: The MUS81 complex is crucial for preserving genome stability through resolution of branched DNA intermediates in mitosis and also for the processing of deprotected replication forks in BRCA2-deficient cells. Because of the existence of two different MUS81 complexes in mammalian cells that act in M- or S-phase, whether and how the PARPi sensitivity of BRCA2-deficient cells is affected by loss of MUS81 function is unclear. Here, using a mutant of MUS81 that impairs its function in M-phase, we show that viability of BRCA2-deficient cells but not their PARPi sensitivity requires a fully-functional MUS81 complex in mitosis. In contrast, expression of a constitutively-active MUS81 is sufficient to confer PARPi resistance. From a mechanistic point of view, our data indicate that deregulated action of the mitotic active form of MUS81 in S-phase leads to the cleavage of stalled replication forks before their reversal, bypassing fork deprotection, and engaging a Polθ-dependent DSBs repair. Collectively, our findings describe a novel mechanism leading to PARPi resistance that involves unscheduled MUS81-dependent cleavage of intact, unreversed replication forks. Since this cleavage occurs mimicking the phosphorylated status of S87 of MUS81, our data suggest that hyperphosphorylation of this residue in S-phase might represent a novel biomarker to identify resistance to PARPi.
Phosphorylation status of MUS81 is a modifier of Olaparib sensitivity in BRCA2-deficient cells / Blandino, Francesca; Malacaria, Eva; Figlioli, Carolina; Noto, Alessandro; Pugliese, Giusj Monia; Franchitto, Annapaola; Pichierri, Pietro. - In: NUCLEIC ACIDS RESEARCH. - ISSN 1362-4962. - 51:13(2023), pp. 6723-6737. [10.1093/nar/gkad470]
Phosphorylation status of MUS81 is a modifier of Olaparib sensitivity in BRCA2-deficient cells
Blandino, FrancescaPrimo
Membro del Collaboration Group
;Malacaria, EvaMembro del Collaboration Group
;Figlioli, CarolinaMembro del Collaboration Group
;Noto, AlessandroMembro del Collaboration Group
;Pugliese, Giusj MoniaMembro del Collaboration Group
;
2023
Abstract
: The MUS81 complex is crucial for preserving genome stability through resolution of branched DNA intermediates in mitosis and also for the processing of deprotected replication forks in BRCA2-deficient cells. Because of the existence of two different MUS81 complexes in mammalian cells that act in M- or S-phase, whether and how the PARPi sensitivity of BRCA2-deficient cells is affected by loss of MUS81 function is unclear. Here, using a mutant of MUS81 that impairs its function in M-phase, we show that viability of BRCA2-deficient cells but not their PARPi sensitivity requires a fully-functional MUS81 complex in mitosis. In contrast, expression of a constitutively-active MUS81 is sufficient to confer PARPi resistance. From a mechanistic point of view, our data indicate that deregulated action of the mitotic active form of MUS81 in S-phase leads to the cleavage of stalled replication forks before their reversal, bypassing fork deprotection, and engaging a Polθ-dependent DSBs repair. Collectively, our findings describe a novel mechanism leading to PARPi resistance that involves unscheduled MUS81-dependent cleavage of intact, unreversed replication forks. Since this cleavage occurs mimicking the phosphorylated status of S87 of MUS81, our data suggest that hyperphosphorylation of this residue in S-phase might represent a novel biomarker to identify resistance to PARPi.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.