Hematopoietic Stem Cell Quiescence Promotes Error-Prone DNA Repair and Mutagenesis

Abstract

SUMMARY Most adult stem cells, including hematopoietic stem cells (HSCs), are maintained in a quiescent or resting state in vivo. Quiescence is widely considered to be an essential protective mechanism for stem cells that minimizes endogenous stress caused by cellular respiration and DNA replication. Here, we demonstrate that HSC quiescence can also have detrimental effects. We found that HSCs have unique cell-intrinsic mechanisms ensuring their survival in response to ionizing irradiation (IR), which include enhanced pro-survival gene expression and strong activation of p53-mediated DNA damage response. We show that quiescent and proliferating HSCs are equally radioprotected but use different types of DNA repair mechanisms. We describe how nonhomologous end joining (NHEJ)-mediated DNA repair in quiescent HSCs is associated with acquisition of genomic rearrangements, which can persist in vivo and contribute to hematopoietic abnormalities. Our results demonstrate that quiescence is a double-edged sword that renders HSCs intrinsically vulnerable to mutagenesis following DNA damage.

The emerging role of p53 in stem cells

“…Three recent papers address the issue of how both mouse and human hematopoietic stem and progenitor cells (HSPCs) respond to radiation-induced DD [57][58][59]. These studies indicate that hematopoietic cells can adopt different means of handling DD, depending on their differentiation stage.…”

“…Surprisingly, they also show that DD responses in mouse or human cells follow opposite routes and unravel a different role for p53 in the DD response of HSPCs. Mouse HSPCs (defined as lin À Sca1 + cKit + flk2 À ) have a unique cell intrinsic mechanism that ensures their survival following X-ray treatment and which involves the activation of p53 and its transcriptional target p21 and DNA repair [58,59]. By contrast, human cord blood HSPCs exhibit p53-dependent radiation-induced apoptosis.…”

Bid protects the mouse hematopoietic system following hydroxyurea-induced replicative stress

“…5 Recently, two groups investigated the response of HSCs and committed progenitor cells to DNA damage induced by ionizing radiation (IR) in mouse and human systems, respectively. 6,7 Murine hematopoietic stem and progenitor cells (HSPCs: lin À /c-kit þ /Sca-1 þ /Flk2 À ) resist IR-induced apoptosis and preferentially utilize error-prone non-homologous end joining for DNA repair. 6 Human HSPCs isolated from human cord blood upregulate p53 in response to DNA damage and are removed by apoptosis.…”

“…6,7 Murine hematopoietic stem and progenitor cells (HSPCs: lin À /c-kit þ /Sca-1 þ /Flk2 À ) resist IR-induced apoptosis and preferentially utilize error-prone non-homologous end joining for DNA repair. 6 Human HSPCs isolated from human cord blood upregulate p53 in response to DNA damage and are removed by apoptosis. 7 In both systems, HSCs appear to maintain long-term genomic integrity at the expense of repopulating ability.…”

TLR9 ligation in pancreatic stellate cells promotes tumorigenesis

“…qPCR was performed using the RT 2 SYBR Green qPCR Mastermix (QIA GEN) on the Stratagene MX3005P (Stratagene). The following forward (F) and reverse (R) primers were used: F, 5′-AAT CGTGC GTGAC ATCAA AG-3′ and R, 5′-ATG CCACA GGATT CCATA CC-3′ for mouse β-actin (Li et al, 2011); F, 5′-GTA CCATG ACACT CTGCA ACC-3′ and R, 5′-GTC AGGAA AATGA CACCT GGC-3′ for mouse Ccl3 (Volat et al, 2012); F, 5′-TGG GATGC CTTTG TGGAA CT-3′ and R, 5′-ACA GCCAG GAGAA ATCAA ACAG-3′ for mouse Bcl2 (Mohrin et al, 2010); F, 5′-GGC TGGGA CACTT TTGTG GAT-3′ and R, 5′-GCG CTCCT GGCCT TTCC-3′ for mouse Bcl2l1 (Bcl-xL; Mohrin et al, 2010); F, 5′-GGA CCTCG AGTGT GAAGC AT-3′ and R, CTG GAGCT CACAG GGTAG GA-3′ for human Tlr9; F, 5′-CTG TGGCA TCCAC GAAAC TA-3′ and R, 5′-AGT ACTTG CGCTC AGGAG GA-3′ for human β-actin (Ho-Pun-Cheung et al, 2009). For mouse Ccl11, predesigned primers were purchased from QIA GEN.…”