The overall survival for patients with glioblastoma multiforme (GBM) has not improved in two decades. A better understanding of the molecular basis for gliomagenesis would aid therapeutic advances. Recombinational based alternative lengthening of telomeres (ALT) is a telomere maintenance mechanism (TMM) distinct from telomerase, which serves as a prognostic factor in GBM. In this thesis, I have compared components of the p53 axis, namely p53, p21[WAF-1] and the paired box-containing transcription factors (PAX) PAX2, 5, and 8, with TMM in gliomas.
Analysis of TP53 status in relation to TMM in 110 gliomas revealed that activation of ALT during tumorigenesis possibly requires loss of normal TP53 function (P < 0.0001). Overexpression of p21[WAF-1] was also found to correlate with telomerase-positive gliomas (P = 0.0002). Moreover, high p21[WAF-1] expression is a poor prognostic factor in patients under 56 years (P = 0.015). Telomere length (TL) was also found as a prognostic factor, such that short TL (< 5 kb) is a poor prognostic factor in the group without defined TMM ("None")(P = 0.0160).
Pax2,5 and 8 belong to Group II of the PAX family. They are expressed at the midbrain-hindbrain boundary (MHB) and in the neural tube of the vertebrate embryo, whereas their expression levels are low in the adult brain. To explore their roles in glioma pathology, I analyzed mRNA levels in 54 gliomas and 16 established glioma cell lines. Increased levels of PAX8 mRNA were detected in 74.1% of gliomas and 62.5% of established glioma cell lines by real time PCR. Sixty-six percent of glioma specimens expressed high levels of active PAX2, 5, and 8 by immunohistochemistry. There were more males than females having high PAX2 expression (P = 0.0408). Suppression of PAX8 by small interfering RNA induced glioma cell death, independent of TP53 status. These findings identify PAX8 as a survival factor for GBM, and PAX2, 5, and 8 expression as contributing to the aggressive behavior of gliomas.
The mRNA level of PAX8 showed a positive correlation with telomerase activity in glioma biopsies (r� = 0.75, P < 0.001). The relationship was explored and I found that PAX2 and PAX8 are able to activate the reporter constructs of both the catalytic subunit (hTERT) and the RNA component (hTR) of telomerase. PAX8 had a stronger effect than PAX2 on the activation of the hTERT and hTR promoters. By electrophoretic mobility shift assay, Western blotting and telomerase activity assay, I showed that PAX8 bound directly to hTERT and hTR promoters, and upregulated hTERT protein and telomerase activity. Moreover, gliomas carrying wild type TP53 had higher levels of PAX8 expression compared to those with mutant TP53 (P = 0.0075) suggesting that PAX8 is significant only in some GBMs during gliomagenesis. These results show that the oncofetal proteins, PAX2 and PAX8, may have roles in telomerase regulation.
Taken together, molecular markers examined in this thesis suggest gliomas with different TMMs are derived from different pathways.
| Identifer | oai:union.ndltd.org:ADTP/266348 |
| Date | January 2008 |
| Creators | Chen, Yu-Jen, n/a |
| Publisher | University of Otago. Department of Pathology |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://policy01.otago.ac.nz/policies/FMPro?-db=policies.fm&-format=viewpolicy.html&-lay=viewpolicy&-sortfield=Title&Type=Academic&-recid=33025&-find), Copyright Yu-Jen Chen |
Page generated in 0.0019 seconds