A non-cell-autonomous buffering mechanism protects cells from replication stress-driven DNA damage
Authors: Benjamin Boumard 1; Tania Maalouf 1; Marwa El Hajj 1; Marine Stefanutti 1; Gwenn Le Meur 1; Reinhard Bauer 2; Allison Bardin 1
Affiliations: 1) Institut Curie, PSL Research University, CNRS UMR 3215, INSERM U934, Stem Cells and Tissue Homeostasis Group, Paris, France.; 2) Molecular Developmental Biology Unit, Life & Medical Sciences Institute (LIMES), University of Bonn, Carl-Troll-Straße 31, 53115 Bonn, Germany.
Keywords: i. DNA replication; g. wing disc
Replication stress is an important driver of genome instability in cancer. It can be triggered by imbalances in the dNTP pool, which is a common strategy of chemotherapeutic drugs. With the aim of understanding the effects of induced replication stress on stem and progenitor cells, we characterized the consequences of depletion of dNTPs in Drosophila adult intestinal stem cells and developing wing disc progenitors. Our findings suggest a previously unrecognized buffering mechanism of the dNTP pool from neighboring cells that depends on Gap Junctions. Specifically, the knock-down in intestinal stem cells of RnRL, a subunit of Ribonucleotide reductase - a rate-limiting enzyme essential for dNTP production, leads to high levels of DNA damage, S phase arrest, and ultimate depletion of stem cells from the intestine. In contrast, the clonal knockdown of RnRL in wing disc progenitor cells leads to little to no DNA damage. However, when Gap Junctions are inactivated along with RnrL, high levels of DNA damage are now induced in the wing disc. This suggests that wing disc progenitor cells participate in dNTP-resource sharing through connections to their neighboring cells via Gap Junctions allowing buffering of induced replication stress. We find that in the intestine, Gap Junctions form between mature enterocytes, whereas intestinal stem cells lack them. Intestinal stem cells, therefore, cannot buffer their dNTP pool via neighboring cells, likely contributing to their exquisite sensitivity to induced replication stress. Overall, our data suggest that a shared dNTP pool can buffer replication stress and that differences in Gap Junction connectivity between cell types may have an important impact on DNA damage susceptibility. These findings have significant implications for understanding replication stress in healthy tissues and cancers.