Direct inhibition of u.v.-induced DNA excision repair in human cells by novobiocin, coumermycin and nalidixic acid

• Published in: Carcinogenesis (New York) 1987-06, Vol.8 (6), p.813-817
• Main Authors: Dresler, Steven L., Robinson-Hill, Rona M.
• Format: Article
• Language: English
• Subjects: Aminocoumarins; Anti-Bacterial Agents - pharmacology; Biological and medical sciences; Cell Line; Coumarins - pharmacology; DNA Polymerase II - isolation & purification; DNA Polymerase II - metabolism; DNA Repair - drug effects; DNA Replication - radiation effects; Fibroblasts - drug effects; Fibroblasts - radiation effects; Fibroblasts - ultrastructure; Fundamental and applied biological sciences. Psychology; Humans; Kinetics; Molecular and cellular biology; Molecular genetics; Mutagenesis. Repair; Nalidixic Acid - pharmacology; Novobiocin - pharmacology; Ultraviolet Rays
• ISSN: 0143-3334; 1460-2180
• DOI: 10.1093/carcin/8.6.813

In permeable human fibroblasts, novobiocin, coumermycin and nalidixic acid completely inhibit u.v.-induced DNA repair synthesis, with 50% inhibition occurring at 500, 24 and 8800 μM respectively. Novobiocin also inhibits damagespecific incision of DNA in u.v.-irradiated permeable human fibroblasts by at least 75%. It has been suggested that effects of novobiocin on DNA excision repair result from changes in ATP pools; this explanation is not applicable to our data because excision repair in the permeable cell system is entirely dependent on exogenous ATP. It has also been suggested that novobiocin-induced inhibition of repair is mediated by alterations of chromatin structure recognizable by electron microscopy as gross chromatin clumping. There were no ultrastructural alterations, however, in the nuclei of permeable cells that had been incubated with 1 mM novobiocin. We conclude that, in human cells, novobiocin, coumermycin, and nalidixk acid directly inhibit the excision repair of u.v. damage to DNA, and that one locus of inhibition lies at or before the incision step. Because 1 mM novobiocin completely abolishes u.v.-induced repair synthesis in permeable cells, but inhibits damage-specific incision by only 75%, there seems to be a second site of inhibition following the incision step. The similarity between the concentrations of novobiocin, nalidixic acid and coumermycin required to inhibit u.v.-induced excision repair and the concentrations required to inhibit human DNA polymerase α suggest that the distal locus of inhibition may be DNA polymerase α-mediated repair patch synthesis. The proximal inhibitory site may be a type II DNA topoisomerase.