Transient induction of photolyase activity in arrested frog cells in response to a short-wave ultraviolet segment of simulated "sunlight"

Damage-recognition proteins as a potential indicator of DNA-damage-mediated sensitivity or resistance of human cells to ultraviolet radiation

We have previously identified damage-recognition proteins that bind to cisplatin[cis-diamminedichloroplatinum(II), a DNA cross-linking agent]- or u.v.-modified DNA in HeLa cells [Chao, Huang, Huang & Lin-Chao (1991) Mol. Cell. Biol. 11, 2075-2080; Chao, Huang, Lee & Lin-Chao (1991) Biochem. J. 277, 875-878]. In the present study we compared damage-recognition proteins in cells expressing different sensitivities to DNA damage. An increase in damage-recognition proteins and an enhancement of plasmid re-activation were detected in HeLa cells resistant to cisplatin and u.v. However, repair-defective cells derived from xeroderma-pigmentosum (a rare skin disease) patients did not express less cisplatin damage-recognition proteins than repair-competent cells, suggesting that damage-recognition-protein expression may not be related to DNA repair. By contrast, cells resistant to DNA damage consistently expressed high levels of u.v.-modified-DNA damage-recognition proteins. The results support the notion that u.v. damage-recognition proteins are different from those that bind to cisplatin. These findings also suggest that the damage-recognition proteins identified could be used as potential indicators of the sensitivity or resistance of cells to u.v.

Loss of inducible photorepair in a frog cell line hypersensitive to solar UV light

The induction of enzymatic photorepair (EPR) in ICR 2A frog cells and a derived mutant cell line DRP36 hypersensitive to solar UV was studied. Using clonogenic assays, when induced wild-type cells demonstrated an 8-fold increase of EPR the mutant cells displayed a near-background level of inducible EPR. The constitutive EPR in mutant cells, however, was the same as in wild-type cells. A mixed culture of ICR 2A and DRP36 cells showed an intermediate inducible EPR depending upon the cell ratio. Inducible EPR was also detected at the DNA level in wild-type cells, but not in mutant cells.