DNA damage response activation in human brain tumors

Despite aggressive therapy comprising surgical resection, radiotherapy and chemotherapy, the prognosis for patients with glioblastoma multiforme (GBM) remains extremely poor. GBM is among the most malignant brain tumors with extensive areas of hypoxia, necrosis and robust angiogenesis. Hypoxia leads to increased oxidative stress, where the physiological function of reactive oxygen species (ROS) involves positive regulation of tumor angiogenesis. Formation of ROS leads to DNA damage and subsequent activation of DNA damage response (DDR) signalling pathways. Our preliminary data show DDR is massively activated in human tumors of astroglial origin, particularly in lower-grade astrocytomas (grade II). p53 mutated tumors (or areas within astrocytomas) are always accompanied by activated DDR but not vice versa, which is consistent with the idea that DDR activation is a relatively early event creating an environment selective to the outgrowth of tumor cells with mutant p53. Indirect immunofloures-cence staining of a variety of GBM cell lines shows extensive yH2AX phosphorylation (Ser139) and foci formation, indicating high levels of spontaneous DNA damage, compared to normal human astrocytes (NHA). Cultivation of GBM
cell lines at lower oxygen levels (3%), together with data collected after in vitro induction of replicative stress allowed us to hypothesize that the high level of spontaneous DNA damage in astroglial tumors and cell lines is a consequence of the simultaneous effect of oxidative and replicative stress. Together, these observations point to oxidative and replicative stress as an enhancer of spontaneous DNA damage in GBM model cell lines in vitro, giving them selective advantage in the expansion of highly aggressive clones.

Supported by grants MSM6198959276 and Lundbeck Foundation R13-A1287