DNA double-strand breaks

Etoposide causes multiple DNA double-strand breaks by inhibiting topoisomerase II. The pharmacokinetics of etoposide are described by a two-compartment model, with an a half-life of 0.5 to 1 hour and a (5 half-life of 3.4 to 8.3 hours. Approximately 30% of the dose is excreted unchanged by the kidney.16 Etoposide has shown activity in the treatment of several types of lymphoma, testicular and lung cancer, retinoblastoma, and carcinoma of unknown primary. The intravenous preparation has limited stability, so final concentrations should be 0.4 mg/mL. Intravenous administration needs to be slow to prevent hypotension. Oral bioavailability is approximately 50%, so oral dosages are approximate two times those of intravenous doses however, relatively low oral daily dosages are used for 1 to 2 weeks. Side effects include mucositis, myelosuppression, alopecia, phlebitis, hypersensitivity reactions, and secondary leukemias. 

Frankenberg-Schwager, M., D. Frankenberg, D. Blocher, and C. Adamczyk, The Linear Ralationship Between DNA Double-Strand Breaks and Radiation Dose (30 MeV Electrons) is Converted Into a Quadratic Function by Cellular Repair, Internat. J. Radiation Biology 37 207-212 (1980). 

Hopfner, K. P., Karcher, A., Shin, D. S., Craig, L., Arthur, L. M., Carney, J. P. and Tainer, J. A. (2000). Structural biology of Rad50 ATPase ATP-driven conformational control in DNA double-strand break repair and the ABC-ATPase superfamily, Cell, 101, 789-800. 

Furuta T, Takemura H, Liao ZY, Aune GJ, Redon C, Sedelnikova OA, et al. Phosphorylation of histone H2AX and activation of Mrell, Rad50, and Nbsl in response to replication-dependent DNA double-strand breaks induced by mammalian DNA topoisomerase I cleavage complexes. J. Biol. Chem. 2003 May 30 278(22) 20303-12. 

Hendrickson, E.A., 1997, CeU-cycle regulation ofmammalian DNA double-strand-break repair, Am.J.Hum.Genet. 61 795-800. 

Qin S, Parthun MR (2006) Recruitment of the type B histone acetyltransferase Hatlp to chromatin is linked to DNA double-strand breaks. Mol.Cell.Biol 26 3649-3658... 

Ross WE, Glaubiger DL, Kohn KW (1978) Protein-associated DNA breaks in cells treated with adriamycin or elhpticine. Biochim Biophys Acta 519(l) 23-30 Rothfuss A, Grompe M (2004) Repair kinetics of genomic interstrand DNA cross-hnks evidence for DNA double-strand break-dependent activation of the Fanconi anemia/BRCA pathway. Mol Cell Biol 24(1) 123-134... 

Chowdhury D, Keogh MC, Ishii H, Peterson CL, Buratowski S, Lieberman J (2005) gamma-H2AX dephosphorylation by protein phosphatase 2A facilitates DNA double-strand break repair. Mol Cell 20 801-809. 

Murr R, Loizou JI, Yang YG, Cuenin C, Li H, Wang ZQ, Herceg Z (2006) Histone acetylation by Trrap-Tip60 modulates loading of repair proteins and repair of DNA double-strand breaks. Nat Cell Biol 8 91-99... 

In Saccharomyces cerevisiae, multiple histone H2A phosphorylation sites have been characterized (Serine 122, Serine 129, Threonine 126) (Wyatt et al, 2003 Harvey et al, 2005 Redon et al, 2006). Histone H2A (S129) is essential for DNA double-strand-break responses (see Section 4) and histone H2A (SI22) is important for survival in the presence of DNA damage (Harvey et al, 2005) (Fig. 2). 

Histone H2B amino-terminal tail is essential for chromatin condensation (de la Barre et al, 2001). In Xenopus, chicken, and human cells phosphorylation of H2B at Serine 14 by Mstl (Mammalian Sterile Twenty) kinase has been finked to chromatin compaction during apoptosis (Ajiro, 2000 Cheung et al, 2003), and DNA double-strand breaks (Fernandez-Capetillo et al, 2004) (Fig. 2) (Table 1). At late time points after irradiation, phosphorylated H2B (S14) accumulates into... 

Recent studies demonstrate that histone H2B phosphorylation also plays a key role in the response to DNA double-strand breaks, apoptosis, meiosis and transcription activation events. However, the details of this mechanism are poorly understood. 

Recent studies have demonstrated that histone H4 (SI) phosphorylation is also a key role in the response to DNA double-strand breaks, cell-cycle progression and gene expression. In particular, this modification may have important roles during mitosis and S-phase-associated events in the cell-cycle and its phosphorylation found on newly synthesized histones during S-phase. However this phosphorylated residue is a novel histone modification site, and the details of this mechanism will be made evident by future experimentation. 

Eernandez-Capetillo O, Allis CD, Nussenzweig A (2004) Phosphorylation of histone H2B at DNA double-strand breaks. J Exp Med 199(12) 1671—1677 Eernandez-Capetillo O, Chen HT, Celeste A, Ward I, Romanienko PJ, Morales JC, Naka K, Xia Z, Camerini-Otero RD, Motoyama N, Carpenter PB, Bonner WM, Chen J, Nussenzweig A (2002) DNA damage-induced G2-M checkpoint activation by histone H2AX and 53BP1. Nat Cell Biol 4(12) 993-997... 

Huyen Y, Zgheib O, Ditullio RA Jr, Gorgoulis VG, Zacharatos P, Petty TJ, Sheston EA, Mellert HS, Stavridi ES, Halazonetis TD (2004) Methylated lysine 79 of histone H3 targets 53BP1 to DNA double-strand breaks. Nature 432 406-411... 

Burma S, Chen BP, Murphy M, Kurimasa A, Chen DJ (2001) ATM phosphorylates histone H2AX in response to DNA double-strand breaks. J Biol Chem 276 42462-42467... 

---