TGF-ß is an inducer of ZEB1-dependent mesenchymal transdifferentiation in glioblastoma that is associated with tumor invasion.

Different molecular subtypes of glioblastoma (GBM) have been recently identified, of which the mesenchymal subtype is associated with worst prognoses. Here, we report that transforming growth factor-ß (TGF-ß) is able to induce a mesenchymal phenotype in GBM that involves activation of SMAD2 and ZEB1, a known transcriptional inducer of mesenchymal transition in epithelial cancers. TGF-ß exposure of established and newly generated GBM cell lines was associated with morphological changes, enhanced mesenchymal marker expression, migration and invasion in vitro and in an orthotopic mouse model. TGF-ß-induced mesenchymal differentiation and invasive behavior was prevented by chemical inhibition of TGF-ß signaling as well as small interfering RNA (siRNA)-dependent silencing of ZEB1. Furthermore, TGF-ß-responding and -nonresponding GBM neurospheres were identified in vitro. Interestingly, nonresponding cells displayed already high levels of pSMAD2 and ZEB1 that could not be suppressed by inhibition of TGF-ß signaling, suggesting the involvement of yet unknown mechanisms. These different GBM neurospheres formed invasive tumors in mice as well as revealed mesenchymal marker expression in immunohistochemical analyses. Moreover, we also detected distinct zones with overlapping pSMAD2, elevated ZEB1 and mesenchymal marker expression in GBM patient material, suggestive of the induction of local, microenvironment-dependent mesenchymal differentiation. Overall, our findings indicate that GBM cells can acquire mesenchymal features associated with enhanced invasive potential following stimulation by secretory cytokines, such as TGF-ß. This property of GBM contributes to heterogeneity in this tumor type and may blur the boundaries between the proposed transcriptional subtypes. Targeting TGF-ß or downstream targets like ZEB1 might be of potential benefit in reducing the invasive phenotype of GBM in a subpopulation of patients.

Checkpoint kinase 2 (Chk2) supports sensitivity to platinum-based treatment in high grade serous ovarian cancer.

OBJECTIVE: Platinum-based chemotherapy is the standard treatment in advanced stage high grade serous ovarian cancer (HGSOC), but the majority of patients will relapse with drug-resistant disease. Platinum induces double-strand DNA breaks and subsequently activation of the DNA damage response (DDR). Drugs targeting DDR pathway components have gained major interest to be combined with chemotherapy as they could increase the therapeutic window. In the present study, we investigated the activation status of the Ataxia Telangiectasia Mutated (ATM) signaling axis within the DDR in a large, well-defined cohort of advanced stage HGSOC patients. METHODS: Pre-therapy activation status of the ATM signaling axis of the DDR was determined by immunohistochemistry in 125 chemo-naive advanced stage HGSOC patients. Ovarian cancer cell lines with stable checkpoint kinase 2 (Chk2) knock down were used to study cell cycle distribution and survival in long-term clonogenic survival assays. RESULTS: All ATM signaling axis components showed high expression levels. In two well-defined groups with the largest contrast in treatment response, high expression of Chk2 was related to good response (OR=0.132; P=0.014). Chk2 depletion abrogated the cisplatin-induced S-phase cell cycle arrest and caused increased resistance to cisplatin in long-term clonogenic survival assays. CONCLUSIONS: Chk2 is related to good response to platinum-based chemotherapy in advanced stage HGSOC patients. Chk2-depleted ovarian cancer cell lines have diminished platinum sensitivity, suggesting that Chk2 should not be considered a therapeutic target along with platinum-based treatment in HGSOC patients.