Repair of I-SceI Induced DSB at a specific site of chromosome in human cells: influence of low-dose,low-dose-rate gamma-rays

We investigated the influence of low-dose, low-dose-rate gamma-ray irradiation on DNA double strand break (DSB) repair in human lymphoblastoid TK6 cells. A single DSB was introduced at intron 4 of the TK+ allele (chromosome 17) by transfection with the I-SceI expression vector pCBASce. We assessed for DSB repair due to non-homologous end-joining (NHEJ) by determining the generation of TK-deficient mutants in the TK6 derivative TSCE5 (TK +/−) carrying an I-SceI recognition site. We similarly estimated DSB repair via homologous recombination (HR) at the same site in the derived compound heterozygote (TK−/−) cell line TSCER2 that carries an additional point mutation in exon 5. The NHEJ repair of DSB was barely influenced by pre-irradiation of the cells with 30 mGy γ-rays at 1.2 mGy h⁻¹. DSB repair by HR, in contrast, was enhanced by ~50% after pre-irradiation of the cells under these conditions. Furthermore, when I-SceI digestion was followed by irradiation at a dose of 8.5 mGy, delivered at a dose rate of only 0.125 mGy h⁻¹, HR repair efficiency was enhanced by ~80%. This experimental approach can be applied to characterize DSB repair in the low-dose region of ionizing radiation.     

Involvement of the H3O+-Lys-164 -Gln-161-Glu-345 charge transfer pathway in proton transport of gastric H+,K+-ATPase

Gastric H(+),K(+)-ATPase is shown to transport 2 mol of H(+)/mol of ATP hydrolysis in isolated hog gastric vesicles. We studied whether the H(+) transport mechanism is due to charge transfer and/or transfer of hydronium ion (H(3)O(+)). From transport of [(18)O]H(2)O, 1.8 mol of water molecule/mol of ATP hydrolysis was found to be transported. We performed a molecular dynamics simulation of the three-dimensional structure model of the H(+),K(+)-ATPase alpha-subunit at E(1) conformation. It predicts the presence of a charge transfer pathway from hydronium ion in cytosolic medium to Glu-345 in cation binding site 2 (H(3)O(+)-Lys-164 -Gln-161-Glu-345). No charge transport pathway was formed in mutant Q161L, E345L, and E345D. Alternative pathways (H(3)O(+)-Gln-161-Glu-345) in mutant K164L and (H(3)O(+)-Arg-105-Gln-161-Gln-345) in mutant E345Q were formed. The H(+),K(+)-ATPase activity in these mutants reflected the presence and absence of charge transfer pathways. We also found charge transfer from sites 2 to 1 via a water wire and a charge transfer pathway (H(3)O(+)-Asn-794 -Glu-797). These results suggest that protons are charge-transferred from the cytosolic side to H(2)O in sites 2 and 1, the H(2)O comes from cytosolic medium, and H(3)O(+) in the sites are transported into lumen during the conformational transition from E(1)PtoE(2)P.     

K+-Cl- Cotransporter-3a Up-regulates Na+,K+-ATPase in Lipid Rafts of Gastric Luminal Parietal Cells

Gastric parietal cells migrate from the luminal to the basal region of the gland, and they gradually lose acid secretory activity. So far, distribution and function of K+-Cl(-) cotransporters (KCCs) in gastric parietal cells have not been reported. We found that KCC3a but not KCC3b mRNA was highly expressed, and KCC3a protein was predominantly expressed in the basolateral membrane of rat gastric parietal cells located in the luminal region of the glands. KCC3a and the Na+,K+-ATPase alpha1-subunit (alpha1NaK) were coimmunoprecipitated, and both of them were highly localized in a lipid raft fraction. The ouabain-sensitive K+-dependent ATP-hydrolyzing activity (Na+,K+-ATPase activity) was significantly inhibited by a KCC inhibitor (R-(+)-[(2-n-butyl-6,7-dichloro-2-cyclopentyl-2,3-dihydro-1-oxo-1H-inden-5-yl)oxy]acetic acid (DIOA)). The stable exogenous expression of KCC3a in LLC-PK1 cells resulted in association of KCC3a with endogenous alpha1NaK, and it recruited alpha1NaK in lipid rafts, accompanying increases of Na+,K+-ATPase activity and ouabain-sensitive Na+ transport activity that were suppressed by DIOA, whereas the total expression level of alpha1NaK in the cells was not significantly altered. On the other hand, the expression of KCC4 induced no association with alpha1NaK. In conclusion, KCC3a forms a functional complex with alpha1NaK in the basolateral membrane of luminal parietal cells, and it up-regulates alpha1NaK in lipid rafts, whereas KCC3a is absent in basal parietal cells.     

Combination of Tumor Necrosis Factor Alpha and Interferon Alpha Induces Apoptotic Cell Death through a c-myc–Dependent Pathway in p53 Mutant H226br Non–Small-Cell Lung Cancer Cell Line

We investigated the role of wild-type p53 and c-myc activity in apoptosis induced by a combination of natural human tumor necrosis factor alpha (TNF-α) and natural human interferon alpha (IFN-α). Studies were performed with two human non–small-cell lung cancer cell lines, H226b, which has wild-type p53, and H226br, which has a mutant p53. The combination of IFN-α and TNF-α significantly inhibited cell growth and induced apoptotic cell death of both H226b and H226br, compared with IFN-α or TNF-α alone. Treatment with one or both cytokines did not affect the expression level of p53 in both cell lines. These results suggest that the combination of IFN-α/TNF-α induces apoptotic cell death through a p53- independent pathway. The c-myc oncogene is known to be involved in apoptosis induced by TNF. Antisense c-myc oligonucleotides have been reported to modulate cell growth or apoptosis in several cell lines. Antisense oligodeoxynucleotides were added to the culture of H226br cells before the addition of IFN-α/TNF-α. Antisense c-myc inhibited IFN-α/TNF-α cytotoxicity and apoptotic cell death. In conclusion, this study provides support for the speculation that TNF-α/IFN-α induce apoptosis through a c-myc–dependent pathway rather than a p53-dependent pathway.     

Formation of the sphenomandibular ligament by Meckel's cartilage in the mouse: possible involvement of epidermal growth factor as revealed by studies in vivo and in vitro

In mammals, the midportion of the soft tissue of Meckel's cartilage at the degenerating stage forms a ligament known as the sphenomandibular ligament. To clarify the mechanism of formation of this ligament by Meckel's cartilage in mouse, we examined the effects of epidermal growth factor (EGF) on the chondrocytes in terms of the proliferation and differentiation of cells and calcification of the matrix in vivo and in vitro. The effects of EGF were examined by immunohistochemical staining, with EGF-soaked beads, by electron microscopy, and by general histochemical analysis of proteoglycans and calcification. Analysis of labeling with bromodeoxyuridine (BrdU) and the rate of cell growth revealed that EGF enhanced DNA synthesis and the proliferation of Meckel's chondrocytes. Histological findings in organ culture and in cell culture, with and without the application of EGF-soaked beads, revealed that EGF inhibited the differentiation of cells to chondrocytes and induced phenotypic changes in fibroblastic cells. The inhibition of alkaline phosphatase activity that resulted from exposure to EGF was accompanied by prolonged calcification of the matrix. Whole-mount staining revealed that subcutaneous injection of EGF enhanced the disappearance of Meckel's cartilage. Our results suggest a possible mechanism whereby the midportion of Meckel's cartilage remains uncalcified and is rapidly transformed into the sphenomandibular ligament.     

The Replicon of the Cryptic Plasmid pSBO1 Isolated from Streptococcus bovis JB1

The cryptic plasmid pSBO1 (3904 bp) was isolated from Streptococcus bovis JB1. pSBO1 contained an open reading frame (ORF) that is homologous to sequences encoding the replication protein (Rep) in pEFC1 (isolated from Enterococcus faecalis), pSK639 (Staphylococcus epidermidis), pLA103 (Lactobacillus acidophilus), and pUCL287 (Tetragenococcus halophila). In addition, four 22-bp direct repeats (DRs) were located upstream of the putative replication gene (rep) of pSBO1. Recombinant plasmids (pSBE10 and pSBE11) containing the DRs and putative rep of pSBO1 replicated in S. bovis 12-U-1 and no8 strains. This result indicates that the putative rep encoded Rep and that the replicon of pSBO1 contained the DRs and the rep. Gel shift assays showed that the Rep of pSBO1 bound the 22-bp DRs. Received: 14 September 2000 / Accepted: 28 November 2000     

Expression of DNA methyltransferase (Dnmt1) in testicular germ cells during development of mouse embryo

The DNA methylation pattern is reprogrammed in embryonic germ cells. In female germ cells, the short-form DNA methyltransferase Dnmt1, which is an alternative isoform specifically expressed in growing oocytes, plays a crucial role in maintaining imprinted genes. To evaluate the contribution of Dnmt1 to the DNA methylation in male germ cells, the expression profiles of Dnmt1 in embryonic gonocytes were investigated. We detected a significant expression of Dnmt1 in primordial germ cells in 12.5-14.5 day postcoitum (dpc) embryos. The expression of Dnmt1 was downregulated after 14.5 dpc after which almost no Dnmt1 was detected in gonocytes prepared from 18.5 dpc embryos. The short-form Dnmt1 also was not detected in the 16.5-18.5 dpc gonocytes. On the other hand, Dnmt1 was constantly detected in Sertoli cells at 12.5-18.5 dpc. The expression profiles of Dnmt1 were similar to that of proliferating cell nuclear antigen (PCNA), a marker for proliferating cells, suggesting that Dnmt1 was specifically expressed in the proliferating male germ cells. Inversely, genome-wide DNA methylation occurred after germ cell proliferation was arrested, when the Dnmt1 expression was downregulated. The present results indicate that not Dnmt1 but some other type of DNA methyltransferase contributes to the creation of DNA methylation patterns in male germ cells.     

Number of glomeruli is increased in the kidney of transgenic mice expressing the truncated type II activin receptor

Histological analyses of the kidney were performed in transgenic mice expressing the truncated type II activin receptor. In these mice, signaling through the activin receptor was attenuated. Size and wet weight of the kidneys were identical to those of normal mice. Histologically, the number of glomeruli was approximately 180% of that in normal mice. The sizes and shapes of the glomeruli were variable, but many of them were smaller than those in normal mice. Morphometrically, the total glomerular area was 130% of that of the normal mice. Abnormality of the epithelia in Bowman's capsule was observed and the number of tubular epithelial cells was increased in the transgenic mice. The serum levels of blood urea nitrogen, creatinine, and creatinine clearance were identical to those in normal mice. These results suggest that the action of activin or related ligands is critical for determination of the nephron number.