The RECQL4 protein, deficient in Rothmund–Thomson syndrome is active on telomeric D-loops containing DNA metabolism blocking lesions

Abstract

Telomeres are critical for cell survival and functional integrity. Oxidative DNA damage induces telomeric instability and cellular senescence that are associated with normal aging and segmental premature aging disorders such as Werner Syndrome and Rothmund-Thompson Syndrome, caused by mutations in WRN and RECQL4 helicases respectively. Characterizing the metabolic roles of RECQL4 and WRN in telomere maintenance is crucial in understanding the pathogenesis of their associated disorders. We have previously shown that WRN and RECQL4 display a preference in vitro to unwind telomeric DNA substrates containing the oxidative lesion 8-oxoguanine. Here, we show that RECQL4 helicase has a preferential activity in vitro on telomeric substrates containing thymine glycol, a critical lesion that blocks DNA metabolism, and can be modestly stimulated further on a D-Loop structure by TRF2, a telomeric shelterin protein. Unlike that reported for telomeric D-Loops containing 8-oxoguanine, RECQL4 does not cooperate with WRN to unwind telomeric D-Loops with thymine glycol, suggesting RECQL4 helicase is selective for the type of oxidative lesion. RECQL4’s function at the telomere is not yet understood, and our findings suggest a novel role for RECQL4 in the repair of thymine glycol lesions to promote efficient telomeric maintenance.

Human RecQ Helicases in DNA Repair, Recombination, and Replication

“…Both WRN and BLM promote the formation and subsequent disruption of regressed replication forks (250, 252), whereas unwinding of four-way junctions by RECQL4 has not been observed (154). By contrast, all three helicases can disrupt telomeric D-loops (55, 73, 177, 179, 253). Intratelomeric D-loops form naturally when the 3′ ssDNA telomeric overhang wraps around and invades the duplex telomeric sequence, forming a large T-loop that is stabilized by the D-loop (Figure 5) (254, 255).…”

“… a Data are from the following published studies: References 11, 151, 154, 253, and 290–294. b DNA, red and blue; RNA, green. c Relative helicase activity: +, weak; ++, moderate; +++, strong; −, no activity; ~/−, partial activity; ND, not determined. d RECQL4 activity in the absence of ssDNA. …”

TheSaccharomyces cerevisiaeHrq1 and Pif1 DNA helicases synergistically modulate telomerase activityin vitro

“…One immediate implication of the work presented here is that the human homologs of Hrq1 and Pif1, RECQL4 and hPIF1 (respectively), may function in a similar synergistic manner to modulate telomere length. Indeed, it has been demonstrated that RECQL4 is involved in telomere maintenance (18,19), and likewise, human PIF1 has shown evidence of being a telomerase inhibitor (46). Therefore, future in vitro experiments should address this issue using recombinant RECQL4, hPIF1, and human telomerase.…”

“…These data are particularly evocative in light of the fact that the human homolog of Hrq1, RECQL4 (or RECQ4), has an important but largely unknown role in telomere maintenance (18,19), and defects in this process could underlie the genomic instability characteristic of RECQL4related diseases (20). Thus, studying the mechanism(s) by which Hrq1 modulates telomerase activity in yeast may shed light on the role of RECQL4 in telomere homeostasis.…”

The Saccharomyces cerevisiae Hrq1 and Pif1 DNA helicases synergistically modulate telomerase activity in vitro

“…These data are particularly evocative in light of the fact that the human homolog of Hrq1, RECQL4 (or RECQ4), has an important but largely unknown role in telomere maintenance (18,19), and defects in this process could underlie the genomic instability characteristic of RECQL4-related diseases (20). Thus, studying the mechanism(s) by which Hrq1 modulates telomerase activity in yeast may shed light on the role of RECQL4 in telomere homeostasis.…”