Photoactivated multivitamin preparation induces poly(ADP-ribosyl)ation, a DNA damage response in mammalian cells

Multivitamin preparation (MVP) is part of total parenteral nutrition given to premature infants. Photoactivated MVP carries an important load in peroxides, but their cellular effects have not yet been determined. We hypothesized that these peroxides may elicit a DNA-damage response. We found that photoactivation of MVP and the resulting peroxide production were time-dependent and required the simultaneous presence of ascorbic acid and riboflavin. Cells treated with photoactivated MVP showed strongly stimulated poly(ADP-ribosyl)ation, an early DNA-damage response in mammals. Poly(ADP-ribosyl)ation stimulation was dependent on the presence of ascorbic acid and riboflavin in the photoactivated MVP. It did not occur in the presence of a specific PARP inhibitor nor in mouse fibroblasts deficient in PARP-1. Photoactivated MVP was able to induce single- and double-strand breaks in DNA, with a predominance of single-stand breaks. The presence of double-strand breaks was further confirmed using a 53PB1 focus analysis. Finally, photoactivated MVP was shown to be toxic to human cells and induced caspase-independent cell death. These results suggest that photoactivated MVP carries an important toxic load able to damage DNA and induce cell death. This study also emphasizes the importance of protecting MVP solution from light before use in preterm infants.

Caenorhabditis elegans LET-767 is able to metabolize androgens and estrogens and likely shares common ancestor with human types 3 and 12 17beta-hydroxysteroid dehydrogenases

Mutations that inactivate LET-767 are shown to affect growth, reproduction, and development in Caenorhabditis elegans. Sequence analysis indicates that LET-767 shares the highest homology with human types 3 and 12 17beta-hydroxysteroid dehydrogenases (17beta-HSD3 and 12). Using LET-767 transiently transfected into human embryonic kidney-293 cells, we have found that the enzyme catalyzes the transformation of both 4-androstenedione into testosterone and estrone into estradiol, similar to that of mouse 17beta-HSD12 but different from human and primate enzymes that catalyze the transformation of estrone into estradiol. Previously, we have shown that amino acid F234 in human 17beta-HSD12 is responsible for the selectivity of the enzyme toward estrogens. To assess whether this amino acid position 234 in LET-767 could play a role in androgen-estrogen selectivity, we have changed the methionine M234 in LET-767 into F. The results show that the M234F change causes the loss of the ability to transform androstenedione into testosterone, while conserving the ability to transform estrone into estradiol, thus confirming the role of amino acid position 234 in substrate selectivity. To further analyze the structure-function relationship of this enzyme, we have changed the three amino acids corresponding to lethal mutations in let-767 gene. The data show that these mutations strongly affect the ability of LET-767 to convert estrone in to estradiol and abolish its ability to transform androstenedione into testosterone. The high conservation of the active site and amino acids responsible for enzymatic activity and substrate selectivity strongly suggests that LET-767 shares a common ancestor with human 17beta-HSD3 and 12.

Altered DNA damage response in Caenorhabditis elegans with impaired poly(ADP-ribose) glycohydrolases genes expression

Poly(ADP-ribosyl)ation is one of the first cellular responses induced by DNA damage. Poly(ADP-ribose) is rapidly synthesized by nick-sensor poly(ADP-ribose) polymerases, which facilitate DNA repair enzymes to process DNA damage. ADP-ribose polymers are rapidly catabolized into free ADP-ribose units by poly(ADP-ribose) glycohydrolase (PARG). The metabolism of poly(ADP-ribose) is a well-defined biochemical process for which a physiological role in animals is just beginning to emerge. Two Caenorhabditis elegans PARGs, PME-3 and PME-4, have been cloned by our group. The pme-3 gene encodes an enzyme of 89kDa having less than 18% overall identity with human PARG but 42% identity with the PARG signature motif. The pme-4 gene codes for a PARG of 55kDa with approximately 22% overall identity with human PARG and 40% identity with the PARG signature motif. Two alternatively spliced forms of PME-3 were identified with an SL1 splice leader on both forms of the mRNA and were found to be expressed throughout the worm's life cycle. Similarly, pme-4 was shown to be expressed in all developmental stages of the worm. Recombinant enzymes that were expressed in bacteria displayed a PARG activity that may partly account for the PARG activity measured in the total worm extract. Reporter gene analysis of pme-3 and pme-4 using a GFP fusion construct showed that pme-3 and pme-4 are mainly expressed in nerve cells. PME-3 was shown to be nuclear while PME-4 localized to the cytoplasm. Worms with pme-3 and pme-4 expression knocked-down by RNAi showed a significant sensitivity toward ionizing radiations. Taken together, these data provide evidence for a physiological role for PARGs in DNA damage response and survival. It also shows that PARGs are evolutionarily conserved enzymes and that they are part of an ancient cellular response to DNA damage.

The Caenorhabditis elegans FancD2 ortholog is required for survival following DNA damage

Fanconi anemia (FA) is an autosomal recessive disease characterized by bone-marrow failure, congenital abnormalities, and cancer susceptibility. There are 11 FA complementation groups in human where 8 genes have been identified. We found that FancD2 is conserved in evolution and present in the genome of the nematode Caenorhabditis elegans. The gene Y41E3.9 (CeFancD2) encodes a structural ortholog of human FANCD2 and is composed of 10 predicted exons. Our analysis showed that exons 6 and 7 were absent from a CeFancD2 EST suggesting the presence of a splice variant. In an attempt to characterize its role in DNA damage, we depleted worms of CeFANCD2 using RNAi. When the CeFANCD2(RNAi) worms were treated with a crosslinking agent, a significant drop in the progeny survival was noted. These worms were also sensitive, although to a lesser extent, to ionizing radiation (IR). Therefore, these data support an important role for CeFANCD2 in DNA damage response as for its human counterpart. The data also support the usefulness of C. elegans to study the Fanconi anemia pathway, and emphasize the biological importance of FANCD2 in DNA damage response throughout evolution.