p38 mitogen-activated protein kinase (MAPK) is rapidly activated by stresses and is believed to play an important role in the stress response. While Chk1 is known to mediate G 2 DNA damage checkpoint control, p38 was also reported to have an essential function in this checkpoint control. Here, we have investigated further the roles of p38 and Chk1 in the G 2 DNA damage checkpoint in cancer cells. We find that although p38 activation is strongly induced by DNA damage, its activity is not required for the G 2 DNA damage checkpoint. In contrast, Chk1 kinase is responsible for the execution of G 2 DNA damage checkpoint control in p53-deficient cells. The inhibition of p38 activity has no effect on Chk1 activation and ␥-H2AX expression. Global gene expression profiling of cancer cells in response to tumor necrosis factor alpha (TNF-␣) revealed that p38 plays a strong prosurvival role through the coordinated downregulation of proapoptotic genes and upregulation of prosurvival genes. We show that the inhibition of p38 activity during G 2 DNA damage checkpoint arrest triggers apoptosis in a p53-independent manner with a concurrent decrease in the level of Bcl2 family proteins. Our results suggest that although p38 MAPK is not required for the G 2 DNA damage checkpoint function, it plays an important prosurvival role during the G 2 DNA damage checkpoint response through the upregulation of the Bcl2 family proteins.

Gliomas are notoriously recurrent and highly infiltrative, and have been shown to arise from stem-like cells. We implicate an elevated O2(-):H2O2 ratio as a prosurvival signal in GPC self-renewal and proliferation. The ROS Index provides quantification of O2(-):H2O2-mediated chemosensitivity, an advancement in a previously qualitative field. Intriguingly, glioma patients with a reduced ROS Index correlate with longer survival and the Proneural molecular classification, a feature frequently associated with tumors of better prognosis. These data emphasize the feasibility of manipulating the O2(-):H2O2 ratio as a therapeutic strategy.

Purpose: Patient-derived glioma-propagating cells (GPC) contain karyotypic and gene expression profiles that are found in the primary tumor. However, their clinical relevance is unclear. We ask whether GPCs contribute to disease progression and survival outcome in patients with glioma by analyzing gene expression profiles. Experimental Design: We tapped into public sources of GPC gene expression data and derived a gene signature distinguishing oligodendroglial from glioblastoma multiforme (GBM) GPCs. By adapting a method in glioma biology, the Connectivity Map, we interrogated its strength of association in public clinical databases. We validated the top-ranking signaling pathways Wnt, Notch, and TGFβ, in GPCs and primary tumor specimens. Results: We observed that patients with better prognosis correlated with oligodendroglial GPC features and lower tumor grade, and this was independent of the current clinical indicator, 1p/19q status. Patients with better prognosis had proneural tumors whereas the poorly surviving cohort had mesenchymal tumors. In addition, oligodendroglial GPCs were more sensitive to Wnt and Notch inhibition whereas GBM GPCs responded to TGFβR1 inhibition. Conclusions: We provide evidence that GPCs are clinically relevant. In addition, the more favorable prognosis of oligodendroglial tumors over GBM could be recapitulated transcriptomically at the GPC level, underscoring the relevance of this cellular model. Our gene signature detects molecular heterogeneity in oligodendroglial tumors that cannot be accounted for by the 1p/19q status alone, indicating that stem-like traits contribute to clinical status. Collectively, these data highlight the limitation of morphology-based histologic analyses in tumor classification, consequently impacting on treatment decisions. Clin Cancer Res; 18(15); 4122–35. ©2012 AACR.