Nearly 45% of oral squamous cell carcinomas (OSCC) are characterized by amplification of chromosomal band 11q13, which occurs by breakage-fusion-bridge (BFB) cycle mechanism. The first step in this cycle involves loss of distal 11q. Consequently, critical genes involved in the DNA damage response pathway, MRE11A, ATM, H2AFX and CHEK1 are lost in the step preceding 11q13 amplification. We hypothesized that this loss on distal 11q may lead to a diminished DNA damage response in OSCC. Characterization of OSCC using fluorescence in situ hybridization revealed partial loss of MRE11A, ATM, H2AFX and CHEK1 in all cell lines with 11q13 amplification and in additional cell lines without 11q13 amplification. Quantitative microsatellite analysis and loss of heterozygosity studies confirmed this loss. Quantitative PCR and immunoblotting revealed reductions in RNA and protein expression of MRE11A, ATM and H2AX. All cell lines with distal 11q loss exhibited aberrant gamma-H2AX foci and increased chromosomal instability to ionizing radiation. Surprisingly, distal 11q loss also correlated with reduced sensitivity to ionizing radiation. Although the literature attributes poor prognosis in OSCC to 11q13 gene amplification, our results suggest that distal 11q deletions may be equally if not more significant.
We observed an upregulation of the ATRCHEK1 pathway in a subset of OSCC with loss of the G1 cell cycle checkpoint. We hypothesized that this upregulation protects OSCC from premature chromatin condensation or mitotic catastrophe (cell death) by enhancing the S phase and G2 phase checkpoints. In OSCC, we observed a gain in ATR gene copy number; whereas CHEK1 is partially lost at the gene level. However, we observed that both ATR and CHEK1 are overexpressed in a subset of OSCC with loss of the G1 cell cycle checkpoint. Inhibition of ATR or CHEK1 with caffeine or with the respective siRNAs results in an increased susceptibility of OSCC to DNA damaging agents. Thus, inhibition of the ATRCHEK1 pathway in OSCC may aid the current therapeutic modalities used in the treatment of OSCC. The public health significance of our studies involves the development and use of distal 11q loss and ATRCHEK1 upregulation as biomarkers for OSCC.
| Identifer | oai:union.ndltd.org:PITT/oai:PITTETD:etd-08012006-195439 |
| Date | 09 October 2006 |
| Creators | Parikh, Rahul Atul |
| Contributors | Susanne M. Gollin, Ph.D., Lin Zhang, Ph.D., William S. Saunders, Ph.D., Baskaran Rajasekaran, Ph.D., Robert E. Ferrell, Ph.D. |
| Publisher | University of Pittsburgh |
| Source Sets | University of Pittsburgh |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.library.pitt.edu/ETD/available/etd-08012006-195439/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to University of Pittsburgh or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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