.

Adult↗
PubMed2001

Isolation and characterization of novel F-plasmid sopB mutants defective in gene silencing.

The product of the sopB gene on the Escherichia coli F-plasmid has been shown to silence genes in the vicinity of its binding region, sopC, when overexpressed. We searched for mutants defective in SopB-dependent silencing by screening for a plasmid incompatibility phenotype, in order to examine the relationship between gene silencing and the intracellular localization of SopB, as revealed by a green fluorescent protein (GFP)-SopB fusion. Nine new mutants were isolated. One of them, in which leucine 92 is replaced by proline, was completely compatible with a sopC-carrying plasmid and was defective in other silencing activities. When expressed as a GFP fusion protein, the L92P mutant was found to be uniformly distributed in the cell. This implies a link between silencing and SopB localization, supporting the view that a high local concentration of SopB drives non-specific DNA binding in segments of the plasmid adjacent to sopC. Despite the lack of apparent localization of GFP fluorescence, the mutant protein, like the wild-type SopB, was found mostly in the inner membrane fraction, indicating that the association with the inner membrane was retained.

Bacterial Proteins↗
PubMed2001

Possible role of natural killer cells in negative selection of mutant lymphocytes that fail to express the human leukocyte antigen-A2 allele.

Increased frequencies of cells carrying mutations at several loci have been found in the blood cells of atomic-bomb (A-bomb) survivors upon testing four or five decades after the bombing. Interestingly, though, we have been unable to demonstrate any radiation-associated increases in the frequencies of mutant blood cells in which human leukocyte antigen (HLA)-A expression has been disrupted; this is true both of preliminary tests on the T cells of a small subset of A-bomb survivors and of the much more extensive study reported here in which we screened a much larger group of survivors for HLA-A2 loss mutations in B cells and granulocytes as well as in T cells. In attempting to explain our inability to detect any increases in HLA-A2-negative cell numbers in HLA-A2 heterozygous individuals exposed to A-bomb irradiation, we decided to test the hypothesis that HLA-A mutant lymphocytes might well have been induced by radiation exposure in much the same way as every other type of mutant we encountered, but may subsequently have been eliminated by the strong negative selection associated with their almost inevitable exposure to autologous natural killer (NK) cells in the bloodstream of each of the individuals concerned. We now report that mutant B lymphocyte cell lines that have lost the ability to express the HLA-A2 antigen do indeed appear to be much more readily eliminated than their parental heterozygous counterparts during co-culture in vitro with autologous NK cells. We make this claim first because we have observed that adding autologous NK cells to in vitro cultures of HLA-A2 heterozygous B or T cell lines appeared to cause a dose-dependent decrease in the numbers of HLA-A2-negative mutants that could be detected over a period of 3 days, and second because when we used peripheral blood HLA-A2 heterozygous lymphocyte cultures from which most of the autologous NK cells had been removed we found that we were able to detect newly-arising HLA-A2 mutant T cells in substantial numbers. Taken together, these results strongly support the hypothesis that autologous NK cells are responsible for eliminating mutant lymphocytes that have lost the ability to express self-HLA class I molecules in vivo, and may well therefore explain why we have been unable to detect increased frequencies of HLA-A2 mutants in samples from any of the 164 A-bomb survivors whose HLA-A2 heterozygote status made their lymphocytes suitable for our tests.

Aged↗
PubMed2001

Control of rectification and permeation by two distinct sites after the second transmembrane region in Kir2.1 K+ channel.

1. The rectification property of the inward rectifier K+ channel is chiefly due to the block of outward current by cytoplasmic Mg2+ and polyamines. In the cloned inward rectifier K+ channel Kir2.1 (IRK1), Asp172 in the second transmembrane region (M2) and Glu224 in the putative cytoplasmic region after M2 are reported to be critical for the sensitivity to these blockers. However, the difference in the inward rectification properties between Kir2.1 and a very weak inward rectifier sWIRK could not be explained by differences at these two sites. 2. Following sequence comparison of Kir2.1 and sWIRK, we focused this study on Glu299 located in the centre of the putative cytoplasmic region after M2. Single-point mutants of Kir2.1 (Glu224Gly and Glu299Ser) and a double-point mutant (Glu224Gly-Glu299Ser) were made and expressed in Xenopus oocytes or in HEK293T cells. 3. Their electrophysiological properties were compared with those of wild-type (WT) Kir2.1 and the following observations were made. (a) Glu299Ser showed a weaker inward rectification, a slower activation upon hyperpolarization, a slower decay of the outward current upon depolarization, a lower sensitivity to block by cytoplasmic spermine and a smaller single-channel conductance than WT. (b) The features of Glu224Gly were similar to those of Glu299Ser. (c) In the double mutant (Glu224Gly-Glu299Ser), the differences from WT described above were more prominent. 4. These results demonstrate that Glu299 as well as Glu224 control rectification and permeation, and suggest the possibility that the two sites contribute to the inner vestibule of the channel pore. The slowing down of the on- and off-blocking processes by mutation of these sites implies that Glu224 and Glu299 function to facilitate the entry (and exit) of spermine to (and from) the blocking site.

Amino Acid Sequence↗
PubMed2001

Characterization of heteromultimeric G protein-coupled inwardly rectifying potassium channels of the tunicate tadpole with a unique pore property.

Two cDNAs that encode the G protein-coupled inwardly rectifying K(+) channel (GIRK, Kir3) of tunicate tadpoles (tunicate G protein-coupled inwardly rectifying K(+) channel-A and -B; TuGIRK-A and -B) have been isolated. The deduced amino acid sequences showed approximately 60% identity with the mammalian Kir3 family. Detected by whole mount in situ hybridization, both TuGIRK-A and -B were expressed similarly in the neural cells of the head and neck region from the tail bud stage to the young tadpole stage. By co-injecting cRNAs of TuGIRK-A and G protein beta(1)/gamma(2) subunits (Gbetagamma) in Xenopus oocytes, an inwardly rectifying K(+) current was expressed. In contrast, coinjection of TuGIRK-B with Gbetagamma did not express any current. When both TuGIRK-A and -B were coexpressed together with Gbetagamma, an inwardly rectifying K(+) current was also detected. The properties of this current clearly differed from those of TuGIRK-A current, since it displayed a characteristic decline of the macroscopic conductance at strongly hyperpolarized potentials. TuGIRK-A/B current also differed from TuGIRK-A current in terms of the lower sensitivity to the Ba(2+) block, the higher sensitivity to the Cs(+) block, and the smaller single channel conductance. Taken together, we concluded that TuGIRK-A and -B form functional heteromultimeric G protein-coupled inwardly rectifying K(+) channels in the neural cells of the tunicate tadpole. By introducing a mutation of Lys(161) to Thr in TuGIRK-B, TuGIRK-A/B channels acquired a higher sensitivity to the Ba(2+) block and a slightly lower sensitivity to the Cs(+) block, and the decrease in the macroscopic conductance at hyperpolarized potentials was no longer observed. Thus, the differences in the electrophysiological properties between TuGIRK-A and TuGIRK-A/B channels were shown to be, at least partly, due to the presence of Lys(161) at the external mouth of the pore of the TuGIRK-B subunit.

Amino Acid Sequence↗
PubMed2001

Multiple PIP2 binding sites in Kir2.1 inwardly rectifying potassium channels.

Inwardly rectifying potassium channels require binding of phosphatidylinositol-4,5-bisphosphate (PIP2) for channel activity. Three independent sites (aa 175-206, aa 207-246, aa 324-365) were located in the C-terminal domain of Kir2.1 channels by assaying the binding of overlapping fragments to PIP2 containing liposomes. Mutations in the first site, which abolished channel activity, reduced PIP2 binding of this fragment but not of the complete C-terminus. Point mutations in the third site also reduced both, channel activity and PIP2 binding of this segment. The relevance of the third PIP2 binding site provides a basis for the understanding of constitutively active Kir2 channels.

Animals↗
PubMed2001

Geomagnetic disturbance associated with decrease in heart rate variability in a subarctic area.

BACKGROUND: Physical environmental variables, such as the natural variation in the geomagnetic field in and around the earth, influence biological processes and human health. The effect of geomagnetic disturbances on heart rate variability (HRV) in healthy students in a subarctic area is studied herein. SUBJECTS AND METHODS: Seven-day records by Holter ECG were obtained from eight clinically healthy subjects in Alta, Norway (70 N). Frequency- and time-domain measures of HRV were compared between 24-hour spans of high geomagnetic disturbance versus quiet conditions. RESULTS: A 5.9% increase in the 24-hour average of HR (P = 0.020) and a 25.2% decrease in HRV (P = 0.002) were documented on days of high geomagnetic disturbance. The decrease in spectral power was found primarily at frequencies lower than 0.04 Hz and was not statistically significant around 3.6 sec. CONCLUSIONS: The physiological mechanism involved may be other than the parasympathetic, usually identified with spectral power centered around 3.6 sec, a spectral region wherein no statistically significant differences were found.

Adult↗
PubMed2001

Impact of circadian amplitude and chronotherapy: relevance to prevention and treatment of stroke.

The long-acting calcium antagonist nifedipine reduces the incidence of stroke in Eastern Asia, as shown by the Shanghai Trial Of Nifedipine in the Elderly (STONE) and the Systolic Hypertension in China (Syst-China) trials. Recent trials in Japan have shown that benidipine may be more efficient than the former drug in preventing strokes in the elderly. Benidipine, commonly prescribed in Japan for a definite depressor effect, reportedly without causing remarkable fluctuations in blood pressure (BP), is investigated herein from a chronobiological viewpoint. Eighteen subjects (nine women and nine men, 39 to 87 years of age) with essential hypertension (office and ambulatory systolic, S/diastolic, D BP values above 160/95 mm Hg and 130/80 mm Hg, respectively) were enrolled in this investigation. Ambulatory BP was monitored at 30-min intervals for at least 24 h (ABPM-630, Colin Medical) before and after 4 weeks of crossover treatment with nifedipine tablets (twice daily, 20 mg/d) and benidipine (once daily, 4 mg/d, in the morning). The results indicate that: 1) benidipine and nifedipine reduce 24-h daytime (10:00-20:00) and nighttime (00:00-06:00) averages of SBP and DBP (P < 0.001); 2) the circadian double amplitude of BP is decreased after treatment with benidipine (from 28.6 to 21.1 mm Hg SBP and from 19.7 to 15.2 mm Hg DBP; P< 0.05), while the day-night difference in SBP is increased after treatment with nifedipine (18.6 vs 27.9 mm Hg, P< 0.01); and 3) the increase in the day-night difference of heart rate (HR) is significant after treatment with benidipine (13.6 vs 18.8 beats per minute, bpm; P< 0.05), but not with nifedipine. We have previously evaluated the usefulness of the circadian amplitude of BP as a prognostic tool of cardiovascular outcome, and found that an excessive circadian SBP or DBP amplitude was associated with an increased risk of vascular disease. The fact that benidipine reduces the circadian BP amplitude may be one reason for the superiority of this treatment over nifedipine in preventing an adverse outcome. A reduced heart rate variability (HRV) also predicts adverse cardiovascular outcomes in patients with overt cardiovascular disease and in hypertensive subjects. The fact that benidipine increases the day-night difference in HR may be another reason for the positive effects of this treatment.

Adult↗
PubMed2001

Intragastric acidity and circadian rhythm.

Most patients with peptic ulcers or gastroesophageal reflex disease develop subjective symptoms of epigastralgia and retrosternal pain during the period of time from the middle of the night to the early dawn (nocturnal pain). Such pain often disappears before breakfast. Disturbed circadian rhythm of gastric acid secretion may have a close relationship with the onset and aggravation of acid-related diseases. On the other hand, Helicobacter pylori has been considered to be an etiological agent of duodenal ulcer, and H. pylori eradication has been conducted in patients with gastritis and peptic ulcers. However, such eradication therapy sometimes results in the onset or deterioration of gastroesophageal reflux diseases. In this context, the question of whether the circadian rhythm of gastric acid secretion varies in accordance with the presence or absence of H. pylori infection is of interest. In the present study, we examined the fluctuation in intragastric acidity via a portable pH meter in 10 H. pylori-positive and 10 H. pylori-negative subjects. As a result, a significant difference in the circadian rhythmicity was observed between the H. pylori-negative and the H. pylori-positive group, with mean values for each parameter of 28.1 and 13.3 for amplitude, 22.7 and 12.4 for the midline-estimating statistic of rhythm (MESOR), and 324.0 and 321.0 for acrophase, respectively (P < 0.001). In both H. pylori-positive and negative groups, a tendency was observed toward an increase in intragastric acidity during the time period from the middle of the night to the early dawn, and toward a decrease in intragastric acidity during the early morning. In the H. pylori-positive group, the values for intragastric acidity over time were lower, and the degree of amplitude was smaller as compared to the H. pylori-negative group. Further, H. pylori-positive individuals were at a more advanced stage of the disease.

Adult↗
PubMed2001

Treatment of pyogenic granuloma with a sclerosing agent.

BACKGROUND: Pyogenic granulomas have been treated by cryosurgery, curettage, electrodesiccation, chemical cauterization, and laser surgery. The therapeutic effects of these conservative treatments are limited, however. OBJECTIVE: In this study, the efficacy of a sclerosing agent (monoethanolamine oleate) was evaluated for the treatment of pyogenic granuloma. METHODS: Pyogenic granuloma was treated by local injection of the monoethanolamine oleate solution in nine patients who were from 1 to 57 years of age (median 18 years). The treatment effect was determined by physical examination. RESULTS: All lesions were removed completely with no recurrence, and scars were inconspicuous in all cases. Complications occurred in only one patient who complained of pain due to an avoidable injection of excess solution. CONCLUSION: Sclerotherapy with monoethanolamine oleate is effective in the treatment of pyogenic granuloma and offers an alternative to conventional methods in cases for which conservative treatment is preferable.

Adolescent↗
PubMed2001

Monoclonal antibody that binds to the central loop of the Tn10-encoded metal tetracycline/H+ antiporter of Escherichia coli.

Mouse monoclonal antibodies were prepared using His-tagged Tn10-encoded metal-tetracycline/H+ antiporter [TetA(B)His] as an antigen. From them, those reacting equally with His-tagged and wild-type TetA(B) were selected and named TCL-1. Cysteine-scanning mutants were used to determine the TCL-1 binding site on the TetA(B) protein. First, 12 Cys mutants of TetA(B) in which one residue in a protruding loop region was replaced by cysteine were constructed. Western blot analysis revealed the binding of TCL-1 to all of these Cys-mutants except for R186C. Then, we constructed 13 cysteine-scanning mutants, F179C to T191C. Among them, eight mutants, F179C to T182C, N184C, and T189C to T191C, exhibited TCL-1 binding, whereas the other five, K183C, T185C, R186C, D187C, and N188C, exhibited no or lower TCL-1 binding. These results clearly indicate that the sequence recognized by TCL-1 is 183Lys-X-Thr-Arg-Asp-Asn188 in the central loop region of TetA(B). TCL-1 is the first reported antibody that binds to a region other than the C-terminus of TetA(B), and the recognized amino acid sequence was identified.

Amino Acid Sequence↗
PubMed2001

Formation of retinoyl-CoA in rat tissues.

Retinoylation (retinoic acid acylation) is a posttranslational modification of proteins occurring in a variety of cell types in vitro and in tissues in vivo. The widespread occurrence of retinoylation suggests that it may play a role in many effects of retinoic acid (RA) on cells. One metabolic pathway for retinoylation involves the intermediate formation of retinoyl-CoA and subsequent transfer and covalent binding of the retinoyl moiety to protein. However, such reactions are not well known. To gain further insight into retinoylation, we studied the synthesis of retinoyl-CoA, the first step in this multi-stage process. The formation of [(3)H]-retinoyl-CoA was determined in incubation mixtures containing rat liver extract, [(3)H]-RA, ATP, CoA, and MgCl(2). No retinoyl-CoA was formed in the presence of boiled extract, or in the absence of ATP, CoA, or MgCl(2) (a divalent cation). A greater amount of retinoyl-CoA was obtained from microsomal fractions of rat liver than from other subfractions. The presence of retinoyl-CoA was also detected in extracts prepared from rat testis, kidney, brain, spleen, and pancreas. The level of retinoylation in various tissue extracts was related directly to the amount of retinoyl-CoA formed. V(max) and K(m) values for RA in the formation of liver retinoyl-CoA were estimated to be 1.0 x 10(-4) micromol/min/mg protein and 24 nM, respectively. Synthesis of retinoyl-CoA was suppressed by fatty acids and fatty acyl-CoAs. These results indicate that ATP-dependent generation of retinoyl-CoA occurs in rat tissues and may play a significant physiological role in RA actions mediated by retinoylation.

Acyl Coenzyme A↗
PubMed2001

Structural and phylogenetic analysis of TRAS, telomeric repeat-specific non-LTR retrotransposon families in Lepidopteran insects.

TRAS1 is a non-LTR retrotransposon inserted specifically into the telomeric repeat (TTAGG)(n) in the silkworm, Bombyx mori. To characterize the evolutionary origin of TRAS-like elements, we identified seven TRAS families (TRAS3, TRAS4, TRAS5, TRAS6, TRASY, TRASZ, and TRASW) from B. mori and four elements from two Lepidoptera, Dictyoploca japonica (TRASDJ) and Samia cynthia ricini (TRASSC3, TRASSC4, and TRASSC9). More than 2,000 copies of various Bombyx TRAS elements accumulated within (TTAGG)(n) sequences as unusual but orderly tandem repeats. The 5' and 3' regions were highly conserved within each class of Bombyx TRAS elements without truncation. This suggests that distinct classes of TRAS have been maintained independently by retrotransposition into (TTAGG)(n). The phylogenetic tree of site-specific retroelements showed that nine TRAS families in Lepidoptera constitute a single phylogenetic group that is closely related to the R1 family that inserts specifically into arthropod 28S rDNA. The higher amino acid sequence identity from endonuclease (EN) to reverse transcriptase (RT) domains between TRAS groups (about 37%-70%) than among TRAS elements and R1Bm (about 25%-30%), may reflect the presence of some DNA structure responsible for their target specificity. Sequence comparison from EN to RT domains among non-LTR elements revealed several regions conserved only within TRAS elements. We found a highly conserved region that resembles the Myb-like DNA-binding structure, between the EN and RT domains. These regions may be involved in site-specific integration of TRAS elements into the (TTAGG)(n) telomeric repeats.

Amino Acid Sequence↗
PubMed2001

Stabilization of cauliflower mosaic virus P3 tetramer by covalent linkage.

Cauliflower mosaic virus (CaMV) open reading frame (ORF) III encodes a 15 kDa protein (P3) that is indispensable for viral infectivity. Although P3 has been shown to be a prerequisite for CaMV aphid transmission, its role in viral replication remains unknown. We previously showed that P3 forms a tetramer in planta and that P3 tetramer co-sediments with viral coat protein on sucrose gradient centrifugation, suggesting that a tetramer may be the functional form of P3. We presumed that disulfide bonds were involved in tetramer formation because 1) the tetramer was detected by Western blotting after electrophoresis under non-reducing conditions, and 2) the cysteine-X-cysteine motif is well conserved in CaMV P3 and P3 homologues among Caulimoviruses. Therefore we mutated either or both of the cysteine residues of CaMV P3. The mutant viruses were infectious and accumulated to a similar extent as the wild-type. An analysis of mutant proteins confirmed that the wild-type P3 molecules in the tetramer are covalently bound with one another through disulfide bonds. It was also suggested that mutant proteins are less stable than wild-type protein in planta. Furthermore, sedimentation study suggested that the disulfide bonds are involved in stable association of P3 with CaMV virions or virion-like particles, or both. The mutant viruses could be transmitted by aphids. These results suggested that the covalent bonds in P3 tetramer are dispensable for biological activity of P3 under experimental situations and may have some biological significance in natural infection in the field.

Alanine↗
PubMed2001

Identification of a H+/glucose and galactose symporter gene glt from Xanthomonas oryzae pv. oryzae.

We identified a glucose and galactose transporter gene from the plant-pathogenic bacterium Xanthomonas oryzae pv. oryzae. Sequence analysis indicated that the gene, named glt, encoded a polypeptide of 592 amino acid residues and the product was significantly homologous with members of the Na+/glucose cotransporter (SGLT) family from mammalian and bacterial origin, especially with vSGLT from Vibrio parahaemolyticus (50% identity). GLT functioned as a glucose and galactose transporter in an Escherichia coli mutant deficient in glucose and galactose transport activity. A protonophore inhibited the transport activity, suggesting that GLT is a H+-coupled glucose/galactose symporter.

Amino Acid Sequence↗
PubMed2001

X-irradiation induces up-regulation of ATM gene expression in wild-type lymphoblastoid cell lines, but not in their heterozygous or homozygous ataxia-telangiectasia counterparts.

Ataxia-telangiectasia (AT) is an autosomal recessive disease. The relevant gene has been cloned and designated ATM. We studied the expression of both ATM mRNA and the ATM protein in unirradiated and X-irradiated EBV (Epstein-Barr virus)-transformed lymphoblastoid cell lines (LCLs) derived from donors who were normal (ATM + / + ), AT heterozygotes (ATM + / - ), or AT homozygotes (ATM - / - ), respectively. In ATM + / + LCLs, the levels of ATM mRNA were found to have increased by approximately 1.5-fold within 1 h of exposure to 10 Gy of X-rays, while the ATM protein levels had increased by 1.5- to 2.0-fold within 2 to 3 h of irradiation. The wild-type mRNA and protein levels both returned to their basal values fairly quickly after this time. The results obtained with the ATM + / - LCLs were quite different, however: neither the mRNA nor protein levels were found to have increased as a consequence of X-irradiation in any ATM + / - LCL. Twelve of the mutations in the ATM - / - LCLs we used were truncating mutations, and we suspected that the corresponding truncated ATM proteins would be too labile to be detected by western blot analysis. However, five of the ATM - / - LCLs produced mutant ATM proteins that were identical in molecular weight to the wild-type ATM protein. When cells from three of these five clones were exposed to X-rays, transcription of the mutant ATM genes appeared to reduce somewhat, as were the levels of protein being produced. These results suggest that the normal ATM gene responds to ionizing radiation by up-regulating its activity, whereas none of the mutant ATM genes we studied were able to respond in this way.

Ataxia Telangiectasia↗