Task Progress:
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Significance of funded research. While traversing through matter, such as spacecraft shielding, an HZE particle may undergo either of two changes: 1) the particle may lose energy as it traverses the shield thereby becoming more ionizing (increased LET) or 2) the particle may fragment into a large number of secondary particles which are generally less ionizing (decreased LET) but result in a more complex radiation field. The net effect of shielding (whether beneficial or detrimental) is thus a trade off between velocity loss and fragmentation and this is largely determined by the composition of the shield. While the physical aspects of interaction of HZE particles with shielding matter are well understood, what is not known at all is the extent and complexity of DNA damage induced by these particles after shield traversal. This is important not only for understanding the risks to humans on space flights but also for determining optimal shielding for spacecrafts. With this backdrop, the specific aims of this project are:
Aim 1. To test the hypothesis that shielded heavy ions may result in more complex DNA damage to the cells as compared to unshielded heavy ions,
Aim 2. To test the hypothesis that the molecular response to shielded radiation is different from that induced by unshielded radiation, and
Aim 3. To test the hypothesis that shielded radiation may have more deleterious effects on the cell as compared to unshielded radiation and to elucidate the mechanisms involved in repair of DNA damage.
Brief summary of progress: In experiments carried out during the first two years of the project we were able to establish the methods that would be required for successful completion of the project. We were also able to obtain preliminary results that allowed us to estimate the feasibility of the proposed objectives. In the third and fourth years, significant progress was made in most of the proposed aims of the project, resulting in a manuscript that was accepted for publication in DNA Repair. In the fifth and final year we expanded upon the results obtained in the first four years to ask questions pertaining to the long-term consequences of particle radiation, i.e., cellular transformation and carcinogenesis. This has resulted in an additional publication in Carcinogenesis. In sum, we have successfully carried out most of experiments proposed in this project and have also carried out additional experiments to further extend our understanding of the long-term consequences of irradiation by heavy ions and its modulation by shielding. These results have been published in relevant journals.
Detailed summary of progress. We have used pertinent responses to DNA double-strand breaks (DSBs) to understand the consequences of energy loss versus nuclear fragmentation of Fe ions during passage through shielding or tissue-equivalent materials. Phosphorylation of histone H2AX and recruitment of 53BP1 were used to generate 3D reconstructions of DNA damage in human cells and to follow its repair. Human cells are unable to repair a significant portion of DNA damage induced by Fe ions. DNA-PK and ATM are required, to different extents, for the partial repair of Fe-induced DNA damage. Aluminum shielding has little effect on DNA damage or its repair, confirming that the hulls of the Space Shuttle and the International Space Station afford scant protection against these particles. Lead shielding, on the other hand, exacerbates the effects of Fe ions due to energy loss during particle traversal. In sharp contrast, polyethylene (PE), a favored hydrogenous shield, results in DNA damage that is more amenable to repair presumably due to Fe ion fragmentation. Human cells are indeed able to efficiently repair DSBs induced by chlorine ions and protons that represent fragmentation products of Fe. Interestingly, activation of the tumor suppressor p53 in Fe-irradiated cells is uniquely biphasic and culminates in the induction of high levels of p21(Waf1/Cip1), p16(INK4a) and senescence-associated beta-galactosidase activity. Surprisingly, these events occur even in the absence of ATM kinase implying that ATR may be a major responder to the complex DNA damage inflicted by Fe ions. Significantly, fragmentation of the Fe beam through PE attenuates these responses and this, in turn, results in better long-term survival in a colony forming assay. Our results help us to understand the biological consequences of ion fragmentation through materials and provide us with a biological basis for the use of hydrogenous materials like PE as effective space shields. However, it is important to point out the caveat that even after extensive fragmentation of the Fe beam through PE, a small portion of (presumably complex) DSBs are still not repaired by human cells and result in persistent (though attenuated) DNA damage signaling. The improved survival of cells irradiated through PE coupled with the presence of persistent DNA lesions raises the specter of genomic instability in these surviving cells which could eventually trigger cellular transformation. Therefore, it is very important to understand the long-term consequences of such unrepaired DNA lesions (i.e. carcinogenesis) using pertinent model systems. In preliminary studies carried out in the final year of this project, we developed a sensitive in vitro model system (“pre-sensitized” cells with targeted deletions of the Ink4a/Arf tumor suppressor locus). Using this model system and in vitro assays for cellular transformation (growth in soft agar), we find that these cells can indeed be transformed by Fe ions even after fragmentation through PE shielding. In the future, it would be important to evaluate the contribution of Fe particles with or without shielding to carcinogenesis in vivo using mouse models of cancer. In sum, our results show that fragmentation of heavy ions through shielding can significantly alter the biological responses of human cells to the ensuing DNA damage.
Peer reviewed publications from the current NASA funding period (2005-2010):
Research Articles
1. Cell cycle dependence of DNA-PK phosphorylation in response to DNA double-strand breaks. B. Chen, D.W. Chan, J. Kobayashi, S. Burma, A. Asaithamby, K. Morotomi-Yano, E. Botvinick, J. Qin, and D.J. Chen Journal of Biological Chemistry 280:14709-14715 (2005)
2. Gene expression profiles of normal human fibroblasts after ionizing radiation: a comparative study with low and high doses. L.-H. Ding, M. Shingyoji, F. Chen, J.-J. Hwang, S. Burma, J.-F. Cheng, and D. J. Chen Radiation Research 164:17-26 (2005)
3. Effect of Ku proteins on IRES-mediated translation. D. Siilvera, N. Koloteva-Levine, S. Burma, and O. Elroy-Stein Biology of the Cell 98:353-361 (2006)
4. DNA-PK phosphorylates histone H2AX during apoptotic DNA fragmentation in mammalian cells. B. Mukherjee, C. Kessinger, J. Kobayashi, B.P. Chen, D.J. Chen, A. Chatterje, and S. Burma DNA Repair 5:575-590 (2006)
5. Nucleophosmin suppresses oncogene-induced apoptosis and senescence and enhances oncogenic cooperation in cells with genomic instability. J. Li, D.P. Sejas, S. Burma, D.J. Chen, and Q. Pang Carcinogenesis 28:1163-1170 (2007)
6. Ku70/80 modulates ATM and ATR signaling pathways in response to DNA double-strand breaks.N. Tomimatsu, G.G. Tahimic, A. Otsuki, S. Burma, A. Fukuhara, K. Sato, G. Shiota, M. Oshimura, D.J. Chen, and A. Kurimasa Journal of Biological Chemistry 282:10138-10145 (2007)
7. Repair of HZE-partcle-induced DNA double-strand breaks in normal human fibroblasts. A. Asaithamby, N. Uematsu, A. Chatterjee, M.D. Story, S. Burma, and D.J. Chen Radiation Research 169:437-446 (2008)
8. Modulation of the DNA-damage response to HZE particles by shielding. B. Mukherjee, C.V. Camcho, N. Tomimatsu, J. Miller, and S. Burma DNA Repair 7:1717-1730 (2008)
9. Phosphorylation of Exo1 modlates homolgous recombination repair of DNA double-strand breaks. E. Bolderson, N. Tomimatsu, D.J. Richards, D. Boucher, R. Kumar, T.K. Pandita, S. Burma, K.K. Khanna Nucleic Acids Res. 38:1821-1831(2009)
10. Histone H2AX participates in the DNA damage-induced ATM activation through interaction with Nbs1. J. Kobayashi, H. Tauchi, B. Chen, S. Burma, S. Tashiro, S. Matsuura, K. Tanimoto, D.J. Chen, K. Komatsu Biochem. Biphys. Res. Commun. 380:752-757 (2009)
11. RIP-1 activates PI3K-Akt via a dual mechanism involving NF-kB-mediated inhibition of mTOR-S6K-IRS1 negative feedback loop and down-regulation of PTEN. S. Park, D. Zhao, K.J. Hatanpaa, B.E. Mickey, D. Saha, D.A. Boothman, M.D. Story, E.T. Wong, S. Burma, M-M. Georgescu, V.M. Rangnekar, S.S. Chauncey, and A.A. Habib Cancer Research 69:4107-4111 (2009)
12. Distinct roles of ATR and DNA-PKcs in triggering DNA damage responses in ATM-deficient cells. N. Tomimatsu, B. Mukherjee, and S. Burma EMBO Reports 10:629-635 (2009)
13. EGFRvIII and DNA Double-Strand Break Repair: A Molecular Mechanism for Radioresistance in Glioblastoma. B. Mukherjee, B. McEllin, C.V. Camacho, N. Tomimatsu, S. Sirasanagandala, S. Nannepaga, K.J. Hatanpaa, B. Mickey, C. Madden, E. Maher, D.A. Boothman, F. Furnari, W.K. Cavenee, R.M. Bachoo, and S. Burma Cancer Research 69:4252-4259 (2009)
14. Down-regulation of human DAB2IP gene expression in prostate cancer cells results in resistance to ionizing radiation. Z. Kong, D. Xie, T. Boike, P. Raghavan, S. Burma, D.J. Chen, A.A. Habib, A. Chakraborty, J-T. Hsieh and D. Saha Cancer Research 70:2829-2839 (2010)
15. WRN participates in translesion synthesis pathway through interaction with NBS1. J. Kobayashi, M. Okui, A. Asaithamby, S. Burma, B. Chen, K. Tanimoto, S. Matsuura, K. Komatsu, D.J. Chen Mech Ageing Dev. 131:436-444 (2010)
16. Epothilone B confers radiation dose enhancement in DAB2IP gene knock-down radioresistant prostate cancer cells. Z. Kong, P. Raghavan, D. Xie, T. Boike, S. Burma, D.J. Chen, A. Chakraborty, J-T. Hsieh and D. Saha Int. J. Radiation Oncology Biol. Phys. 20:250-257 (2010)
17. Loss of p15/Ink4b accompanies tumorigenesis triggered by complex DNA double-strand breaks. C. V. Camacho, B. Mukherjee, B. McEllin, L-H. Ding, B. Hu, A. Habib, X-J. Xie, C. Nirodi, D. Saha, M. Story, A. Balajee, R. M. Bachoo, D. A. Boothman, and S. Burma Carcinogenesis 31:1889-1896 (2010)
18. PTEN loss compromises homologous recombination repair in astrocytes: implications for glioblastoma therapy with temozolomide or PARP inhibitors. B. McEllin, C.V. Camacho, B. Mukherjee, B. Hahm, N. Tomimatsu, R.M. Bachoo, and S. Burma Cancer Research 70:5457-5464 (2010)
Invited Reviews and Book Chapters
1. Role of non-homologous end joining (NHEJ) in maintaining genomic stability in mammalian cells. S. Burma, B.P. Chen, and D.J. Chen DNA Repair 5:1042-1048 (2006)
2. Role of non-homologous end joining in the repair of DNA double-strand breaks. S. Burma, B. Chen, D.J. Chen in DNA Repair Genetic Instability and Cancer (Q. Wei, L. Li, and D.J. Chen, eds), World Scientific Publishing Co., p157-175 (2007)
3. Epidermal growth factor receptor in glioma: signal transduction, neuropathology, imaging, and radioresistance. K.J. Hatanpaa, S. Burma, D. Zhao, A.A. Habib Neoplasia 12:675-684 (2010)
4. Targeting Non-Homologous End-Joining Through Epidermal Growth Factor Receptor Inhibition: Rationale and Strategies for Radiosensitization. B. Mukherjee, H. Choy, C. Nirodi, and S. Burma Seminars in Radiation Oncology 20:250-257 (2010)
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