NELF ‐E is recruited to DNA double‐strand break sites to promote transcriptional repression and repair

Abstract

Double-strand breaks (DSBs) trigger rapid and transient transcription pause to prevent collisions between repair and transcription machineries at damage sites. Little is known about the mechanisms that ensure transcriptional block after DNA damage. Here, we reveal a novel role of the negative elongation factor NELF in blocking transcription activity nearby DSBs. We show that NELF-E and NELF-A are rapidly recruited to DSB sites. Furthermore, NELF-E recruitment and its repressive activity are both required for switching off transcription at DSBs. Remarkably, using I-SceI endonuclease and CRISPR-Cas9 systems, we observe that NELF-E is preferentially recruited, in a PARP1-dependent manner, to DSBs induced upstream of transcriptionally active rather than inactive genes. Moreover, the presence of RNA polymerase II is a prerequisite for the preferential recruitment of NELF-E to DNA break sites. Additionally, we demonstrate that NELF-E is required for intact repair of DSBs. Altogether, our data identify the NELF complex as a new component in the DNA damage response.

MST2 kinase suppresses rDNA transcription in response to DNA damage by phosphorylating nucleolar histone H2B

“…In agreement with ATM acting upstream of MST2 and regulating rDNA transcription via activating several responses (Ciccia et al , ; Larsen et al , ), we observed a more profound impact on rDNA transcription in the absence of ATM compared with MST2 deletion alone and combination of both did not have a greater impact on rDNA silencing (Fig C). Recent studies have shown involvement of DNA‐PK and PARP in Pol I and Pol II transcriptional repression in the presence of DNA damage (Pankotai et al , ; Calkins et al , ; Awwad et al , ). We therefore checked whether inhibition of DNA‐PK or PARP could affect MST2 kinase activity but did not observe any impact (Fig EV3F).…”

Switching genes to silent mode near DNA double‐strand breaks

“…Finally, Awwad et al investigate the physiological relevance of NELF‐mediated silencing in response to DNA damage by assessing the importance of NELF‐E for DSB repair. NELF‐E knock‐down moderately increases cell sensitivity to ionizing radiation and impairs DSB repair by homologous recombination and non‐homologous end‐joining . These results suggest that NELF‐E silencing activity at DSBs may be critical to promote repair, although this still needs to be formally demonstrated.…”

“…This first set of data suggests that NELF‐E acts locally to switch off genes close to DSBs. In line with this hypothesis, Awwad et al investigate NELF‐E recruitment to damaged DNA, using once again three complementary approaches: laser‐induced damage, I‐SceI cut, and Cas9‐mediated DSB. Thus, they establish that both NELF‐E and NELF‐A relocalize to DSBs.…”

“…In this issue of EMBO Reports , Awwad et al uncover a hitherto unknown role for the negative elongation factor NELF in blocking transcription of genes close to DSBs in human cells. NELF is a four subunit protein complex, comprising NELF‐A, B, C/D, and E, which cooperates with DRB sensitivity‐inducing factor (DSIF) to repress transcription elongation by RNAPII .…”

“…Yet, how DNA lesions signal to the transcription machinery to coordinate DNA repair with transcriptional silencing is not fully elucidated. In this issue of EMBO Reports , Awwad et al bring a new piece to the puzzle by identifying the negative transcription elongation factor NELF as a critical player in this process. They demonstrate that NELF is recruited to DNA double‐strand breaks ( DSB s) near transcriptionally active genes in a poly( ADP ‐ribose)‐ and RNAPII ‐dependent manner to promote transcriptional repression and facilitate DSB repair.…”