Monomeric Base Damage Products from Guanine, Adenine, and Thymine Induced by Exposure of DNA to Ultraviolet Radiation

Abstract

The formation of monomeric products in DNA upon exposure to UV radiation was investigated. Three novel products were identified in DNA in aqueous solution upon exposure to UV radiation at 254 nm in a dose range from 100 to 10,000 J/m2. These were 4,6-diamino-5-formamidopyrimidine, 2,6-diamino-4-hydroxy-5-formamidopyrimidine, and 5-hydroxy-5,6-dihydrothymine. These three products are known to be substrates for base excision repair enzymes involved in the reversal of oxidative DNA damage. The dependence of the yields of formamidopyrimidines on UV radiation dose was nonlinear, whereas the yield of 5-hydroxy-5,6-dihydrothymine was increased linearly in the entire dose range. Of these products, 4,6-diamino-5-formamidopyrimidine was the only compound produced in appreciable amounts at 310 nm. At the highest dose used, the formation of other pyrimidine- and purine-derived products was also observed. Their amounts, however, were increased above control levels up to 2-fold only. The hydroxyl radical scavenger dimethyl sulfoxide had no effect on product yields excluding the involvement of hydroxyl radical in product formation. 4,6-Diamino-5-formamidopyrimidine and 2,6-diamino-4-hydroxy-5-formamidopyrimidine may be produced by hydration of adenine and guanine, respectively, across the N(7)-C(8) double bond by mechanisms similar to those proposed previously for well-known formation of pyrimidine hydrates with the hydroxyl group located at C(6). Formation of 5-hydroxy-5,6-dihydrothymine indicates that hydration of thymine with the hydroxyl group located at C(5) of the pyrimidine ring also occurs.(ABSTRACT TRUNCATED AT 250 WORDS)

Preferential Binding of High Mobility Group 1 Protein to UV-damaged DNA

“…Moreover, a recent study demonstrated that the exposure of DNA in aqueous solution to UV radiation at relatively low doses caused formation of several monomeric base damage products (40). As seen in Figs.…”

“…These data have been taken into account upon calculation of dissociation constants (see above). At higher doses there is a continued accumulation of a broad range of lesions including photoproducts, thymine glycols, interstrand cross-links, and monomeric photoproducts (36,40,41). Formation of (6-4) photoproducts upon irradiation of TT oligonucleotide was not detected (see Fig.…”

Protection of normal human reconstructed epidermis from UV by catalase overexpression

“…[37][38][39][40][41][42] Western blot analysis of serine-15 phosphorylated p53 showed that overexpression of CAT downregulated this protein in normal RE. The interaction between UV irradiation and DNA produces a number of oxidative 43,44 and non-oxidative lesions. 1,45,46 Among various types of DNA damage, cyclobutane pyrimidine dimers (CPD) or 6-4 photoproducts are believed to be the major type of damage resulting from UVB exposure.…”

Catalase overexpression reduces UVB-induced apoptosis in a human xeroderma pigmentosum reconstructed epidermis

“…18,19 Briefly, epidermis was separated from dermis, homogenized with a Potter homogenizer in lysis buffer (25 mM HEPES pH 7.4, 150 mM NaCl, Triton X-100 1% v/v) and then incubated at 4 1C for 30 min. After 10 min of centrifugation at 12 000 g, aliquots of the supernatant were stored at À80 1C.…”

“…8,[13][14][15] UVB irradiation produces two types of DNA damage: direct lesions, which are due to the absorption of photons by nucleobases; and indirect damage, which is dependent on the production of reactive oxygen species (ROS: H 2 O 2 , OH, 1 O 2 y.). [16][17][18][19][20] Several studies have shown that keratinocyte exposure to UVB irradiation generates ROS in excessive quantities that quickly overwhelm various antioxidant defense systems including non-enzymatic (a-tocopherol and vitamin C) and enzymatic antioxidants (catalase and superoxide dismutase). [21][22][23][24] UVB-induced ROS production leads to cytotoxicity through proteins, lipids and DNA oxidation both in vitro and in vivo.…”