Autophagy regulates ageing in C. elegans.

The role of autophagy in ageing regulation has been suggested based on studies in C. elegans, in which knockdown of the expression of bec-1 (ortholog of the yeast and mammalian autophagy genes ATG6/VPS30 and beclin 1, respectively) shortens lifespan of the daf-2(e1370) mutant C. elegans. However, Beclin1/ATG6 is also known to be involved in other cellular functions in addition to autophagy. In the current study, we knocked down two other autophagy genes, atg-7 and atg-12, in C. elegans using RNAi. We showed that RNAi shortened the lifespan of both wild type and daf-2 mutant C. elegans, providing strong support for a role of autophagy in ageing regulation.

Role of apoptotic nuclease caspase-activated DNase in etoposide-induced treatment-related acute myelogenous leukemia.

Etoposide-induced treatment-related acute myelogenous leukemia (t-AML) is characterized by rearrangements of the mixed lineage leukemia (MLL) gene with one of its >50 partner genes, most probably as a consequence of etoposide-induced DNA double-strand breaks (DSBs). Recent studies have shown that etoposide-induced DSBs occur predominantly within the breakpoint cluster region (bcr) of the MLL gene. However, bcr-specific DSBs induced by etoposide are not topoisomerase II-linked but the result of apoptotic nuclease-mediated DNA cleavage. Here, we test the involvement of caspase-activated DNase (CAD) and other apoptotic components in etoposide-induced gene rearrangements using two methods. First, we measured the effect of etoposide on the integration frequency of a transfected plasmid. Etoposide strongly stimulated plasmid integration in CAD cDNA-complemented mouse embryonic fibroblasts (MEFs) but not in CAD knockout (KO) MEFs. Consistently, down-regulation of ICAD (inhibitor of CAD, also required for proper folding of CAD) in an HT29-derived cell line, which leads to decreased CAD activity, significantly reduced etoposide-induced plasmid integration. Second, we used long-template inverse PCR to focus on gene rearrangements at the MLL locus. Etoposide stimulated MLL fusion product formation in CAD cDNA-complemented MEFs but not in CAD KO MEFs. Together, these results suggest that CAD and other apoptotic components may play an important role in etoposide-induced t-AML.

Characterization of ARC-111 as a novel topoisomerase I-targeting anticancer drug.

8,9-Dimethoxy-5-(2-N,N-dimethylaminoethyl)-2,3-methylenedioxy-5H-dibenzo[c,h][1,6] naphthyridin-6-one (ARC-111, topovale) is a new synthetic antitumor agent. In the current study, we show that ARC-111 is highly potent in scid mice carrying human tumor xenografts. ARC-111 was shown to be as active as camptothecin (CPT)-11 in the HCT-8 colon tumor model, and compared favorably with CPT-11 and topotecan in the SKNEP anaplastic Wilms' tumor model. In tissue culture models, ARC-111 exhibited low nM cytotoxicity against a panel of cancer cells. ARC-111 cytotoxicity as well as ARC-111-induced apoptosis was reduced >100-fold in CPT-resistant topoisomerase I (TOP1)-deficient P388/CPT45 cells as compared with P388 cells. Similarly, ARC-111 cytotoxicity was greatly reduced in CPT-resistant CPT-K5 and U937/CR cells, which express CPT-resistant mutant TOP1, suggesting that the cytotoxic target of ARC-111 is TOP1. Indeed, ARC-111, like CPT, was shown to induce reversible TOP1 cleavage complexes in tumor cells as evidenced by specific reduction of the TOP1 immunoreactive band in a band depletion assay, as well as elevation of small ubiquitin modifier-TOP1 conjugate levels and activation of 26S proteasome-mediated degradation of TOP1. Unlike CPT, ARC-111 is not a substrate for the ATP-binding cassette transporter breast cancer resistance protein. In addition, ARC-111 cytotoxicity was not significantly reduced in the presence of human serum albumin. These results suggest that ARC-111 is a promising new TOP1-targeting antitumor drug with a different drug resistance profile than CPT.

Single-stranded DNA induces ataxia telangiectasia mutant (ATM)/p53-dependent DNA damage and apoptotic signals.

Single-stranded DNA has been speculated to be the initial signal in the DNA damage signaling pathway. We showed that introduction of single-stranded DNA with diverse sequences into mammalian cells induced DNA damage as well as apoptosis signals. Like DNA damaging agents, single-stranded DNA up-regulated p53 and activated the nuclear kinase ataxia telangiectasia mutant (ATM) as evidenced by phosphorylation of histone 2AX, an endogenous ATM substrate. Single-stranded DNA also triggered apoptosis as evidenced by the formation of caspase-dependent chromosomal DNA strand breaks, cytochrome c release, and increase in reactive oxygen species production. Moreover, single-stranded DNA-induced apoptosis was reduced significantly in p53 null cells and in cells treated with ATM small interfering RNA. These results suggest that single-stranded DNA may act upstream of ATM/p53 in DNA damage signaling.