Heterochromatic breaks move to the nuclear periphery to continue recombinational repair

Abstract

Heterochromatin mostly comprises repeated sequences prone to harmful ectopic recombination during double-strand break (DSB) repair. In Drosophila cells, ‘safe’ homologous recombination (HR) repair of heterochromatic breaks relies on a specialized pathway that relocalizes damaged sequences away from the heterochromatin domain before strand invasion. Here we show that heterochromatic DSBs move to the nuclear periphery to continue HR repair. Relocalization depends on nuclear pore and inner nuclear membrane proteins (INMPs) that anchor repair sites to the nuclear periphery via the Smc5/6-interacting proteins STUbL/RENi. Both the initial block to HR progression inside the heterochromatin domain, and the targeting of repair sites to the nuclear periphery, rely on SUMO and SUMO E3 ligases. This study reveals a critical role for SUMOylation in the spatial and temporal regulation of HR repair in heterochromatin, and identifies the nuclear periphery as a specialized site for heterochromatin repair in a multicellular eukaryote.

PolySUMOylation by Siz2 and Mms21 triggers relocation of DNA breaks to nuclear pores through the Slx5/Slx8 STUbL

“…In flies, it was shown that dRad60 (the homolog of Rad60 in fission yeast, Esc2 in budding yeast, and NIP45 in humans) contributes to the shift of DSBs away from heterochromatin in irradiated Drosophila cells (Ryu et al 2015). This class of factors, called RENi, is thought to stimulate the ubiquitination activity of the Slx5/8 STUbL in yeast (Prudden et al 2007).…”

“…Although Rad52 SUMOylation influenced damage relocation from the nucleolus to the nucleoplasm (Torres-Rosell et al 2007), Rad52 was not needed for the relocation of a euchromatic DSB to pores (Horigome et al 2014). In flies, the STUbL subunit Dgrn, along with the SMC5/6 complex, was necessary for DSB relocation away from heterochromatin (Chiolo et al 2011;Ryu et al 2015). This shift required the STUbL interactor Rad60 (ScEsc2/HsNIP45) and the Nup84 pore complex (Ryu et al 2015).…”

“…In both yeast and flies, Nup84-linked damage sensitivity and the closely associated nuclear pore basket proteins Nup60 and Mlp1/Mlp2 have been linked to enzymes that control SUMO metabolism (Zhao et al 2004;Palancade et al 2007;Nagai et al 2008;Ryu et al 2015). Indeed, DSBs that occur in the ribosomal DNA in budding yeast (Torres-Rosell et al 2007) and in heterochromatin in flies (Chiolo et al 2011) were shown to shift away from the domain of repetitive sequences in a manner dependent on the SMC5/6 complex and its associated SUMO ligase, Mms21.…”

“…In flies, the STUbL subunit Dgrn, along with the SMC5/6 complex, was necessary for DSB relocation away from heterochromatin (Chiolo et al 2011;Ryu et al 2015). This shift required the STUbL interactor Rad60 (ScEsc2/HsNIP45) and the Nup84 pore complex (Ryu et al 2015).…”

“…Besides conferring sensitivity to exogenous agents (Bennett et al 2001), nuclear pore mutants showed impaired replication fork restart (for review, see Bukata et al 2013;Geli and Lisby 2015) and have recently been implicated in the repair of subtelomeric DSBs by strand invasion events . In human cells, components in the Nup84 complex were found to suppress elevated levels of H2AX phosphorylation in cells exposed to aphidicolin (Paulsen et al 2009), and, in flies, the loss of the corresponding complex enhanced the appearance of damage foci provoked by ionizing irradiation (Ryu et al 2015).…”