Abstract 3813: Role of the ERG transcription factor in the resistance of prostate cancer cells to the topoisomerase I inhibitor camptothecin

Prostate cancer (PCa) is a major public health issue as it is the second cause of death among cancers in industrialized countries, and its incidence is rising. Surgery is the main option for the curative treatment of localized forms of PCa and recurrences are managed with androgen deprivation strategies. In the case of advanced metastatic PCa and when tumors become resistant to castration (mCRPC), chemotherapy with taxanes is initiated. However, response rates remain low with a restricted number of alternatives due to the intrinsic resistance of CRPC to a wide range of cytotoxic agents. Advanced PCa are particularly resistant to topoisomerase I (Top1) inhibitors from the camptothecin (CPT) family, but the mechanistic bases of this resistance have not been investigated in details. Top1 is a nuclear enzyme that induces transient single strand breaks in duplex DNA to ensure the removal of torsional constraints associated with crucial DNA transactions such as replication, transcription, chromosome segregation or DNA recombination. We have previously shown that interaction of Top1 with DNA-PKcs, a kinase involved in non-homologous end-joining, could regulate the cellular response to CPT independently of DNA repair. This was further confirmed by the fact that NU7441, a specific inhibitor of the kinase activity of DNA-PKcs, had no effect on Hela cell sensitivity to CPT. Recently, it was shown that, in PCa cells, DNA-PKcs could interact with ERG, a transcription factor of the ETS family. As advanced PCa are often characterized by a TMPRSS2-ERG fusion leading to wild-type ERG overexpression, we investigated whether ERG could play a role in the resistance of PCa cells to CPT by regulating Top1/DNA-PKcs interaction. We showed that VCaP cells harboring the TMPRSS2-ERG fusion resulting in a 6-fold increase of ERG protein as compared to ERG fusion-negative (control) DU145 or PC3 cells were >100-fold more resistant to CPT. RWPE-1 stably overexpressing low levels of wild-type ERG (2-fold increase) did not show a major change in resistance to CPT as compared to control RWPE-1 cells stably expressing lacZ. Using two specific siRNA, we also showed that transient downregulation of ERG drastically reduced the sensitivity of VCaP cells to CPT, this effect being dependent on the efficacy of ERG repression. Interestingly, this effect was not due to a change in Top1 levels, suggesting that ERG downregulation may affect Top1-DNA-PKcs interaction. We detected this interaction in VCaP cells by immunoprecipitation in the presence of ethidium bromide, indicating that it was independent of DNA and it remains to be seen whether it is disrupted following ERG repression. Our preliminary findings provide evidences for a new mechanism by which ERG and its interaction with DNA-PKcs could explain, at least in part, the intrinsic resistance of PCa to Top1 inhibitors by the regulation of Top1-DNA-PKcs interaction.

Citation Format: Emmanuel Roche, Danièle Montaudon, Samer Kayali, Nadine Houédé, Philippe Pourquier. Role of the ERG transcription factor in the resistance of prostate cancer cells to the topoisomerase I inhibitor camptothecin. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3813. doi:10.1158/1538-7445.AM2014-3813

Spi-1, Fli-1 and Fli-3 (miR-17-92) oncogenes contribute to a single oncogenic network controlling cell proliferation in friend erythroleukemia

Clonal erythroleukemia developing in susceptible mice infected by Friend virus complex are associated with highly recurrent proviral insertions at one of three loci called Spi-1, Fli-1 or Fli-3, leading to deregulated expression of oncogenic Spi-1 or Fli-1 transcription factors or miR-17-92 miRNA cluster, respectively. Deregulated expression of each of these three oncogenes has been independently shown to contribute to cell proliferation of erythroleukemic clones. Previous studies showed a close relationship between Spi-1 and Fli-1, which belong to the same ETS family, Spi-1 activating fli-1 gene, and both Spi-1 and Fli-1 activating multiple common target genes involved in ribosome biogenesis. In this study, we demonstrated that Spi-1 and Fli-1 are also involved in direct miR-17-92 transcriptional activation through their binding to a conserved ETS binding site in its promoter. Moreover, we demonstrated that physiological re-expression of exogenous miR-17 and miR-20a are able to partially rescue the proliferation loss induced by Fli-1 knock-down and identified HBP1 as a target of these miRNA in erythroleukemic cells. These results establish that three of the most recurrently activated oncogenes in Friend erythroleukemia are actually involved in a same oncogenic network controlling cell proliferation. The putative contribution of a similar ETS-miR-17-92 network module in other normal or pathological proliferative contexts is discussed.

Application and Quantitative Validation of Computer-Automated Three-Dimensional Counting of Cell Nuclei

: This study provides a quantitative validation of qualitative automated three-dimensional (3-D) analysis methods reported earlier. It demonstrates the applicability and quantitative accuracy of our method to detect, characterize, and count Feulgen stained cell nuclei in two tissues (hippocampus and testes). These methods can provide important insights into the interpretation of biological, pharmacological, pathological, and toxicological events. A laser-scanned confocal light microscope was used to record 3-D images in which our algorithms automatically identified individual nuclei from the optical sections given an estimate of minimum nuclear size. The hippocampal data sets were also manually counted independently by five trained observers using the STERECON 3-D image reconstruction system. The automated and manual counts were compared. The computer counts were lower ( approximately 14%) than the manual counts, mainly because the algorithms counted a nucleus only if it was present in five consecutive optical sections but the human counters included nuclei that were in fewer optical sections. A nucleus-by-nucleus comparison of the manual and automated counts verified that the automated analysis was accurate and reproducible, and permitted additional quantitative analyses not available from manual methods. The algorithms also identified subpopulations of nuclei within the hippocampal samples, and haploid and diploid nuclei in the testes. Our methods were shown to be repeatable, accurate, and more consistent than manual counting. Nuclei in regions of high (hippocampal pyramidal layer) and low (extrapyramidal layer) density were distinguished with equal ease. Haploid and diploid nuclei were distinguished in the testes, demonstrating that our automated method may be useful for ploidy analysis. The results presented here on hippocampus and testis are consistent with other qualitative results from the liver and from immunohistochemically labeled substantia nigra, demonstrating the applicability of our software across tissues and preparation methods.

Enterohemorrhagic Escherichia coli. A dangerous food-borne pathogen

Since 1982, several outbreaks of hemorrhagic colitis due to EHEC, or E coli O157:H7, have occurred in the United States and other parts of the world. Contaminated, undercooked ground beef has been most frequently implicated in the outbreaks, although unpasteurized dairy products and other foods have also been the source of infection in sporadic cases. The most common clinical manifestation of EHEC infection is abdominal cramps and watery, bloody diarrhea. HUS secondary to the initial colitis develops in about 10% of patients under 10 years of age. Definitive diagnosis is made by isolation and identification of EHEC in stool samples. Treatment focuses on rehydration and supportive therapy. The use of antimicrobial agents, narcotics, or antimotility agents is not recommended, because they neither shorten the course of illness nor prevent the development of sequelae.