A human cellular sequence implicated in trk oncogene activation is DNA damage inducible.

Xeroderma pigmentosum cells, which are deficient in the repair of UV light-induced DNA damage, have been used to clone DNA-damage-inducible transcripts in human cells. The cDNA clone designated pC-5 hybridizes on RNA gel blots to a 1-kilobase transcript, which is moderately abundant in nontreated cells and whose synthesis is enhanced in human cells following UV irradiation or treatment with several other DNA-damaging agents. UV-enhanced transcription of C-5 RNA is transient and occurs at lower fluences and to a greater extent in DNA-repair-deficient than in DNA-repair-proficient cells. Southern blot analysis indicates that the C-5 gene belongs to a multigene family. A cDNA clone containing the complete coding sequence of C-5 was isolated. Sequence analysis revealed that it is homologous to a human cellular sequence encoding the amino-terminal activating sequence of the trk-2h chimeric oncogene [Kozma, S. C., Redmond, S. M. S., Xiao-Chang, F., Saurer, S. M., Groner, B. & Hynes, N. E. (1988) EMBO J. 7, 147-154]. The presence of DNA-damage-responsive sequences at the 5' end of a chimeric oncogene could result in enhanced expression of the oncogene in response to carcinogens.

Determination of poly(ADP-ribose) chain length distribution on polyacrylamide gels by silver staining.

Silver staining and polyacrylamide gel electrophoresis were used to visualize chain length distribution of poly(ADP-ribose) enzymatically synthesized from NAD by rat liver nuclei. The method described has the advantage that synthesis does not require radioactive-labeled NAD, and microgram quantities (greater than 5 micrograms) of poly(ADP-ribose) can be resolved and visualized as discrete bands according to chain lengths which range from 8 to 60 residues. This method can be applied to estimate size distribution of poly(ADP-ribose) chains in cells or tissues.

DNA repair and induction of plasminogen activator in human fetal cells treated with ultraviolet light.

We have tested human fetal fibroblasts for development associated changes in DNA repair by utilizing nucleoid sedimentation as an assay for excision repair. Among skin fibroblasts the rate of excision repair was significantly higher in non-fetal cells than in fibroblasts derived from an 8 week fetus; this was evident by a delay in both the relaxation and the restoration of DNA supercoiling in nucleoids after irradiation. Skin fibroblasts derived at 12 week gestation were more repair proficient than those derived at 8 week gestation. However, they exhibited a somewhat lower rate of repair than non-fetal cells. The same fetal and non-fetal cells were also tested for induction of the protease plasminogen activator (PA) after u.v. irradiation. Enhancement of PA was higher in skin fibroblasts derived at 8 week than in those derived at 12 week gestation and was absent in non-fetal skin fibroblasts. These results are consistent with our previous findings that in human cells u.v. light-induced PA synthesis is correlated with reduced DNA repair capacity. Excision repair and PA inducibility were found to depend on tissue of origin in addition to gestational stage, as shown for skin and lung fibroblasts from the same 12 week fetus. Lung compared to skin fibroblasts exhibited lower repair rates and produced higher levels of PA after irradiation. The sedimentation velocity of nucleoids, prepared from unirradiated fibroblasts, in neutral sucrose gradients with or without ethidium bromide, indicated the presence of DNA strand breaks in fetal cells. It is proposed that reduced DNA repair in fetal cells may result from alterations in DNA supercoiling, and that persistent DNA strand breaks enhance transcription of PA gene(s).

Induction of plasminogen activator by UV light in normal and xeroderma pigmentosum fibroblasts.

Normal and DNA repair-deficient human fibroblasts have been used to study induction of plasminogen activator (PA) by DNA damage. UV light induced the synthesis of PA in skin fibroblasts of all types of xeroderma pigmentosum (XP) in XP heterozygotes and in human amniotic cells. Enzyme induction was, however, not observed in fibroblasts of normal adults. In classical XP, which are deficient in excision repair, PA synthesis occurred in a narrow range of low-UV fluences. In such strains, the level of enzyme produced was correlated with the extent of repair deficiency. UV fluences required for PA induction in XP variants and XP heterozygotes were at least 10 times those inducing enzyme synthesis in excision-deficient XP. Maximum enzyme induction occurred 48 hr after irradiation, and the highest levels of enzyme produced were 15-20 times those of PA baseline levels. Electrophoretic analysis showed that UV irradiation enhances the synthesis of the Mr 60,000 human urokinase-type PA, which is present in low amounts in untreated cells. Our results suggest that PA induction in human cells is caused by unrepaired DNA damage and represents a eukaryotic SOS-like function. In addition, PA induction may provide a sensitive assay for detection of cellular DNA repair deficiencies and identification of XP heterozygotes.

Two modes of excision repair in toluene-treated Escherichia coli.

In toluene-treated Escherichia coli incision breaks accumulate during post-irradiation incubation in the presence of adenosine 5'-triphosphate (ATP). It is shown that incised deoxyribonucleic acid (DNA) is converted to high-molecular-weight DNA during reincubation in the presence of the four deoxyribonucleoside triphosphates (dNTP's) and nicotinamide adenine dinucleotide (NAD). This restitution process is ATP independent and N-ethylmaleimide insensitive and takes place only in polA+ strains. It is defective in strains carrying a mutation in the 5' leads to 3' exonucleolytic activity associated with DNA polymerase I. Repair of accumulated incision breaks differs from repair in which all the steps of the excision repair process occur simultaneously or in rapid succession. The latter is observed if toluene-treated E. coli are incubated immediately after irradiation in the presence of the four dNTP's, NAD, and ATP. It is shown that under these conditions dimer excision occurs to a larger extent than during repair of accumulated incision breaks and that, except in strains defective in polynucleotide ligase, incision breaks do not accumulate. This consecutive mode of repair is detectable in polA+ strains and at low doses also in polA mutants.

Excision-repair in primary cultures of mouse embryo cells and its decline in progressive passages and established cell lines.

Fibroblasts of mouse embryo cells from early subcultures excise pyrimidine dimers to an extent and at a rate comparable to those observed in human cells. The only apparent difference is that in primary mouse cells dimers are excised in an acid-insoluble form. Dimer excision in mouse embryo fibroblasts declines abruptly after the fourth to the sixth subculture and is not detectable in the permanent cell line 3T3. It is suggested that cessation of excision-repair may be due to genetic repression.

Role of ATP in excision repair of ultraviolet radiation damage in Escherichia coli.

The effect of ATP on the first step of excision repair of ultraviolet damage in DNA has been studied using toluene-treated E. coli. During postirradiation incubation, five to six times more single-strand breaks are formed in DNA in the presence of exogenous ATP than in its absence. The ATP-dependent as well as the ATP-independent endonucleolytic activities appear to be catalyzed by the same enzyme since both activities are almost completely absent in uvrA and uvrB mutants. An ATP-dependent endonucleolytic activity has been detected in nonirradiated toluene-treated E. coli. It is concluded that ATP is required in vivo for either the incision step of repair or an enzymatic reaction preceding it.

Postirradiation cell division in 5-fluorouracil-pre-treated Escherichia coli.

The correlation between 5-fluorouracil-induced resistance to ultraviolet (UV) light and the ability of bacterial cells to repair irradiation damage was investigated in various strains of Escherichia coli. Preincubation with 5-fluorouracil did not influence the dark-repair mechanism. It affected, however, the UV light-induced damage of cell division in filament-forming strains. It is suggested that the delay in postirradiation macromolecular synthesis of 5-fluorouracil-pretreated bacteria plays a decisive role in the recovery process leading to cross cell wall-forming ability in the damaged strains.