Ahn, Byungchan et al. (2011) International Worm Meeting "The Caenorhabditis elegans WRN-1 RecQ helicase participates in both DNA damage signaling and DNA Repair."

Park, H, Park, S, Ahn, Byungchan, Kim, E, Hyun, M

[International Worm Meeting, 2011]

RecQ helicases play essential roles in maintenance of genomic stability from E. coli to humans. The RecQ helicases interact with proteins involved in DNA metabolic pathways such DNA repair, recombination, and replication. We found that C. elegans wrn-1 mutant is more sensitive to CPT than N2 and that the wrn-1 mutant failed to arrest the S-phase since DNA synthesis was continued following CPT treatment. In addition, more DNA strand breaks accumulate in the wrn-1 mutant. These data suggest that WRN-1 is involved in DSB processing and/or DNA damage signaling. WRN-1 colocalized with CeRPA in nucleus in germ line cells following CPT, but CeRPA foci formation was independent of WRN-1. In addition, WRN-1 foci formation was not affected in atm-1 and atl-1 mutants and WRN-1 was required for phoshorylation of CHK-1 induced by DSBs. WRN-1 also colocalized with RAD51. These results suggest that WRN-1 functions downstream of RPA and upstream of ATM-1/ATL-1 and CHK-1 in the DSB checkpoint pathway and is in involved in a DNA repair pathway with RAD51.

Byungchan Ahn et al. (2008) "Longevity and Resistance to Stress Correlate with DNA Repair Capacity in Caenorhabditis elegans"

Byungchan Ahn, Moonjung Hyun, Hana Jung, Vilhelm A. Bohr

[2008]

"DNA repair is an important mechanism by which cells maintain genomic integrity. Decline in DNA repair capacity or defects in repair factors are thought to contribute to premature aging in mammals. The nematode Caenorhabditis elegans is a good model for studying longevity and DNA repair because of key advances in understanding the genetics of aging in this organism. Long-lived C. elegans mutants have been identified and shown to be resistant to oxidizing agents and UV irradiation, suggesting a genetically-determined correlation between DNA repair capacity and life span. In this report, gene-specific DNA repair is compared in wild-type C. elegans and stress-resistant C. elegans mutants for the first time. DNA repair capacity is higher in long-lived C. elegans mutants than in wild type animals. In addition, RNAi knockdown of the nucleotide excision repair gene xpa-1 increased sensitivity to UV and reduced the life span of long-lived C. elegans mutants. These findings support that DNA repair capacity correlates with longevity in C. elegans. "

Pham, B.T.T. et al. (2017) International Worm Meeting "The genetic interaction of wrn-1 with mre-11 or him-6 in embryonic development."

Ahn, Byungchan, Pham, B.T.T.

[International Worm Meeting, 2017]

Werner's syndrome (WS) is an autosomal recessive disorder in humans characterized by the premature development of age-associated pathologies. WRN, the gene defective in WS, plays a key role in protecting the genome. The cell derived from WS patients show genomic instabilities such as sister chromatid exchange and telomere shortening. Caenorhabditis elegans (C. elegans) with a WRN-1 ortholog also exhibits a shorter life span. Our results showed wrn-1 interacts with mre-11 or him-6 and affects during embryonic and larval development. When inhibiting the expression of mre-11 or him-6 in wrn-1 (gk99) by RNA interference (RNAi) resulted in a significant increase of embryonic lethality and the retarded larval development compared with control worms of N2 (RNAi) worms. In addition, wrn-1 (gk99):him-6 (RNAi) or wrn-1 (gk99):mre-11 (RNAi) worms displayed abnormal premeiotic nuclei and multiple chromosomal abnormalities in oocyte nuclei at the diakinesis stage. Furthermore, observation of embryo cell division showed the slower development. These results suggest that MRE-11 and HIM-6 may interact with WRN-1, which is involved in embryonic development.

Hyun, Moonjung et al. (2009) International Worm Meeting "CeWRN-1 RecQ protein is responsible for processing DSB with CeRPA."

Ahn, Byungchan, Hyun, Moonjung, Jung, Hana, Lee, Jina

[International Worm Meeting, 2009]

RecQ helicases play essential roles in maintenance of genomic stability from E. coli to humans. The RecQ proteins interact with proteins involved in DNA metabolic pathways such DNA repair, recombination, and replication. Our previous studies showed that C. elegans WRN-1 RecQ protein (human WRN ortholog) has ATP-dependent 3''-5'' helicase activity and that C. elegans replication protein A stimulates WRN-1 helicase activity on a long DNA duplex substrate. However, the mechanism for CeRPA stimulation of DNA unwinding is not characterized yet. We found that CeWRN-1 physically interacted with both subunits of CeRPA. However, a CeRPA73 subunit only stimulated CeWRN-1 helicase activity on a long DNA duplex, indicating a functional interaction of CeWRN-1 with the CeRPA73 subunit. When treated with CPT, replication-associated DSBs inducer, C. elegans wrn-1(gk99) is more sensitive than N2 and it was detected by COMET assay that DNA strand breaks more accumulated in wrn-1(gk99), suggesting that WRN-1 is required for responding to DSBs. Furthermore, we observed nuclear colocalization of CeWRN-1 and CeRPA in germ line cells after CPT. These findings propose that the WRN-1 is involved in processing DSB during replication with CeRPA protein.

Jung, Hana et al. (2009) International Worm Meeting "Caenorhabditis elegans him-6 protein exhibits RecQ helicase activity."

Jung, Hana, Lee, Jina, Hyun, Moonjung, Ahn, Byungchan

[International Worm Meeting, 2009]

Mutations in human RecQ helicases result in rare diseases of aging and cancer characterized by genome instability. Bloom syndrome is known as segmental progerias. A BLM helicase ortholog, him-6, has been identified in Caenorhabditis elegans. Defects in the him-6 mutant show a shortened lifespan and phenotypic signs of genomic instability. However, little is known about their enzymatic activities. Recombinant CeBLM proteins were purified from E. coli. We found that Ce BLM is a 3''-5'' helicase and characterized its substrate specificities in vitro in order to better understand their function in vivo. The abilities of CeBLM to unwind these DNA structures may increase access for DNA repair and replication proteins that are important for preventing the accumulation of abnormal structures, contributing to genome stability.

Park, sojin et al. (2011) International Worm Meeting "Detection of DNA Strand Breaks detection in Caenorhabditis elegans using Comet assay."

Hyun, Moonjung, Park, sojin, Kim, eunsun, Park, hyejin, Ahn, Byungchan

[International Worm Meeting, 2011]

DNA damage responses (DDR) are important for organisms to maintain genome stability and to survive. DDR is activated in the presence of DNA damage and leads to cell cycle arrest, apoptosis and DNA repair. In C. elegans, double strand breaks (DSBs) induced by DNA damaging agents have been detected indirectly by antibody against DSB recognizing protein, RAD-51. To detect DNA strand breaks induced by IR and CPT, UV at single cells in C. elegans, we developed COMET assay. We treated C. elegans DDR gene mutants (atm-1, brc-1, hus-1) with IR, CPT, and UV. C. elegans atm-1, brc-1 and hus-1 mutants were more sensitive to CPT than N2. DNA strand breaks in a single cell of these mutants atm-1, brc-1,and hus-1 could be detected using COMET assay and more DNA strand breaks accumulate than N2, which corresponds to more RAD-51 foci formation in a single cell in each mutant. This study is the first report in a direct measuring DNA strand breaks in a single cell of C. elegans and this developed assay can be applied to detect DNA strand breaks in different C. elegans mutants which are sensitive to DNA damaging agents.

Kim, eunsun et al. (2011) International Worm Meeting "Caenorhabditis elegans HIM-6 has a 3'-5' helicase activity and is responsible for DNA damage processing."

Ahn, Byungchan, Kim, eunsun, Park, sojin, Park, hyejin, Hyun, Moonjung

[International Worm Meeting, 2011]

Mutations in human RecQ genes display various features of premature aging, cancer predisposition, and developmental abnormalities. Bloom syndrome is characterized by severe growth retardation and dramatic cancer predisposition and caused by mutations in BLM gene. A BLM helicase ortholog, him-6, has been identified in Caenorhabditis elegans. However, little is known about the enzymatic activities and roles of the HIM-6 protein. We show that him-6 is sensitive to CPT and the accumulation of DNA strand breaks in the mutant was detected using RAD-51 foci and Comet assay. We purified the recombinant HIM-6 protein from E. coil. The HIM-6 protein has a 3' -> 5' helicase activity and needs at least 5-nt overhang for its helicase activity. HIM-6 is able to unwind various DNA structures related to intermediates generated during replication and repair. However, HIM-6 shows a limited processivity on forked duplexes, suggesting that the processivity may be regulated by other proteins in vivo. These characterized properties suggest that HIM-6 may play roles in DNA metabolic pathways and its defect may give rise to genomic instability.