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.

The E2F family of transcription factors plays a pivotal role in the regulation of cellular proliferation. On the basis of sequence homology and function, eight distinct members of E2F transcription factors (E2F-1 to E2F-8) have been distinguished to date. The regulation of E2F transcription factors is closely associated with the function of the retinoblastoma family of tumor suppressors (RB pathway). In the last decade various alterations of distinct components of the RB-E2F pathway were found to be associated with tumor progression. However, no data on the role of E2F family members are available in tumor biology of ovarian cancer. Here we describe an expression study of E2F transcription factors in various human ovarian cancer cell lines; its clinical relevance was examined in a training set of 77 ovarian cancer patients. Expression levels of E2F-1, E2F-2, and E2F-8 were elevated in all the ovarian cancer cell lines studied when compared with human peritoneal mesothelial cells (HPMCs). Interestingly, EGF treatment showed a time-dependent upregulation of the activating transcription factor E2F-3 and a simultaneous increase of DP-1, the heterodimeric partner of E2F-3. High expression of E2F-1, E2F-2, and E2F-8 was found to be associated with histopathologic grade 3 tumors and residual tumor over 2 cm in diameter after primary debulking surgery in ovarian cancer patients. Taken together, these data suggest that the proliferation-promoting E2F transcription factors E2F-1 and especially E2F-2 play a pivotal role in tumor biology of ovarian cancer and may be candidates for specific therapeutic targets.

There is growing evidence that deregulation of E2F transcription factors is causatively involved in the patho-physiology of various tumors. However, no data on the role of E2F family members in tumor biology of ovarian cancer are available. We here describe an expression study of all known E2F transcription factors and their coactivators DP-1 and DP-2 in various human ovarian cancer cell lines and the breast cancer cell line T47D and their involvement in pathways affected by interferon-γ and EGF. A significant overexpression of the proliferation-promoting E2F1 and especially E2F2 points to a pivotal role in modulating the uncontrolled proliferation in ovarian cancer cells. Of special note is the fact that interferon-γ treatment did not only caused a reduction of the proliferation-promoting transcription factors E2F1 and E2F2, but also increased the inhibiting transcription factors E2F4 and E2F5, thus underlining the importance of an E2F cross-talk in the anti-proliferative function of interferon-γ. Moreover, an increase in DP-1 and E2F3 is probably involved in the proliferation-enhancing effect of EGF. Our study provides a new insight in the crucial role of E2F cross-talk, especially the role of the inhibiting transcription factors E2F4 and E2F5, in the tumor biology of cancer and its possible usefulness as targets in anti-cancer therapy.