Yoshimitsu Nakashima

MOUSE DEOXYRIBONUCLEASE I (DNASE I) : BIOCHEMICAL AND IMMUNOLOGICAL CHARACTERIZATION, CDNA STRUCTURE AND TISSUE DISTRIBUTION

Mouse urinary deoxyribonuclease I (DNase I) resembles rat and human DNase Is in terms of its proteochemical and enzymological properties. Furthermore, mouse DNase I was demonstrated to be immunologically closer to the rat than to the human enzyme. A 1176 bp full length cDNA encoding mouse DNase I was constructed from RNA obtained from the kidney and parotid glands. The amino acid sequence up to the 45th residue from the N‐terminal of the mature enzyme was identical to that deduced from the cDNA sequence. This DNase I was distributed most densely in the parotid glands from the standpoint of both enzyme activity and gene transcript levels.

Identification of the three non‐identical subunits constituting human deoxyribonuclease II

We purified DNase II from human liver to apparent homogeneity. The N‐terminal amino acid sequences of each of three components constituting the purified mature enzyme were then separately determined by automatic Edman degradation. A combination of this chemical information and the previously reported nucleotide sequence of the cDNA encoding human DNase II [Yasuda et al. (1998) J. Biol. Chem. 273, 2610–2626] allowed detailed elucidation of the enzymes subunit structure: human DNase II was composed of three non‐identical subunits, a propeptide, proprotein and mature protein, following a signal peptide. Expression analysis of a series of deletion mutants derived from the cDNA of DNase II in COS‐7 cells suggested that although a single large precursor protein may not be necessary for proteolytic maturation, the propeptide region L17–Q46 may play an essential role in generating the active form of the enzyme.

Two novel screening methods for selecting monoclonal antibodies which specifically inhibit DNase I enzyme activity

Two novel screening methods, single radial enzyme diffusion and the DNA-cast polyacrylamide gel electrophoresis, for selecting monoclonal antibodies which detect human deoxyribonuclease I (DNase I) enzyme activity are described. The former was adopted for initial screening to select potential objective antibodies from numerous hybridoma culture supernatants, because it was easy to perform and a powerful mass-screening tool. The latter was utilized for the subsequent precise selection of the antibodies in the supernatants selected after preliminary screening by the former, because it was clearly more accurate and sensitive, although the procedure was slightly more complicated. The consecutive use of these two methods resulted in the isolation of 25 anti-human DNase I antibodies, all of which specifically inhibited the activity of human DNase I.

Molecular, biochemical and immunological studies of hen pancreatic deoxyribonuclease I.

Deoxyribonuclease I (DNase I) was purified from the hen pancreas to electrophoretic homogeneity using six-step column chromatography. The purified enzyme showed a molecular mass of about 33 kDa and maximum activity at pH 7.0. It required divalent cations, Mg2+ and Ca2+, for its activity and was inhibited by EDTA, EGTA and an antibody specific to the purified enzyme but not by G-actin. A 1066-bp cDNA encoding hen DNase I was constructed from the total RNA of a hen pancreas using a combination of the reverse transcriptase-polymerase chain reaction and rapid amplification of cDNA ends methods, followed by sequencing. The cDNA was expressed in Escherichia coli, and the recombinant polypeptide exhibited significant enzyme activity. The mature hen DNase I protein was found to consist of 262 amino acids. In human and bovine DNase I four amino acid residues, Glu-13, Tyr-65, Val-67 and Ala-114 are involved in actin binding, whereas in the hen DNase I these positions were occupied by Asp, Phe, Ser and Phe, respectively. A survey of the DNase I distribution in 15 hen tissues showed that the pancreas had the highest levels of both DNase I enzyme activity and DNase I gene expression. The results of our phylogenetic and immunological analyses indicate that the hen DNase I is not closely related to the mammalian enzymes. This is the first report in which has been described the results of molecular, biochemical and immunological analyses on hen DNase I.

The molecular basis for genetic polymorphism of human deoxyribonuclease II (DNase II): a single nucleotide substitution in the promoter region of human DNase II changes the promoter activity.

Deoxyribonuclease II (DNase II) levels in human vary depending on whether the individual has the DNASE2*H (high) allele or the DNASE2*L (low) allele. We examined the promoter activity of the 5′‐flanking region of each of these alleles by transient transfection luciferase assay. DNASE2*H had 5‐fold higher promoter activity than DNASE2*L in human hepatoma HepG2 cell. Comparison of the nucleotide sequences of the proximal promoter regions revealed a G to A transition at position −75; G and A residues were assigned to DNASE2*H and *L, respectively. Since no differences were found between the open reading frame sequences of these alleles, it is likely that the A−75G transition causes the allelic difference in the promoter activity of the gene, underlying the genetic polymorphism.

Geographical North-South Decline in DNASE1*2 in Japanese Populations

Allele frequencies for human deoxyribonuclease I (DNase I) phenotypes were determined using blood samples from about 2000 Japanese subjects living in nine prefectures, and compared with one another. DNase I phenotyping was performed principally using isoelectric focusing electrophoresis and activity staining. The DNase I system was shown to have enhanced potential for anthropologic, genetic, and clinical studies of Japanese populations. DNase I phenotypes were analyzed to evaluate the degree of genetic variation at the DNASE1 locus. Our examination of DNase I types revealed a decreasing north-to-south gradient in the DNASE1allele.

Structure and organization of the human deoxyribonuclease II (DNase II) gene

The structure of the human gene for deoxyribonuclease II (DNase II; EC 3.1.22.1) was determined using several specific primers based on the human DNase II cDNA sequence [Yasuda et al. (1998). J. Biol. Chem.273, 2610–2616] in a polymerase chain reaction‐based strategy. The gene spanned about 6 kb and consisted of 6 exons. No canonical TATA or CAAT boxes could be identified within the 1341 nucleotides upstream of the putative transcription start site, although the 5′‐flanking region contained a CpG island and several putative binding motifs for transcription factors Sp1 and ETF. These properties indicate that the DNase II gene is a housekeeping gene and this is compatible with its ubiquitous expression in human tissues. Three different cleavage/polyadenylation sites were identified in the 3′‐flanking region, leading to the production of multiple DNase II mRNA species. However, a comparison of the entire translated sequences of the gene from a pair of subjects with homozygous DNase II phenotypes H and L revealed no differences in the nucleotide sequences.

Postmortem absorption of dichloromethane: a case study and animal experiments.

Abstract A case of accidental death after occupational exposure to an atmosphere containing dichloromethane (DCM) is reported. The concentrations of DCM in the blood and tissues of a 40-year-old man who died while observing an industrial washing machine filled with DCM vapour were blood 1660 mg/l, urine 247 mg/l, brain 87 mg/ kg, heart muscle 199 mg/kg and lungs 103 mg/kg which are 3–7 times higher than previously reported fatal levels. The body was left undiscovered in the machine filled with DCM vapour for about 20 h. The present study was designed to determine whether all the DCM detected in the tissues and body fluids had been inhaled while alive using rats as the experimental model. The concentrations of DCM in the tissues and body fluids of a rat that died from DCM poisoning and was left for 20 h in a box containing DCM vapour were the same as those in the tissues and body fluids of a rat that had died from an injected overdose of barbiturates and had then been placed in the DCM box in a similar manner. Moreover, the concentrations of DCM in the tissues and body fluids of the carcasses that were exposed to the DCM vapour increased gradually throughout the period of exposure. These findings imply that DCM is able to penetrate the tissues and body fluids of rat carcasses through a route other than inhalation such as through the skin.

Rapid Purification of Human DNase I Using Mouse Monoclonal Anti-DNase I Antibodies and Characterization of the Antibodies

Five anti-human deoxyribonuclease I (DNase I) monoclonal antibodies were obtained from BALB/c mice immunized with DNase I purified from human urine. Four of them inhibited DNase I enzyme activity, as did a rabbit polyclonal antibody; these 4 did not have immunostaining ability. The remaining one had immunostaining ability but no inhibitory activity. A Sepharose 4B column conjugated with 1 of the 4 antibodies that had inhibitory activity effectively adsorbed and eluted the DNase I enzyme; this did not occur with the rabbit polyclonal antibody. We showed that adding an immunoaffinity chromatography step made the purification of human DNase I easier and faster than the conventional procedure.

Xenopus laevis Pancreatic DNase I: Purification and Immunological Characterization

Deoxyribonuclease I (DNase I) was purified from Xenopus laevis pancreas to apparent electrophoretic homogeneity using a series of column chromatographies. The purified enzyme showed a molecular mass of about 36 kDa and maximum activity at pH 7.0–8.0, required divalent cations, Ca2+ and Mg2+, for its activity, and was inhibited by EDTA, EGTA and an antibody specific to the enzyme, but not by G-actin. The N-terminal amino acid sequence of the enzyme up to the 37th residue shared 38–44% homology with that of mammalian DNases I derived from bovine, ovine, porcine, rat, mouse, rabbit and human. A systematic survey of DNase I activity distribution in 20 different kinds of frog tissues showed that the pancreas and rectum produced higher amounts than other tissues. This is the first report concerning the purification and chemical and immunological characterization of frog pancreatic DNase I.