Towards a cohesive understanding of the DNA damage response as a therapeutic target

Abstract

At the basis of the complexity that forms a human being is a highly regulated interplay of factors found at a molecular, cellular, and macroscopic level. Ever since we evolved to work this way, even the slightest dysregulation at the molecular level can cascade and manifest as a non-communicable disease which ultimately affects the whole organism. Among the most lethal ones is cancer. In order to combat this disease efficiently, we need to understand its features at each regulatory level, a concept commonly referred to as “bench-to-bedside”. This thesis explores this concept at different steps of the way.

Genomic instability is a cornerstone of oncogenesis, the process of developing cancer, caused by inability of cells to maintain the integrity of their genome. DNA damage poses a serious risk to this integrity rendering cells susceptible to malignant transformation. A key player in the DNA damage response is Cohesin, a member of the Structural Maintenance of Chromosomes (SMC) complexes. Known for its role in sister chromatid cohesion and DNA damage repair, Cohesin can connect distant segments of DNA both in cis and trans.

In Paper I (the bench), we interrogate the mechanisms driving the recruitment of the Cohesin loader complex Scc2/4 to DNA double strand breaks in Saccharomyces cerevisiae. Failure to do so impairs Cohesin from exerting its function, critical for accurate repair and maintenance of genomic integrity. We show that Scc2/4 recruitment coincides with DNA end resection, and following accelerated and decelerated kinetics in a likewise manner. This process is largely driven by Tel1 (ATM) mediated phosphorylation of histone H2A, but contrary to Cohesin loading independent of Mec1 (ATR). We also provide the first evidence for Cohesin loading occurring directly at the break.

In Paper II (the transition from bench to bedside), we analyze how FGF2, a potent mitogenic growth factor, shapes the tumor microenvironment. We show that FGF2, aside from its angiogenic functions, affects the tumor vasculature by multiple distinct mechanisms. First, by stimulating proliferation of pericytes directly via FGFR2. Second, by preventing degradation of PDGFRβ in pericytes augmenting PDGF-B signaling. And third, by inducing expression of PDFG-B and D in endothelial cells via FGFR1.

In Paper III (the bedside) we provide a rationale for a therapeutic approach to treat FGF2+ cancers. We show that growth of FGF2+ tumors can be inhibited by concurrently targeting pericytes with imatinib (a tyrosine kinase inhibitor) and the vasculature with bevacizumab (a monoclonal Anti-VEGFA antibody). We thereby provide evidence that this combinational approach can sensitize treatment resistant breast cancer to antiangiogenic therapy.