The role of DNA replication fork remodeling proteins in lymphomagenesis and hematopoietic cell replication stress

Abstract

Genome maintenance is essential for the viability of eukaryotic cells and for the prevention of tumorigenesis. DNA replication stress is a significant contributor to genomic instability. As such, cells employ a complex replication stress response to prevent replication fork collapse upon experiencing DNA replication stress. In this dissertation, I evaluated the roles of the closely related replication fork remodeling proteins Smarcal1 and Zranb3 in lymphomagenesis. With genetic mouse models, I showed these proteins function by stabilizing replication forks in vivo in response to multiple replication stress-inducing stimuli, and determined their loss greatly impacts tumor development phenotypes. Specifically, loss of Smarcal1 significantly increased susceptibility to γ-radiation-induced replication stress and delayed T-cell lymphoma formation in vivo. This phenotype was due to elevated sensitivity to replication stress in Smarcal1-deficient hematopoietic stem cells, as evidenced by increased DNA damage and apoptosis of these cells during forced proliferation. Moreover, by utilizing the Eµ-myc B-cell lymphoma mouse model, I determined that Smarcal1 and Zranb3 are essential for stabilizing replication forks during oncogenic stress, and that they do so in a non-redundant fashion. Loss of one or both alleles of either protein resulted in distinct alterations in lymphoma formation, replication fork stability, DNA damage accumulation and apoptosis, depending on whether one, two or no alleles of either protein were expressed. These data are the first to directly link both Smarcal1 and Zranb3 to the cellular response to replication stress in vivo and identify Myc as the first endogenous source of replication stress that requires both proteins for resolution. Moreover, these data provide mechanistic insight into how replication stress and fork remodeling proteins influence cancer development and establish two novel proteins as significant contributors to hematologic malignancies.