Reis, M. S. | bioRxiv Science

bioRxiv2018

Transcription activity contributes to the activation of non-constitutive origins to maintain the robustness of S phase duration in African trypanosomes

The cosynthesis of DNA and RNA potentially generates conflicts between replication and transcription, which can lead to genomic instability. In trypanosomatids, eukaryotic parasites that perform polycistronic transcription, this phenomenon and its consequences have not yet been investigated. Here, using equations and computational analysis we demonstrated that the number of constitutive origins mapped in the Trypanosoma brucei genome is close to the minimum required to complete replication within S phase duration. However, taking into account the location of these origins in the genome, the replication in due time becomes virtually impossible, making it necessary to activate non-constitutive origins. Moreover, computational and biological assays pointed to transcription being responsible for activating non-constitutive origins. Together, our results suggest that transcription action through conflicts with replication contributes to the firing of non-constitutive origins, maintaining the robustness of S phase duration. The usage of this entire pool of origins seems to be of paramount importance for the survival of this parasite that infects million people around the world since it contributes to the maintenance of the replication of its DNA.

molecular biology↗

bioRxiv2017

Fibroblast Growth Factor 2 lethally sensitizes cancer cells to stress-targeted therapeutic inhibitors

In malignant transformation, cellular stress response pathways are dynamically mobilized to counterbalance oncogenic activity, keeping cancer cells viable. Therapeutic disruption of this riskily balanced homeostasis might change the outcome of many human cancers, particularly those for which no effective therapy is available. Here, we report the use of Fibroblast Growth Factor 2 (FGF2) to demonstrate that further mitogenic activation disrupts cellular homeostasis and strongly sensitizes cancer cells to stress-targeted therapeutic inhibitors. We show that FGF2 enhanced replication and proteotoxic stresses in a K-Ras-driven murine cancer cell model, and combinations of FGF2 and proteasome or DNA damage response-checkpoint inhibitors triggered cell death. CRISPR/Cas9-mediated K-Ras depletion suppressed the malignant phenotype and prevented these synergic toxicities in these murine cells. Moreover, in a panel of human Ewings sarcoma family tumor cells, sub-lethal concentrations of bortezomib (proteasome-inhibitor) or VE-821 (ATR-inhibitor) induced cell death when combined with FGF2. Sustained MAPK-ERK1/2 overactivation induced by FGF2 underlies these synthetic lethalities, once late pharmacological inhibition of this pathway restored cell homeostasis and prevented these described synergies. Our results highlight how mitotic signaling pathways frequently overridden in malignant transformation might be exploited to disrupt the risky robustness of cancer cells, ultimately sensitizing them to stress-targeted therapies. This approach provides a new therapeutic rationale for human cancers, with important implications for tumors still lacking effective treatment, and for those that frequently relapse after available therapies.

cancer biology↗