Hypermethylation of regulatory sequences at the locus of the pi-class glutathione S-transferase gene GSTP1 was detected in 20 of 20 human prostatic carcinoma tissue specimens studied but not in normal tissues or prostatic tissues exhibiting benign hyperplasia. In addition, a striking decrease in GSTP1 expression was found to accompany human prostatic carcinogenesis. Immunohistochemical staining with anti-GSTP1 antibodies failed to detect the enzyme in 88 of 91 prostatic carcinomas analyzed. In vitro, GSTP1 expression was limited to human prostatic cancer cell lines containing GSTP1 alleles with hypomethylated promoter sequences; a human prostatic cancer cell line containing only hypermethylated GSTP1 promoter sequences did not express GSTP1 mRNA or polypeptides. Methylation of cytidine nucleotides in GSTP1 regulatory sequences constitutes the most common genomic alteration yet described for human prostate cancer.

https://www.pnas.org/content/pnas/91/24/11733.full.pdf

Cytidine methylation of regulatory sequences near the pi-class glutathione S-transferase gene accompanies human prostatic carcinogenesis

INTRODUCTION In 1971, Wang (1) discovered the first DNA topoisomerase in Escherichia coli. The enzyme (E. coli DNA topoisomerase I, or w protein) catalyzed relaxation of negatively supercoiled DNA in the absence of any energy cofactor (1). Wang proposed that this enzyme also catalyzed transient nicking of the DNA double helix and possessed both DNase and ligase activity in one polypeptide (1). The lack of any energy cofactor for the reaction also led Wang to the proposal that the enzyme may form a high-energy covalent bond between itself and the transiently broken DNA phosphodiester bond (1). Both of these predictions have turned out to be correct (2). Since the discovery of E. coli topoisomerase I, investigators have isolated many other DNA topoisomerases from both prokaryotes and eukaryotes. In 1972, Champoux & Dulbecco isolated an enzyme with activity similar to that of E. coli topoisomerase I from mouse embryo cells (3). In 1976, Gellert and his colleagues identified an enzyme activity opposing E. coli DNA topoisomerase I (4). They demonstrated that this enzyme (E. coli DNA topoisomerase II, or gyrase) catalyzed the conversion of relaxed DNA into negatively supercoiled DNA in a reaction requiring ATP hydrolysis (4). These two opposing activities are important for maintaining the super­ helical state of the chromosomal DNA during various DNA transactions (5-8). In 1979, Liu et al (9) isolated an enzyme from bacteriophage

DNA Topoisomerases: Essential Enzymes and Lethal Targets

Drug development is needed to improve chemotherapy of patients with locally advanced or metastatic colon carcinoma, who otherwise have an unfavorable prognosis. DNA topoisomerase I, a nuclear enzyme important for solving topological problems arising during DNA replication and for other cellular functions, has been identified as a principal target of a plant alkaloid 20(S)-camptothecin. Significantly increased concentrations of this enzyme, compared to that in normal colonic mucosa, were found in advanced stages of human colon adenocarcinoma and in xenografts of colon cancer carried by immunodeficient mice. Several synthetic analogs of camptothecin, selected by tests with the purified enzyme and tissue-culture screens, were evaluated in the xenograft model. Unlike other anticancer drugs tested, 20(RS)-9-amino-camptothecin (9-AC) induced disease-free remissions. The overall drug toxicity was low and allowed for repeated courses of treatment.

http://science.sciencemag.org/content/sci/246/4933/1046.full.pdf

DNA topoisomerase I--targeted chemotherapy of human colon cancer in xenografts

Mechanism of action of eukaryotic dna topoisomerase i and drugs targeted to the enzyme

DNA topoisomerases are double-edged swords. They are essential for many vital functions of DNA during normal cell growth. However, they are also highly vulnerable under various physiological and nonphysiological stresses because of their delicate act on breaking and rejoining DNA. These stresses (e.g. exposure to topoisomerase poisons, acidic pH, and oxidative stresses) can convert DNA topoisomerases into DNA-breaking nucleases, resulting in cell death and/or genomic instability. The importance of topoisomerase-mediated DNA cleavage in tumor cell death and carcinogenesis has been recognized. This review focuses on recent findings concerning the molecular mechanisms of the stress responses to topoisomerase-mediated DNA damage. The involvement of ubiquitin/26S proteasome and SUMO/UBC9 in these processes, as well as the role of topoisomerase cleavable complexes in apoptotic cell death are discussed.

Tumor Cell Death Induced by Topoisomerase-Targeting Drugs

cDNA clones of the human TOP1 gene encoding DNA topoisomerase I (EC 5.99.1.2) have been obtained by immunochemical screening of phage lambda libraries expressing human cDNA segments, using rabbit antibodies raised against purified HeLa DNA topoisomerase I. Hybridization patterns between the cloned cDNA sequences and human cellular DNA and cytoplasmic mRNAs indicate that human TOP1 is a single-copy gene. The chromosomal location of the gene has been mapped to the long arm of chromosome 20, in the region q12-13.2, by hybridization of a radioactively labeled TOP1 cDNA probe to human metaphase chromosomes and to a panel of rodent-human somatic hybrids retaining overlapping subsets of human chromosomes.

http://www.pnas.org/content/85/23/8910.full.pdf

Leroy F. Liu

Papers

Human DNA topoisomerase I is encoded by a single-copy gene that maps to chromosome region 20q12-13.2.