Enzymatic removal of O6-ethylguanine from mitochondrial DNA in rat tissues exposed to N-ethyl-N-nitrosourea in vivo

DNA repair is essential for maintaining the integrity of the genetic material, and a number of DNA repair mechanisms have been fairly well characterized for the nuclear DNA of eukaryotic cells as well as prokaryotes. However, little is known about DNA repair in mitochondria. Using highly sensitive immunoanalytical methods to detect specific DNA alkylation products, we found active removal of O6-ethyl-2'-deoxyguanosine (O6-EtdGuo) from rat liver mitochondrial DNA after pulse-exposure to N-ethyl-N-nitrosourea in vivo. In the kidney, O6-EtdGuo was removed from mitochondrial DNA with moderate efficiency, but nearly no removal was observed from the DNA of brain mitochondria. Among the rat tissues examined, the kinetics of O6-EtdGuo elimination from mitochondrial DNA was very similar to the kinetics of removal from nuclear DNA. O4-Ethyl-2'-deoxythymidine, another premutagenic DNA ethylation product, was stable in both mitochondrial and nuclear DNA of rat liver.     

Replication of X chromosomes in complete moles

Summary DNA replication patterns of X chromosomes in complete hydatidiform moles were studied using cultured fibroblasts from three 46,XX moles resulting from duplication of a haploid sperm, and from a 46,XY mole originating from dispermy. Control cultures included skin fibroblasts from an adult woman and a female fetus as well as PB lymphocytes from an adult woman. Cultures were treated with 5-bromodeoxyuridine for the last 2–4h of the S phase, and the chromosome slides prepared were stained by the Hoechst 33258-Giemsa procedure. Each of the three XX moles studied revealed one early-replicating and one late-replicating X chromosomes, while the XY mole revealed one early-replicating X chromosome. DNA replication patterns of molar X chromosomes were similar to those of adult and fetal fibroblasts, but different from those in adult lymphocytes. These findings indicate that DNA replication kinetics of molar fibroblasts are tissue-specific rather than origin- or developmental-stage specific.     

Translocation of hepatocyte lysosomes following partial hepatectomy and its inhibition by colchicine

Hepatocyte microtubules were studied during the translocation of lysosomes which follows partial hepatectomy. In hepatocytes of normal rat liver the lysosomes are seen mainly along the bile canaliculi. After partial hepatectomy, these lysosomes lose their pericanalicular arrangement and move towards large inclusions (‘protein droplets’) which result from the marked pinocytosis induced by the removal of about two-thirds of the liver mass. The lysosomes fuse with the inclusions, and by 4 h after partial hepatectomy most of the inclusions demonstrate acid phosphatase activity histochemically. Many microtubules are found in close proximity to the lysosomes. When the rats are treated with colchicine prior to the partial hepatectomy, events are markedly different. The lysosomes change their location but do not hit the cytoplasmic inclusions, and the inclusions remain negative for acid phosphatase activity even 4 h post-hepatectomy. Quantitative ultrastructural study shows that the volume density of microtubules in the hepatocytes decreases to one-third of that in control hepatocytes. This strongly suggests an involvement of microtubules in giving orientation to the translocation of hepatocyte lysosomes under these conditions.     

Biochemical characteristics of a preneoplastic marker enzyme glutathione S-transferase P-form(7-7)

Investigation of biochemical characteristics of the glutathione S-transferase P-form (GST 7-7), a specific marker enzyme for preneoplastic cells arising during chemical hepatocarcinogenesis in the rat, revealed distinct functional differential from six other major GST forms. While the GST 7-7 substrate specificity was generally broader, binding ability for diverse organic anions such as bilirubin, hematin, and sulfobromophthalein was as high as in any of the other six forms. Furthermore, the enzymatic activity of GST 7-7 was found to be highly insensitive to the inhibitory actions of a wide range of organic anions at physiological pH in contrast to the other forms which proved more susceptible. The functional characteristics of GST 7-7 may in part account for its overproduction in the preneoplastic cells.