Human PIF1 helicase supports DNA replication and cell growth under oncogenic-stress

Abstract

Unwinding duplex DNA is a critical processing step during replication, repair and transcription. Pif1 are highly conserved non-processive 5′->3′ DNA helicases with well-established roles in maintenance of yeast genome stability. However, the function of the sole member of Pif1 family in humans remains unclear. Human PIF1 is essential for tumour cell viability, particularly during replication stress, but is dispensable in non-cancerous cells and Pif1 deficient mice. Here we report that suppression of PIF1 function slows replication fork rates and increases arrested forks during normal cycling conditions. Importantly, PIF1-dependent replication impediments impair S-phase progression and reduce proliferation rates of RAS oncogene-transformed fibroblasts, where replication fork slowing is exacerbated, but not parental, non-cancerous cells. Disrupted fork movement upon PIF1-depletion does not enhance double-stranded break formation or DNA damage responses but affects resumption of DNA synthesis after prolonged replication inhibitor exposure, accompanied by diminished new origin firing and mainly S-phase entry. Taken together, we characterised a functional role for human PIF1 in DNA replication that becomes important for cell growth under oncogenic stress. Given that oncogenes induce high levels of replication stress during the early stages of tumorigenesis, this function of PIF1 could become critical during cancer development.

Translesion Polymerases Drive Microhomology-Mediated Break-Induced Replication Leading to Complex Chromosomal Rearrangements

“…The search for MMBIR mutations could also be applied to cell lines where the overexpression of oncogenes leading to replication collapse initiates BIR followed by CGRs (Costantino et al, 2014). While the role of Pif1 in BIR in humans remains to be determined, Pif1 helicase has been recently implicated in the recovery from oncogene-induced replication stress (Gagou et al, 2014), a process that requires PolD3 (Pol32)-mediated BIR (Costantino et al, 2014). Thus Pif1 levels may impact the frequency of BIR/MMBIR events in humans.…”

Targeted Reduction of Pathogenic Heteroplasmy Through Binding of G-Quadruplex DNA

“…TFAM, the ubiquitous mtDNA binding protein, has high affinity for GQ DNA (39). The Pif1 helicase, which is resident in the mitochondrial matrix, is stimulated by the presence of GQ and may interact and unwind the structures (40,41). GQs may also bear responsibility for mtDNA deletions, as shown by the association of high-GQ potential regions with the ends of deletion breakpoints (17).…”

TheDrosophila melanogasterPIF1 helicase promotes survival during replication stress and processive DNA synthesis during double-strand gap repair

“…These damaged nuclei are subject to nuclear fallout; too many lost nuclei result in gaps in the typically uniform monolayer of nuclei, as we also observed. Intriguingly, human PIF1 helicase has been shown to support DNA replication and cell growth during oncogenic stress (GAGOU et al 2014). Thus, one conserved feature of PIF1 in all organisms may be to promote efficient DNA synthesis during replication stress.…”

“…Furthermore, the cellular functions of PIF1 homologs in eukaryotes are variably conserved. Because human PIF1 appears to act as a tumor suppressor but is also required for the survival of cancer cells (GAGOU et al 2014), a better understanding of its contribution to genome stability in diverse cellular and organismal contexts is needed.…”