Clinical Relevance of E2F Family Members in Ovarian Cancer—An Evaluation in a Training Set of 77 Patients

Abstract

Purpose: The major obstacle in treating ovarian cancer is the rapid development of platinum resistance during therapy. Deregulation of members of the E2F family of transcription factors is crucially involved in carcinogenesis and probably in mechanisms underlying platinum resistance. We therefore investigated the relevance of the whole set of E2F family members in predicting clinical outcome and their significance in predicting platinum resistance. Experimental Design: Real-time PCR of all E2F family members was done from 77 ovarian carcinomas, defined as our training set, and 8 healthy control samples. The correlation with clinicopathologic characteristics, platinum resistance, and survival was investigated. Furthermore, the cross-talk of E2F family members was assessed for its value in predicting survival and platinum resistance. Results: The proliferation-promoting E2F1and E2F2 were associated with grade 3 tumors and residual disease >2 cm in diameter after initial surgery. Survival analyses showed low expression of E2F1or E2F2 to be significantly associated with favorable disease-free and overall survival (E2F1, P = 0.039 and 0.047, respectively; E2F2, P = 0.009 and 0.006, respectively). In contrast, high expression of inhibiting E2F4 or E2F7 predicted favorable disease-free and overall survival (E2F4, P = 0.047 and 0.042, respectively; E2F7, P = 0.048 and 0.042, respectively). A high E2F2 to E2F4 ratio was the most valuable prognostic variable for disease-free survival in multivariate analysis (hazard ratio, 6.494; P = 0.002). Tumors considered platinum resistant were associated with lower E2F4 and E2F7 expression (P = 0.012 and 0.009, respectively) compared with platinumsensitive tumors. Again, ratios of E2F1 or E2F2 to E2F7 were the most favorable variables in predicting platinum resistance. Conclusions: We here show that deregulation of both proliferation-promoting and proliferationinhibiting E2F transcription factors and their cross-talk is crucially involved in the tumor biology of ovarian cancer and influences clinical outcome. Furthermore, down-regulation of E2F7 may contribute to mechanisms underlying platinum resistance, and calculation of ratios of proliferationpromoting E2F1to E2F7 could serve as a putative predictor of platinum resistance.

Regulation of transcription factor E2F3a and its clinical relevance in ovarian cancer

“…In keeping with the results obtained from ovarian cancer cell lines and primary cultured healthy ovarian surface epithelial and mesothelial cells, both E2F3a and E2F3b were found to be overexpressed in ovarian cancers as compared with normal ovarian tissue. These findings are in agreement with earlier data showing both proliferation-promoting and -inhibiting E2F family members to be overexpressed in ovarian cancer specimens (Reimer et al, 2007). Nevertheless, E2F3a expression by far exceeded that of E2F3b in the cancer tissues.…”

“…Total RNA extraction and real-time PCR amplification Total RNA extraction from cell lines or patient samples, DNAse treatment and reverse transcription were performed as previously described by Reimer et al (2007). RT-PCRs were performed using an ABI Prism 7900 Detection System as described previously by Reimer et al (2010).…”

The atypical E2F family member E2F7 couples the p53 and RB pathways during cellular senescence

“…Interestingly, the genetics of pancreatic cancer suggest that this is a setting where oncogene-induced senescence restricts tumorigenesis, as activating KRAS mutations frequently co-occur with mutations targeting the INK4A/ ARF locus or p53 in later stages of the disease. Underexpression of E2F7 is also associated with platinum resistance and reduced survival in ovarian cancer patients (Reimer et al 2007). Still, somatic mutations in E2F7 have yet to be described, raising the possibility that its activity is not rate-limiting for tumorigenesis.…”

Coordinate regulation of Fanconi anemia gene expression occurs through the Rb/E2F pathway

“…Interestingly, gene expression signatures of platinum-resistant advanced stage ovarian cancers revealed activation of E2F3 pathways, and the targeting of E2F pathways with roscovitine could be exploited for improved response to chemotherapy in vitro (Dressman et al, 2007). Additionally, high levels of activating relative to repressing E2Fs have recently been shown to be clinical predictors of poor response to chemotherapy in ovarian cancer patients (Reimer et al, 2007). Future analyses of the relative contribution of FA upregulation to E2F-dependent chemotherapy resistance in cancer patients will be important for an assessment of possible treatment implications.…”