Reduced FANCD2 influences spontaneous SCE and RAD51 foci formation in uveal melanoma and Fanconi anaemia

Abstract

Uveal melanoma (UM) is unique among cancers in displaying reduced endogenous levels of sister chromatid exchange (SCE). Here we demonstrate that FANCD2 expression is reduced in UM and that ectopic expression of FANCD2 increased SCE. Similarly, FANCD2-deficient fibroblasts (PD20) derived from Fanconi anaemia patients displayed reduced spontaneous SCE formation relative to their FANCD2-complemented counterparts, suggesting that this observation is not specific to UM. In addition, spontaneous RAD51 foci were reduced in UM and PD20 cells compared with FANCD2-proficient cells. This is consistent with a model where spontaneous SCEs are the end product of endogenous recombination events and implicates FANCD2 in the promotion of recombination-mediated repair of endogenous DNA damage and in SCE formation during normal DNA replication. In both UM and PD20 cells, low SCE was reversed by inhibiting DNA-PKcs (DNA-dependent protein kinase, catalytic subunit). Finally, we demonstrate that both PD20 and UM are sensitive to acetaldehyde, supporting a role for FANCD2 in repair of lesions induced by such endogenous metabolites. Together, these data suggest FANCD2 may promote spontaneous SCE by influencing which double-strand break repair pathway predominates during normal S-phase progression.

Bloom Syndrome Radials Are Predominantly Non-Homologous and Are Suppressed by Phosphorylated BLM

“…Though spontaneous radials are unique to BS and FA cells, induced radials are not and can be found after ICL damage in cells depleted of proteins that function in DNA repair or maintenance of genome stability, including BRCA1 or BRCA2, non-homologous end joining (NHEJ) proteins Ku70 ( now known as XRCC6 ) and LIG4, and HR proteins RAD51 and RAD52 (Hanlon Newell et al 2008). However, unlike BS cells, FA cells generally do not exhibit elevated spontaneous SCEs (Gravells et al 2013; Hemphill et al 2009). Studies characterizing BS radials have previously classified them as homologous, or occurring between homologous chromosomes (German et al 1974; Schroeder and German 1974).…”

Chromosomal Integrity after UV Irradiation Requires FANCD2-Mediated Repair of Double Strand Breaks

“…Our results suggest that low levels of replication-associated DSBs may be an important oncogenic factor if FANCD2 is not available to direct them into an error free pathway. FANCD2 is also required for the spontaneous levels of SCEs in uveal melanoma [ 88 ], thus we speculate that even during unperturbed replication FANCD2 regulates the pathway choice for DSBs repair. We propose a surveillance role for FANCD2 that is required to resolve replication-associated DSBs arising from any stress source and which might be relevant for the etiology of cancer in FA patients.…”

Loss of FANCD2 and related proteins may predict malignant transformation in oral epithelial dysplasia

“…FANCD2 monoubiquitylation, which is thought to be promoted by ATR-CHK1 mediated FANCD2 phosphorylation (19,30), is a critical step in FA pathway activation (29,39) and evidence suggests that a reduction in FANCD2 monoubiquitylation has a greater influence on genomic instability than down regulation of FANCD2 expression (40). In our study, it was observed that transforming samples have lower levels of FANCD2 monoubiquitylation (FANCD2 L expression) compared to non-transformers, and interestingly, they consistently displayed lower levels of total FANCD2 expression.…”