Slow DNA rejoining in ultraviolet-irradiated human diploid fibroblasts treated with the mitogens trypsin and insulin

Journal Article · Sat Aug 15 04:00:00 EDT 1987 · Cancer Res.; (United States)

OSTI ID:6122599

Squires, S; Elliott, G C; Johnson, R T

Normally in mammalian cells the postincision steps of UV-induced excision repair are much more rapid than the recognition of damage and incision. This means that at any one time the level of repair-generated single-stranded DNA breaks is very low. Here we report that detectable levels of DNA breaks accumulate in quiescent human fibroblasts which are UV irradiated a few hours after replating in conditions that stimulate progress through the cell cycle. Most DNA breaks accumulate in cultures trypsinized and seeded in medium supplemented with insulin, and irradiated in early G1. Because trypsin and insulin have no effect on UV-induced incision rates, as measured by DNA break accumulation in the presence of DNA synthesis inhibitors, we argue that our ability to detect incomplete repair-sites is due to a significant reduction in the rate of gap sealing indicative of a shift in the steady state of excision repair. Provision of DNA precursors prevents the enhancing effect of trypsin and insulin on the accumulation of DNA breaks, implying that these agents affect DNA precursor metabolism. Perturbation of the repair process, which leads to the accumulation of 1500-2000 DNA breaks/genome, is also associated with other effects including increased lethality, the appearance of double-strand breaks and the loss of NAD, the last effect presumably arising as a consequence of break-stimulated poly(ADPR) transferase activity. Addition of 3-amino-benzamide, an inhibitor of poly(ADPR) synthesis, completely blocks the decline in NAD levels, but does not change the rate of sealing of the accumulated DNA breaks. These results strongly suggest that ligation is largely, if not entirely, independent of ADP ribosylation in this system.

• Research Organization: Cambridge Univ., England
• OSTI ID: 6122599
• Journal Information: Cancer Res.; (United States), Journal Name: Cancer Res.; (United States) Vol. 47:16; ISSN CNREA
• Country of Publication: United States
• Language: English

Related Subjects

560120* -- Radiation Effects on Biochemicals
Cells
& Tissue Culture
63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
ADP
ANIMAL CELLS
ANIMALS
BIOLOGICAL EFFECTS
BIOLOGICAL RADIATION EFFECTS
BIOLOGICAL RECOVERY
BIOLOGICAL REPAIR
COENZYMES
CONNECTIVE TISSUE CELLS
DNA
DNA REPAIR
ELECTROMAGNETIC RADIATION
ENZYMES
FIBROBLASTS
GENETIC EFFECTS
GENETIC RADIATION EFFECTS
HORMONES
HYDROLASES
INSULIN
MAMMALS
MAN
MITOGENS
NAD
NUCLEIC ACIDS
NUCLEOTIDES
ORGANIC COMPOUNDS
PEPTIDE HORMONES
PEPTIDE HYDROLASES
PRIMATES
RADIATION EFFECTS
RADIATIONS
RADIOINDUCTION
RADIOSENSITIVITY EFFECTS
RECOVERY
REPAIR
SERINE PROTEINASES
SOMATIC CELLS
STRAND BREAKS
TRANSFERASES
TRYPSIN
ULTRAVIOLET RADIATION
VERTEBRATES