Markers indicative of ongoing DNA replication stress (Chk1 activation, Rad17 phosphorylation, replication protein A foci and single-stranded DNA) were present in GBM cells under high- or low-oxygen culture conditions and in clinical specimens of both low- and high-grade tumors.
Several components of the DNA damage response machinery were also identified, including Rad17, which acts as a haploinsufficient tumor suppressor that responds to oncogenic stress and whose loss is associated with poor prognosis in human patients.
The results of normalized, quantitative RT-PCR showed decreased expression of hRAD17 mRNA in tumor tissue (mean value 0.2166) when compared with normal tissue (mean value 0.3957, p < .05).
Sequencing of some of the tumor-specific altered regions indicated that they code for regions of UDP-GalNAc and hRAD 17 genes, which were lost (deleted) in oral cancer.
Although not significantly different, expression of HRad17 mRNA tended to correlate with tumor size (P = 0.06) and expression of mutant p53 protein (P = 0.10).
When primary tumor samples were analyzed, we observed that the majority (74%) of non-small cell lung carcinoma samples exhibited a significantly higher level of hRad17 expression compared with matched normal tissue controls.