Radiation and chemotherapeutic agents eradicate tumors by inducing irreparable DNA damage. However, cancer cells often develop resistance to therapy by manipulating the DNA repair machinery. Conversely, a dividing cell constantly exposed to environmental and endogenous DNA damaging agents can transform into a tumor due to incorrect repair. Therefore the expression level of DNA repair proteins is critical both for cancer therapy and tumorigenesis. In our preliminary studies we have discovered a novel connection between a new class of gene expression regulators, microRNAs and DNA repair proteins. MicroRNAs (miRNAs) are small non-coding RNAs that typically dampen gene expression. There is accumulating evidence that miRNAs are mis-expressed in cancer cells. It is noteworthy that ectopic overexpression of miRNAs downregulating DNA repair proteins could sensitize cancer cells to radiation and other genotoxic reagents. Alternatively, tumors that delete these miRNAs may develop resistance to conventional cancer therapy. DNA repair is a 'house keeping'function, and micro-RNA mediated attenuation of DNA repair may appear counter intuitive. However, normal cells down modulate DNA repair in a terminally differentiated state where overall DNA repair is downregulated. Using the experimental system of in vitro hematopoietic cell differentiation, we have identified microRNAs (miRNAs), miR-24 and a polycistronic miRNA cluster including miRNAs (183, 96, 182), that are upregulated in terminally differentiated non-dividing cells but are rapidly down regulated in response to ionizing radiation (IR) in dividing cells. We hypothesize that in post-mitotic cells DNA damage induces apoptosis and miRNAs attenuate the DNA repair machinery promoting cell death. Conversely, in response to IR the miRNAs are downmodulated in dividing cells to accentuate the production of DNA repair proteins and boost the DNA damage response. In support of this contention, we observed, that miR-24, downregulates the expression of a key DSB repair protein, H2AX and impedes DSB repair in terminally differentiated blood cells. The miRNAs (182,183 and 96) that we propose to study have already been noted for aberrant expression in a variety of tumors. A direct effect of these miRNAs on cancer could be by dysregulation of the DNA repair machinery. Bioinformatic predictions suggest that several DNA repair genes, such as, BRCA1, ATR, XLF, etc. are targeted by the miRNAs-183, 96 and 182. Preliminary experiments validate the prediction that miR-182 regulates BRCA1.
In Aim #1 we will use different computational, and biochemical strategies, to identify and validate DNA repair factors targeted by miRNAs-183, 96 and 182 in transformed cell lines and primary cells.
In Aim #2 we will systematically study the effect of these miRNAs on DSB repair and determine their impact on each repair pathway. Finally we will evaluate the radiosensitivity of cancer cells expressing these miRNAs. There is limited understanding of the role of miRNAs in DNA repair and this study will address this issue and also elucidate the impact of miRNAs on radiotherapy.

Public Health Relevance

Radiation and chemotherapeutic agents eradicate tumors by inducing irreparable DNA damage, and cancer cells often counter this treatment by manipulating the DNA repair machinery to develop resistance. In our preliminary studies we have discovered a novel connection between a new class of gene expression regulators, microRNAs (miRNAs) and DNA repair proteins, and the miRNAs (182, 183 and 96) that we propose to investigate have already been recognized for aberrant expression in a variety of tumors. Identifying specific miRNAs that suppress DNA repair, and their functional impact upon the DNA repair pathways, and radiosensitivity of cells, will have significant clinical implications in cancer biology.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Research Project (R01)
Project #
5R01CA142698-03
Application #
8210943
Study Section
Radiation Therapeutics and Biology Study Section (RTB)
Program Officer
Mietz, Judy
Project Start
2010-02-01
Project End
2015-01-31
Budget Start
2012-02-01
Budget End
2013-01-31
Support Year
3
Fiscal Year
2012
Total Cost
$352,231
Indirect Cost
$150,956
Name
Dana-Farber Cancer Institute
Department
Type
DUNS #
076580745
City
Boston
State
MA
Country
United States
Zip Code
02215
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