Role of Chk1 and the Fanconi anemia pathway in Myc-dependent tumorigenesis
Final Report Abstract
High levels of the Myc oncogene drive cellular proliferation, but at the same time elicit genotoxic stress during DNA replication, trigger a DNA damage response and, depending on the cellular context, induce apoptosis and/or senescence. The Chk1 kinase is a central effector of the replication checkpoint and is essential for cellular survival. As shown for other checkpoint proteins, Chk1 might conceivably act as a tumor suppressor. On the other hand, maintaining minimal levels of Chk1 might be critical for tumor growth and/or survival. In this project we addressed the role of Chk1 in Myc-induced lymphomagenesis, based on the study of Eμ-myc transgenic mice carrying either a heterozygous knockout allele of the Chk1 gene, or an additional Chk1 transgene (Super-Chk1). We monitored disease-free survival in both cohorts. Eμ-myc/Chk1 +/- mice showed no alteration in Myc-induced tumorigenesis relative to wild-type controls. Also, characterization of the pre-tumoral disease stage in B-cells and of Mycoverexpressing mouse embryonic fibroblasts (Myc-ER) did not reveal any difference between the Chk1+/- and Chk1+/+ genotypes. Thus, at the genetic level, Chk1 showed no haploinsufficient activity upon Myc activation. Eμ-myc/Super-Chk1 transgenic mice showed a slight tendency for accelerated disease onset in comparison to the wild-type control, although the difference remained below statistical significance. Altogether, these experiments suggest that the replication checkpoint is buffered against slight changes in Chk1 levels in live cells. In parallel with the above genetic experiments, we used pharmacological targeting of Chk1, which yielded much stronger and more conclusive effects. We made use of two chemical inhibitors of Chk1 (SB-218078 and UCN01). Treatment of either mouse embryonic fibroblasts, or Eμ-myc lymphomas with these inhibitors increased DNA damage (γH2AX) and cell death specifically in a Myc-dependent manner. Therefore, Chk1 inhibitors were highly effective in killing Myc-driven lymphomas in vivo, and showed a remarkable therapeutic window in the mouse model. These results are of striking relevance for ongoing clinical trials with Chk1 inhibitors for cancer treatment. Finally, our preliminary data also support the idea that the Chk1-interacting Fanconi Anemia pathway might also be required to maintain genome stability in Myc-overexpressing cells.
Publications
- Exploiting oncogene-induced replicative stress for the selective killing of Myc-driven tumors. Nat Struct Mol Biol. 2011 Nov 27;18(12):1331-5
Murga M, Campaner S, Lopez-Contreras AJ, Toledo LI, Soria R, Montaña MF, D'Artista L, Schleker T, Guerra C, Garcia E, Barbacid M, Hidalgo M, Amati B, Fernandez-Capetillo O
