The phospho-dependent role of BRCA2 on the maintenance of chromosome integrity

Figures & data

Figure 1. Schematic view of BRCA2 protein and some of its interacting partners. (a) BRCA2 is a 3418 aa protein, exhibiting a unique folded domain (PDB 1IYJ [45]). It comprises several binding motifs, here represented by gray rectangles (two of them are displayed in yellow (F1, F2) and further represented in (b, c)). The motifs targeted by kinases and phosphatases are also highlighted. Some of the residues phosphorylated by CDK1/2 and PLK1 are indicated in blue and red, respectively. Docking sites for PLK1 are underlined. Phosphorylation of S3291 is involved in RF protection. Phosphorylation of T77, S193 and T207 are involved in the control of mitotic progression and cytokinesis and indirectly in the HR function of RAD51 (T77). (b) BRCA2 complex involved in HR: Cartoon representation of the BRC4 repeat of BRCA2 (in orange) interacting with the RecA homology domain of RAD51 (in gray) (PDB 1N0W [13]). (c) BRCA2 complex involved in mitosis: Stick representation of BRCA2 peptide from aa 194 to aa 210 (in orange) phosphorylated at T207 (in red) interacting with the Polo-Box domain of PLK1 (cartoon representation in gray) (PDB 6GY2 [42])

Table 1. Phosphorylation of BRCA2 in G2/M. List of phosphorylation sites is discussed in the text showing BRCA2 phosphorylation site, the responsible kinase, function and consequences in the cell

Phosphorylation site	Kinase	Function	Consequences of phosphorylation
T77	CDK1/2	PLK1 docking and phosphorylation of S193-BRCA2 and S14-RAD51	CK2 phosphorylation of RAD51 and RAD51 interaction with NBS1 (MRN complex) at stressed RF or DSBs^[Citation37,Citation46,Citation54]
S193	PLK1	Localization of BRCA2 at the midbody	Completion of cytokinesis^[37]
T207	PLK1	BRCA2:PLK1:BUBR1:PP2A complex formation at the kinetochore	Faithful chromosome alignment and segregation^[42]
S3291	CDK1/2	Negative regulation of BRCA2-RAD51 interaction	Protection of stalled RF from aberrant degradation^[Citation47,Citation53^]

Figure 2. Schematic view of phosphorylation events regulating BRCA2 function and cell aberrations related to these events. (a) Scheme of BRCA2 showing main phosphorylation by CDK and PLK1 and related interacting partners. BRCA2 is phosphorylated by the kinases CDK (phosphorylation sites in blue) and PLK1 (phosphorylation sites in red) which regulate the interaction between BRCA2 and several of its interaction partners. (b) Scheme showing the role of pT77 and S3291 at DSB/stalled forks. At stalled replication forks, the C-terminal region of BRCA2 interacts with the oligomeric form of RAD51 inhibiting aberrant degradation of the nascent DNA by nucleases like MRE11; phosphorylation by CDK at S3291 negatively regulates this interaction. In response to DSB, CDK phosphorylates BRCA2 at T77 priming PLK1 binding to BRCA2 which favors the phosphorylation of RAD51 by PLK1. PLK1-phosphorylated RAD51 triggers subsequent phosphorylation of RAD51 by CK2 and binding to NBS1 at DSBs [46,54]. A phospho-mimic or phospho-defective mutation at S3291 of BRCA2 leads to unprotected replication forks. Unprotected forks or failure to resume replication of stalled forks, as in the context of BRCA2 loss, result in under replicated DNA leading to anaphase/DNA bridges [65,66,79] as illustrated on the right. (c) Scheme showing the role of pT207 of BRCA2 in mitosis. In mitosis, PLK1 phosphorylates BRCA2 at T207 triggering the formation of the BRCA2:PLK1:BUBR1:PP2A tetrameric complex at the kinetochore important for proper chromosome alignment [42]. Defects in this phosphorylation lead to misaligned and lagging chromosomes due to altered activities of BUBR1 and PP2A at the kinetochore as illustrated on the right. (d) Scheme of the role of pT77 and pS193 in midbody localization and cytokinesis. The phosphorylation of T77 by CDK favors further phosphorylation of S193 by PLK1 allowing BRCA2 localization at the midbody where it

serves as a platform for several proteins regulating cytokinesis and promoting abscission: the motor protein NMCII and the actin-binding protein Filamin A favoring the recruitment of ESCRT-associated proteins Tsg1, CEP55 and Alix [36,37]. Failure of the CDK phosphorylation of T77 and/or phosphorylation of S193-BRCA2 by PLK1 generate cytokinetic aberrations resulting in bi- or multi-nucleated cells [36,37]. NTD, N-terminal DNA-binding domain; CTD, C-terminal DNA-binding domain

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