RNF8- and RNF168-dependent degradation of KDM4A/JMJD2A triggers 53BP1 recruitment to DNA damage sites

Abstract

In response to DNA damage, cells initiate complex signalling cascades leading to growth arrest and DNA repair. The recruitment of 53BP1 to damaged sites requires the activation of the ubiquitination cascade controlled by the E3 ubiquitin ligases RNF8 and RNF168, and methylation of histone H4 on lysine 20. However, molecular events that regulate the accessibility of methylated histones, to allow the recruitment of 53BP1 to DNA breaks, are unclear. Here, we show that like 53BP1, the JMJD2A (also known as KDM4A) tandem tudor domain binds dimethylated histone H4K20; however, JMJD2A is degraded by the proteasome following the DNA damage in an RNF8‐dependent manner. We demonstrate that JMJD2A is ubiquitinated by RNF8 and RNF168. Moreover, ectopic expression of JMJD2A abrogates 53BP1 recruitment to DNA damage sites, indicating a role in antagonizing 53BP1 for methylated histone marks. The combined knockdown of JMJD2A and JMJD2B significantly rescued the ability of RNF8‐ and RNF168‐deficient cells to form 53BP1 foci. We propose that the RNF8‐dependent degradation of JMJD2A regulates DNA repair by controlling the recruitment of 53BP1 at DNA damage sites.

K48-linked ubiquitination and protein degradation regulate 53BP1 recruitment at DNA damage sites

“…In response to DNA breaks, both RNF8 and RNF168 can directly ubiquitinate JMDJ2A, leading to its proteasomal degradation. Depletion of RNF8 in the cell caused marked defects in the recruitment of 53BP1, but combined depletion of JMJD2A and JMJD2B in these cells restores the formation of 53BP1 foci [15]. These results suggest that JMJD2A and JMJD2B are bound to methylated H4K20 in untreated cells and that RNF8-and RNF168-dependent activity lead to their chromatin extraction and proteasomal degradation to allow the unmasking of H4K20 and binding of 53BP1.…”

“…Hence, the local enrichment of H4K20(me2) triggered by MMSET does not explain the requirement of RNF8 for the recruitment of 53BP1 [5][6][7]. It was initially thought that RNF8 only catalyzes K63-linked ubiquitination, but multiple recent reports describe the ability of RNF8 to stimulate the formation of K48-linked ubiquitin chains [4,14,15], confirming a role for RNF8-mediated degradation or chromatin extraction during the DNA damage response.…”

“…We identified the lysine demethylases JMJD2A and JMJD2B as novel targets of RNF8-mediated K48-linked ubiquitination ( Figure 1) [15]. Both JMJD2A and JMJD2B possess a hybrid tandem tudor domain conferring the ability to bind methylated H4K20.…”

“…Both JMJD2A and JMJD2B possess a hybrid tandem tudor domain conferring the ability to bind methylated H4K20. In fact, JMJD2A (K D = 2.0 µM) and JMJD2B (K D = 27.7 µM) bind dimethylated H4K20 with a higher relative affinity than 53BP1 (K D = 50.8 µM) and they can block the formation 53BP1 foci when ectopically expressed [15]. In response to DNA breaks, both RNF8 and RNF168 can directly ubiquitinate JMDJ2A, leading to its proteasomal degradation.…”

A small ubiquitin binding domain inhibits ubiquitin-dependent protein recruitment to DNA repair foci

“…20,21 The ability of 53BP1 to bind efficiently also relies on chromatin reorganization mediated by ubiquitin-dependent removal of specific chromatin proteins in order to reveal dimethylated K20 of histone H4. 22,23 Importantly, chromatin spreading of both BRCA1 and 53BP1 within the vicinity of a DSB is thought to be important for their antagonistic roles in regulating the proper choice between homologous recombination (HR) and nonhomologous end joining (NHEJ) during the cell cycle. 1 The E3 ubiquitin ligase RAD18 also localizes to K63-linked ubiquitinated histones via its UBZ domain in a RNF8 and RNF168-dependent manner.…”