Rinalducci, S. | bioRxiv Science

bioRxiv2022

CHK2 Regulates MUS81-EME2 Function in Response to Replication Stress and BRCA2 Deficiency

MUS81 is a structure-specific endonuclease that processes DNA intermediates in mitosis and in S-phase following replication stress. MUS81 is crucial to cleave deprotected reversed forks in BRCA2-deficient cells. However, how MUS81 is regulated during replication stress in human cells remains unknown. Our study reveals that CHK2 binds the MUS81-EME2 complex and positively regulates formation of DSBs upon replication stress or in the absence of BRCA2. The association with MUS81 occurs through the FHA domain of CHK2 and is disabled by the I157T mutation but not by the R117A mutation. The CHK2-MUS81 complex forms downstream fork reversal and degradation, and phosphorylation of MUS81 at CHK2-targeted sites is crucial to introduce DSBs at deprotected replication forks ensuring the replication fork recovery in BRCA2-deficient cells. Collectively, our work sheds light into the regulation of the MUS81 complex and identifies a novel function of the ATM-CHK2 axis in the response to deprotected replication forks in the absence of BRCA2.

cell biology↗

bioRxiv2018

Phosphorylation By CK2 Regulates MUS81/EME1 In Mitosis And After Replication Stress

The MUS81 complex is crucial for preserving genome stability through the resolution of branched DNA intermediates in mitosis. However, untimely activation of the MUS81 complex in S-phase is dangerous. Little is known about the regulation of the human MUS81 complex and how deregulated activation affects chromosome integrity. Here, we show that the CK2 kinase phosphorylates MUS81 at Serine 87 in late-G2/mitosis, and upon mild replication stress. Phosphorylated MUS81 interacts with SLX4, and this association promotes the function of the MUS81 complex. In line with a role in mitosis, phosphorylation at Serine 87 is suppressed in S-phase and is mainly detected in the MUS81 molecules associated with EME1. Loss of CK2-dependent MUS81 phosphorylation contributes modestly to chromosome integrity, however, expression of the phosphomimic form induces DSBs accumulation in S-phase, because of unscheduled targeting of HJ-like DNA intermediates, and generates a wide chromosome instability phenotype. Collectively, our findings describe a novel regulatory mechanism controlling the MUS81 complex function in human cells. Furthermore, they indicate that, genome stability depends mainly on the ability of cells to counteract targeting of branched intermediates by the MUS81/EME1 complex in S-phase, rather than on a correct MUS81 function in mitosis.

cell biology↗